Molecular Fragments: Alkane Isomers


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Occasionally I get a request to name the isomers of a particular alkane. Sometimes that alkane is decane and I can't help wondering what the instructor asking such a problem had in mind. Perhaps the instructor was not aware of the immensity of the task. Anyway, to settle this once and for all, here then is a list of the names of all the alkane isomers up to and including decane.

First: What is Isomerism?

1. Isomers are covalent compounds which have exactly the same number and kind of atoms in them.

2. There are two major types of isomers:


Now: A Table of Alkane Isomers.

First in this section: How many constitutional isomers do alkanes have?

Number of Constitutional Isomers of Alkanes.

Number of
Carbon Atoms
Number of Isomers
42
53
65
79
818
935
1075
12355
154,347
20366,319


So as you can see, as the number of atoms in the alkane molecule increases, so does the number of different ways of arranging them. Not too surprising! Except, perhaps, how fast the numbers of isomers increases.

As a consequence, the table next will only look at alkanes with 10 or fewer carbons.


Second in this section: A Table of Alkane Isomers

In this table streoisomers are indicated thusly:
Enantiomers separated by /, e.g. (R/S)
Diastereoisomers separated by //, e.g. (SS//RS)

Available models are referenced.


C4H10
(2 isomers)
ButaneMethylpropane

C5H12
(3 isomers)
PentaneMethylbutaneDimethylpropane

C6H14
(5 isomers)
Hexane2-Methylpentane3-Methylpentane
2,2-Dimethylbutane2,3-Dimethylbutane

C7H16
(9 isomers)
Heptane2-Methylhexane3-Methylhexane
(R/S)
2,2-Dimethylpentane2,3-Dimethylpentane
(R/S)
2,4-Dimethylpentane
3,3-Dimethylpentane3-Ethylpentane2,2,3-Trimethylbutane

C8H18
(18 isomers)
Octane2-Methylheptane3-Methylheptane
(R/S)
4-Methylheptane2,2-Dimethylhexane2,3-Dimethylhexane
(R/S)
2,4-Dimethylhexane
(R/S)
2,5-Dimethylhexane3,3-Dimethylhexane
3,4-Dimethylhexane
(RR/SS//meso)
3-Ethylhexane2,2,3-Trimethylpentane
(R/S)
2,2,4-Trimethylpentane2,3,3-Trimethylpentane2,3,4-Trimethylpentane
3-Ethyl-2-methylpentane3-Ethyl-3-methylpentane2,2,3,3-Tetramethylbutane

C9H20
(35 isomers)
Nonane2-Methyloctane3-Methyloctane
(R/S)
4-Methyloctane
(R/S)
2,2-Dimethylheptane2,3-Dimethylheptane
(R/S)
2,4-Dimethylheptane
(R/S)
2,5-Dimethylheptane
(R/S)
2,6-Dimethylheptane
3,3-Dimethylheptane3,4-Dimethylheptane
(RR/SS//meso)
3,5-Dimethylheptane
4,4-Dimethylheptane3-Ethylheptane4-Ethylheptane
2,2,3-Trimethylhexane
(R/S)
2,2,4-Trimethylhexane
(R/S)
2,2,5-Trimethylhexane
2,3,3-Trimethylhexane2,3,4-Trimethylhexane
(RR/SS//RS/SR)
2,3,5-Trimethylhexane
(R/S)
2,4,4-Trimethylhexane3,3,4-Trimethylhexane3-Ethyl-2-methylhexane
(R/S)
3-Ethyl-3-methylhexane3-Ethyl-4-methylhexane
(R/S)
4-Ethyl-2-methylhexane
2,2,3,3-Tetramethylpentane2,2,4,4-Tetramethylpentane2,2,3,4-Tetramethylpentane
(R/S)
2,3,3,4-Tetramethylpentane3-Ethyl-2,3-dimethylpentane3-Ethyl-2,2-dimethylpentane
3-Ethyl-2,4-dimethylpentane3,3-Diethylpentane

C10H22
(75 isomers)
Decane2-Methylnonane3-Methylnonane
(R/S)
4-Methylnonane
(R/S)
5-Methylnonane2,2-Dimethyloctane
2,3-Dimethyloctane
(R/S)
2,4-Dimethyloctane
(R/S)
2,5-Dimethyloctane
(R/S)
2,6-Dimethyloctane
(R/S)
2,7-Dimethyloctane3,3-Dimethyloctane
3,4-Dimethyloctane
(RR/SS//RS/SR)
3,5-Dimethyloctane
(RR/SS//RS/SR)
3,6-Dimethyloctane
(RR/SS//meso)
4,4-Dimethyloctane4,5-Dimethyloctane
(RR/SS//meso)
3-Ethyloctane
4-Ethyloctane
(R/S)
2,2,3-Trimethylheptane
(R/S)
2,2,4-Trimethylheptane
(R/S)
2,2,5-Trimethylheptane
(R/S)
2,2,6-Trimethylheptane2,3,3-Trimethylheptane
2,3,4-Trimethylheptane
(RR/SS//RS/SR)
2,3,5-Trimethylheptane
(RR/SS//RS/SR)
2,3,6-Trimethylheptane
(R/S)
2,4,4-Trimethylheptane2,4,5-Trimethylheptane
(RR/SS//RS/SR)
2,4,6-Trimethylheptane
2,5,5-Trimethylheptane3,3,4-Trimethylheptane
(R/S)
3,3,5-Trimethylheptane
(R/S)
3,4,4-Trimethylheptane
(R/S)
3,4,5-Trimethylheptane
(RR/SS//meso)
3-Ethyl-2-methylheptane
3-Ethyl-3-methylheptane3-Ethyl-4-methylheptane
(R/S)
3-Ethyl-5-methylheptane
(R/S)
4-Ethyl-2-methylheptane
(R/S)
4-Ethyl-3-methylheptane
(RR/SS//RS/SR)
4-Ethyl-4-methylheptane
5-Ethyl-2-methylheptane4-Propylheptane4-Isopropylheptane
2,2,3,3-Tetramethylhexane2,2,3,4-Tetramethylhexane
(RR/SS//RS/SR)
2,2,3,5-Tetramethylhexane
(R/S)
2,2,4,4-Tetramethylhexane2,2,4,5-Tetramethylhexane
(R/S)
2,2,5,5-Tetramethylhexane
2,3,3,4-Tetramethylhexane
(R/S)
2,3,3,5-Tetramethylhexane2,3,4,4-Tetramethylhexane
(R/S)
2,3,4,5-Tetramethylhexane
(RR/SS//meso)
3,3,4,4-Tetramethylhexane3-Ethyl-2,2-dimethylhexane
(R/S)
3-Ethyl-2,3-dimethylhexane
(R/S)
3-Ethyl-2,4-dimethylhexane
(RR/SS//RS/SR)
3-Ethyl-2,5-dimethylhexane
(R/S)
3-Ethyl-3,4-dimethylhexane
(R/S)
4-Ethyl-2,2-dimethylhexane4-Ethyl-2,3-dimethylhexane
(R/S)
4-Ethyl-3,3-dimethylhexane4-Ethyl-2,4-dimethylhexane3,3-Diethylhexane
3,4-Diethylhexane3-Isopropyl-2-methylhexane2,2,3,3,4-Pentamethylpentane
2,2,3,4,4-Pentamethylpentane3-Ethyl-2,2,4-trimethylpentane
(R/S)
3-Ethyl-2,3,4-trimethylpentane
3-Ethyl-2,2,3-trimethylpentane3,3-Diethyl-2-methylpentane3-Isopropyl-2,4-dimethylpentane


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