Chapter 3. The structural theoryThe structural theory is the basis of organic chemistry: Organic...

Chapter 3

• The structural theoryThe structural theory is the basis of organic chemistry:

Organic compounds can be grouped into families by their common structural features

The members of a given family often have similar chemical and physical behavior

IntroductionIntroduction

• HydrocarbonsHydrocarbons - - are organic molecules consisting only of carbon (C)

and hydrogen (H) atoms.

Alkanes Alkenes Alkynes

Aliphatic Hydrocarbons Arom atic Hydrocarbons

Hydrocarbons

I. Functional GroupsI. Functional Groups I. Functional GroupsI. Functional Groups

A.A. Definition Definition

B.B. Types of Functional GroupsTypes of Functional Groups

A.A. Definition Definition


A.A. DefinitionDefinition

A.A. DefinitionDefinition

• Functional GroupFunctional Group - is a group of atoms within a larger molecule that

has a characteristic chemical reactivity

• It reacts in a typical way, generally independent of the rest of the molecule

The chemistry of every organic molecule, The chemistry of every organic molecule, regardless of size and complexity, is determined regardless of size and complexity, is determined by its functional groups.by its functional groups.



• Table 3.1Table 3.1 lists a wide variety of functional groups.

• The functional groups of a compound affect:• its reactions• its structure• its physical properties

Functional Groups with Carbon-Carbon Functional Groups with Carbon-Carbon Multiple BondsMultiple Bonds

Functional Group with Carbon-Carbon Multiple Functional Group with Carbon-Carbon Multiple Bonds: Bonds: AlkeneAlkene

• AlkenesAlkenes have a C-C double bond

Functional Group with Carbon-Carbon Multiple Functional Group with Carbon-Carbon Multiple Bonds: Bonds: AlkyneAlkyne

• AlkynesAlkynes have a C-C triple bond

Functional Group with Carbon-Carbon Multiple Functional Group with Carbon-Carbon Multiple Bonds: Bonds: AreneArene

• Arenes Arenes have special bonds that are represented as alternating single and double C-C bonds in a six-membered ring

Functional Groups with Carbon Singly Bonded Functional Groups with Carbon Singly Bonded to an Electronegative Atomto an Electronegative Atom

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: Alkyl halideAlkyl halide

• Alkyl halides Alkyl halides have a C bonded to a halogen (C-X)

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: AlcoholAlcohol

• Alcohols Alcohols have a C bonded to O of a hydroxyl group (C-OH)

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: EtherEther

• EthersEthers have two C’s bonded to the same O (C-O-C)

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: AmineAmine

• AminesAmines have a C bonded to N (C-N)

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: Thiol Thiol

• ThiolsThiols have a C bonded to SH group (C-SH)

Functional Group with Carbon Singly Bonded Functional Group with Carbon Singly Bonded to an Electronegative Atom: to an Electronegative Atom: SulfideSulfide

• Sulfides Sulfides have two C’s bonded to same S (C-S-C)

Bonds are polar, with partial positive charge on C (Bonds are polar, with partial positive charge on C (+) and +) and partial negative charge (partial negative charge (-) on electronegative atom-) on electronegative atom

Functional Groups with Carbon-Oxygen Functional Groups with Carbon-Oxygen Double Bond (Carbonyl Groups)Double Bond (Carbonyl Groups)

• These compounds behave similarly but differ depending on the identity of the atoms attached on the carbonyl-group carbon.


• AldehydesAldehydes: have one hydrogen bonded to C=O

• Ketones:Ketones: have two C’s bonded to the C=O


• Carboxylic AcidsCarboxylic Acids: have -OH bonded to the C=O

• Esters:Esters: have one ether-like C-O bonded to the C=O


• AmidesAmides: have one amine-like N bonded to the C=O

• Acid chlorides:Acid chlorides: have a Cl bonded to the C=O

Carbonyl C has partial positive charge (+)Carbonyl O has partial negative charge (-).

Practice ProblemPractice Problem: Identify the functional groups in each of the : Identify the functional groups in each of the following molecules: following molecules:

Practice ProblemPractice Problem: Propose structures for simple molecules that : Propose structures for simple molecules that contain the following functional groups: contain the following functional groups:

a. Alcohol

b. Aromatic ring

c. Carboxylic acid

d. Amine

e. Both ketone and amine

f. Two double bonds

Practice ProblemPractice Problem: Identify the functional groups in the following : Identify the functional groups in the following model of arecoline, a veterinary drug used to model of arecoline, a veterinary drug used to control worms in animals. Convert the control worms in animals. Convert the drawing into a line-bond structure and a drawing into a line-bond structure and a molecular formula (red = O, blue = N) molecular formula (red = O, blue = N)

II. AlkanesII. Alkanes II. AlkanesII. Alkanes

A.A. Alkane IsomersAlkane Isomers

B.B. Alkyl GroupsAlkyl Groups

C.C. Naming AlkanesNaming Alkanes

D.D. Properties of AlkanesProperties of Alkanes




D.D. Properties of AlkanesProperties of Alkanes

OverviewOverview

• AlkanesAlkanes - are saturated aliphatic hydrocarbons.

• They are compounds that contain only carbons and hydrogens (hydrocarbons), all connected exclusively by single bonds (saturated)

• They are a large family of molecules

• AlkanesAlkanes - have the general formula

CnH2n+2

where n is an integer



• Isomers -Isomers - are different compounds with the same molecular formula

Constitutional Isom ers

Enantiom ers Diastereom ers

Stereoisom ers

Isom ers

• For an alkane with less than threeless than three carbons, there is only one possible structure.

• The molecular formula of an alkane with more than more than threethree carbons can give more than one structure

• Straight-chain alkanesStraight-chain alkanes or normal alkanesnormal alkanes - are compounds whose carbons are connected in a row.

• The C’s are connected to no more than 2 other C’s

• Branched-chain alkanesBranched-chain alkanes - are compounds whose carbon chains branch.

• There are one or more C’s connected to 3 or 4 C’s

• Constitutional Isomers Constitutional Isomers - are isomers that differ in how their atoms are arranged in chains

• They are isomers with different connectivity, i.e different order of attachment of their atoms

• Constitutional isomers may haveConstitutional isomers may have:

Condensed Structures of AlkanesCondensed Structures of Alkanes

• An alkane can be represented in a brief form or in many types of extended form

• A condensed structurecondensed structure does not show bonds but lists atoms, such as

CH3CH2CH3 (propane) CH3C(CH3)2CH3 (2,2-dimethylpropane)

Practice ProblemPractice Problem: Draw structures of the five isomers C: Draw structures of the five isomers C66HH1414

Practice ProblemPractice Problem: Propose structures that meet the following : Propose structures that meet the following descriptions descriptions

a. Two isomeric esters with the formula C5H10O2

b. Two isomeric nitriles with the formula C4H7N

Practice ProblemPractice Problem: How many isomers are there with the : How many isomers are there with the following descriptions? following descriptions?

a. Alcohols with the formula C3H8O

b. Bromoalkanes with the formula C4H9Br



• AlkyI group -AlkyI group - is the partial structure that remains when a hydrogen atom is removed from an alkane

-- has the general abbreviation “R”“R” (for RadicalRadical, an incomplete species or the “rest”“rest” of the molecule)

Naming Alkyl groupsNaming Alkyl groups

• Replace -ane ending of alkane with -yl ending-CH3 is “methyl” from methane

-CH2CH3 is “ethyl” from ethane

• Combining an alkyl group with any of the functional groups gives the name of the compound

Degree of a Carbon atomDegree of a Carbon atom

Degree (o) is applied to spsp33 carbons only !

Degree (o) of a carbon is equalequal to the number of carbons attached directly to it.

11oo primary primary 22oo secondary secondary 33oo tertiary tertiary 44oo quaternary quaternary

Types of Alkyl groupsTypes of Alkyl groups

Alkyl groups are classified by the connection site

primaryprimary alkyl group (attached to 1oC)

secondarysecondary alkyl group (attached to 2oC)

tertiarytertiary alkyl group (attached to 3oC)

quaternaryquaternary alkyl group (attached to 4oC)

Naming Alkyl groups: Naming Alkyl groups: Common SystemCommon System

• Free valence indicates carbon # 1

• Prefixes are necessary to indicate arrangement of carbons in structure:

• n n – unbranched chain and free valence is on 1o C

• isoiso – one -CH3 on next to lastnext to last carbon

• secsec – free valence on 22oo C and used only for butylbutyl

• terttert – free valence is on 33oo C

• neoneo – two -CH3’s next to the last last carbon


• secsec – free valence on 22oo C and used only for butylbutyl

• tert tert – free valence is on 33oo C


• terttert – free valence is on 33oo C

• neoneo – two -CH3’s next to the last last carbon

Degree of a Hydrogen atomDegree of a Hydrogen atom

Degree (o) of a hydrogen is the samesame as the o

of carbon to which it is attached

No such thing as a quaternary H !

Practice ProblemPractice Problem: Draw the eight 5-carbon alkyl groups (pentyl : Draw the eight 5-carbon alkyl groups (pentyl isomers) isomers)

Practice ProblemPractice Problem: Identify the carbon atoms in the following : Identify the carbon atoms in the following molecules as primary, secondary, tertiary or molecules as primary, secondary, tertiary or quaternary quaternary

Practice ProblemPractice Problem: Identify the hydrogen atoms on the : Identify the hydrogen atoms on the compounds shown as primary, secondary, compounds shown as primary, secondary, or tertiary or tertiary

Practice ProblemPractice Problem: Draw structures of alkanes that meet the : Draw structures of alkanes that meet the following descriptions following descriptions

a. An alkane with two tertiary carbons

b. An alkane that contains an isopropyl group

c. An alkane that has one quaternary and one secondary carbon



• The IInternational nternational UUnion of nion of PPure and ure and AApplied pplied CChemistryhemistry (IUPACIUPAC) devised a system of nomenclature that uses:

Steps to naming alkanesSteps to naming alkanes11

1.1. Find the parent hydrocarbonFind the parent hydrocarbon

a.a. Find the longest continuous chain of carbon atomsFind the longest continuous chain of carbon atoms



a.a. Find the longest continuous chain of carbon atomsFind the longest continuous chain of carbon atoms

b.b. If two chains have equal length, choose the main chain with more substituentsIf two chains have equal length, choose the main chain with more substituents


2.2. Number the atoms in the main chainNumber the atoms in the main chain

• The correct sequence is when the substituents have the The correct sequence is when the substituents have the lowest possible number lowest possible number


3.3. Identify and number the substituentsIdentify and number the substituents

• Name and locate the substituentsName and locate the substituents


4.4. Write the name as a single wordWrite the name as a single word

a.a. Use hyphens to separate the different prefixes, and use commas to Use hyphens to separate the different prefixes, and use commas to separate numbers.separate numbers.

b.b. Use multiplicity prefixes di-, tri-, tetra-, …Use multiplicity prefixes di-, tri-, tetra-, …

b.b. Put the substituents in alphabetical order (Do not consider multiplier Put the substituents in alphabetical order (Do not consider multiplier prefixes)prefixes)


5.5. Name a complex substituent as though it were itself a Name a complex substituent as though it were itself a compoundcompound

a.a. Name the complex substituent using the point of attachment as C#1Name the complex substituent using the point of attachment as C#1

b.b. Put it in alphabetical order (numerical prefix is included) Put it in alphabetical order (numerical prefix is included)

c.c. Set it off in parenthesesSet it off in parentheses

Practice ProblemPractice Problem: Give IUPAC names for the following : Give IUPAC names for the following compounds compounds

Practice ProblemPractice Problem: Draw structures corresponding to the : Draw structures corresponding to the following IUPAC names following IUPAC names

a. 3,4-Dimethylnonane

b. 3-Ethyl-4,4-dimethylheptane

c. 2,2-Dimethyl-4-propyloctane

d. 2,2,4-Trimethylpentane

Practice ProblemPractice Problem: Name the eight 5-carbon alkyl groups: Name the eight 5-carbon alkyl groups

Practice ProblemPractice Problem: Give the IUPAC name for the following : Give the IUPAC name for the following hydrocarbon, and convert the drawing into hydrocarbon, and convert the drawing into skeletal structure. skeletal structure.

DD.. Properties of AlkanesProperties of Alkanes

DD.. Properties of AlkanesProperties of Alkanes

• Alkanes are called paraffins (low affinity compounds)

• They do not react as most chemicals, i.e. they are chemically inert to most lab reagents

• However, they do react with O2, halogens and a few other substances

Oxidation: Reaction with OOxidation: Reaction with O22

• Alkanes will burn in a flame, producing carbon dioxide, water, and heat

Alkane CO2 + H2O H = -O2

• The larger the value of H, the less stable the alkane• If hydrocarbons do not contain the same amount of

carbons, one must compare H/CH2 rather than H

HalogenationHalogenation

• Alkanes react with Cl2 in the presence of light to replace H’s with Cl’s (not controlled)

Alkane Alkyl halides + HXX2

h

• X2 = Br2 or Cl2

Physical PropertiesPhysical Properties

1.1. Intermolecular Forces Intermolecular Forces

2.2. SolubilitySolubility


2.2. SolubilitySolubility


• To a first approx. C-H C-H and C-C C-C bonds are nonpolar:nonpolar:

• Dipole moments of alkanes are ~0

• Alkanes are nonpolar

• The IMF’s for alkanes are van der Waals interactions (i.e induced-dipole-induced-dipole forces, London or dispersion forces)

• For compounds of similar M.W., alkanes have lower b.p’s and m.p’s.

• Boiling points and melting points increase as size of alkane increases.

• This is due the presence of dispersion forces

• Dispersion forces are weak intermolecular forces that arise due to transient nonuniform electron distribution (temporary molecular dipoles).

• Increased branching lowers an alkane’s boiling pointIncreased branching lowers an alkane’s boiling point

CompoundsCompounds Boiling PointBoiling Point

Pentane 36.1 oC

Isopentane 27.85 oC

Neopentane 9.5oC

Octane 125.7oC

Isooctane 99.3oC

Branched-chain alkanes are more nearly spherical than straight-chain alkanes, thus have smaller surface areas, and consequently have smaller dispersion forces.

2.2. Solubility Solubility

• “Like dissolves like”• Alkanes are nonpolar; they dissolve best in

solvents which are either nonpolar or weakly polar

# Carbons 4 ~

# Hydrophilic sites 1

III. CycloalkanesIII. Cycloalkanes III. CycloalkanesIII. Cycloalkanes

A.A. Naming Cycloalkanes Naming Cycloalkanes

B.B. Cis-Trans IsomerismCis-Trans Isomerism

A.A. Naming Cycloalkanes Naming Cycloalkanes

B.B. Cis-Trans IsomerismCis-Trans Isomerism

OverviewOverview

• Cycloalkanes Cycloalkanes – are alialicyclic (aliphatic cyclic) compounds

• They are alkanes that have carbon atoms that form a ring

• Their structure is shown as a regular polygon with the number of vertices equal to the number of C’s

• CycloalkanesCycloalkanes – are rings of -CH2- units.

– have the general formula

CnH2n


Simple CycloalkanesSimple Cycloalkanes

• Naturally occurring materials contain cycloalkane structures

• ExamplesExamples: chrysanthemic acid, prostaglandins, steroids

Complex CycloalkanesComplex Cycloalkanes

(cyclopropane)(cyclopropane)

(cyclopentane)(cyclopentane)

(cyclohexane(cyclohexane and cyclopentane)cyclopentane)

• Boiling points increase as ring size increases.

• Melting points are affected by the shapes and the way that crystals pack so they do not change uniformly

Properties of CycloalkanesProperties of Cycloalkanes

AA.. Naming CycloalkanesNaming Cycloalkanes

AA.. Naming CycloalkanesNaming Cycloalkanes

• Cycloalkanes are also named by the rules devised by the IInternational nternational UUnion of nion of PPure and ure and AApplied pplied CChemistryhemistry (IUPACIUPAC).

Steps to naming cycloalkanesSteps to naming cycloalkanes11


a.a. Count the number of carbon atoms in the ring and the number in the largest substituent chainCount the number of carbon atoms in the ring and the number in the largest substituent chain

• If # Cring = or > # Csubstituent, then it is named as an alkyl-substituted cycloalkane• If # Cring < # Csubstituent, then it is named as an cycloalkyl-substituted alkane


2.2. Number the substituents and write the nameNumber the substituents and write the name

• The correct sequence is when the substituents have the lowest possible number The correct sequence is when the substituents have the lowest possible number

• For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible.

• When two or more substituents could potentially be assigned the same numbers, number them by alphabetical order.

When two or more substituents could potentially be assigned the same numbers, number them by alphabetical order.

Practice ProblemPractice Problem: Give IUPAC names for the following : Give IUPAC names for the following cycloalkanes cycloalkanes

Practice ProblemPractice Problem: Draw structures corresponding to the : Draw structures corresponding to the following IUPAC names following IUPAC names

a. 1,1-Dimethylcyclooctane

b. 3-Cyclobutylhexane

c. 1,2-Dichlorocyclopentane

d. 1,3-Dibromo-5-methylcyclohexane

Practice ProblemPractice Problem: Name the following cycloalkane: Name the following cycloalkane

BB.. Cis-Trans IsomerismCis-Trans Isomerism

BB.. Cis-Trans IsomerismCis-Trans Isomerism

• In open-chain alkanes, free rotation is possible around C-C bonds because bonds are cylindrically symmetrical:

• In cycloalkanes, free rotation is limited by the ring structure

• The common ring sizes (C3, C4, C5, C6, C7) are severely restricted in their molecular motions

• Larger cycloalkanes have increasingly more rotational freedom

one with the two methyls on the same side (ciscis) of the ring

one with the methyls on opposite

sides (transtrans)

• Rings have two “faces” and substituents are labeled as to their relative facial positions

• There are two different 1,2-dimethyl-cyclopropane isomers:

StereoisomersStereoisomers

• Stereoisomers Stereoisomers – are compounds with atoms connected in the same order but which differ in three-dimensional orientation

• The terms “cis” and “trans” should be used to specify stereoisomeric ring structures

• Constitutional isomersConstitutional isomers – are compounds with atoms connected in different order

Practice ProblemPractice Problem: Name the following substances, including the : Name the following substances, including the ciscis- or - or transtrans- prefix- prefix

Practice ProblemPractice Problem: Draw the structures of the following molecules: Draw the structures of the following molecules

a. trans-1-Bromo-3-methylcyclohexane

b. cis-1,2-Dimethylcyclobutane

c. trans-1-tert-Butyl-2-ethylcyclohexane

Practice ProblemPractice Problem: Name the following substances, including the : Name the following substances, including the ciscis- or - or transtrans- prefix (red-brown = Br)- prefix (red-brown = Br)

IV. Bicyclic Alkane SystemsIV. Bicyclic Alkane Systems IV. Bicyclic Alkane SystemsIV. Bicyclic Alkane Systems

A.A. Naming Bicyclic Systems Naming Bicyclic Systems

A.A. Naming Bicyclic Systems Naming Bicyclic Systems

OverviewOverview

• Bicycloalkanes Bicycloalkanes – are alkanes containing two rings that share two carbon atoms

• Bridgehead atoms – are the shared carbon atoms• Bridges – are the carbon chains connecting the bridgeheads

• Bicycloalkanes Bicycloalkanes – have the general formula

CnH2n-2


• Spiroalkanes Spiroalkanes – are cycloalkanes in which two rings share only one carbon atom

AA.. Naming Bicyclic Alkane SystemsNaming Bicyclic Alkane Systems

AA.. Naming Bicyclic Alkane SystemsNaming Bicyclic Alkane Systems

• The IInternational nternational UUnion of nion of PPure and ure and AApplied pplied CChemistryhemistry (IUPACIUPAC) has devised rules to name bicyclic alkane systems.

Steps to naming bicycloalkanesSteps to naming bicycloalkanes11

1.1. Find the parent nameFind the parent name

• The parent name of a bicycloalkane is that of the unbranched The parent name of a bicycloalkane is that of the unbranched alkane of the same number of carbon atoms as are in the bicyclic alkane of the same number of carbon atoms as are in the bicyclic ring system ring system

2.2. Numbering begins at one bridgehead carbon Numbering begins at one bridgehead carbon atomatom

#1

CH3

#1


3.3. Number the bridges in order of decreasing sizeNumber the bridges in order of decreasing size

• Longest bridge is written firstLongest bridge is written first

• Proceed along the longest bridge to the second bridgehead carbon, then along the next longest bridge back to the original bridgehead carbon, and so on until all carbon atoms are numbered.

• If there are two bridges of the same length, the correct sequence is when the substituents have the lowest possible numberIf there are two bridges of the same length, the correct sequence is when the substituents have the lowest possible number

• If there are more than one substituents, give an alphabetical preference.


4.4. Show the bridge lengths in bracketsShow the bridge lengths in brackets

• Count the number of carbons linking the bridgeheads and place them Count the number of carbons linking the bridgeheads and place them in decreasing order in brackets between the prefix bicyclo and the in decreasing order in brackets between the prefix bicyclo and the parent name and with periods separating each number. parent name and with periods separating each number.

Bicyclo [3.2.0] heptane

CH3

7-methylbicyclo [4.2.0]octane

Chapter 3

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