2
Hydrocarbons
Chapter 10
2-1

2
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

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

2
Alkanes have the general formula CH
2n+2
Name methane ethane propane butane pentane hexane heptane
Molecular Condensed
Formula Structural Formula
CH 4
C 2 H 6
C 3 H 8
C 4 H 10
C 5 H 12
C
C
6
7
H
H
14
16
CH 4
CH 3 CH 3
CH 3 CH 2 CH 3
CH 3 (CH 2 ) 2 CH 3
CH 3 (CH 2 ) 3 CH 3
CH 3 (CH 2 ) 4 CH 3
CH 3 (CH 2 ) 5 CH 3
2-4

2
Alkanes (contd.) octane nonane decane dodecane
C
C
C
C
8
9
10
12
H
H
18
20
H
H
22
26 tetradecane C 14 H 30 hexadecane C 16 H 34 octadecane C 18 H 38 eicosane C 20 H 42
CH 3 (CH 2 ) 6 CH 3
CH 3 (CH 2 ) 7 CH 3
CH 3 (CH 2 ) 8 CH 3
CH 3 (CH 2 ) 10 CH 3
CH 3 (CH 2 ) 12 CH 3
CH 3 (CH 2 ) 14 CH 3
CH 3 (CH 2 ) 16 CH 3
CH 3 (CH 2 ) 18 CH 3
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2
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
2
CH
2
CH
3
Butane
CH
3
CH
3
CHCH
3
2-Methylpropane
2-6

2
Which sets represent pairs of constitutional isomers?
O
(a) CH
3
CH
2
OH and CH
3
OCH
3
(b)
O
CH
3
CCH
3 and CH
3
CH
2
CH
O O
(c) CH
3
COCH
3 and CH
3
CH
2
COH (d)
OH O
CH
3
CHCH
2
CH
3 and CH
3
CCH
2
CH
3
(e) and CH
3
CH
2
CH
2
CH
2
CH
3
(f) and CH
2
= CHCH
2
CH
2
CH
3
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2
Molecular Constitutional
Formula Isomers
CH
C
C
C
C
C
5
10
15
25
30
4
H
12
H
H
H
H
22
32
52
62
75
4,347
1
3
36,797,588
4,111,846,763
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2
Suffix ane specifies an alkane
Prefix tells the number of carbon atoms methethpropbutpenthexheptoctnondec-
Prefix Carbons
1
2
3
4
5
6
7
8
9
10
Prefix Carbons undecdodec-
11
12 tridec13 tetradec14 pentadec15 hexadec16 heptadec17 octadec18 nonadec19 eicos20
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2
Parent name: the longest carbon chain
Substituent: a group attached to the parent chain
• alkyl group: a substituent derived by removal of an H from an alkane and given the symbol R-
Alkane Name
CH
4
Alkyl group
Methane CH
3
-
Name
Methyl group
CH
3
CH
3
Ethane CH
3
CH
2
Ethyl group
2-10

2
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
CH
3
CHCH
3
2-Methylpropane
1 3
4. If there is one substituent, number the chain from the end that gives it the lower number
CH
3
CH
3
CH
2
CH
2
CHCH
3
2-Methylpentane
5
4
3
2
1
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2
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
CH
3
CH
3
CH
2
CHCH
2
CHCH
2
CH
3
CH
2
CH
3
3-Ethyl-5-methylheptane
1
2
3
4
5
6
7
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2
7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization
CH
3
CH
2
CH
3
CH
3
CCH
2
CHCH
2
CH
3
CH
3
4-Ethyl-2,2-dimethylhexane
1
2
3
4
5
6
8. Substituents are named by the same set of rules.
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2
Alkyl groups
Name butyl
Condensed
Structural Formula
- CH 2 CH 2 CH 2 CH 3
2-methylpropyl
(isobutyl)
- CH 2 CHCH 3
CH 3
1-methylpropyl - CHCH
( secbutyl)
CH 3
2
CH
3
1,1-dimethylethyl
( tertbutyl)
CH 3
- CCH 3
CH 3
Name methyl ethyl
Condensed
Structural Formula
- CH 3
- CH 2 CH 3 propyl - CH 2 CH CH
3
1-methylethyl - CHCH
(isopropyl)
CH 3
3
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2
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 other carbons
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2
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

2
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
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2
Constitutional isomers have different physical properties
Name mp bp Density
( ° C) ( ° C) (g/mL) hexane
2-methylpentane
3-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
-95 68.7
0.659
-154 60.3
0.653
-118 63.3
0.664
-129 58.0
0.661
-98 49.7
0.649
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2
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
D
H ° kJ (kcal)/mol
CH
4
+ 2O
2
Methane
CO
2
+2H
2
O -890 (-212)
CH
3
CH
2
CH
3
Propane
+ 5O
2
3CO
2
+ 4H
2
O -2220 (-530)
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2
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
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2
Octane rating: the percent 2,2,4-trimethylpentane
(isooctane) in a mixture of isooctane and heptane that has equivalent antiknock properties
CH
3
(CH
2
)
5
CH
3
Heptane
(octane rating 0)
CH
3
CH
3
CH
3
CCH
2
CHCH
3
CH
3
2,2,4-Trimethylpentane
(octane rating 100)
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2
A mixture of carbon monoxide and hydrogen in varying proportions which depend on the means by which it is produced
C + H
2
O
Coal heat
CO + H
2 catalyst
CH 4 +
Methane
1
2
O
2
CO + 2H 2
2-22

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