Chem Module 7 PhotoMaster

Chem Module 7 “Organic Chemistry” PhotoMastercopyright © 2005-19 KEEP IT SIMPLE SCIENCEwww.keepitsimplescience.com.au

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KISS Resources for NSW Syllabuses & Australian Curriculum.

Topic Outline

What is this topic about?To keep it as simple as possible, (K.I.S.S. Principle) this topic covers:

1. Nomenclature (Naming)What is Organic Chemistry? Concept of an “homologous series”.

Naming basic organic compounds according to IUPAC rules, including simple isomers.

2. The HydrocarbonsPhysical properties relate to bonding within & between molecules. Saturated & unsaturated.Chemical reactions: substitution in saturated types, addition reactions in unsaturated types.

Environmental & socioeconomic impacts of using hydrocarbons.

3. The AlcoholsPhysical properties of alkanols related to bonding. Chemical reactions: combustion,

halogen substitution, dehydration & oxidation. Alcohols as “bio-fuels”.

4. Organic Acids & BasesComparison of alcohols & carboxylic acids. Esterification. Names of esters. Properties.

Chemistry of fats & oils. Soap & saponification. Emulsification. Detergents. Amines & amides.

5. PolymersAddition polymers. Uses related to properties & structures.

Condensation polymers... polyamides & polyesters. Biopolymers.

1. Naming OrganicCompounds

Rules for naming alkanes, alkenes,alkynes, alcohols, etc. as per syllabus.

Naming simple isomers

4. Organic Acids& Bases

5. Polymers

3. Alcohols

Addition polymers

2. Hydrocarbons

KEEP IT SIMPLE SCIENCEPhotoMaster Format

Chemistry Module 7

Organic Chemistrykeep it simple science

®

Alcohols cf. carboxylic acidsPhysical properties related to bonding.

Physical properties related to bonding.

Chemistry: saturated v. unsaturatedSubstitution & addition reactions

Environmental & socioeconomic impacts

Chemistry: combustion, dehydration, etc.

Oxidation of 1o, 2o & 3o alcohols Alcohols as fuels

Esters & their formationChemistry of fats & oils

Saponification & emulsificationDetergents Amines & amides

Uses, properties & structuresCondensation polymers

Biopolymers




keep it simple science® What is “Organic Chemistry”?

The word “organic” refers to living things. In the early days, Chemistry was divided into 2 fields... “Organic Chemistry” referred to the chemicals in, or derived from, living things. These were generallybelieved to contain a “vital force” (or “life force”) from which “life” arose.

“Inorganic Chemistry” was everything else in the chemical world and was lacking in “life force”.

During the 19th century great progress was made in the understanding of Chemistry, including therealisation that all the complex chemicals which living things are built from, are compounds of the elementcarbon combined with (mostly) hydrogen, oxygen & nitrogen. The concept of the “vital force” was droppedand the study of Organic Chemistry became the scientific study of carbon compounds.

So “Organic Chemistry” is really “Carbon Chemistry”, although (just to confuse you) the very simplecompounds of carbon such as CO2, CO or CS2, are actually considered as “inorganic”.

To confuse the issue further, in popular culture, mass media & (especially) product-marketing, “organic” hascome to mean “pure”, “natural”, “healthy”, “chemical-free”, or some combination of these. Anyone who hasstudied the Science of Organic Chemistry finds it quite humorous to be told that we should all eat only“organic, chemical-free foods”. Technically, the phrase “chemical-free substance” is an oxymoron (since allsubstances contain chemicals) and it is impossible to have “inorganic foods” anyway. Even the mostdisgusting “junk food” imaginable is in fact organic because its nutrient ingredients (no matter how heavilyprocessed, deep-fried and adulterated) are actually carbon compounds.

Carbon CompoundsAll life on Earth is based on carbon compounds,operating within an aqueous (water) environment.We have good reason to believe that, if there is lifeelsewhere in the Universe, it will also be carbon andwater based, although the details of E.T.’s chemistry,biology and appearance cannot be predicted.

Water is the solvent without equal, and carbon is theonly element capable of forming the variety ofintricate and complex molecules needed to make aliving organism.

Carbon rarely forms ions. The immense scope ofcarbon’s chemistry is based on covalent bonding, andthe key is that a carbon atom can readily form bondswith other carbon atoms, as well as (notably) hydrogen,oxygen and nitrogen atoms.

C C

C C

C C

Single BondsA single C-C bond involves sharing one pair ofelectrons. Each carbon atom has 3 other bondpositions available, allowing the formation ofchains, rings and networks.

Double C=C BondsCarbon atoms can also share 2 pairs of electrons toform double covalent bonds between two carbonatoms, or between a carbon atom and a differentatom such as oxygen.

Triple BondsCarbon atoms can even manage to share 3 pairs ofelectrons.

(Before you ask: No, carbon atoms cannotform a quadruple bond.)

Detergent molecule

The result is that carbon can form more possiblecompounds than all the other elements puttogether.

Organic Chemistry caninvolve huge, intricate,complicated molecules.

In this module weintroduce the basics...

H

H

C

H H H

HHH

C C CH

H

CH

H

C

HH H

H

C

H H

S

O

O

O-

H

H

H C

H H H

HHH

C C CH

H

C C

C C

C

CC




keep it simple science® 1. Naming Organic Compounds

Your first challenge is to become familiar with the basic organic compounds, their general properties,names, molecular structures & their formulas.

Since there is such a vast number of possible carbon compounds (millions of them!!) this seems animpossible task. The key to understanding is that there are patterns. All carbon compounds can be

classified in groups called “homologous series” AND there are systematic rules for naming them all.

These rules are set by the International Union of Pure and Applied Chemistry (IUPAC) and are used byscientists throughout the world. In Chemistry, everyone speaks the same language.

The HydrocarbonsWe begin with a class of organic chemicals which(as their name suggests) are composed entirely ofcarbon and hydrogen atoms bonded covalently.

The simplest of the hydrocarbons are The “Alkanes”This homologous series of compounds have onlycarbon & hydrogen atoms and only single chemicalbonds between adjacent carbon atoms.

Methane

Molecular Formula CH4

Structural Formula

Ethane

Molecular FormulaC2H6

Structural Formula

“CondensedStructural Formula” CH3-CH3

Propane

Molecular FormulaC3H8

Structural Formula

“CondensedStructural Formula” CH3-CH2-CH3

See the pattern beginning to emerge?The Syllabus requires that you learn the first 8compounds in this series... the “Alkanes”

H

HH

H

C

H HH

H

H

H

C C

MolecularModel

Molecular Model

H H H

H

HH

H

H

C C C

Molecular Model

Naming AlkanesThe Alkanes are just one of many “HomologousSeries” of carbon compounds. An HomologousSeries means a group of chemicals which form alogical series or pattern, in terms of their molecularstructure. As you’ll learn, they also have similarproperties which also follow patterns.

You must learn the following rules for naming:

No. of Carbon Atoms Prefix1 Meth-2 Eth-3 Prop-4 But-5 Pent-6 Hex-7 Hept-8 Oct-

We now continue the series...

ButaneMolecular Formula C4H10Structural Formula

“CondensedStructural Formula”

CH3-(CH2)2-CH3

PentaneMolecular Formula C5H12Structural Formula

“CondensedStructural Formula”

CH3-(CH2)3-CH3

Hexane C6H14 CH3-(CH2)4-CH3

Heptane C7H16 CH3-(CH2)5-CH3

Octane C8H18 CH3-(CH2)6-CH3

H H H

HH

H

H

C C CH

H

C

HH

H

C

H H H

HH

H

H

C C CH

H

C H

To name any ALKANE, just add “-ANE”to the appropriate prefix above.

...there aremany more, butthis is as far asthe Syllabusexpects you tolearn.




keep it simple science®

Short-Cuts to Molecular FormulasFor each Homologous Series there is a general formula for finding any molecular formula.

where n = number of carbon atoms

The Alkenesare also hydrocarbons, but each alkene moleculecontains one C= C double bond.

Since there have to be at least 2 carbon atoms tohave a double bond, the series begins with...

EtheneMolecular Formula C2H4Structural Formula

“Condensed StructuralFormula” CH2=CH2

PropeneMolecular Formula C3H6Structural Formula

“Condensed Structural Formula” CH2=CH-CH3

ButeneMolecular FormulaC4H8

Structural Formula

“Condensed Struct. Form.” CH2=CH-CH2-CH3

Pentene C5H10 CH2=CH-(CH2)2-CH3

Hexene C6H12 CH2=CH-(CH2)3-CH3

Heptene C7H14 CH2=CH-(CH2)4-CH3

Octene C8H16 CH2=CH-(CH2)5-CH3

... and, you guessed it...The AlkynesMore hydrocarbons, but each alkyne moleculecontains one C C triple bond.

Name Molecular Cond.Struct.Formula Formula

Ethyne C2H2 CH CH

Propyne C3H4 CH C-CH3

Butyne C4H6 CH C-CH2-CH3

Pentyne C5H8 CH C-(CH2)2-CH3

Hexyne C6H10 CH C-(CH2)3-CH3

Heptyne C7H12 CH C-(CH2)4-CH3

Octyne C8H14 CH C-(CH2)5-CH3

Suggested Prac WorkYou may be able to use a molecular model kit toconstruct models of these molecules, as suggestedby the photos on these pages.

This is one of the most important ways for you to“get your head around” these series of compounds.

Resist the temptation to use the kits as toys and“play Lego”. Work towards methodically buildingeach molecule, in turn.

Count the atoms to confirm the molecular formula.

Compare the model to the 2-D “structural formula”to get used to the conventions often used to depictthese compounds.

Compare also the “condensed structural formula”.These vary in the style used, but it would be best tounderstand how to read & interpret them.

H H

HH

C C

H H H

H

H

H

C C C

H H H

HH

C C C

H

H

H

C

Double C= C Bond

Double C= C Bond

Double C= C Bond

To name, just add “-ENE”to the appropriate prefix.

To name, just add “-YNE”to the appropriate prefix.

The Hydrocarbons (cont.)

AlkanesCnH2n+2

AlkenesCnH2n

AlkynesCnH2n-2




keep it simple science® Isomers

Consider these two hydrocarbon molecules:(shown in another variation of the “condensedstructural formula”)

You should buildeach of these with a model kit as you consider the following.

Each of these moleculeshas exactly the same molecular formula: C5H12(don’t trust our word... check!)

They contain exactly the same numbers of the sameatoms with exactly the same type & number ofchemical bonds holding them together.

BUT THEY ARE DIFFERENT COMPOUNDS !!

Their physical & chemical properties (later) are quitesimilar, but NOT identical. These are NOT the samecompound and therefore, they must be given differentnames.

Compounds like this are said to be “isomers”.

CH3 CH3CH2 CH2 CH2

CH3

CH3

CH CH2 CH3

ISOMERShave the same molecular formula,

but different structures.They are different compounds,

with different properties and must be givendifferent names.

So, what are they called?The first one (you should figure out) is “pentane”.

The 2nd, according to IUPAC rules is called“methylbutane”. It is an isomer of pentane.

Explanation: the longest linear chain in the moleculehas 4 carbon atoms joined by single bonds. Therefore, “butane” is its “backbone”.

It has a -CH3 “side-branch”. This is called a “methyl-”(1-carbon) side-branch.

A 2-carbon side-branch (-CH2CH3) is “ethyl-”.

A 3-C side-branch (-CH2CH2CH3) is “propyl-”,then “butyl-”, “pentyl-”, and so on.

Another ExampleConsider these 3 (labelled A,B,C)

A.

B.

C.

All 3 have the same formula C6H14. You will figure out that all are isomers of hexane.

All have a 5-carbon “backbone” with a “methyl-”side-branch, so they are all “methylpentane”.

To give each a unique name, we must now numberthe carbon atoms of the backbone and use anumber to indicate the position of the side-branch.

Numbering from the left, it means that A = “2-methylpentane”

andB = “3-methylpentane”

Does this mean that C = “4-methylpentane”? NO !

If you build a model of A, then turn it around, youwill see that you have C. A and C are the samemolecule, so C = “2-methylpentane”You must number from either right or left so thatthe number(s) used are as small as possible.

Can you also see that the example above left(methylbutane) has NO NEED for any numbers?

CH3

CH3

CH CH2 CH2 CH3

CH3

CH3

CH =C CH2 CH3

CH3

CH3

CH2 CH CH2 CH3

CH3

CH3

CH2 CH2 CH CH3

CH3

CH3

CH CH2 CH2 CH3

So, is this molecule called“1-methylpentane”?Build a model and you will see that it issimply “hexane”. It has NO side-branch.

Isomers of Alkenes & AlkynesJust like the alkanes, the alkenes & alkynes can alsohave isomers with side-branches, and the same rulesapply.

Additionally, the position of the double or triple bondmay require isomer numbering, such as:

“butene” (number not needed if “1”) “2-butene”

CH2 CH3= CH CH2 CH3 CH3CH = CH

Can you suggesta name for this

isomer ofhexene?

The correct IUPAC name is “hidden” on the next page.




keep it simple science® The Alcohols (Alkanols)

Now you are introduced to another importanthomologous series... the alkanols, knowncommonly as “alcohols”.

The alkanols contain all C-C single bonds, but onone of the carbon atoms there is an -OH group... anoxygen atom and hydrogen atom.

This is NOT a hydroxide ion (as in NaOH). It doesNOT ionise in water. It is referred to as a “hydroxyl”group. You will see later that the hydroxyl groupinvolves a polar covalent bond and that this hasgreat significance to the physical & chemicalproperties of these compounds.

Methanol CH3OH(Formula could be written CH4O,but it is usual to emphasise the -OH group)

Ethanol C2H5OH

This is by far, the mostimportant member of theseries.

Condensed StructuralFormula

CH3-CH2OH

Propanol C3H7OH

CH3-CH2-CH2OH

and then...

Butanol C4H9OH CH3-(CH2)2-CH2OH

Pentanol C5H11OH CH3-(CH2)3-CH2OH

Hexanol C6H13OH CH3-(CH2)4-CH2OH

Heptanol C7H15OH CH3-(CH2)5-CH2OH

Octanol C8H17OH CH3-(CH2)6-CH2OH

To name any ALKANOLadd “-ANOL” to the appropriate prefix.

General Formula CnH2n+1OH

O-H

HH

H

C

H O-H

H

H

H

H

C C

H H O-H

H

HH

H

H

C C C

Isomers of AlkanolsIt is completely possible for an alkanol to have“side-branch” isomers, just like the alkanes. In thatcase, the same rules would apply.

However, side-branch isomers are NOT the mostsignificant type of isomer among the alkanols.Much more important is the position of the hydroxylgroup within the molecule. Exactly where the -OHgroup is, turns out to have a major influence on thechemistry of the alkanol... details later.

Primary (1o) AlcoholsThis simply refers to alkanols in which the hydroxylgroup is located on the terminal (end) carbon atomin the molecule.

All the examples at left are 1o alcohols.

Secondary (2o) AlcoholsThis refers to alkanols in which the hydroxyl groupis located “inside” the carbon chain on a non-terminal carbon atom.

Examples:

2-pentanol

3-pentanol

All 2o alcohols can be described ina general way by this structuralformula, where R1 and R2 refer toany carbon-hydrogen chain.

Note that the carbon atom connected to thehydroxyl group is also carrying a hydrogen atom.Compare that to the tertiary alcohols below.

Tertiary (3o) AlcoholsThis refers to an alkanol with thegeneral structure shown, right.Note that the carbon atom carryingthe hydroxyl group is bonded to 3other carbon atoms and is NOTdirectly bonded to a hydrogen atom.This changes the way that 3o alchols react. (later)

Tertiary alcohols must have a side-chain.

Example:

2-methyl-2-butanol

(sometimes written as2-methylbutan-2-ol

This is also an isomer of pentanol, C5H11OH.

From prev.page. “3-methyl-2-pentene”

CH3

OH

CH2 CH CH2 CH3

CH3

OH

CH3 C CH2 CH3

OH

R1 CH R2

OH

R1 C R3

R2

CH3

OH

CH CH2 CH2 CH3

hexanol




keep it simple science® The Carboxylic Acids

This homologous series is defined by the presenceof a “functional group” called the “carboxyl” group(-COOH).

The general structure of a carboxylicacid is shown, where “R” can be assimple as a single hydrogen atom(methanoic acid, at right) or it mightbe a long carbon-hydrogen chain, with branches,multiple double C= C bonds and other variations.

The -COOH group must be on a terminal C-atom.

Because of the presence of the C= O bond attachedto the same carbon atom, the O-H bond in thehydroxyl group becomes more polarised and willionise in water forming hydronium ions.

That’s why they are called acids. However, they areweak acids because the degree of ionisation istypically only 1% or less.

OH

O

R C + H2O + H3O+O-

O

R C

OH

O

R C

To name any CARBOXYLIC ACIDadd “-ANOIC ACID” to the appropriate prefix.

Methanoic acid HCOOH (also known as “formic acid” ...research why)

The best known member of thisseries is ethanoic acid CH3COOH.

Also known as “acetic acid”, it isthe main ingredient in vinegar.

Then follow propanoic acid (C2H5COOH),butanoic acid (C3H7COOH), pentanoic (C4H9COOH),hexanoic (C5H11COOH), and so on.

OH

O

H C

OH

O

CCH3

C

O-H

OThis group is

usuallyabbreviatedas “-COOH”

and is alwaysacidic.

This bond is polar, and can ionise in water

These C-H bonds are non-polar, and never ionise.

Aldehydes & KetonesThe alkanals (traditionally called “aldehydes”) forman homologous series with the generalstructure as shown, where “R” could beas simple as a single hydrogen atom(methanal, below) or it might be alonger carbon-hydrogen chain.

The functional group (-CHO) must occur on aterminal carbon atom. The hydrogen attached tothe terminal carbon does NOT ionise to give anyacidic properties.

Methanal CH2O(traditionally known as “formaldehyde”and famously used as a preservative.)

Ethanal C2H4O

Propanal C3H6O CH3-CH2-CHO

Butanal C4H8O CH3-(CH2)2-CHO

Pentanal C5H10O CH3-(CH2)3-CHO

Hexanal C6H12O CH3-(CH2)4-CHOand so on.

The alkanones (traditionally called “ketones”) formanother series containing a C= O group, but it is ona carbon atom “inside” a carbon chain instead ofon a terminal carbon.

The general structure is shown, with R1 & R2 representing carbon-hydrogen chains.

Since the functional group ( C= O) must be “inside”the carbon chain, it follows that the first member ofthe series must have 3 carbons and is, therefore,

propanone CH3-CO-CH3(Traditionally called “acetone”and well known as “nail polishremover”)

butanone CH3-CO-CH2-CH3Once you get to 5 or more carbon atoms, theposition of the C= O group within the molecule canvary, so that isomers require numbers.

For example:CH3-CO-CH2-CH2-CH3 is 2-pentanone,whileCH3-CH2-CO-CH2-CH3 is 3-pentanone.

You might figure out the rest with your model kit.

H

O

R C

H

O

CH

H

O

CCH3

O

C R2R1

O

C CH3CH3

This acid behaviour was brieflycovered in Module 6... revise.

Note that each aldehyde & its corresponding ketone are isomers, since both have the formula CnH2nO




Halogenated Compoundskeep it simple science

®

“Halo-” refers to the “halogens”... the general namefor the elements of group 7 of the Periodic Table;fluorine, chlorine, bromine and iodine.

Halogen atoms can readily substitute for ahydrogen atom in any organic molecule whether itis an alkane, an alcohol, carboxylic acid, alkene, orwhatever. Here, we will apply the KISS Principleand cover only halogen substitution in alkanes.

The simplest example is a methane molecule withone of its hydrogens replaced by (say) a chlorineatom.

If, instead of chlorine, the replacement was:

• fluorine... CH3F = fluoromethane.• bromine... CH3Br = bromomethane.• iodine... CH3I = iodomethane.

Cl

HH

H

CCH3Cl

chloromethane

What if 2, or more, hydrogens were replaced bychlorine atoms?

Prefixes to use for the number ofhalogen atoms:1 = no prefix 3 = tri 5 = penta2 = di 4 = tetra 6 = hexa

When the molecule gets bigger, another variation that canoccur is in the position of the various atoms.

For example, these 2 molecules are ethane, with 2chlorines substituted in place of hydrogens.

Both Cl atoms attached Cl atoms attached toto same carbon. different carbon atoms.

1,1-dichloroethane 1,2-dichloroethane

Isomers of HaloalkanesMore Examples

C4H5Cl3F2

Best to number thecarbons from the right.

1,2,2-trichloro-1,3-difluorobutane

C5H5Br3F4

Best to numberfrom the left.

2,3,4-tribromo-1,1,1,5-tetrafluoropentane.

H F Cl

ClH

H

H

C C CCl

H

C F

F Br Br

HH

F

F

C C C

Br

H

C

HF

H

C

Where is this going next?The syllabus requires that we keep going with the “naming

thing” for a couple more homologous series.We think this is getting monotonous!

We will now switch to the study of the uses, properties &reactions of some important organic compounds.

If any of the groups we’re about to ignore come up, we’llgive you a quick lesson on their names at that time.

These molecules have the same molecularformula (C2H4Cl2) but have a differentstructure, and are different compounds. Their m.p. & b.p., density, and otherproperties would be slightly different. Wemust give them a different name.

This is done by numbering the carbonatoms (from whichever end gives thesmallest result) and stating the positionnumber for every halogen atom present.

Now Try Worksheet 1

CH2Cl2Dichloromethane

CHCl3Trichloromethane

CCl4Tetrachloromethane

Cl

ClH

H

C

Cl

ClCl

H

C

Cl

ClCl

Cl

C

This little beauty, CBrClF2 is called“bromochlorodifluoromethane”

ClBrF C

What if there is more than one type of halogen atomsubstituted? They must be ordered alphabetically byhalogen name... (not by any prefixes used, though). F




keep it simple science® 2. The Hydrocarbons

As you now know, “hydrocarbons” includes the alkane,alkene & alkyne homologous groups. (as well as some otherswe’re not getting into.)

You may already know the significance of these compoundsfor our society:

Energy SourcesAll our important liquid & gas fuels & lubricants are mixturesof hydrocarbon compounds. For example:

“Natural Gas” and L.P.G. are mostly methane.

“Bottled Gas” is usually propane or butane, or a mixture. Aswell as BBQ’s, bottled gas is used extensively in regionalareas for cooking & heating.

Petrol is a mixture of various alkanes (& some alkenes)ranging from pentane to octane, including branched-chainisomers.

Diesel fuel is a mixture of hydrocarbons with formulas fromabout C10H20 to about C15H32.

These fuels are the energy “backbone” ofour transport systems and havetraditionally been obtained from petroleum,a fossil fuel.

The use of petroleum fuels is stillincreasing, despite the link to climatechange by global warming. Our societydepends heavily on hydrocarbon fuels andironically this may contribute to theultimate downfall of our civilisation.But that’s another story... (later)

Chemical IndustryOne of our key industrial chemicals isethene (C2H4), commonly called “ethylene”.

More than 150 million tonnes is producedper year because it is a critical startingmaterial for making many of our plasticsand synthetic fabrics, plus many otherchemical products. Most of our ethene isrefined from petroleum.

Physical Properties of HydrocarbonsWhen the values for b.p. are graphed the patternbecomes obvious, and also the great similaritybetween the alkanes and alkenes (at least for thisproperty).

Inter-molecular Forces?Inside each molecule (“intra-molecular”) are strong,non-polar, covalent bonds.

However, the only forces between the molecules(“inter-molecular”) are weak “dispersion forces”, sothe molecules separate from each other easily. Thisexplains why m.p. & b.p. are generally low.

Dispersion forces arise due to transient electricalattractions from momentary imbalances of theelectric charge distribution within each molecule as itvibrates & rotates. These weak forces exist within allsubstances, but in ionic or polar comounds they areinsignificant. In hydrocarbons, that’s all there is.

Dispersion forces become stronger as the size andmass of the molecule increases, which explains thepattern of the graph.

Boi

ling

Poin

t (o C

)-2

00-1

000

100

1 2 3 4 5 6 7 8No. of Carbon Atoms

AlkanesAlkenes

Boiling Points rise as the molecules

get larger

Can you guess what thecorresponding graph for

alkynes would be? Prove it!

As you know by now, the properties of anychemical substance are determined by the bondingwithin.

Alkanes and alkenes contain only 3 types of bondwithin the molecules:

• Single C-C bonds• Double C= C bonds• C-H bonds

Therefore, you would expect these compounds to:

• have relatively low m.p. & b.p.’s and you’d• be insoluble in water be correct !• be non-conductors of electricity

To keep it simple, (K.I.S.S. principle) consider justthe boiling points:

Alkane b.p. State Alkene b.p. State (oC) 25oC (oC) 25oC

Methane -162 gasEthane -89 gas Ethene -104 gasPropane -42 gas Propene -48 gasButane -1 gas Butene -6 gasPentane 36 liquid Pentene 30 liquidHexane 69 liquid Hexene 64 liquidHeptane 98 liquid Heptene 94 liquidOctane 126 liquid Octene 121 liquid

all non-polarcovalent bonds

More on States & DensityAlkanes with more than about 25 carbon atoms are

solid at room temp. The stuff we call “wax” is amixture of alkanes with an average of 32 carbons.

Densities are lower than water. All liquid or solidhydrocarbons float in water.





Chemical Reactions of the HydrocarbonsThe fact that most of our hydrocarbons come frompetroleum which formed millions of years ago, shouldgive you a clue about their chemistry... these are(generally) stable chemicals which do not react orchange readily, even though many of them seem to belarge, fragile molecules.

The most important chemical reaction of thehydrocarbons (according to their human uses) is notmentioned in the syllabus for this module...

CombustionYou have studied this in the past, so this is a briefreminder. All hydrocarbons will burn by reacting withoxygen to form CO2 and water vapour.

We will compare the combustion reactions of ethane,ethene and ethyne so you see the differences betweencompounds with the same number of carbon atoms.

Energy releaseEthane (kJ per gram)

C2H6 + 7/2 O2 2CO2 + 3H2O 51.8

EtheneC2H4 + 3 O2 2CO2 + 2H2O 50.4

EthyneC2H2 + 5/2 O2 2CO2 + H2O 50.0

Safety ConsiderationsSafety ConsequencesWe haven’t yet looked at the chemical properties of alkanesand alkenes, but don’t forget that these are fuel compounds...they contain a lot of energy, are highly inflammable, and nowwe find out they are highly volatile as well! DANGER, DANGER!

Natural Gas is mostly methane.It is stored in high pressurecylinders, outdoors & kept cool.

Propane & Butane areused as bottled “BBQ gas”.They are stored as pressurisedliquids in pressure cylindersand used outdoors, or in well-ventilated areas only. Smallamounts of “smelly” chemicalsare added to gas fuels so thatleaks are easily detected bysmell.

Petrol, Kerosene & Diesel are highly volatile liquidfuels. They must be stored in sealed drums or tanks, and allsparks or flames (even mobile phones) kept well away. Alltransfer of fuel from tank to tank (e.g. filling the car) must bedone outdoors.

You will NOT be doing any practical work with thesesubstances because of safety concerns, plus their fumes areharmful if inhaled.

VolatilityA substance is said to be volatile if, atroom temperature, it vaporises readily. Asimple indicator of volatility is the boilingpoint, but it is not the only factor.

Obviously, the alkanes and alkenes with 4or less carbon atoms are already gases atroom temperature, but even those whichare liquids are highly volatile.

Consider octane, a component of petrol. Itsboiling point is a little above that of water,but it is much more volatile. At roomtemperature, octane (petrol) in an opencontainer vaporises rapidly compared towater under the same conditions.

The explanation is, again, all aboutbonding. Water molecules tend to clingtogether because of the dipole-dipoleattractions of hydrogen bonding. Octanemolecules have only the weak “dispersionforces” holding them, and manymolecules have enough energy to escapeinto the gas state, even at temperatureswell below the boiling point.

The volatility of the alkanes and alkeneshas important safety consequences.

Note the different molar quantities of oxygenrequired for complete combustion in eachcase. Less oxygen is needed if there is lesshydrogen in the hydrocarbon, & slightly lessenergy is released. (if measured per gram offuel) Less water is formed, per mole of fuel.

No-one uses ethene (ethylene) as a fuelbecause it is too valuable for making plastics,etc. Ethyne (also known as “acetylene”) isused in high-temperature “oxy-acetylenetorches” for welding and cutting metals.

Now compare the ethane reaction with that ofoctane, a component of petrol.

Octane (kJ per gram)

C8H18 + 25/2 O2 8CO2 + 9H2O 47.9

Compared to ethane, mole-for-mole thisproduces 4x as much CO2, but only 3x asmuch water, with about 7% less energy yieldper gram, although this is still high.

Undoubtably, the hydrocarbons (especiallyalkanes) ARE high-energy, convenient fuels.They are really useful, but we need to findalternative, renewable sources of them.




keep it simple science® Reactions of the Hydrocarbons (cont.)

ALL the hydrocarbons will undergo combustion,but (chemically) that is where their similarity ends.

In other chemical reactions, the alkanes are verydifferent to the alkenes & alkynes. It is as if we candivide the hydrocarbons into 2 distinct chemicaltypes... and so we do:

Saturated v. UnsaturatedThe alkanes are said to be “saturated” (withhydrogen), meaning that each molecule has themaximum number of hydrogen atoms possible.

This is because all the C-C bonds are single, soevery other bond position is occupied by hydrogen.

The alkenes and alkynes have at least one double(or triple) C= C bond. This reduces the number ofhydrogens possible in the molecule. This conditionis described as “unsaturated”.

One of the few reagents which will react with analkane is one of the halogen elements... F2, Cl2 andBr2. (I2 has lower activity; doesn’t react easily)

The reaction is called “substitution” because ahalogen atom substitutes for a hydrogen atom.

eg CH4 + Cl2 CH3Cl + HClmethane chlorine hydrogen chloride

chloromethane

Reactions of this type can be initiated by UV lightand can result in a complex mixture of differentproducts. This is because substitution reactionsproceed by a chemical process involving “free-radicals”, explained below.

Step 1. Free-Radical Formation

Cl Cl Cl• + Cl•

A Cl2 molecule struck by high frequency light suchas ultra-violet rays can split to form 2 unbondedsingle chlorine atoms.

These bare atoms are highly reactive and will“attack” almost any other substance. Highlyreactive chemical species like this, with a “naked”electron are “desperate” to form a chemical bond,and are called “free-radicals”.

Step 2 Free-Radical Attack

If a Cl• free-radical meets an alkane it will “steal” ahydrogen atom to form HCl:

Some long-chain molecules may have multiple C= Cbonds. These are said to be “polyunsaturated”, aterm you may have heard in relation to fat & oilmolecules in our food.

Whether a hydrocarbon is saturated or unsaturatedhas consequences in terms of which chemicalreactions (apart from combustion) each compoundwill undergo.

Basically, the story is:

• the C-C and C-H covalent bonds are quite stableand relatively unreactive, except for combustion,

BUT

• the C= C double (or triple) bond is much morereactive and will readily undergo a variety ofchemical changes.

Halogen Substitution Reactions in (Saturated) Alkanes

UV energy

H

•H

H

C

H

HH

H

C + Cl• + HCl

Step 3 Free-Radical Propagation

The CH3• species is another free-radical (“methylfree-radical”) and is also highly reactive. If it bumps into a Cl2 molecule:

Can you see what is happening? Each attack by afree-radical produces yet another free-radical.

Free-radicals are propagating or “reproducing”.This produces a “chain-reaction” or cascade ofreactions. A mixture of an alkane with chlorine,kept in the dark, will not react. Expose it tosunlight (or certain catalysts) and there may be asudden explosion as free-radical reactions occur!

There can be a great variety of products because amolecule that already reacted, may react again:

eg CH3Cl + Cl2 CH2Cl2 + HCl

and even:

Typically, if there is an adequate supply ofchlorine, the final product mixture may containdozens of different haloalkanes, including somewith longer alkane chains.

H

•H

H

CH

ClH

H

C+ Cl2 + Cl•

H

•H

H

C

H

•H

H

C+ C2H6

chloromethane product

chloromethane + chlorine dichloromethane + hydrogen chloride

Two methyl free-radicals ethane




keep it simple science® Addition Reactions in Unsaturated Hydrocarbons

PetrochemicalsWhen petroleum is refined, the major products arethe fuels such as petrol and diesel. However, it’snot all about fuel. Our chemical industry dependson a whole range of other compounds extractedfrom petroleum, which are collectively called“Petrochemicals”.

Petrochemicals are vital raw materials for themanufacture of• plastics and synthetic fibres• pigments for inks, dyes and paints• detergents & adhesives• cosmetics & pharmaceuticals• explosives

... and much more.

One of the most important petrochemicals is

Ethene C2H4Ethene is also knownby its common name,“Ethylene”.

We will use ethene asour prime example for the reactions following,because:

• it is one of the most useful chemicals on Earthand• it is the smallest & simplest example of anunsaturated hydrocarbon. (KISS Principle!)

H

HHHC C

H

HH

H

C C

X Y

XThe double

bond is highlyreactive

Many substances will“attack” this bond

It readily “splits open”leaving a single C-C

bond, and creating 2 newbond positions for otheratoms/groups to attach

to the molecule.

THIS IS CALLED AN “ADDITION REACTION”

Reactions of EtheneFor each of the following you should use yourmolecular model kits to construct and follow thecourse of the reaction. Be sure you can see whythese are called “addition reactions”.

Reaction with Hydrogen

+ H2

Ethene + Hydrogen Ethane

Reaction with Bromine (or any halogen)

+ Br2

Ethene + Bromine 1,2-dibromoethane

Reaction with HCl

+ HCl

Ethene + Hydrogen Chloride Chloroethane

Reaction with Water

+ H2O

Ethene + Water Ethanol

These are just a few of the possible additionreactions that can occur across the double bond.

You may be required to study these in more detail.For example, some of these require heating, somerequire a catalyst, etc.

For now,

H H

HHC C

H H

HHC C

H H

HHC C

H H

HHC C

H H

HH

C C

H H

H H

HH

C C

Br Br

H H

HH

C C

H OH

H H

HH

C C

H Cl

Now Try Worksheet 2

The difference between the “substitution” reaction of a saturated alkaneand the “addition” reactions of any unsaturated hydrocarbon,

opens up a simple chemical test to tell them apart...

Y





You may do simple experiments to learn how an alkene can bequickly and easily identified, and differentiated from an alkane.

A water solution of bromine (Br2(aq)) has a brown colour.If it is in contact with a liquid hydrocarbon, the water and thehydrocarbon form separate layers... they are immiscible liquids.Water, being denser, will always be at the bottom.

Bromine is actually more soluble in a hydrocarbon, so whenshaken, it will dissolve into the top hydrocarbon layer, andchanges colour from brown to purple.

Now this can be confusing! This switching of layers and colourchange is NOT the test result you are looking for.

In an alkane (hexane is often used) the colour will change andswitch layers, but it will remain coloured because no reactionoccurs. (Substitution reactions with bromine require a lot ofactivation energy to form some free radicals.)

In an alkene (e.g. hexene) the bromine totally loses all colourbecause an addition reaction occurs readily at room temperature.

The Reaction of Bromine with Hexene

+ Br2

Hexene Bromine 1,2-dibromohexane

H

HHC C

H H H

HHH

C C CH

H

C H H

BrBr

HH

C C

H H H

HHH

C C CH

H

C H

Practical Work Identifying Alkenes with Bromine

Before Shaking

Hexene layer

Brown “BromineWater” layer

After Shaking

Clear Hexene layer

Clear water layer

The bromine isdiscoloured by anyalkene.

Shapes of Hydrocarbon MoleculesWe might draw a structuralformula like this diagram,with all the carbons in astraight line.

However, we believe that the bonding positionsaround each carbon atom stay as far away fromeach other as possible, so in 3D the bonds point tothe corners of a triangular pyramid... a tetrahedron.

You will have seen this whenbuilding models, such asmethane, shown here.

When you build longer chains,the carbons are NOT in straightlines like this,

but zig-zag like this.Furthermore, C-C single bonds are believed to beable to rotate around the axis

of the bond, so each molecule must be a riot ofmovement, with atoms spinning on their bonds,vibrating internally, tumbling in space, etc.

If you build a model of (say) hexane, try twisting itaround the C-C bonds in all directions... whateverthe model can do, the real molecules can do, andthey probably do so millions of times per second!

Effect of Double & Triple BondsTry building models of ethane, ethene & ethyne forcomparison.

Ethane is very much a 3Dmolecule. With the H-atomssticking out and able to rotate, itis like a pair of little propellersstuck back-to-back.

Ethene is more rigid and 2D.The double bond does NOTallow rotation and the H-atomslie in the same flat plane.

Ethyne is rigid (no rotationaround the bond) and linear.

These models are thought tomimic the real molecules, sowhat you see is at leastsome indication of reality.

Try building larger modelswith, and without, doublebonds, to see the effects onmolecular shape. Forinterest, build this model.(alternating C-C and C= C)It’s not in the syllabus, butworth finding out about.

H H H

HH

H

H

C C CH

H

C

HH

H

C

C C C C C

CC

CC

C




keep it simple science® Environmental & Socioeconomic Impacts

The consequences of humans obtaining and usingpetroleum could fill many books... and have doneso. What follows here is the briefest outline. It is upto you to research more detail as needed.

Obtaining PetroleumPetroleum deposits (including Natural Gas) are thefossilised chemical remnants of ancient sea creatures.Petroleum is a complex mixture containing alkanes,alkenes and many other carbon compounds, trapped insedimentary rocks.

To obtain the fuels weneed, the first step is, ofcourse, to locate thepetroleum, drill down andpump it to the surface.

The next step is toseparate the crude petroleum mixture into moreuseful “fractions”. This is achieved by...Fractional Distillationwhich separates the mixture according todifferences in boiling point.

Oil Well Pump,Alberta, Canada

Tem

pera

ture

dec

reas

es

up th

e to

wer

Petrol

Heating &Fuel Oil

LubricatingOils

Residue:Grease &Bitumen

Diesel &Kerosene

Fractionating Tower in a RefinerySimplifiedSchematicDiagram

VaporisedCrude

Oilinjected

Gas fractionL.P.G.

Vapours rise through

the tower

Vapours condense oncollection trays...

at different levels...

according to boiling point

Each fraction is still a mixture. For example, petrolcontains dozens of individual compounds, and theexact composition varies from place to place, andfrom time to time. It depends on which crude oilsource is being refined, and on any adjustmentsmade by the chemical engineers at the refinery.

When the“fractions”areseparatedby fractionaldistillation,there is alargefraction oflow-valuealkanes with 15 or more carbon atoms. e.g. pentadecane C15H32

These large molecules are broken into smallermolecules by a process called “Cracking”, whichcan be done by simply heating (“Thermal Cracking”)or by the use of a catalyst... “Cat Cracking”.

When the molecule is broken into fragments, somepieces form as alkanes, but others must form asalkenes, because there are no extra hydrogen atoms tooccupy the bond positions that are created.

Once “cracked”, the mixture is fed back into theFractional Distillation process. Many of the smallermolecules end up in the valuable petrol or dieselfractions. Any ethene (valuable as a major“feedstock” for plastics manufacture) formed isrecovered from the gas fraction.

H

H

C

H H

H

HH

C C

H

HC

H H

HHH

C C C

H

H

C H

H

H

H C

H H H

HHH

C C CH

H

C

H H

HHC C

“Cracking” of C15H32used as an example

If you add up all theatoms in these 3 productmolecules, you’ll see that

the total is the sameEthene, C2H4

Pentene, C5H10Octane, C8H18

Oil RefineryFractionating Tower

Some of the environmentalimpacts of obtainingpetroleum have been bignews whenever they occur.

However, such accidentsare insignificant comparedto the threat of climatechange and massextinctions which arealready happening. Burning Oil-Rig, 2010.

Image by US Coast Guard

Now Try Worksheets

3 & 4




The Climate Change Debate

Is the World Warming Up?Apparently yes! Since 1850, there is evidence in weather records, and inthe ice cores, of a rise in average global temperature.Each of the last 3 decades has set, in turn, a new recordfor being the hottest decade ever recorded. All scientistsagree that the average world temperature is rising.

Cause of Global Warming? The mass media seem to have accepted that globalwarming is a direct result of an “enhanced greenhouseeffect” due to emissions of (mainly) CO2 from fossil fuelburning. Public opinion now generally accepts this, sothat politicians are also forced to accept it, or run the riskof losing votes.

What is the Science?

Greenhouse Effect due to CO2?Laboratory experiments prove that CO2 does “trap” heat,and so it can act as a “greenhouse gas”.

There is clear evidence that atmospheric CO2 levels haveincreased by almost 30% since 1850. The correlation withrecent global warming is a very strong one.

Furthermore, we know that ice core data shows a strongcorrelation between global temperatures and CO2 levelsover the past 500,000 years or more. In this time theworld has gone through a series of “ice ages” and warm“interglacials” and the CO2 levels have changed in lock-step with these global climate changes.

For the past 20+ years, the IPCC (an international groupof experts in many fields, commissioned by the UnitedNations) have reported their conclusions on 5 separateoccasions. Their latest report can be summarised as:

• global warming is really happening.• its cause is most likely due to increased CO2 emissions

from human activities.• average global temperature are likely to rise by at least

2oC this century. (This may be an under-estimate)• polar regions will be affected most quickly and severely.• sea levels WILL rise. Predictions are 0.5 - 5m by 2100.

The next IPCC report is due in 2022.

Natural Climate Cycle?Until recently, some scientists were notconvinced that the current global warming istotally due to CO2 emissions. They pointed outthat there have been major, natural fluctuationsof “ice ages” and “interglacials” over the pastfew million years.

Since the most recent ice age ended onlyabout 15,000 years ago, they argued that partof global warming could be due to ourcontinuing emergence into the nextinterglacial.

However, the latest climate data has made itclear that Global Warming IS happening and ISmainly due to human activities.

Assessing the Predictions Whatever its cause, the warming itself is nowaccepted as a fact, and scientists arecontinually refining the various “climatemodels” which allow predictions of what theimpacts will be.

Everyone agrees that global warming has thepotential to (at least partially) melt the ice-capsand raise sea levels. There is concensus thatthere will be more violent storms, and shifts inrainfall patterns.

All models agree that the effects will not beuniform: some places will be affected morethan others, and some places will experienceeffects quite the opposite of others.

However, there is still a lot of uncertaintybecause the Earth’s climates are so verycomplex. We do not yet know enough aboutthese complexities to make perfectly accuratepredictions.

Some climate factors may be very stable andself-correcting, others may reach some criticalpoint and then undergo a major “tipping-over”change. One such factor (worthy of yourresearch) is the possible release of vastquantities of methane from the Arcticpermafrost and from the ocean floor.

Simplistic ViewpointsMany people deny that climate change is happening, and/or they refuse to believe that its cause is

connected to human activities. For example, in January 2019, when extreme winter blizzards struck in partsof the northern hemisphere, the US President asked sarcastically “so, where is Global Warming when youneed it?” Such simplistic ideas about this debate reveal an alarming lack of understanding of the Science.

“Global Warming” does not just mean that the weather gets warmer. The important concept is that it meansthat more energy is driving weather and climate. Yes, temperatures will rise on average, but more energy

generates more wind, more storms, more extremes of weather, including occasional colder blizzards.

Our climate models predict shifts in climatic zones. Rainfall patterns will change. Areas which can now grow food, may decline. Other areas may become more productive.

This might even out eventually, but during the period of change it is likely there will be economicdisruptions, vast movements of populations and possible human conflicts. (Sound familiar?)

The impacts on natural environments & extinction rates of plants & animals are already ramping-up.





Environmental Impacts

Socioeconomic Impacts

Causes of ExtinctionScientific studies have identified that the main causes ofextinction of a species are: (in random order)• Habitat loss due to deforestation, land-clearing, etc.• Pollution • Climate Change• Introduction of alien species

A 2004 report in the leading journal “Nature” summarisedthe work of over 10,000 leading scientists. It concludedthat the current extinction rate is hundreds of timeshigher than normal. At that rate, we can expect 10% of allspecies of plants and animals to disappear by 2050, and 50% by 2100.

Over the history of the Earth there have been at least 5 “Mass Extinction Events” whena large percentage (50%+) of living things died out quite suddenly. In every case, we think the cause was

rapid climate change caused by meteorite impact, or episodes of massive volcanic activity. Many scientists believe we are now entering another “Mass Extinction Event” due to human activities.

Deforestation in Central America

In January 2012, 100 European researchers met inCopenhagen to discuss the latest findings. Theyestimated that about 30,000 species are becoming extincteach year. Many are species that we know little or nothingabout.

Does it Matter?People might worry about whales and Polar Bears, but sowhat if some obscure plant or insect disappears?

The problem is that every species can be connected tomany others in an ecosystem. There are many complexrelationships which we do not understand.

Extinction of one life-form breaks a connectionand weakens an entire ecosystem. Like adomino effect, each extinction helps bring onthe next, until the entire system may collapse.

Many ecosystems are vital to us. Ocean foodchains give us millions of tonnes of food.Rainforests are the “lungs” which absorb CO2and produce O2. Collapse of these systemswould threaten our own survival.

There are many practical, ethical and moralreasons to be concerned about biodiversity.

Refugees from drought &conflict, east Africa, 2011.

Changes in Wealth & SocietyIn recent decades, many societies have become moreaffluent and politically aware. Generally speaking, thesechanges are good things, but affluence brings moreconsumption of goods, resources & energy. Theemergence of a huge “middle-class” in countries suchas India & China is especially notable. This socialchange does not help to counteract climate change.(We mention this NOT to criticise any particular countries, but simply state the facts.)

Meanwhile, across the Middle East & N.Africa there hasbeen political unrest and conflict for some decades. Thishas resulted in, not only great destruction & suffering,but movements of millions of refugees seeking greaterfreedom, safety & security. Who can blame them?

Food Production & Water SupplyAs weather patterns shift, some areas which are now toocold, or too dry for much farming may become moreproductive. However, other places which now grow a lotof food, may become hotter, drier and less productive.

It may all eventually even out, but meanwhile there willbe a time of disruption to food supply. The greatestworry is in Africa, where vast areas that can barely growenough food now, seem likely to be badly affected byboth lack of water and food due to climate change.

Human Societies & HealthWarmer average temperatures are predicted tohelp the spread of certain tropical diseases andparasites. These could be devastating incommunities where malnutrition is morecommon.

Changes to food & water supplies will causemore people to become refugees and try tomove elsewhere.

The movements of millions of people willinevitably bring some groups into conflict. Weshould expect even more regional warfare andcivil unrest, especially in parts of Africa.


Wow! Can it really be true that all these things are due to humans using hydrocarbons? Well, coal isinvolved too, but certainly the human usage of fossil fuels is one of many direct threats to our global future.

Our use of petroleum is still increasing, despite development of “green alternatives”. People travel more & buy more manufactured items which are transported world-wide. We are “addicted” to

cheap energy & goods and “locked into” a global economy. Are YOU prepared to give up the benefits?




keep it simple science® 3. The Alcohols

The structures, formulas and names for the alkanols, including 1o, 2o & 3o alcohols, were covered earlier.

Physical Properties of AlkanolsWhat a difference that oxygen atom makes!

The polar covalent bond in the -OH group creates acharge dipole, and strong hydrogen bonding existsbetween the molecules.

This results in mp’s and b.p’s being much higher thanthe corresponding alkanes. The first 8 alkanols are allliquids at room temperature. (none are gases)

δδ+δδ-

Polar Covalent Bond

Non-Polar CovalentBonds

createselectricchargedipole

Ethanol

Boi

ling

Poin

t (o C

)-2

00-1

000

100

200

1 2 3 4 5 6 7 8No. of Carbon Atoms

AlkanesAlkenes

Primary Alkanols

The smaller alkanols are soluble and fully misciblein water, because they can form hydrogen bondswith water molecules. The larger ones become lesssoluble as the non-polar hydrocarbon chain growslonger.

The alkanols (especially ethanol) are excellentsolvents, able to dissolve many water-soluble(polar) solutes, but also able to dissolve many non-polar substances which do not dissolve well inwater. This is why ethanol is widely used inindustry to dissolve reagents, pharmaceuticals andfood chemicals. Around the home “methylatedspirit” is used as a cleaning agent... it dissolvesthings that won’t wash off easily with water.

(Methylated Spirit, or “metho” is about 95% ethanol,5% water with small amounts of additives to make itdistasteful to discourage anyone from drinking it)

Alkanols are inflammable, and can be used as fuels,although their energy content is not as high as thecorresponding alkanes. (More on that later)

Ethanol is, of course, the alcohol in beer, wine andspirits. These are made by the process offermentation (below) carried out by living microbes,especially yeast, which is a single-celled fungusorganism.

You should be aware that, despite our society’sacceptance of the consumption of alcohol as asocial drug, all the alcohols are toxic. Our bodiescan tolerate ethanol in small doses, but others suchas methanol or propanol, are quite dangerous andpotentially lethal.

Boiling Points of alcoholscompared to alkanes & alkenes.

Prac Work FermentationYou may have carried out an experiment toferment sugar to ethanol.

The photo shows a typical laboratory set-up. The flask contains sugar & yeast in water. Temp. should be kept at about 25oC.

Overall reactionGlucose Ethanol + Carbon dioxideC6H12O6(aq) 2 C2H5OH(aq) + 2 CO2(g)

You might weigh the flask before, and after, several days offermentation. It will lose mass due to the loss of CO2 gas.

You will also observe bubbling in the flask over several days,and the limewater would rapidly go “milky” proving that thegas produced is CO2.

When the bubbling subsides, the contents of the flask mayhave the yeasty, alcohol smell of beer.

You may have even distilled your brew to collect ethanol, asdescribed at right.

Fractional Distillation of Your “Home-Brew”Heat gently and monitor

the vapour temp.Collect only the fractionproduced at about 80oC.

To test your distillate: poura few drops into a watch

glass and ignite carefully ina darkened room or fume-cupboard. If it burns with ablue flame, your distillate is

80-90% ethanol.

Any gas produced bubblesthrough a beaker of limewater

Fermentation

Distillation

Electric heating.NO FLAMES !!




keep it simple science® Chemistry of the Alkanols

CombustionYou are reminded (from Module 4) of the equationfor the combustion of ethanol:

C2H5OH(g)+ 3O2(g) 2CO2(g)+3H2O(g)(The tricky part is balancing... be careful balancing the

oxygen atoms, noting that there is already 1 oxygen atom on the left side in the ethanol molecule.)

All the smaller alkanols burn well and can be usedas fuels. Ethanol is added to petrol (at 10%) as an“extender” and as a token attempt to reducegreenhouse gas emissions. This is discussed laterin this section.

Enthalpy of CombustionThe Syllabus requires you to measure the enthalpyof combustion for a range of alcohols.

This was covered previously in Module 4.

Our description of a simple experiment is repeatedbelow.

This technique is notoriously inaccurate, (theanswer you get may be very wrong) but in the caseof comparing the heats of combustion of differentalcohols, what is important is to achieve somereliability in your results.

Prac Work: Measuring ΔΔHc of AlcoholsYou may be able to carry out experiments to measure and calculate values for the Heat of Combustion of

several alcohol fuels. A typical school experimental set-up is shown:Thermometermeasures temp.change in water.

Metal can holds ameasured quantity ofwater. It acts as acalorimeter, absorbingheat released by thefuel.

“Spirit burner” burnsan alcohol fuel using awick.

Burner is weighedbefore and after to

measure the mass offuel used.

Typical results using EthanolMass of ethanol burnt = 0.80g Mass of water in metal can = 100gStarting temperature of water = 16oC Final temperature of water = 42oC

ΔΔT = 26oCAnalysis of ResultsHeat absorbed by water in the calorimeter:

Q = m.c.ΔΔT = 0.100 x 4,183 x 26 = 10,876 J ≅≅ 11 kJThis is the heat absorbed by the water for 0.80g of ethanol burnt.

∴∴ Heat of Combustion per gram = 11 / 0.80 = 13.75 kJ/g

MM(ethanol) = 46.1g∴∴ Molar Heat of Combustion = 13.75 x 46.1 ≅≅ 630 kJmol-1.

Chemical Summary:C2H5OH(g) + 3O2(g) 2CO2(g) + 3H2O(g) ΔΔHc ≅≅ 630 kJmol-1.

Hopefully, you might be able to repeat this activity with severaldifferent alcohols.

DiscussionFirstly, those of you paying attention will have spotted that our chemical summary is not correct! The statesgiven for the ethanol and for the water vapour are a correct description of what happened in the experiment,but are incorrect for the formal definition of “Heat of Combustion”. (Revise in Mod.4)

What about the value obtained? The “text book value” of ΔΔHc (ethanol) = 1367 kJmol-1. Typically, in a schoolexperiment, values of only about half, or less, are obtained. Why?

The analysis of results assumes that all the heat released by the burning fuel is absorbed by the water in the“calorimeter”. However, this calorimeter is very primitive and inefficient. A lot of (most of?) the heat of the fuelcan escape into the surroundings, and therefore does not get measured. Accuracy can be improved by using alarger can, wind baffles, insulation, etc., but will always give results well below “text” values.

To improve reliability you must ensure that every detail (eg distance from burner to tin can, time of heating, etc.)is the same from one trial to the next. This way, the results may be inaccurate, but will be consisently wrongfrom one trial to the next, which allows valid comparisons from one alcohol to another.

If you wish to find out how scientists obtain accurate measurements of combustionenergies, research “Bomb Calorimeter”.




keep it simple science® Chemistry of the Alkanols (cont.)

Dehydration ReactionYou previously saw that ethene can be converted toethanol by an Addition Reaction across the doublebond. You may have used molecular model kits tohelp visualise this reaction. The reaction isfacilitated by dilute sulfuric acid, which acts as acatalyst.

CH2= CH2 + H2O CH3-CH2-OH

Ethanol to EtheneThe reverse reaction is also possible:

CH3-CH2-OH CH2= CH2 + H2O Once again a catalyst is needed to make thereaction run at a practical rate for an industrialprocess. The same catalyst, sulfuric acid is used,but in concentrated (not dilute) form.

The reaction is called “dehydration” because wateris removed from the molecule.

The significance of this reaction is that ethanol canbe made from plant materials by fermentation, aprocess that is renewable and sustainable. Makingethylene (ethene) by dehydration of ethanol wouldresult in a major chemical resource being availablewithout needing petrochemicals.

Substitution with HX“HX” is a chemical shorthand for hydrogen bondedto one of the halogen elements. “HX” might meanHF, HCl, HBr or HI. Most commonly it refers to HCl,hydrochloric acid.

Concentrated HCl will react with an alcohol toproduce chloroethane.

ethanol + HCl chloroethane + water

CH3-CH2-OH + HCl CH3-CH2Cl + H2OThis reaction is described as “substitution”, but itdoes NOT proceed (like halogen-substitution in analkane) via the formation of free-radicals. Free-radical reactions can take a variety of directionsand produce a mixture of many different products.

This substitution cleanly replaces the -OH groupwith the halogen, without variations.

A 2o alcohol such as 2-propanol would react:

2-propanol + HBr 2-bromopropane + water

CH3-CH-CH3 + HBr CH3-CH-CH3 +H2O| |

OH BrYou might use molecular models to clarify these.

dilute H2SO4 catalyst

+

conc. H2SO4 catalyst

+Ethanol

WaterEthene

OxidationIf necessary, you should revise the concepts of“REDOX” chemistry, covered in Module 3.

In your REDOX Data Sheet, you will find two strongoxidising agents (near the bottom) of interest here.

Cr2O72- is the “dichromate ion”.

MnO4- is the “permanganate ion”.

You might see from the half-equations in the DataSheet that these ions need to be acidified. Thenthey act as strong oxidising agents. One of thethings they will attack is an alcohol.

Primary Alcohol example

ethanol ethanal ethanoic acid

CH3CH2OH CH3CHO CH3COOH

A 1o alcohol is oxidised to an aldehyde. This can befurther oxidised to the carboxylic acid.

As the reaction proceeds, the Cr2O72- may change

colour. This can be a useful “indicator” for thereaction.

Both these ions areused in the form ofsalts of potassium:K2Cr2O7 & KMnO4

acidified dichromate,more heat + reflux

acidified dichromate,gentle heating

Secondary Alcohol example

2-propanol propanone

CH3-CH-CH3 CH3-C-CH3| ||OH O

A 2o alcohol is oxidised to a ketone.

Tertiary Alcohol2-methyl-2-butanol NO REACTION

acidified dichromate,heat + reflux

CH3

OH

CH3 C CH2 CH3

acidified dichromate

Tertiary alcohols doNOT react.

These differences areuseful for identifyingan alcohol as either

1o, 2o or 3o.




keep it simple science® Alcohols As Fuels

(and other issues)

Future Bio-FuelsBecause of the “Fuel v. Food” controversy, the European Union has declared that “1st generation bio-fuels”(those which require crops growing on arable land) will be banned by 2030. Research has been underway foryears to develop the next generation of biofuels. There are several promising directions being investigated:

Using Agricultural WasteEvery year, millions of tonnes of plant wastes are produced (stems, husks, etc) from our food plants. Using

genetically modified micro-organisms, (GMO’s) it should be possible to break these wastes down to amaterial which could then be fermented to produce ethanol, etc. without reducing the land available for food.

Using Non-Arable LandSome research projects are aimed at using non-arable land, such as salt water ponds in deserts, to grow GMalgae (or other GMO’s) to produce sugars or oils for bio-fuel. Promising, but not yet commercially available.

Electric Cars?Recent developments in light-weight storage batteries have seen great improvements in electric cars.

However, if these are re-charged using coal-generated power, we are not much better off environmentally. As renewable electricity systems (solar, wind, etc.) continue to grow and dependance on coal declines,

it may be that we can wean ourselves off petrol, to the electric car.

However, that seems unlikely to happen for heavy transport. Trucks, trains, ships & aircraft may depend on petroleum for some time yet.

Ethanol to Replace Petrol?Using the process of fermentation, followed bydistillation, ethanol can be manufactured on anindustrial scale from either sugar or corn starch.

High-yielding oil crops can be grown to producealternative “bio-diesel” fuel for heavy transport.

The use of these alternative “bio-fuels” isto try to reduce CO2 emissions from fossilfuels and reduce our dependance on them.

(Bio-fuels also release CO2, but this is equal tothe amount absorbed by the growing plants.

Therefore, these fuels are claimed to be“carbon-neutral”. If you do some research on

this, you will find that such claims may be“optimistic” with current methods.)

Ethanol can be added to petrol in mixturesup to about 10-20% and burnt in carengines without any modifications needed,and with only a slight loss of engineperformance.

This use of ethanol as an “extender” toconserve petrol and help reduceemissions, has been around for years, so10% ethanol fuel is now common.

Sounds good so far, but the concern isabout the amount of arable land required togrow the crops for bio-fuel. It can becalculated that, to totally replace petroleumfuels with bio-fuels would require up to75% of all the farm land in the world!

This is obviously not a viable way to go.

Pro’s & Con’s of Ethanol FuelAdvantages• Ethanol is a renewable fuel, when made

from plant chemicals.• The technology is already known and proven.• It is (theoretically) “Greenhouse-friendly”.• It can be mixed with petrol up to about 20% andused without any modifications to existing engines.

This, however, is only part of the story...

Disadvantages & Difficulties• To totally replace petrol with ethanolup to 75% of agricultural land wouldhave to be dedicated to growing cropsto supply the ethanol industry. Theattempt by Brazil to do exactly this inthe 1980’s was an economic failure, anddisrupted a lot of their food productionfarming to make way for “ethanolfarming”.

• The current technology for ethanolproduction requires massive amountsof energy for the distillation process.Currently fossil fuels are used forheating and transport, and so theprocess is not as renewable, nor“Greenhouse-friendly” as first thought.

• To run vehicles on pure ethanol fuelrequires a total new engine design toallow for the fact that ethanol tends tobe corrosive, has a different energycontent, ignition temperature and burncharacteristics. The cost of the change-over, to both manufacturers and car-owners makes this unlikely to happen.

(Note: Australian ethanolproduction uses only wastes

from the sugar industry.)

Now TryWorksheets 5 & 6




keep it simple science® 4. Organic Acids & Bases

Comparison of Physical Properties:Alcohols cf. Carboxylic Acids

You learnt previously how the alkanol “hydroxylgroup” (-OH) contains a polar bond, and how thiscauses the properties of the alkanols to be quitedifferent to those of the corresponding alkanes.

Polarity of the alkanol functional group

In an alkanol, the dipoles result in hydrogen bondingbetween molecules.

For example, in ethanolthe molecules are

attracted by their dipole charges andform a hydrogen bond.

O-H

CH3 CH2

R O HThis bond is polar

δδ+

δδ+δδ-O-H

CH3 CH2

δδ+δδ-

δδ-

Hydrogen bond

So, for example, in ethanoic acid...

each pair of molecules has 2 sets of dipoles,so twice as manyH-bonds can form.

You already know that the alkanols have muchhigher m.p’s & b.p’s than the correspondingalkanes, because of the hydrogen bonding betweenmolecules.

The m.p’s & b.p’s of the carboxylic acids are higherstill, due to the presence of extra dipole-dipoleattractions.

For comparison:Ethane Ethanol Ethanoic acid

Boiling Pt (oC) -89 +78 +118

O-H

OCH3 C

O-H

O

CH3C

δδ+

δδ+

δδ-

δδ-δδ-

δδ-

Dipole-Dipoleattractions

Carboxylic Acids + Alcohols = Esters“Esters” are a group of organic compounds formed by the reaction between an alcohol & a carboxylic acid.The reaction to form an ester is described as a“condensation” because it produces a watermolecule, but it is so widespread in nature, and soimportant, that it rates its own name, “esterification”.

The reaction can be visualised as follows:

OHR1 R2H-OO

R2C

Carboxylic acid(R2 is the rest of the

molecule)

Alcohol(R1 is therest of themolecule)

These atoms form water, and the 2 molecules join together

+ H2OEster

OO

R1 C

Example: If ethanoic acid reacted with butanol:

CH3COOH + C4H9OH CH3COOC4H9 + H2O

ester name = butyl ethanoate

You should use a molecular kit to visualise structure.

Remnant of CH3COOH Remnant of C4H9OH

Naming an EsterAlcohol name first. Drop-off “-ANOL”, and add “-YL”. In the example at left, “butanol” becomes “butyl”.

Acid name second. Drop-off “-IC ACID”, and add “-ATE”In our example, “ethanoic acid” becomes“ethanoate” (the same as the ion from this acid).

The name of the ester is “butyl ethanoate”

The names & structures of the carboxylic acidhomologous group were covered earlier.

This diagram is a reminder of why thesecompounds are considered acids. In water...

OH proton transfer

O

R C + H2O + H3O+O-

O

R C

Now, compare theCOOH functionalgroup of thecarboxylic acids:

Because of thepresence of anotherelectronegativeoxygen atom, thereare two sets of dipoles on the molecule.

CO

O

HR Both these

bonds arepolar

δδ+

δδ+

δδ-

δδ-

The polarity of the molecules also explains why, in both homologous series, the smaller alcohols ANDcarboxylic acid are all soluble in water because they form hydrogen bonds with water molecules.

In both series, the larger molecules become less soluble in water and more “fatty” or “waxy” as thehydrocarbon chain becomes longer.

B-LAcid

B-L Base ConjugateAcid

ConjugateBase





All esters contain this chemical “functional group” inside themolecule, with hydrocarbon chains on either side.

The zone around the oxygen atoms is polar, but bothends of the molecule are non-polar.

Because of this, esters generally have low solubilityin water (some exceptions), and have lower mp’s &bp’s than the alcohol & carb.acid they come from.

Esters are volatile with a strong odour... often sweetand fruity. This is their “job”; to give the smells and flavours to many foods and perfumes.

The Esters (cont.)

R2OO

R1 C Thedelicioussmell andtaste of

ripe fruit islargelydue to naturalesters

Practical Work: Making an EsterYou may make an ester in the laboratory using a process knownas Reflux.

A simple laboratory reflux set-up is shown.

The reflux condenser is open to the atmosphere at the top.

This is vital to avoid any dangerous build-up of pressure whichwould occur in a sealed flask.

Volatile chemical vapours rise, but are condensed and drip backinto the flask... “reflux”.

The reaction flask is heated to speed up the otherwise very slowreaction. Note that the mixture must NOT be heated by a bunsenflame because the mixture could ignite and explode. Electrical

Heating Element

As well as a carboxylic acid and an alcohol, it is usual to add the catalyst, concentratedsulfuric acid, H2SO4.

carboxylic acid + alkanol ester + water

As well as speeding the reaction up, the H2SO4 catalyst also absorbs the water product.This has the effect of shifting the equilibrium to the right (according to Le Chatelier’sPrinciple) and increasing the yield of the ester.

conc. H2SO4

Occurrence of EstersEsters occur widely in nature, especially in fruits and flowers.They are largely responsible for the smell & taste of many foods.

There may be a complex mixture of esters and othercompounds which give the complete smell of (say) a ripestrawberry, but there’s always an ester giving the main smelland taste sensation.

Some examples:Strawberry ethyl butanoate, C3H7COOC2H5

Orange octyl ethanoate, CH3COOC8H17

Fats & Oils are Esters, TooEsters made from very long chaincarboxylic acids (the “fatty acids”),are used by all living things as high-energy foods and energy storagechemicals.

We call them fats or oils, dependingon their melting point.

We study them next, plus some usefulchemicals derived from them.

Notice that the“remnant” of the

alcohol comes firstin the name, but

last in the formula. Now Try Worksheets 7 & 8




Triglycerides“Triglyceride” is the general name given to a compound made from 3 molecules of “fatty acid” joined to a

“glycerol” molecule. This joining-together is actually esterification.“Fatty Acids” are the long-chain carboxylic acids, with 12 or more C-atoms.

Example below is an 18-carbon fatty acid called stearic acid, CH3(CH2)16COOH

H

H

C

H H H

HHH

C C C

H

H

C

H

H

C

H H H

HHH

C C C

H

H

C

H H

HH

C CO

OC

HH

H

H C

H H H

HHH

C C C

H

H

C

This long, non-polar, hydrocarbon section The -COOH group isis “hydrophobic” (=”water-hating”) polar and “hydrophilic”

(=”water-loving”) Note these properties... they become important later.

Chemistry of Fats & Oilskeep it simple science

®

There are many different fatty acids; • some have more (or fewer) carbon atoms. • some have one or more double (C= C) bonds.

(and less hydrogen atoms)

To keep it simple (K.I.S.S!) all the fatty acids can berepresented schematically by the diagram below.

Glycerol is a “triple alcohol” molecule containing 3 hydroxyl (OH) groups. Its systematic name is “propane-1,2,3-triol”.

Structural Formula Schematic DiagramH

H

C

H

H

H

C

C

OH

OH

OH

This represents thehydrophobic hydrocarbon chain

This represents thehydrophilic -COOHend of eachmolecule

Fats v. Oils?“Fats” are simply triglycerides which are solid at

room temperature (like beef fat), while oils areliquid at room temperature (like olive oil). The

difference is simply the melting point. This in turnis due to the different fatty acids in the

triglyceride... animal fats tend to contain“saturated” fatty acids (all single C-C bonds likestearic acid above) while the vegetable oils often

contain “unsaturated” fatty acids containing manydouble C=C bonds and less hydrogen.

Fewer H-atoms tends to lower the melting point.

Triglycerides are esters in which 3 fatty acids arebonded to a glycerol molecule.

Schematically, it can be depicted as follows:

This is what we call “fat” or “oil”.

3 fatty acidsG

lyce

rol

Properties of Fats & Oils (Triglycerides)All pretty obvious really !

Fats & oils are soft, greasy substances which tastegreat when heated to about 300oC and used to cookslivers of potato, which are then sprinkled withcrystalline sodium chloride. Good chemistry that!

All the triglycerides are completely insoluble inwater because their long, non-polar hydrocarbonchains have no affinity with polar water molecules.

They have lower density than water and, whenmixed, will float on top.

Without any mobile charges within, they are non-conductors of electricity.

Overall, their physical properties are similar to thelarger members of the alkanes. This should not besurprising.

However, one of their chemical reactions may surprise (and intrigue) you...





The making of soap involves reacting a triglyceridewith a strong base such as NaOH. It can bedepicted schematically as follows:

+ 3 NaOH(aq)

Triglyceride (fat) glycerol + +

3NaOH 3 salts of fatty acids(soap)

If the fatty acid was stearic acid, CH3(CH2)16COOH,then the soap molecule would be sodium stearate,CH3(CH2)16COO-Na+.

Na+ -

Na+ -

Na+ -

The hydroxide ions(OH-) attach to

re-formthe glycerol

molecule

Each fatty acid moleculebecomes a sodium salt.

This is soap.

Prac Work: SaponificationYou may have carried out a simple experiment inthe laboratory to make some soap from vegetableoil and NaOH. (Strong base... use risk analysis &

safety precautions!)

Simply mixing the ingredients in hot water, thenstirring or shaking for a few minutes is enough to

make the soap.

Adding some salt and allowing the mixture to coolis usually effective in causing a layer of soap toseparate into a solid layer on top. This is best

washed to remove NaOH residues before handling.

This is how soap has been made for thousands of years.

Your crude cake of soap can be tested by shakinga piece in warm water to see it “lather”

and form a soapy foam.

Saponification = to make SoapAny fat or oil can be used to make a soap.Traditionally, animal fats from meat wastes andscraps were used. Tallow (from beef) and lard (frompork) have been the main sources of soap forcenturies. Whale oil was used extensively well intothe 20th century.

In the modern industry, vegetable oils are mostlyused because they can be more reliably supplied inlarge quantities at consistent quality and price. Theyalso have a better “marketing appeal”. The main oilsused include palm, olive, coconut and soybean oil.

Soap as an EmulsifierThe reason that soap works for washing andcleaning is that it is able to emulsify fats in water... it is an emulsifier.

You need to realise that water by itself will often notwash away “dirt” because usually there is some fattymaterial in the “dirt”. This is not water soluble, andtends to cling to skin and fabrics and resist beingsimply rinsed away.

As you know, when water and oil are mixed, theyrapidly separate with the oil forming a layer on top.This is because oils (triglycerides) are large, non-polar molecules which are immiscible with water.

However, if water, oil and soap are mixed andagitated, the oil becomes broken up into tinydroplets which remain mixed into the water, and tendto separate more slowly, or not at all. Why?

Remember that soap is the sodium salt of a fattyacid.

If each soap molecule is represented by then what happens when soap emulsifies fat isshown in this diagram.

Notice howthe non-polar end ofeach soapmoleculedissolves inthe fatdroplet, withthe ionic,hydrophilicend stickingout into thewater.

Each tiny droplet of fat remains suspended in thewater. Droplets cannot join together & float on top.Eventually they are rinsed down the drain.

Na+

This end is ionic,hydrophilic andwater-soluble.

This end is non-polar andhydrophobic. It will readily

dissolve in oil.

Each droplet of fat becomessurrounded by soap molecules.These suspend each droplet in thewater and prevent droplets joiningtogether

Water Water

WaterFat Fat

Fat





Now Try Worksheet 9

Detergents are “artificial soaps”. They were firstinvented during the 1940’s and have largely replacedsoap in many cleaning roles because they are morepowerful as emulsifiers, can be made to have variousproperties suitable for specialist tasks, and work wellin a wider variety of applications.

Chemistry & Molecular StructureThere are many different detergents, but one of themost common types has a structure as shown. Notethe basic similiarity (in general terms) to a soapmolecule, but also the differences in detail.

The molecule can be represented as:

This molecule acts very efficiently to emulsify fatsinto water, so that greasy “dirt” is cleaned off orwashed away.

Effect of “Hard Water”Some water supplies contain significantconcentrations of Ca2+ and/or Mg2+ ions. This watertends to cause mineral deposits to build up in pipesand kettles and so has come to be called “hardwater”.

Apart from clogging up water pipes, hard water hasone other major problem... soap will not work inhard water.

If you attempt to use soap in hard water, it will notlather, and a greasy “scum”forms. It does not causeemulsification and will notclean anything.

The problem is that Ca2+ orMg2+ ions will combine withthe fatty acid ions to form aninsoluble compound. Themolecules precipitate and clingtogether forming the “scum”.

An important characteristic of detergents is thattheir ion (alkyl-benzene sulfonate ion) remains insolution, so detergents will work quite normally inhard water.

This is one of the reasons that detergents havemostly taken over from soap as cleaning products.

You can test this effect yourself by trying toproduce a soap lather in seawater, or bore water.Then try with some dishwashing detergent or hairshampoo... big difference!

SO3- Na+

H

H

C

H H H

HHH

C C CH

H

CH

H

C

HH H

H

C

H H

S

O

O

O- Na+H

H

H C

H H H

HHH

C C CH

H

C C

C C

C

CCThe long hydrocarbon chain is

non-polar and hydrophobic.It is derived from an alkane from petroleum.

Sodium Alkylbenzene Sulfonate Detergent Molecule

The ring structure comesfrom benzene, derived from

petroleum.

This end group isderived from

H2SO4 and is ionic& water soluble.

Definition of an EmulsionWhat exactly is an emulsion anyway?

Two liquids which will not dissolve in each otherand always separate when mixed together are said

to be “immiscible”... like water and oil.

An emulsion is when 2 immiscible liquids arecombined so that they form a stable, uniform

mixture which does not separate.

It is NOT a solution. The molecules are notintimately associated at all. In an emulsion, one of

the liquids is broken up into tiny, microscopicdroplets which are spread uniformly throughout

the other liquid.

To achieve an emulsion, a 3rd chemical (the“emulsifier”) is required to keep the dropletsdispersed, and stop them joining together.

For each pair of immiscible liquids there are 2possible types of emulsion.

For example, with cosmetic creams:A sorbolene (or “vanishing cream”) is an emulsion

where the oil phase is dispersed in the water.

A “cold cream” is an emulsion where the water phase is dispersed in the oil.

Ca2+ --

In hard water, soap moleculesbecome insoluble and

will not emulsify.

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+

Ca2+SO3

-

SO3-

In “hard water”, detergentmolecules remain in solutionand still work as emulsifiers

Detergents




If you follow a logical progression from the earlierhomologous series, the amines can be thought of astypical hydrocarbon chains with a nitrogen-hydrogen (-NH2 “amine”) group attached.

The simplest amine has thisstructure and its formula iswritten CH3NH2.

You might logically name this as“methanamine”, but the standard IUPAC name is“methylamine”.

This one is “ethylamine”,C2H5NH2

and C3H7NH2is “propylamine”

The reason for this naming pattern is to emphasise theimportance of the -NH2 group. Instead of thinking “Oh, that’s methane with NH2 attached”, the name“methylamine” tells you “this is an amine structure witha methyl group attached”.

You need to understand that the aminegroup is derived from ammonia, NH3.

Ammonia is chemically (you will recall) a base, because in water:

proton transfer

NH3 + H2O NH4+ + OH-

ammonium ion

This is made possible because the nitrogen atom in NH3has an unshared pair of electrons. It can accept an extraproton (H+ ion) which bonds with the spare electron pair,forming the ammonium ion, NH4

+.

Similarly, an amine compound can do the same. We use the simplest amine, methylamine, as theexample:

H C

H

H

NH

H

CH3 N:H

HCH3 N :

H

H+

H

CH3 CH2 NH

HCH3 CH2CH2 N

H

H

Primary, Secondary, Tertiary AminesNow that you are thinking in terms of addinghydrocarbon bits onto ammonia, then you willappreciate that all preceding examples havebeen “1o amines” which have just one CnH2n+1group attached.

A “2o amine” has 2 suchgroups attached to theammonia structure. Thestructure shown would be

N-methylmethylamine,where the “N” indicates that another methylgroup is attached to the nitrogen atom. Thiscompound is also known as “dimethylamine”.

And (as you were about to guess) if there are 3groups attached to the N-atom this is a tertiaryamine. The simplest is

N,N-dimethylmethylamine

or simply “trimethylamine”.

This 3o aminewould becalled...

N-ethyl-N-methylpropylamine.

(Propyl chain is longest, so it has priority in theamine name. Ethyl side-branch comes before

methyl side-branch alphabetically.)

N

H

H H

NCH3 CH3

CH3

NCH3 CH3CH3CH3

CH3CH3

NCH3 CH3

H

keep it simple science® Amines At this point we must introduce 2 homologous series

which we deliberately ignored previously.

+ H2O

+ OH-

protontransfer

methylammonium ion,CH3NH3

+

In fact, the amines are slightly stronger bases thanammonia itself, although still classified as “weak”.

Physical Properties of AminesThe -NH2 group is polar, so hydrogen bondsform between molecules. This means that mp’s& bp’s are much higher than correspondingalkanes. However, nitrogen is lesselectronegative than oxygen, so the polarity islower than in the corresponding alcohols.

Ethane Ethanol Eth.acid Ethylaminebp(oC) -89 +78 +118 +17

Small amines are soluble in water, but solubilitydecreases rapidly as the hydrocarbon chainsget bigger. Solubility also declines rapidly in 2o

and 3o amines.

Amines are volatile and their vapours smelldistinctly of ammonia. Some amines smell“fishy”... in fact the characteristic smell of fish,especially if it is a bit “off”, is due totrimethylamine.

B-L Acid

B-L BaseConjugate

Acid

ConjugateBase

Now Try Worksheet 10




This is another homologous series whichwe deliberately ignored previously.Amides

Recall that: carboxylic + alcohol ester + water

acidWell, similarly:

carboxylic + amine amide + wateracid

Once again the reaction can be described as a“condensation” because water is produced.

OH

O

R1 C

O

R1 C

R2NH

H

R2N H2OH

+

+

These form water

carboxylicacid

amine

amide

For example, if butanoic acid (C3H7COOH) reactedwith ethylamine (C2H5NH2):(we have turned the amine formula around to make the reaction clearer)

C3H7COOH + NH2C2H5 H2O+ C3H7CO.NHC2H5

N-ethylbutanamide

Notice that the name begins with reference to theamine and ends with the acid’s name, modified with“amide”. So “N-ethylbutanoic acid + amide”.

This reaction is very important in Biology; this ishow amino acids join together to form proteins.

Later in this module you will see that some of ourimportant plastics are made by this “amidereaction”.


Reaction Pathway FlowchartsIf, by now, you are feeling a little overwhelmed by the number of different homologous series of organic

chemicals and all their different reactions, the following may help... BUT you have to do it yourself !Begin with small notebook pages, or separate sheets.

Summarise all the reactions studied for one group ofchemicals (say, the hydrocarbons) as a simple flow-chart on one sheet: example shown.

Do the same for another group such as thealcohols. Alkene

AlcoholHaloalkanes

Alkaneadd H2

add H2Oaddition reaction

HCl, Br2 etc.

substitutio

n reactio

n

with Cl 2

etc

Alcohol

Alkene

Haloalkanes

Aldehyde

Ketone

Carb.acidEster

oxidations dehydration

subst. HX

react withcarb.acid

Continue to do this for all the groups we have covered,then look for connections and overlaps.

You’ll end up with a very useful summary & studyguide. More importantly, by doing this you will

learn and understand lots more about Organic Chemistry. Have Fun !

Move your little sheets around to see how they connectto each other. You may have to re-draw each one into abetter structure so they connect in a better way.

As your diagrams get better connected, merge themonto a larger page or a chart. Add details such asreagents & catalysts needed for each reaction. Addexample equations for each reaction type.

If you need some help,or need to cheat,

search for “flowchartsof organic chemreactions” on the

internet.

Look for

connections

After This, Try Worksheet 11




keep it simple science® 5. Polymers

Polymers are large molecules made by joiningtogether many small molecules, called monomers.(“poly” = many, “mono” = one, “mer” = unit)

Many of the important molecules in living cells arepolymers, for example:

• starch is a polymer of many glucose molecules.• proteins are polymers of amino acids.• DNA is a polymer of nucleotides, sugar and

phosphate.

Many common, widely used substances aremanufactured polymers, including all the differentplastics and synthetic fibres such as nylon.

Ethylene is the starting chemical (“feedstock”) in themanufacture of many polymers.

Addition Polymerisation of EtheneYou should recall that ethene (ethylene) can carry outaddition reactions with bromine, water, etc., by“opening-up” its double bond. Under the rightconditions and with an appropriate catalyst, manyethylene molecules can react with each other by thesame mechanism.

You may have used molecular models to helpvisualise the process.

The result is that the ethylene monomers jointogether by addition reactions across the doublebond. This is an “Addition Polymerisation” processand results in a polymer called “Polyethene”, or“Polyethylene”, also known by the trade name“Polythene”.

Addition Polymerisation is anAddition Reaction across a double C= C bond

which joins monomers to make a polymer.Polymers can be named by adding “poly-”

as a prefix to the monomer name.

CH2=CH2 CH2=CH2CH2=CH2

Condensed Structural Formula (-CH2-CH2-)n

Industrial Production of PolyetheneMore polyethene is manufactured than all otherplastics put together... it is one of the most usedsynthetic materials in our world. There arebasically two different production methods, whichproduce two different forms of polyethene.

Low Density PolyetheneIf the monomer ethene is treated with

• high pressure (over 1,000 atmospheres)• high temperature (300oC)• an “initiator” chemical

addition polymerisation occurs, with about 2,000monomers joining to form each “super-molecule”of polymer. In this case, the initiator chemical alsocauses the polymer molecules to have side-branches.

TTTThhhhiiiissss mmmmaaaakkkkeeeessss CCCCllll iiiinnnngggg--WWWWrrrraaaapppp FFFFiiii llllmmmm&&&& PPPPllllaaaasssstttt iiiicccc BBBBaaaaggggssss....

High Density Polyetheneis manufactured

• at lower pressure (2-3 atmospheres)• at lower temperature (about 60oC)• with a complex catalyst

This time there are no side-branches. The longpolymer molecules can pack together forming ahigher-density, harder plastic used for toys, plasticutensils, and tough, “crinkly” carry bags.

As with all materials, the uses of these plastics isclosely linked to the properties they have, and theirproperties are controlled by their chemical andmolecular structure and bonding.

This idea is taken further on the next page.

These molecules cannotpack together closely, sothe plastic is low-density,highly flexible, soft and

clear...





Other Addition PolymersThe compound chloroethene is an ethene moleculewith one hydrogen atom replaced by a chlorine.

Chloroetheneis also known by its common name “vinyl chloride”

Since this molecule contains a double bond, it canundergo addition polymerisation to form “polyvinylchloride” or PVC.

(-CH2-CHCl-)n

If one of the hydrogen atoms of an ethene moleculeis replaced by the ring-shaped “benzene” group, thecompound has the technical name“ethenylbenzene”, but is commonly known as“styrene”.

If this undergoes addition polymerisation, thepolymer is “polystyrene”, so familiar in insulation,hot-drink cups, bean-bag filling, etc.

Polystyrene (-CH2-CH(C6H5)-)n

Tetrafluoroethene is the monomerwhich produces an addition polymercalled “polytetrafluoroethene”, abbreviated PTFE.

This plastic is better know as “teflon”. (TM trademark)The strength of the C-F bonds give teflon one of thelowest known ratings for friction. It is so “slick” thata gecko lizard (which can run vertically up a pane ofwindow glass) cannot climb it.

It is also highly resistant to chemical attack, so ithas many applications (beyond “non-stick”cookware) in medicine, electronics and industry.

Uses, Properties & StructureThe molecular structure and bonding of eachplastic determines its properties, and the propertiesdetermine what uses the material is best suited for.

To keep it simple (K.I.S.S. Principle) we willcompare just 3 of the plastics mentioned so far.

In low-density polyethene, the molecules are long,non-polar, branched chains (diagram previouspage). Being non-polar (so only weak dispersionforces operate) and unable to get close together,each molecule can bend and twist easily.

So, the plastic is soft and very flexible. It is perfectfor cling-wrap film, sandwich bags and as theplastic lining in milk or juice cartons.

In PVC, thechlorine atomsmore than doublethe mass of eachmonomer. Sincedispersion forcesincrease withmolecular weight,it means that thepolymermolecules attracteach other morestrongly. Each molecule is held in place more, sothe entire substance is harder and less flexible.

PVC is a tougher, more rigid plastic. This makes itideal for drainage pipes, guttering and electricalconduit pipes.

In polystyrene, the compact benzene side group isalmost twice the mass of a chlorine atom, so themolecules are even heavier and dispersion forcesstronger. Polystyrene is a hard, tough, rigid plastic,often used for making handles for cookware andhand-tools such as hammers or chisels.

Note that the morefamiliar use ofpolystyrene is inlight-weight “foam-plastic” forinsulation, hot-cupsand packaging. Inthis form it hasbeen injected withgas to make it verylight and “fluffy”.

The plastic itself ishard and rigid.

H H

ClHC C

F F

FFC C

H

Cl

C

H H

ClH

C CH

H

C

H H H

ClHCl

C C CH

H

C

H H

H

H H

HH

HC C

C

C

C

C

C

C

H H

HC C

H H

H

C C

H H

H

C C

H H

H

C C

H H

H

C C

H H

H

C C

Benzene ring

This structure iscommonly

abbreviated as

Addition Polymers (cont.)





There is another way that polymers can form.For example, the monomer “6-aminohexanoic acid”has the structure

This can be abbreviated as

Two of these molecules can join together as follows

H

H

C

H O-H

OH

C CH

H H

HHH

N C CH

H

C

O-H

O

CH

H

N (CH2)5

O

CH

H

N (CH2)5

O-H

O

CH N (CH2)5

NH2“amine”group

COOHacidgroup

O-H H

These atoms formwater, H2O

and the molecules join together atthe vacant bond positions

Condensation Polymers are formed when monomer molecules join together in either an“amide condensation” or an “ester condensation”. As well as all the synthetic fibres,

many biologically important macro-molecules are condensation polymers.

Condensation PolymersYou can see it is an “amide condensation” reaction.

The result is:

Each molecule can join to another at each end, somany monomers can join in long chains... a polymer is formed.

The example above results in the polymer we call“nylon”, widely used in fabrics and clothing.

Remember that the reactioncarboxylic + alcohol ester + wateracid

is also a “condensation” reaction.

Therefore, if you begin with a monomer with astructure HO R COOHit can react at each end by “ester condensation” toform a polymer we call a “polyester”. These arewidely used to make fabrics, carpets, etc.

O

CH

H

N (CH2)5 O

CH N (CH2)5

O-H

+ water

BiopolymersThe word “biopolymer” refers to those naturallyoccurring polymers made by living things, suchas proteins, starch and cellulose.

Humans have used these polymers for thousandsof years. e.g. cellulose is a polymer of the sugarglucose which forms the cell walls of all plantcells. Humans use cellulose fibres (in cotton andlinen) for clothing fabrics and for nearly 100 yearshave been using chemically-modified versions ofit. For example, “rayon” is a synthetic fibre madefrom chemically-modified cellulose.

Research has been going on for many years onways to get living things to grow polymers withproperties more like those of the usefulpetrochemical-based plastics.

A lot of the research has centred around thepolymer “polyhydroxybutyrate” (PHB) which hasproperties not too different from polyethene. Itwas discovered 80 years ago that PHB can bemade by a species of bacteria, Bacillusmagaterium.

In recent years, the Monsanto company has used Genetic Engineering(GE) to transfer the genes for PHB production from bacteria into cornplants. The crop is grown, harvested and can be eaten as usual, but thestalks and leaves are also harvested for their PHB content, which is ashigh as 20% of the dry weight.

Analysis• PHB has properties which makeit suitable to replace some plasticsfor packaging, but it tends to bebrittle, and extra breakages mustbe accepted.

• PHB has the major advantage ofbeing biodegradable, but this alsolimits its range of uses, since itcan rot and disintegrate duringuse.

• There is resistance from farmersand consumers regarding the useof GE plants.

• The production of PHB is not yetas cheap as using petrochemicalplastics.

ConclusionPHB grown in corn has potential,but is unlikely to become widelyused yet.

Now Try Worksheets 12 & 13

Chem Module 7 PhotoMaster

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