# How many isomers of [insert straight-chained alkane here] exist?

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This is a reference for those who need it! Saves lots of time in case you want to know how many for a large alkane.

This is a reference for those who need it! Saves lots of time in case you want to know how many for a large alkane.

##### 2 Answers

You can find how many here:

http://www-jmg.ch.cam.ac.uk/tools/isomercount/

Since there is no set formula, it must be done computationally! A list of examples (including optical isomers):

methane: 1

ethane: 1

propane: 1

butane: 2

pentane: 3

hexane: 5

heptane: 11

octane: 24

nonane: 55

decane: 136

dodecane: 3396667

Actually, all you need is the number of carbon atoms in the alkane.

#### Explanation:

There is a formula, but it is complicated and requires a computer to do the calculations.

However, you can find the number of constitutional isomers of alkanes with up to 100 carbon atoms here.

Let's hope that your instructor doesn't ask you to draw all the isomers of

With the software (from the link above), you can determine the number of isomers of

You can even construct them and display them on the screen.