22

2-1

Chapter 10Chapter 10

HydrocarbonsHydrocarbons

22

2-2

StructureStructure Hydrocarbon:Hydrocarbon: a compound composed only of

carbon and hydrogen Saturated hydrocarbon:Saturated hydrocarbon: a hydrocarbon

containing only single bonds Alkane:Alkane: a saturated hydrocarbon whose carbons

are arranged in a open chain Aliphatic hydrocarbon:Aliphatic hydrocarbon: another name for an

alkane

22

2-3

StructureStructure Shape

• tetrahedral about carbon• all bond angles are approximately 109.5°

22

2-4

NomenclatureNomenclature Alkanes have the general formula CnH2n+2

Condensed Structural Formula

Molecular FormulaName

heptane

hexane

pentane

butane

propaneethanemethane CH4 CH4

C2H6 CH3CH3

C3H8 CH3CH2CH3C4H10 CH3(CH2)2CH3

C5H12 CH3(CH2)3CH3

C6H14 CH3(CH2)4CH3

C7H16 CH3(CH2)5CH3

22

2-5

NomenclatureNomenclature Alkanes (contd.)

tetradecane

hexadecane

octadecaneeicosane

decane

nonane

octane C8H18 CH3(CH2)6CH3

C9H20 CH3(CH2)7CH3C10 H22 CH3(CH2)8CH3

C14 H30 CH3(CH2)12 CH3

C16 H34 CH3(CH2)14 CH3

C18 H38 CH3(CH2)16 CH3C20 H42 CH3(CH2)18 CH3

dodecane C12 H26 CH3(CH2)10 CH3

22

2-6

Constitutional IsomerismConstitutional Isomerism Constitutional isomers:Constitutional isomers: compounds with the

same molecular formula but a different connectivity (order of attachment of their atoms)• example: C4H10

CH3CH2CH2CH3 CH3CHCH3

CH3

Butane 2-Methylpropane

22

2-7

Prob 1Prob 1 Which sets represent pairs of constitutional isomers?

(a) (b)CH3CH2OH andCH3OCH3 CH3CCH3 andCH3CH2CHO O

(c) (d)CH3COCH3 andCH3CH2COH CH3CHCH2CH3 andCH3CCH2CH3

O O OH O

(e) (f)andCH3CH2CH2CH2CH3 and CH2=CHCH2CH2CH3

22

2-8

Constitutional IsomerismConstitutional Isomerism

4,111,846,763

4,347

75

31

Constitutional Isomers

MolecularFormula

CH4

C5H12

C10H22

C15H32

C30H62

36,797,588C25H52

22

2-9

Nomenclature - IUPACNomenclature - IUPAC Suffix -aneane specifies an alkane Prefix tells the number of carbon atoms

undec-dodec-

tetradec-pentadec-hexadec-heptadec-

nonadec-eicos-

tridec-

11121314151617

octadec- 181920

Prefixmeth-eth-prop-but-pent-hex-

oct-non-dec-

1234567hept-89

10

Carbons CarbonsPrefix

22

2-10

Nomenclature - IUPACNomenclature - IUPAC Parent name: the longest carbon chain Substituent: a group attached to the parent chain

• alkyl group: a substituent derived by removal of a hydrogen from an alkane; given the symbol R-

Alkane Alkyl group

CH4

Name Name

Methane CH3- Methyl group

CH3CH3 Ethane CH3CH2- Ethyl group

22

2-11

NomenclatureNomenclature1.The name of a saturated hydrocarbon with an

unbranched chain consists of a prefix and suffix

2. For branched alkanes, the parent chain is the longest chain of carbon atoms

3. Each substituent is given a name and a number

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

CH3CHCH3

CH3

2-Methylpropane1

23

2-Methylpentane

CH3

CH3CH2CH2CHCH3 14 3 2

5

22

2-12

NomenclatureNomenclature6. If there are two or more different substituents,• list them in alphabetical order• number from the end of the chain that gives the

substituent encountered first the lower number

CH3CH2CHCH2CHCH2CH3

3-Ethyl-5-methylheptane

CH3

CH2CH3

65

43

21 7

22

2-13

NomenclatureNomenclature7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization

8. Substituents are named by the same set of rules.

CH3CCH2CHCH2CH3

CH3 CH2CH3

CH3

4-Ethyl-2,2-dimethylhexane

1 2 34 5

6

22

2-14

NomenclatureNomenclature Alkyl groups

1-methylethyl (isopropyl)

propyl

ethyl

methyl

CondensedStructural FormulaName

CH3

-CH2CH3

-CH3

-CH2CH2CH3

-CHCH3

1,1-dimethylethyl (tert-butyl)

1-methylpropyl (sec-butyl)

2-methylpropyl (isobutyl)

butyl

CH3

CH3

CH3

CH3

-CH2CH2CH2 CH3

-CH2CHCH3

-CHCH2CH3

-CCH3

CondensedStructural FormulaName

22

2-15

Classification of C & HClassification of C & H Primary (1°) C:Primary (1°) C: a carbon bonded to one other

carbon• 1° H: a hydrogen bonded to a 1° carbon

Secondary (2°) C:Secondary (2°) C: a carbon bonded to two other carbons• 2° H: a hydrogen bonded to a 2° carbon

Tertiary (3°) C:Tertiary (3°) C: a carbon bonded to three other carbons• 3° H: a hydrogen bonded to a 3° carbon

Quaternary (4°) CQuaternary (4°) C: a carbon bonded to four other carbons

22

2-16

Physical PropertiesPhysical Properties Intermolecular forces of attraction

• ion-ion (Na+ and Cl- in NaCl)• ion-dipole (Na+ and Cl- solvated in aqueous solution)• dipole-dipole and hydrogen bonding• dispersion forces (very weak electrostatic attraction

between temporary dipoles)

22

2-17

Physical PropertiesPhysical Properties Low-molecular-weight alkanes

(methane....butane) are gases at room temperature

Higher molecular-weight alkanes (pentane, decane, gasoline, kerosene) are liquids at room temperature

High-molecular-weight alkanes (paraffin wax) are semisolids or solids at room temperature

22

2-18

Physical PropertiesPhysical Properties Constitutional isomers have different physical

properties

NameDensity (g/mL)

hexane2-methylpentane

3-methylpentane

2,3-dimethylbutane

2,2-dimethylbutane

68.7

60.3

63.358.0

49.7

-95

-154

-118-129

-98

0.659

0.653

0.6640.661

0.649

bp (°C)

mp (°C)

22

2-19

Oxidation of AlkanesOxidation of Alkanes Oxidation is the basis for their use as energy

sources for heat and power• heat of combustion:heat of combustion: heat released when one mole of a

substance in its standard state is oxidized to carbon dioxide and water

Methane

++CH4 2O2 CO2 2H2O -890 (-212)

++

Propane

CH3CH2CH3 3CO25O2 4H2O -2220 (-530)

H°kJ (kcal)/mol

22

2-20

Sources of AlkanesSources of Alkanes Natural gas

• 90-95% methane

Petroleum• gases (bp below 20°C)• naphthas, including gasoline (bp 20 - 200°C)• kerosene (bp 175 - 275°C)• fuel oil (bp 250 - 400°C)• lubricating oils (bp above 350°C)• asphalt (residue after distillation)

Coal

22

2-21

GasolineGasoline Octane rating:Octane rating: the percent 2,2,4-trimethylpentane

(isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties

CH3(CH2)5CH3 CH3CCH2CHCH3

CH3

CH3 CH3

Heptane(octane rating 0)

2,2,4-Trimethylpentane(octane rating 100)

22

2-22

Synthesis GasSynthesis Gas A mixture of carbon monoxide and hydrogen in

varying proportions which depend on the means by which it is produced

C + H2O heat CO + H2Coal

1+catalyst +

2CH4 2H2COO2

Methane

22

2-23

Synthesis GasSynthesis Gas Synthesis gas is a feedstock for the industrial

production of methanol and acetic acid

• it is likely that industrial routes to other organic chemicals from coal via methanol will also be developed

CH3OH + COcatalyst

CH3COHO

Methanol Acetic acid

+CO 2H2 CH3OHcatalyst

Methanol