Chemistry Reference
In-Depth Information
ISOMERS
With five carbons in a hydrocarbon molecule, there are three isomers
with the molecular formula C
H
:
5
12
H
3
C
CH
3
CH
3
CH
2
CH
2
CH
2
CH
3
C
H
3
C
3
n-pentane
neopentane
H
3
C
CH
2
CH
2
CH
3
H
3
C
isopentane
H
2
C
H
2
C
CH
2
and a single ring of C
H
5
10
H
2
CCH
2
cyclopentane
As the number of carbon atoms increases, the number of possible isomers
becomes larger. Whereas there are only two isomeric butanes, there are three
isomeric pentanes. With five carbons, in addition to the open-chain com-
pounds shown, a stable ring compound known as cyclopentane is also possible.
Five- and six-membered carbon rings are very stable because the bonds
between carbon atoms in these size rings are close to the 109
angle preferred
by carbon. Three- and four-membered hydrocarbon rings are also known,
but they are less stable because of the required distortion of the bond angle.
Note that whereas n-, neo-, and isopentanes have the same molecular
formula, C
5
H
12
, and are therefore isomers, cyclopentane has the formula
C
5
H
10
, and so is not an isomer of the open-chained pentanes.
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