Aliphatic Hydrocarbons
2. Branched & Isomeric
Alkanes
1
C5H12
CH3CH2CH2CH2CH3
(CH3)2CHCH2CH3
n-Pentane
Isopentane
(CH3)4C
Neopentane
2
Common alkyl groups
(C1 through C4)
CH3
CH3 CH2 CH2 CH2
Methyl
Butyl
CH3
Isobutyl
CH3 CH2
(2-Methylpropyl)
Ethyl
CH3 CH2 CH2
Propyl
CH3 CH
CH3
CH3 CH CH2
CH3
CH3 CH2 CH
CH3
CH3 C
CH3
sec-Butyl
tert-Butyl
(1-Methylpropyl)
(1,1-Dimethylethyl)
Isopropyl
(1-Methylethyl)
3
Number the Carbons
• Start at the end closest to the first attached
group.
• If two substituents are equidistant, look for
the next closest group.
1
CH3
3
4
H3C CH CH CH2
2
CH2CH3
5
CH2
CH3
CH CH3
6
7
4
4
3
2
1
CH3 CH2 CH CH3
CH3
2-methylbutane
5
Find the longest continuous
carbon chain
1
2
3
CH3 CH2 CH CH3
CH2 CH3
4
5
3-methylpentane
6
You must choose the longest
continuous carbon chain
4
3
2
1
CH3 CH2 CH CH2 CH2 CH3
CH2 CH2 CH3
5
6
7
4-ethylheptane
7
Number from the end nearest
the first substituent
CH2 CH3
CH3 CH2 CH2 CH CH CH2 CH3
7
6
5
4
3
2
1
CH3
4-ethyl-3-methylheptane
8
Number from the end nearest
the first substituent
CH3
CH3 CH2 CH2 CH CH2 CH CH2 CH3
8
7
6
5
4
3
2
1
CH2 CH3
3-ethyl-5-methyloctane
9
Use “di-” with two substituents
CH3
CH3 CH CH CH3
1
2
3
4
CH3
2,3-dimethylbutane
10
Every substituent must get a number
CH3
CH3 CH2 C
CH2 CH2 CH3
1
4
2
3
5
6
CH3
3,3-dimethylhexane
11
Number from the end nearest
first substituent
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3
10
9
8
7
6
5
4
3
CH3
2
1
CH3
2,7,8-trimethyldecane
12
Number from the end which has
the “first difference”
CH3
CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3
1
2
3
4
5
6
7
CH3
8
9
10
CH3
3,4,8-trimethyldecane
13
A More-Highly-Substituted
Carbon Takes Precedence
CH3
CH3
CH3 CH CH2 C
5
4
3
2
CH3
1
CH3
2,2,4-Trimethylpentane
14
Which end do we number from?
CH3 CH2 CH CH2 CH2 CH CH2 CH3
8
7
6
CH3
5
4
3
2
1
CH2 CH3
3-ethyl-6-methyloctane
15
Halogens and other side groups
•
•
•
•
•
Flouro –F
Chloro –Cl
Bromo –Br
Iodo –I
Nitro –NO2
O
N
O
16
CH 3 CH 2 Br
Bromoethane
“Ethyl bromide”
17
CH3
CH3 C
Cl
CH3
2-Chloro-2-methylpropane
“tert-Butyl chloride”
18
CH 3 CH
Br
CH
CH 2 CH 3
CH 3
2-Bromo-3-methylpentane
19
In normal conditions alkanes do not react with acids
and alkalis because -bonds in their molecules are
very strong. But alkanes take part in such reactions
as:
-Substitution Reactions
-Oxidation Reactions
-Destruction Reactions
21
Halogenation of alkanes.
Alkanes react with halogens (except I2).
CH4 + Cl2
HCl + H3C
Cl
chlormethane
Cl
H3C
Cl + Cl2
HCl + H2C
Cl
dichlormethane
22
Alkanes can burn if oxygen is present. As the
result H2O and CO2 appear.
CH4 + 2O2 → CO2 + 2H2O
Cracking is the destroying of some −C−C− and −C−H
bonds in the molecule of alkanes at high
temperature.
CH3−CH3 → CH2=CH2 + H2
23
Practice Exercise: Circle each molecule
that can be classified as an alkane
24
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