ch 10

1. 2
Hydrocarbons
Chapter 10
2-1

2. 2 Structure
Hydrocarbon: a compound composed only of
carbon and hydrogen
Saturated hydrocarbon: a hydrocarbon
containing only single bonds
Alkane: a saturated hydrocarbon whose
carbons are arranged in a open chain
Aliphatic hydrocarbon: another name for an
alkane
2-2

3. 2 Structure
Shape
• tetrahedral about carbon
• all bond angles are approximately
109.5°
2-3

4. 2 Nomenclature
Alkanes have the general formula C nH 2n+2
Molecular Condensed
Name Formula Structural Formula
methane CH 4 CH 4
ethane C2 H6 CH 3 CH 3
propane C3 H8 CH 3 CH 2 CH 3
butane C 4 H 10 CH 3 (CH 2 ) 2 CH 3
pentane C 5 H 12 CH 3 (CH 2 ) 3 CH 3
hexane C 6 H 14 CH 3 (CH 2 ) 4 CH 3
heptane C 7 H 16 CH 3 (CH 2 ) 5 CH 3
2-4

5. 2 Nomenclature
Alkanes (contd.)
octane C8 H18 CH 3 (CH 2 ) 6 CH 3
nonane C9 H20 CH 3 (CH 2 ) 7 CH 3
decane C10 H22 CH 3 (CH 2 ) 8 CH 3
dodecane C12 H26 CH 3 (CH 2 ) 10 CH 3
tetradecane C14 H30 CH 3 (CH 2 ) 12 CH 3
hexadecane C16 H34 CH 3 (CH 2 ) 14 CH 3
octadecane C18 H38 CH 3 (CH 2 ) 16 CH 3
eicosane C20 H42 CH 3 (CH 2 ) 18 CH 3
2-5

6. 2 Constitutional Isomerism
Constitutional isomers: compounds with the
same molecular formula but a different
connectivity (order of attachment of their
atoms)
• example: C 4 H 10
CH 3
CH 3 CH 2 CH 2 CH 3 CH3 CHCH3
Butane 2-Methylpropane
2-6

7. 2 Prob 1
Which sets represent pairs of constitutional
isomers? O O
(a) CH3 CH2 OH and CH 3 OCH 3 (b) CH3 CCH3 and CH3 CH2 CH
O O OH O
(c) CH 3 COCH 3 and CH 3 CH2 COH (d) CH3 CHCH2 CH3 and CH3 CCH2 CH 3
(e) and CH 3 CH 2 CH2 CH2 CH3 (f) and CH2 = CHCH2 CH2 CH3
2-7

8. 2 Constitutional
Isomerism
Molecular Constitutional
Formula Isomers
CH4 1
C5 H1 2 3
C1 0 H2 2 75
C1 5 H3 2 4,347
C2 5 H5 2 36,797,588
C3 0 H6 2 4,111,846,763
2-8

9. 2 Nomenclature - IUPAC
Suffix - ane specifies an alkane
Prefix tells the number of carbon atoms
Prefix Carbons Prefix Carbons
meth- 1 undec- 11
eth- 2 dodec- 12
prop- 3 tridec- 13
but- 4 tetradec- 14
pent- 5 pentadec- 15
hex- 6 hexadec- 16
hept- 7 heptadec- 17
oct- 8 octadec- 18
non- 9 nonadec- 19
dec- 10 eicos- 20
2-9

10. 2 Nomenclature - 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; group Name symbol R-
Alkane Name Alkyl
given the
CH 4 Methane CH3 - Methyl group
CH 3 CH 3 Ethane CH3 CH 2 - Ethyl group
2-10

11. 2 Nomenclature
1.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
CH 3
2
CH3 CHCH 3 1 3
2-Methylpropane
4. If there is one substituent, number the chain
from the end that gives it the lower number
CH3
4 3 2
CH3 CH2 CH 2 CHCH3 5 1
2-Methylpentane
2-11

12. 2 Nomenclature
6. 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
CH3 2 4 6
3 5 7
CH3 CH2 CHCH2 CHCH2 CH3 1
CH2 CH3
3-Ethyl-5-methylheptane
2-12

13. 2 Nomenclature
7. The prefixes di-, tri-, tetra-, etc. are not
included in alphabetization
CH3 CH2 CH3
CH3 CCH2 CH CH2 CH3 4 6
1 2 3 5
CH3
4-Ethyl-2,2-dimethylhexane
8. Substituents are named by the same set
of rules.
2-13

14. 2 Nomenclature
Alkyl groups
Condensed Condensed
Name Structural Formula Name Structural Formula
butyl - CH 2 CH2 CH2 CH 3 methyl - CH 3
2-methylpropyl - CH 2 CHCH3 ethyl - CH 2 CH3
(isobutyl)
CH3 propyl - CH 2 CH2 CH3
1-methylpropyl - CH CH 2 CH3 1-methylethyl - CH CH 3
(sec- butyl) (isopropyl)
CH3 CH3
CH3
1,1-dimethylethyl - CCH3
(tert-butyl)
CH3
2-14

15. 2 Classification of C & H
Primary (1° ) C: a carbon bonded to one
other carbon
• 1° H: a hydrogen bonded to a 1° carbon
Secondary (2° ) C: a carbon bonded to two
other carbons
• 2° H: a hydrogen bonded to a 2° carbon
Tertiary (3° ) C: a carbon bonded to three
other carbons
• 3° H: a hydrogen bonded to a 3° carbon
Quaternary (4° ) C: a carbon bonded to four
C
other carbons
2-15

16. 2 Physical 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)
2-16

17. 2 Physical 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
2-17

18. 2 Physical Properties
Constitutional isomers have different
physical properties
mp bp Density
Name (°C) (°C) (g/mL)
hexane -95 68.7 0.659
2-methylpentane -154 60.3 0.653
3-methylpentane -118 63.3 0.664
2,3-dimethylbutane -129 58.0 0.661
2,2-dimethylbutane -98 49.7 0.649
2-18

19. 2 Oxidation of Alkanes
Oxidation is the basis for their use as energy
sources for heat and power
• heat of combustion: heat released when one mole
of a substance in its standard state is oxidized to
carbon dioxide and water ∆H°
kJ (kcal)/mol
CH4 + 2 O 2 CO 2 + 2 H2 O -890 (-212)
Methane
CH3 CH2 CH3 + 5 O 2 3 CO 2 + 4 H 2 O -2220 (-530)
Propane
2-19

20. 2 Sources 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
2-20

21. 2 Gasoline
Octane rating: the percent 2,2,4-trimethylpentane
(isooctane) in a mixture of isooctane and heptane
that has equivalent antiknock properties
CH3 CH3
CH3 ( CH2 ) 5 CH 3 CH3 CCH2 CH CH3
CH3
Heptane 2,2,4-Trimethylpentane
(octane rating 0) (octane rating 100)
2-21

22. 2 Synthesis Gas
A mixture of carbon monoxide and hydrogen
in varying proportions which depend on the
means by which it is produced
C + H2 O heat CO + H2
Coal
1 catalyst
CH4 + O2 CO + 2 H2
2
Methane
2-22

23. 2 Synthesis Gas
Synthesis gas is a feedstock for the
industrial production of methanol and acetic
acid catalyst
CO + 2 H2 CH 3 OH
Methanol
O
catalyst
CH3 OH + CO CH 3 COH
Methanol Acetic acid
• it is likely that industrial routes to other organic
chemicals from coal via methanol will also be
developed
2-23