What are the possible isomers for #H_3C - CH_2 - O - CH_2 - CH_2 - CH_3#? In which class do each of these isomers fall into (eg. chain, positional, functional isomerism)?

1 Answer
Dec 28, 2015

I count 14 isomers.


Let's start with the alcohols.

Five carbons in a row


Three isomers are

1. Pentan-1-ol
2. Pentan-2-ol
3. Pentan-3-ol

Four carbons with a methyl side-chain


Four more isomers are

4. 2-Methylbutan-1-ol
5. 2-Methylbutan-2-ol
6. 3-Methylbutan-2-ol
7. 3-Methylbutan-1-ol

Three carbons with two methyl groups


Only one more isomer

8. 2-2-Dimethylpropan-1-ol

Now we do the ethers

Start by inserting an oxygen into a five-carbon chain.


This gives two more isomers

9. 1-Methoxybutane
10. 1-Ethoxypropane

Repeat with four carbons and a methyl side-chain

One Branch

Three more isomers

11. 2-Methoxybutane
12. 2-Ethoxypropane
13. 1-Methoxy-2-methylpropane

And finally, a three-carbon chain with two methyl groups.

Two branches

The final isomer

14. 2-Methoxy-2-methylpropane

And we now have all the constitutional isomers (I hope!).

"We leave it as an exercise for the student" to identify the chain, positional, and functional isomers.