Destroyer OC question

[djangowagontooth]

I have a question on #60 in the 2015 destroyer.
Question: "How many isomers (including both constitutional and stereoisomers) exist for the below molecule?"
The molecule is 1,2-dimethylcyclopentane.
I looked at the solution, but I'm still lost. Can anybody give a step by step process for doing this one?

 

[DAT Destroyer]

I have a question on #60 in the 2015 destroyer.
Question: "How many isomers (including both constitutional and stereoisomers) exist for the below molecule?"
The molecule is 1,2-dimethylcyclopentane.
I looked at the solution, but I'm still lost. Can anybody give a step by step process for doing this one?

The way to do this question is to keep the cyclopentane skeleton, and move the other 2 groups in different combinations. These other combinations are called isomers. Place the two methyl groups in a 1,1.....1, 2, 1,3 fashion. The problem is very tricky because many of them have enantiomers. This problem is challenging indeed, but worth the effort. Keep an eye out for meso compounds. All the cyclopentane isomers as well as stereoisomers are shown in the solution.

Hope this helps.

Dr. Jim Romano

 

[djangowagontooth]

Thank you Dr. Romano!

 

[Dental_Is_Life]

Hey Dr. Romano,

Couldn't you break the molecule apart and make 1,2,3-trimethylcyclobutane? Will that count as a constitutional isomer?