Lecture 4 - Alkanes and Cycloalkanes smart board

General

Organic ChemistryTwo credits

Second Semester 2009

King Saud bin Abdulaziz University for Health Science

Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. CareyThird Edition

Instructor: Rabih O. Al-Kaysi, PhD.

Chapter 2Chapter 2

Alkanes and Cycloalkanes

Lecture 3

IUPAC Nomenclature ofIUPAC Nomenclature of

Unbranched Alkanes Unbranched Alkanes

Retained:Retained:

methanemethane CHCH44

ethaneethane CHCH33CHCH33

propanepropane CHCH33CHCH22CHCH33

butanebutaneCHCH33CHCH22CHCH22CHCH33

IUPAC Names of Unbranched AlkanesIUPAC Names of Unbranched Alkanes

Note:Note:nn-prefix is not part of IUPAC name of-prefix is not part of IUPAC name ofany alkane.any alkane.

For example: For example: nn-butane is "common name" -butane is "common name" for CHfor CH33CHCH22CHCH22CHCH33;; butane is "IUPAC name."butane is "IUPAC name."

Others:Others:

Latin or Greek prefix for number of Latin or Greek prefix for number of

carbons + ane suffixcarbons + ane suffix


Number of carbons Number of carbons NameName StructureStructure

55 pentanepentane CHCH33(CH(CH22))33CHCH33

66 hexanehexane CHCH33(CH(CH22))44CHCH33

77 heptaneheptane CHCH33(CH(CH22))55CHCH33

88 octaneoctane CHCH33(CH(CH22))66CHCH33

99 nonanenonane CHCH33(CH(CH22))77CHCH33

1010 decanedecane CHCH33(CH(CH22))88CHCH33


Number of carbons Number of carbons NameName StructureStructure

1111 undecaneundecane CHCH33(CH(CH22))99CHCH33

1212 dodecanedodecane CHCH33(CH(CH22))1010CHCH33

1313 tridecanetridecane CHCH33(CH(CH22))1111CHCH33

1414 tetradecanetetradecane CHCH33(CH(CH22))1212CHCH33

1515 pentadecanepentadecane CHCH33(CH(CH22))77CHCH33

1616 hexadecanehexadecane CHCH33(CH(CH22))88CHCH33


Applying the IUPAC Rules:Applying the IUPAC Rules:The Names of the CThe Names of the C66HH1414 Isomers Isomers

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33

(CH(CH33))22CHCHCHCH22CHCH22CHCH33

(CH(CH33CHCH22))22CHCHCHCH33

(CH(CH33))22CHCH(CHCHCH(CH33))22

(CH(CH33))33CCHCCH22CHCH33

The CThe C66HH1414 Isomers Isomers

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33

The IUPAC name of the unbranched alkaneThe IUPAC name of the unbranched alkanewith a chain of 6 carbons is hexane.with a chain of 6 carbons is hexane.

HexaneHexane


Step 1) Step 1) Find the longest continuous carbonFind the longest continuous carbonchain and use the IUPAC name of thechain and use the IUPAC name of theunbranched alkane as the basis.unbranched alkane as the basis.

Step 2) Step 2) Add name of substituent as a prefix.Add name of substituent as a prefix.

Step 3) Step 3) Number the chain from the end nearestNumber the chain from the end nearestthe substituent, and identify the carbon to the substituent, and identify the carbon to which the substituent is attached by number.which the substituent is attached by number.

IUPAC Nomenclature of Branched IUPAC Nomenclature of Branched AlkanesAlkanes

(CH(CH33))22CHCHCHCH22CHCH22CHCH33

(CH(CH33CHCH22))22CHCHCHCH33

2-Methylpentane2-Methylpentane

3-Methylpentane3-Methylpentane


(CH(CH33))22CHCH(CHCHCH(CH33))22

(CH(CH33))33CCHCCH22CHCH33

2,3-Dimethylbutane2,3-Dimethylbutane

2,2-Dimethylbutane2,2-Dimethylbutane

Use replicating prefixes (di-, tri-, tetra-, etc.) Use replicating prefixes (di-, tri-, tetra-, etc.) according to the number of identical substituentsaccording to the number of identical substituentsattached to the main chain.attached to the main chain.


Alkyl GroupsAlkyl Groups

Methyl and Ethyl GroupsMethyl and Ethyl Groups

MethylMethyl

EthylEthyl CC CCHH

HH HH

HH HH

CHCH33CHCH22

CCHH

HH

HH

CHCH33oror

oror

Unbranched Alkyl GroupsUnbranched Alkyl Groups

If potential point of attachment is at the endIf potential point of attachment is at the endof the chain, take the IUPAC name of theof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacecorresponding unbranched alkane and replacethe -the -aneane ending by - ending by -ylyl..

RRHHRR

ButylButyl

If potential point of attachment is at the endIf potential point of attachment is at the endof the chain, take the IUPAC name of theof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacecorresponding unbranched alkane and replacethe -the -aneane ending by - ending by -ylyl..

RRHHRR

CHCH33CHCH22CHCH22CHCH22CC CCHH

HH HH

HH HH

CC CC

HH HH

HH HH

oror


HexylHexylCHCH33(CH(CH22))44CHCH22

CHCH33(CH(CH22))55CHCH22

CHCH33(CH(CH22))1616CHCH22

HeptylHeptyl

OctadecylOctadecyl


The CThe C33HH77 Alkyl Groups Alkyl Groups

CHCH33CHCH22CHCH22CC CCHH

HH HH

HH HH

CC

HH

HH

oror

andand

CHCH33CHCHCHCH33CC CCHH

HH HH

HH

HHCC

HH

HH

oror


HH HH

HH HH

CC

HH

HH

oror

IUPAC name: PropylIUPAC name: Propyl

Common name: Common name: nn-Propyl-Propyl


Naming Alkyl GroupsNaming Alkyl Groups

Step 1:Step 1: Identify longest continuous chain starting at Identify longest continuous chain starting at point of attachment.point of attachment.

Step 2: Step 2: Drop -Drop -aneane ending from name of unbranched ending from name of unbranched alkane having same number of carbons as alkane having same number of carbons as longest continuous chain and replace by -longest continuous chain and replace by -ylyl..

Step 3:Step 3: Identify substituents on longest continuous Identify substituents on longest continuous chain.chain.

Step 4:Step 4: Chain is always numbered starting atChain is always numbered starting atpoint of attachment.point of attachment.

IUPAC name: 1-MethylethylIUPAC name: 1-Methylethyl

Common name: IsopropylCommon name: Isopropyl


HH HH

HH

CC

HH

HH

ororHH



HH HH

HH HH

CC

HH

HH

oror

Classification: Primary alkyl groupClassification: Primary alkyl group

Alkyl groups are classified according to theAlkyl groups are classified according to thedegree of substitution at the carbon that bears thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlypoint of attachment. A carbon that is directlyattached to one other carbon is a primary carbon.attached to one other carbon is a primary carbon.


Classification: Secondary alkyl groupClassification: Secondary alkyl group

Alkyl groups are classified according to theAlkyl groups are classified according to thedegree of substitution at the carbon that bears thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlypoint of attachment. A carbon that is directlyattached to two other carbons is a secondary carbon.attached to two other carbons is a secondary carbon.


HH HH

HH

CC

HH

HH

ororHH


IUPAC name: 2-MethylpropylIUPAC name: 2-Methylpropyl

Common name: IsobutylCommon name: Isobutyl

Classification: Primary alkyl groupClassification: Primary alkyl group

112233CC

HH

CHCH22

CHCH33

CHCH33


IUPAC name: 1,1-DimethylethylIUPAC name: 1,1-Dimethylethyl

Common name: Common name: terttert-Butyl-Butyl

Classification: Tertiary alkyl groupClassification: Tertiary alkyl group

11 22CC CHCH33

CHCH33

CHCH33


IUPAC Names of HighlyIUPAC Names of Highly

Branched AlkanesBranched Alkanes

Branched alkanesBranched alkanes OctaneOctane

4-Ethyloctane4-Ethyloctane

Branched alkanesBranched alkanes

4-Ethyl-3-methyloctane4-Ethyl-3-methyloctane

List substituents in alphabetical order.List substituents in alphabetical order.


4-Ethyl-3,5-dimethyloctane4-Ethyl-3,5-dimethyloctane

List substituents in alphabetical order.List substituents in alphabetical order.But don't alphabetize di-, tri-, tetra-, etc.But don't alphabetize di-, tri-, tetra-, etc.


First Point of Difference RuleFirst Point of Difference Rule

The chain is numbered in the direction that The chain is numbered in the direction that gives the lower locant to the substituent at the gives the lower locant to the substituent at the first point of difference in the names.first point of difference in the names.

Don't add locants!Don't add locants!

2,2,6,6,7-Pentamethyloctane?2,2,6,6,7-Pentamethyloctane?


What is correct name?What is correct name?

1122 33

4455

6677

88

88

77 6655

4433

2211

Just for general knowledge, will not be tested on

First Point of Difference RuleFirst Point of Difference Rule

The chain is numbered in the direction that The chain is numbered in the direction that gives the lower locant to the substituent at the gives the lower locant to the substituent at the first point of difference in the names.first point of difference in the names.

Don't add locants!Don't add locants!


What is correct name?What is correct name?

88

77 6655

4433

2211

Just

for

gen

eral

kn

owle

dge

, wil

l not

be

test

ed o

n

CCnnHH22nn

Cycloalkane NomenclatureCycloalkane Nomenclature

CycloalkanesCycloalkanes

Cycloalkanes are alkanes that contain a ring of Cycloalkanes are alkanes that contain a ring of three or more carbons.three or more carbons.

Count the number of carbons in the ring, and Count the number of carbons in the ring, and add the prefix add the prefix cyclocyclo to the IUPAC name of the to the IUPAC name of the unbranched alkane that has that number of unbranched alkane that has that number of carbons.carbons.

CyclopentaneCyclopentane CyclohexaneCyclohexane

EthylcyclopentaneEthylcyclopentane


CHCH22CHCH33

Name any alkyl groups on the ring in the usual Name any alkyl groups on the ring in the usual way.way.

Name any alkyl groups on the ring in the usual Name any alkyl groups on the ring in the usual way.way.

List substituents in alphabetical order and countList substituents in alphabetical order and countin the direction that gives the lowest numericalin the direction that gives the lowest numericallocant at the first point of difference.locant at the first point of difference.

3-Ethyl-1,1-dimethylcyclohexane3-Ethyl-1,1-dimethylcyclohexane

CHCH22CHCH33

HH33CC CHCH33


Sources of Alkanes and CycloalkanesSources of Alkanes and Cycloalkanes


Crude oilCrude oil


Crude oilCrude oil

Refinery gasRefinery gasRefinery gasRefinery gas

CC11-C-C44

Light gasolineLight gasoline(bp: 25-95 °C)(bp: 25-95 °C)

Light gasolineLight gasoline(bp: 25-95 °C)(bp: 25-95 °C)

CC55-C-C1212

NaphthaNaphtha(bp 95-150 °C)(bp 95-150 °C)

NaphthaNaphtha(bp 95-150 °C)(bp 95-150 °C)

KeroseneKerosene(bp: 150-230 °C)(bp: 150-230 °C)

KeroseneKerosene(bp: 150-230 °C)(bp: 150-230 °C)

CC1212-C-C1515

Gas oilGas oil(bp: 230-340 °C)(bp: 230-340 °C)

Gas oilGas oil(bp: 230-340 °C)(bp: 230-340 °C)

CC1515-C-C2525

ResidueResidueResidueResidue


CrackingCrackingconverts high molecular weight hydrocarbons converts high molecular weight hydrocarbons to more useful, low molecular weight onesto more useful, low molecular weight ones

ReformingReformingincreases branching of hydrocarbon chainsincreases branching of hydrocarbon chainsbranched hydrocarbons have better burningbranched hydrocarbons have better burningcharacteristics for automobile enginescharacteristics for automobile engines

Petroleum RefiningPetroleum Refining

Physical Properties of AlkanesPhysical Properties of Alkanes

and Cycloalkanesand Cycloalkanes

Boiling Points of Alkanes Boiling Points of Alkanes

governed by strength of intermolecular governed by strength of intermolecular attractive forcesattractive forces

alkanes are nonpolar, so dipole-dipole and alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absentdipole-induced dipole forces are absent

only forces of intermolecular attraction are only forces of intermolecular attraction are induced dipole-induced dipole forcesinduced dipole-induced dipole forces

Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces

++––++

––

two nonpolar moleculestwo nonpolar molecules

center of positive charge and center of negative center of positive charge and center of negative charge coincide in eachcharge coincide in each


++––++

––

movement of electrons creates an movement of electrons creates an instantaneous dipole in one molecule (left)instantaneous dipole in one molecule (left)



++––++––

temporary dipole in one molecule (left) induces temporary dipole in one molecule (left) induces a complementary dipole in other molecule a complementary dipole in other molecule (right)(right)



++––++ ––

temporary dipole in one molecule (left) induces temporary dipole in one molecule (left) induces a complementary dipole in other molecule a complementary dipole in other molecule (right)(right)



++––++ ––

the result is a small attractive force between the result is a small attractive force between the two moleculesthe two molecules



++–– ++ ––

the result is a small attractive force between the result is a small attractive force between the two moleculesthe two molecules



increase with increasing number of carbonsincrease with increasing number of carbons

more atoms, more electrons, more more atoms, more electrons, more opportunities for induced dipole-inducedopportunities for induced dipole-induceddipole forces dipole forces

decrease with chain branchingdecrease with chain branching

branched molecules are more compact withbranched molecules are more compact withsmaller surface area—fewer points of contactsmaller surface area—fewer points of contactwith other molecules with other molecules

Boiling PointsBoiling Points


more atoms, more electrons, more more atoms, more electrons, more opportunities for induced dipole-inducedopportunities for induced dipole-induceddipole forces dipole forces

HeptaneHeptanebp 98°Cbp 98°C

OctaneOctanebp 125°Cbp 125°C

NonaneNonanebp 150°Cbp 150°C



branched molecules are more compact withbranched molecules are more compact withsmaller surface area—fewer points of contactsmaller surface area—fewer points of contactwith other molecules with other molecules

Octane: bp 125°COctane: bp 125°C 2-Methylheptane: bp 118°C2-Methylheptane: bp 118°C

2,2,3,3-Tetramethylbutane: bp 107°C2,2,3,3-Tetramethylbutane: bp 107°C


All alkanes burn in air to giveAll alkanes burn in air to givecarbon dioxide and water.carbon dioxide and water.

Chemical Properties:Chemical Properties:

Combustion of AlkanesCombustion of Alkanes


more moles of Omore moles of O22 consumed, more moles consumed, more molesof COof CO22 and H and H22O formedO formed

Heats of CombustionHeats of Combustion

4817 kJ/mol4817 kJ/mol





HeptaneHeptane

OctaneOctane

NonaneNonane




more moles of Omore moles of O22 consumed, more moles consumed, more molesof COof CO22 and H and H22O formedO formed


branched molecules are more stablebranched molecules are more stable(have less potential energy) than their(have less potential energy) than theirunbranched isomersunbranched isomers






5 kJ/mol5 kJ/mol

8 kJ/mol8 kJ/mol

6 kJ/mol6 kJ/mol



Isomers can differ in respect to their stability.Isomers can differ in respect to their stability.

Equivalent statement:Equivalent statement:

Isomers differ in respect to their potential energy.Isomers differ in respect to their potential energy.

Differences in potential energy can be measured by Differences in potential energy can be measured by comparing heats of combustion.comparing heats of combustion.

Important PointImportant Point

8CO8CO22 + 9H + 9H22OO

5452 kJ/mol5452 kJ/mol5458 kJ/mol5458 kJ/mol


5466 kJ/mol5466 kJ/molOO22++ 2525

22

OO22++ 2525

22 OO22++ 2525

22 OO22++ 2525

22


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Lecture 4 - Alkanes and Cycloalkanes smart board