Chapter 7 :Introduction to Organic Chemistry

IntroductionElements that make up organic compounds.

Organic chemistry is a branch of chemistry.

It is a study of carbon compounds, other than CO, CO2 etc…

All organic compounds contain carbon and in the majority of cases, also hydrogen.

Some organic compounds also contain elements such as oxygen, nitrogen, phosphorus, sulphur and halogen in their molecules.

Classes of Organic Compounds

The branch of chemistry that deals with carbon compounds is – organic chemistry.

Classes of organic compounds can be distinguished according to functional groups- group of atoms that is largely responsible for the chemical behavior of the parent molecule.

Most organic compounds are derived from hydrocarbon.

There are four types of hydrocarbons – saturated, unsaturated, aliphatic & aromatic.

1. Saturated hydrocarbonsThe simplest of the hydrocarbon species and are composed entirely of single bonds and are saturated with hydrogen. The general formula for saturated hydrocarbons is CnH2n+2 (assuming non-cyclic structures).

Types of Hydrocarbon

2. Unsaturated hydrocarbons Have one or more double or triple bonds between carbon atoms. Those with one or more double bonds are called alkenes. Those with one double bond have the formula CnH2n (assuming non-cyclic structures)

3. Aromatic hydrocarbons Hydrocarbons that have at least one aromatic ring. also known as arenes.

4. Aliphatic hydrocarbonsHydrocarbons which do not contain a benzene ring

Is a group of atoms in a compound, which will involve in the chemical reaction.

the compound with the same functional group

will have the same chemical reaction.

Example:

Table 1: The structures of the main functional group

The functional group

The general formula for various compounds is shown below:

Functional Group

• Is a series of organic compounds with a similar

general formula e.g: all alkanes have the general

formula of CnH2n+2

• It has the same functional group.

• For example, the alkane homologous series:

– methane (CH4)

– ethane (C2H6)

– propane (C3H8)

– butane (C4H10), and

– pentane (C5H12)

Each member differing from the previous one by a

CH2 group

No. of C atom

General Name

1 Meth-

2 Eth-

3 Prop-

4 But-

5 Pent-

6 Hex-

7 Hep-

8 Oct-

9 Non-

10 Dec-

Example:

AlkaneAlkeneAlkyneAlkyl

Replace the underlined part to the general name

Classification of Carbon Atoms in Organic Molecules

An alkyl group is a group obtained by removing a hydrogen atom from an alkane.

The symbol for an alkyl group is R. R has the general formula CnH2n+1. Example of the alkyl groups are the methyl

group, -CH3 and the ethyl group, -C2H5. Carbon atoms in organic molecules can be

classified as primary, secondary ,tertiary or quaternary carbons depending on the number of alkyl groups attached to the carbon atom.

Type of carbon atom

Formula Comments

Primary carbon (1°)

Only one alkyl group attached to the carbon atom

Secondary carbon (2°)

Two alkyl groups attached to the carbon atom

Tertiary carbon (3°)

Three alkyl groups attached to the carbon atom

Quaternary carbon (4°)

Four alkyl groups attached to the carbon atom

Molecular & structural formulae – Structural Formula Not only shows the actual number of

atoms in the molecule, it also shows how they are bonded together.

Molecular formula only shows the number of atoms for each element present in one molecule of the compound but does not show how these atoms are arranged.

Examples: Molecular formula – C3H6O

They are generally 3 different ways of writing the structural formula.

Condensed structural formula

In the condensed structural formula, carbon-hydrogen and carbon-carbon single bonds are not shown, but double and triple bonds are shown.

When writing a condensed structural formula, branches in the carbon chain are indicated in parentheses.

Example- CH3CH2CH2CH3

or

Expanded structural formula The expanded formula shows every atom and

type of covalent bond in the molecule.

In writing expanded formula, it is important to remember the types of covalent bonds that can be formed between atoms.

Between C-C Between C-H Between C-halogen Between C-O Between C-N

Skeletal structures Skeletal structures do not show carbon and

hydrogen atoms or C-H bonds unless they are part of a functional group.

Single covalent bonds are indicated with a single line, double bonds with double lines and triple bonds with triple lines.

The ends of the lines and corners between lines indicate the presence of a carbon atom.

Examples are given below.

Draw the condensed structure for each of the compounds. i)

ii)

iii)

iv)

OH

O

Cl

OH

O

Isomerism

Organic compounds that have the same molecular formula but different arrangements of atoms are known as isomers.

The existence of two or more organic compounds with the same molecular formula but different arrangements of atoms is called isomerism.

Generally, there are two types of isomerism: constitutional isomerism and stereoisomerism. Constitutional ( structural ) isomers have the same

molecular formula but different structural formulae. In other words, their atoms are linked together in

different sequences.

Constitutional Isomerism Molecules that have the same molecular

formula but different structural formulae.

Constitutional isomerism can be subdivided into 3 categories: Chain isomerism Positional isomerism Functional group isomerism

Chain Isomerism Chain isomerism are those which differ in the

structure of their carbon chains, that is, they differ in the length of their straight chains or branches. For example, butane has two chain isomers;

Chain isomers possess the same fuctional group, and belong to the same homologous series. Chain isomers have different physical properties, but they have similar chemical properties.

Positional Isomerism Positional isomers have the same carbon skeleton

and belong to the same homologous series but differ in the position of the functional group.

In general, positional isomers have similar chemical properties because they have the same functional group.

However they have different physical properties. The following are the examples of positional

isomerism. Bromoalkanes with the molecular formula, C3H7Br Alcohols with the molecular formula C3H7OH Alkenes with the molecular formula C5H10

CH3CH2CH2CH2OH CH3CHCH2CH3

OHButan-1-ol

Butan-2-ol

Functional group Isomerism Functional group isomerism is shown by isomers

which have the same molecular formula but contain different functional group.

Types of compounds : alcohol and ether (C3H8O) Aldehyde and ketone

Stereoisomerisms Stereoisomers have the same molecular formula

and the same connectivity but different orientations of their atoms in space.

a. Cis-trans isomerism

a. Enantiomers/ optical isomerismStereoisomers that are nonsuperimposable mirror images of each other.

Chirality centre & enantiomers

An organic molecule will exhibit optical isomerism or optical activity if it contains at least one chiral carbon atom, that is, a carbon atom attached to four different atoms or groups.

A chiral carbon atom is also known as an asymmetric carbon atom and is often shown as ‘C*’.

A molecule that contains an asymmetric carbon would have a mirror image that cannot be superimposed on it.

In short, the mirror image does not have the same structure and is a stereoisomer.

A chiral molecule and its mirror image are called enantiomers or optical isomers.

EnantiomersEnantiomers have the same structural formula but

different spatial arrangement of the atoms.They are mirror images of each other, but

because of the asymmetry of their molecules, the two mirror images cannot be superimposed on each other.

It is important to note that there are two subdivisions of stereoisomers:

a) Enantiomers (mirror image)b) Diastereomers (non- mirror image)

Diastereomers include cis-trans isomers.

3-D formula Spatial arrangements of atoms or groups of

atoms within the molecule is significantly important in organic chemistry.

Therefore there are methods of writing structural formula in 3-D projection.

The wedges represents the covalent bond coming out of the plane of the paper.

The dash represents the bond behind the plane of the paper.

The line represents the bond lying in the plane of the paper.

Summary

Functional Groups

Hydrocarbons Alcohols Aldehydes & Ketones Carboxylic Acids Esters Amines

Functional Groups

Alcohol The functional group for alcohol is an hydroxyl

group (-OH) Alcohols are classified as primary (1°) , secondary

(2°) or tertiary (3°).

Aldehydes and Ketones The functional group of both aldehydes and

ketones is the C= O (carbonyl group).

Carboxylic Acids The functional group is a –COOH Carboxyl : Carbonyl + hydroxyl group.

Esters Derivative of a carboxylic acid in which the H of

the carboxyl group is replaced by a carbon group.

Amines (-NH2) The functional group is an amino group. Amines are classified as primary (1°) , secondary

(2°) or tertiary (3°).

1. Hydrocarbons

Organic compounds that are composed of only carbon and hydrogen.

Examples : alkanes, alkenes, alkyne and arenes. A saturated hydrocarbon contains only single

bonds - alkanes An unsaturated hydrocarbon may contains double

bonds or triple bonds – alkenes and alkynes Aromatic hydrocarbons, also commonly known as

arenes – unsaturated hydrocarbon. Arenes are compounds which contain benzene or

benzene-like ring and have the chemical properties characteristic of benzene.

Alkanes General formula for alkanes - CnH2n+2 , n ≥ 1 Nomenclature (IUPAC System)

Eg: methane, ethane, propane…….

Condensed formula

CH3CH2CH2CH3

IUPAC System1. The longest chain of carbon atoms is taken as

the parent chain.2. Each substituent is given a name and a number.

The number shows the carbon atom of the parent chain to which the substituent is bonded.

3. If there is one substituent, number the parent chain from the end that gives it the lower number.

4. If the same substituent appears more than once, number the parent chain from the end that gives the lower number to the substituent encountered first.

5. If there are two or more different substituents, list them in alphabetical order.Use hyphens to separate numbers from words and commas to separate numbers

The name of a hydrocarbon has three portions:

34

PREFIX + ROOT + SUFFIX

Tells the type of organic compound the molecule represents (functional group)

Identifies a group attached to the main chain and the number of the carbon to which it is attached have –yl as their ending

Tells the number of C atoms in the molecule (the longest and continuous)

PREFIX = PENDANT + LOCATION

Example:

35

2-methyl but aneIs the

PREFIX A 1 C

branch is attached to C – 2 of the main chain

PREFIX + ROOT + SUFFIX

1234

Is the ROOT The main

chain has 4 C atoms

Is the SUFFIX The

compound is an alkane

Roots No. of C

atoms

meth- 1

eth- 2

prop- 3

but- 4

pent- 5

hex- 6

hept- 7

oct- 8

non- 9

dec- 10

Alkane FormulaBoiling point

[°C]Melting point

[°C]Density [g·cm3]

(at 20°C)

Methane CH4 -162 -183 gas

Ethane C2H6 -89 -172 gas

Propane C3H8 -42 -188 gas

Butane C4H10 0 -138 gas

Pentane C5H12 36 -130 0.626(liquid)

Hexane C6H14 69 -95 0.659(liquid)

Heptane C7H16 98 -91 0.684(liquid)

Octane C8H18 126 -57 0.703(liquid)

Nonane C9H20 151 -54 0.718(liquid)

Decane C10H22 174 -30 0.730(liquid)

Cycloalkanes

• Alkanes whose carbon atoms are joined in rings

• General formula for cycloalkanes - CnH2n , n ≥ 3

• Eg: cyclopropane, cyclobutane, cyclopentane, cyclohexane

Cyclopropane Cyclobutane

CyclopentaneCyclohexane

Physical properties The b.p of straight chain alkanes increase steadily

with relative molecular mass. The increase in b.p is due to the increasing forces of attraction between molecules of increasing size.

Effect of branching on b.p A branched chain alkane boils at lower temperature than

the straight chain alkane with the same number of carbon atoms.

This is because the branched chain alkanes are more compact and have smaller surface area, smaller van der Waals forces = low b.p

Comparing the b.p of alkanes and cycloalkanes. The b.p of cycloalkanes are 10 - 15°C higher than the

corresponding straight chain.

Alkenes

Contain at least one carbon-carbon double bond. General formula for alkenes – CnH2n , n ≥ 2 Eg: CH2=CH2

The cis-, trans- system

Nomenclature Identify and name the parent hydrocarbon Number the carbon atoms in the main chain When the carbon chain contains more than 3

carbon atoms, a number is used to indicate the position of ‘=‘

Indicate the positions of the double bond and the substituent.

ClCH2CH2CH2

Contain at least one carbon-carbon triple bond.General formula for alkynes – CnH2n-2 , n ≥ 2Eg: 1-butyne, 2-butyne

HC CH2C CH3

But-1-yne

H3C C C CH3

But-2-yne

A hydrocarbon that contains hydroxyl group, -OHSUFFIX end with – olAlcohol with the –OH group attached to the end

carbon atom is commonly called propyl alcohol or 1-propanol

The PREFIX 1-indicates that the –OH groups is on the first or end of C atom.

The alcohol with the –OH group attached to the middle carbon atom is commonly called isopropyl alcohol or 2-propanol

The PREFIX 2-indicates that the –OH groups is on the second C atom from the end.

• Example:

• Alcohols, R-OH• R is the alkyl group• -OH is the functional group

H3CH2C

H2C OH

H3CHC

CH3

OH

123

3 2

1

1-propanol

2-propanol

CH3OH CH3CH2OH CH3CH2CH2OH CH3CHCH3

OHmethanol(methyl alcohol)

ethanol(ethyl alcohol)

1-propanol(propyl alcohol) 2-propanol

(propyl alcohol)

Carbonyl compounds Aldehyde and ketones are carbonyl compounds

because they contain the carbonyl group, C=O In the carbonyl group, the carbon and oxygen

atoms are joined together by a double bond. Thus, the C=O bond consists of a sigma and a pi

bond. Aldehydes and ketones have the same

molecular formula, CnH2nO. The general formula of aliphatic aldehydes and

ketones are shown below. R and R’ may be alkyl or aryl groups.

Nomenclature

Aliphatic aldehydes

The rules for naming aldehydes are similar to those for naming alkanes, except that the final ‘e’ of the corresponding alkane name is dropped and replaces by the suffix ‘al’.

The carbon of the aldehyde group is counted as part of the carbon chain.

Thus, aldehyde with the formula CH3CHO is called ethanal.

O

H

2,2-dimethylbutanal

O

H

4-phenylpentanal

Example:

Nomenclature of Ketones The rules for naming ketone are similar to those

for naming alkanes, except that the final ‘e’ of the corresponding alkane name is dropped and replaces by the suffix ‘one’.

The carbon of the ketone group is counted as part of the carbon chain.

When naming the carbon atoms, the carbonyl group is given preference over any substituents.

O

O O2-propanone

4-penten-2-one

2-methyl-4-phenyl-3-pentanone

alphabetical order

Example:

• term “carboxylic” is derived from “carbonyl” and “hydroxyl”.

• carboxylic acid also contain carbonyl group, C=O in its structure

Carboxylic Acids

C

O

OH

Nomenclature

• count number of carbons in the longest carbon chain containing the – COOH group

• replace the –e with the suffix –oic acid • compound containing multiple -COOH groups

do not drop the –e but add a di- or tri- to the ending – carboxylic acid or add a di- or tri- to the suffix –oic acid.

Structural Formula

Condensed Structural Formula

CH3COOH CH3CH2COOHHOOCCH2COO

H

IUPAC ethanoic acidpropanoic

acidpropandioic

acidCommon

Nameacetic acid - malonic acid

C

O

OHCH3C

O

OHCH2CH3 C

O

OHCH2C

O

HO

Esters• to create an ester, an alcohol is reacted with a carboxylic acid• an ester is named for its starting materials, the acid and the alcohol• the first part names the alcohol, use the side chain abbreviation, i.e. methyl, ethyl…• the second part names the carboxylic acid• to end the second part change the –ic of the carboxylic acid to -ate

Structural Formula

Condensed Structural Formula

CH3COOCH3

CH3CH2COOCH2CH3

CH3COOC6H5

IUPACmethyl

ethanoateethyl propanoate

phenyl ethanoate

Common Name

methyl acetate

ethyl propyrate phenyl acetate

C

O

CH3 O CH3 C

O

CH2 O CH2CH3 CH3C

O

OCH3

Aromatic Compounds

Introduction An organic compound that contains a benzene ring in

its molecule is known as an aromatic compound. Aromatic hydrocarbons are sometimes called arenes. Benzene is a colourless compound with a melting

point of 6°C and a boiling point of 80°C. Benzene’s molecular formula, C6H6, suggests a high

degree of unsaturation. Benzene is remarkably unreactive! When benzene reacts, it does so by substitution in

which a hydrogen atom is replaced by an other atom or group of atoms.

This unusual stability is called aromaticity.

Resonance

 is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula.

NomenclatureA. Monosubstituted Benzenes

Monosubstituted alkylbenzenes are named as derivatives of benzene, as for example ethylbenzene. The IUPAC system retains common names for several of the simpler monosubstituted alkylbenzenes.Examples :

The common names phenol, aniline, benzaldehyde, benzoic acid, and anisole are also retained by the IUPAC system.

B. Disubstituted BenzenesWhen 2 substituents occur on a benzene ring, three constitutional isomers are possible. The substituents may be located by numbering the atoms of the ring or by using the locators ortho, meta, and para.

Electrophilic Substitution Reactions

+

+

Halogenation of benzene

Benzene does not react with chlorine in the dark. However in the presence of catalyst, a substitution

reaction occurs when chlorine reacts with benzene at room temperature to form chlorobenzene and steamy fumes of hydrogen chloride.

Bromination

+

+

Nitration of benzenenitronium

Friedel-Crafts alkylation

Friedel-Crafts acylation In the presence of anhydrous aluminium chloride,

benzene reacts with an acyl chloride or an acid anhydride (RCO-O-COR) to form a ketone.

An example of an acyl chloride is ethanoyl chloride and an example of an acid anhydride is ethanoic anhydride.

Summary Electrophilic Aromatic Substitution

Halogenation :

Nitration :

2

Friedel-Crafts acylation

Friedel-Crafts alkylation

Reactions of benzene derivatives - Toluene

The methyl group activates the benzene nucleus.

Hence, toluene reacts considerably faster than benzene in all electrophilic substitutions.

Toluene undergoes reactions in the methyl side chain or the benzene ring, depending on 2 factors: The type of reagent used The conditions of the reaction

i- Oxidation of alkylbenzenes

If toluene is refluxed with a strong oxidising agent, K2Cr2O7 or KMnO4 , the side chain is oxidised to –COOH and benzoic acid is formed.

If a milder oxidising agent is used, such as manganese(IV) oxide or chromium(VI) dichloride oxide, CrO2Cl2, the side chain of –CH3 is oxidised to the aldehyde group - CHO

Halogenation of toluene

Side chain substitution

Benzene ringCH3

Introduction to amines Organic compounds derived by replacing one or more of the

H atoms in ammonia with alkyl or aryl groups are called amines.

Class General formula

Primary (1 o )

Secondary (2o )

Tertiary (3 o )

IUPAC Nomenclature

Primary Amines In IUPAC nomenclature, the suffix ‘amine’

replaces the final ‘e’ in the name of the parent alkane, for example,

The prefix ‘amino’ is used to indicate the presence of an –NH2 group in a molecule containing more than one functional group.

Aromatic primary amines

Secondary & tertiary amines

B.P of Amines The b.p increase with increasing relative molecular mass. Amines are polar compounds and both primary and

secondary amines associate by H-bonding. For isomeric amines, the b.p decrease in the order

1o amine > 2o amine > 3o amine

THIS IS DUE TO THE PROGRESSIVE DECREASE IN H-BONDING

The b.p of aliphatic amines are higher than those alkanes or haloalkanes of similar mass due to H-bonding.

The H-bond in amine is more polar than H-bond in alkane but less polar than O-H.

Hence, H-bond in amine is weaker than that of alcohols or carboxylic acids.

The Basicity of amines

All three classes of aliphatic amines are capable of forming Hydrogen bonds with water molecules.

According to Bronsted-Lowry theory, a basic is a proton acceptor.

The base dissociation constant or basicity constant, Kb or pKb are given by the following expressions.

The larger the value of Kb, the greater the tendency of the amine to accept a proton from water, thus the stronger the base.

Conversely, the smaller the value of pKb, the stronger the base.

RNH2 (aq) + H2O (I) RNH3+ (aq) + OH-

(aq)

Kb =

[RNH3+] [OH-]

[RNH2]mol dm-3

pKb = - log Kb

Examples,Ammonia - Kb = 1.8 x 10-5 pKb = 4.74Methylamine – Kb = 4.4 x 10-4 pKb = 3.36Benzylamine - Kb = 2.2 x 10-5 pKb = 4.66

We notice that mostly primary aliphatic amines are somewhat stronger basesthan ammonia because the alkyl group is electron donating.

Preparation of AminesReduction of nitro compounds. This method is particularly useful for producing

aromatic amines from aromatic nitro compounds. For example, aniline is prepared by the reduction of nitrobenzene using Tin and concentrated hydrochloric acid Zinc and hydrochloric acid Tin(II) chloride, SnCl2, in hydrochloric acid

Reduction of Nitriles Primary aliphatic amines can be obtained by the

reduction of nitriles using the following reagents. Lithium aluminium hydride in ethoxyethane Hydrogen in the presence of a nickel catalyst at

140oC ( catalytic hydrogenation)

When the vapour of propanitrile is mixed with hydrogen and passed over a nickel catalyst at a temperature of 140 celcius, reduction takes place and propylamine is formed.

CH3CH2C≡N + 2H2 CH3CH2CH2NH2

Ni, 140oC

Reduction of Amides Primary amines, secondary amines and tertiary amines are

also formed by the reduction of primary amides with LiAlH4

Hofmann degradation of Amides On warming a primary amide with bromine in a

solution of NaOH, a primary amine is formed. In this reaction, the C=O group from the amide is

removed and the primary amine is formed. The elimination of a C=O group provides a means

of shortening the length of a carbon chain by one carbon atom.

RCONH2 + Br2 + 4NaOH RNH2 + 2NaBr + Na2CO3 + 2H2O

Amino Acids Organic compounds that possess both the amino group

and the carboxyl group are called amino acids. Almost all occurring amino acids are α-amino acids. These are amino acids in which both the amino and

carboxyl groups are attached to the α- carbon atom of a carboxylic acid.

The α- carbon is the carbon atom next to the carbonyl group.

Amino acids can be classified as neutral, basic or acidic, depending on the number of –NH2 and –COOH groups present in the molecule.

Neutral – 1 COOH and 1 NH2 present

Basic - NH2 > COOH

Acidic - NH2 < COOH

1. Classify each amine as primary, secondary, or tertiary. i)

ii)

b) Name the following α-amino acids using the IUPAC nomenclature: i) ii) iii) iv)

NH2CHCOOH

CH(CH3)2

NH2CHCOOH

CH2C6H5

NH2CHCOOH

CH2OH

NH2CHCH2CH2COOH

COOH

Zwitterion Amino acids – white crystalline solids, high b.p & m.p. Amino acids dissolve in water to form neutral solutions but

have low solubility in organic solvents such as ethanol. These 2 properties indicate that amino acids exist as a

polar ions. A dipolar ions is also known as zwitterion or an internal salt. Zwitterion – any ion that carries both a positive and

negative charge on the same group of atoms is called zwitterion.

In neutral solutions and in the solid state, a.a exist as zwitterions.

A zwitterion is formed when a proton from the –COOH group is donated to the –NH2 group of the same molecule.

A zwitterion is amphoteric in nature. It acts as a base in the presence of an acid and as

an acid in the presence of a base.

Therefore in an acidic solution, the cation H3N+ – CH2 – COOH predominates.

In an alkaline solution, the anion H2N – CH2 – COO- predominates.

In a neutral solution, the zwitterion H3N+ – CH2 – COO- predominates

87

Amino acids are the basic structural units of proteins.

• Contain at least one amino group (-NH2)

• And at least one carboxyl group (-COOH)

•Existing form is pH dependent

88

Amino acids are joined in a protein by the formation of a peptide bond

Peptide (amide) bond

Dipeptide – contains two amino acid residues

planar

H3N C

H

R1

C

O

O H3N C

H

R1

C

O

O+

H3N C

H

R1

C

O

N C

H

H

R1

C

O

O + H2O

89

20 amino acids can form 202 or 400 dipeptides.

Protein with 50 amino acid residues can be arranged in 2050 or 1065 ways.

Importance of amino acids There are about 22 amino acids that are mostly

found in nature. Only 20 of these a.a are required to synthesise

proteins. However there are 8 a.a, known as essential a.a

which cannot be synthesised by human body and must be obtained from the proteins in the diet.

Type of protein

Fuction in the body Example

Structural Provide structural components

Collagen in tendons and cartilage;Keratin in hair, skin and nails.

Transport Carry essential substances throughout the body

Haemoglobin in the blood transports oxygen

Hormone Regulate body metabolism

Insulin regulates blood glucose level

Enzyme Catalyse biochemical reaction in the cells

Trypin catalyses the hydrolysis of proteins

Introduction to Polymers

Monomers – are small molecules used to synthesis polymers.

Polymer – a large molecule made up of many smaller molecules (monomer).

PolymerisationThe chemical reaction in which the

monomers are joined together by covalent bonds.

Homopolymer & Copolymer Homopolymers Polymers synthesised from a

single type of monomer.Ex: polyethylene, polypropylene.

Copolymers polymers formed from 2 or more different types of monomers.Ex: nylon 6.6, Terylene

Styrene-butadiene rubber

HC CH-CH-CH=CH-CH3

nCH2-CH2 n

polyethylene

Natural Polymers Examples of natural polymers are proteins,

carbohydrates and natural rubber.

Tetrapeptide - protein Lactose - carbohydrate

Isoprene – natural rubber

Preparation of synthethic polymers

Condensation polymerisation

Addition polymerisation

The chemical process in which 2 monomers react to form a large molecule and eliminate a smaller molecule (usually water, ammonia)

The addition reaction in which monomers with double bonds are joined together by covalent bonds to form a large molecule without a loss of a small molecule.

The monomers must have at least 2 functional groups to act as the reactive ends.

Monomers for making addition polymers may be alkenes or alkene derivatives.

Examples: Kevlar, Nylon and Terylene.

Examples: polyvinyl chloride, polystyrene

Kevlar

Is an aramide (aromatic polyamide) prepared by the reaction of 1,4-benzenedicarboxylic acid (terephthalic acid) with1,4-diaminobenzene.

It is a very strong material and is used for bulletproof vests.

Nylon 6 Nylon 6 is produced by the prolonged

heating of caprolactam with a trace of water.

OR

HOOC-(CH2)5- NH2

(6-aminohexanoic acid)

PVC

The monomer for making polyvinyl chloride (PVC) is vinyl chloride.

The IUPAC name for polyvinyl chloride is poly(chloroethene), while the IUPAC name for vinyl chloride is chloroethene.

Polystyrene (PS)

The monomer for making polysyrene (PS) is styrene. The IUPAC name for polystyrene is poly(phenylethene), while

the IUPAC name for styrene is phenylethene, C6H5CH=CH2