Can you account for the stereochemistry of #"1,2-dimethylcyclohexane"#?

1 Answer
anor277
Mar 18, 2017

Well, as far as I know, ONLY #"B"# can exhibit cis-trans isomerism.

Explanation:

Both molecules can support optical isomerism; but ONLY #"1,2-dimethylcyclohexane"# can support #"cis-trans isomerism"#.

For #"(b)"#, #"1,2-dimethylcyclohexane"#, CLEARLY, the pendant methyl groups can lie on the same side of the ring, or on opposite sides of the ring.

![http://scbt.c0m](https://useruploads.socratic.org/oCegAbyeSnexiNlEdNYQ_cy_2.jpg)

And this cis isomer, clearly has a plane of symmetry bisecting the #"MeCH-CHMe"# bond.

On the other hand, for #"trans-1,2-dimethylcyclohexane"#, this has a #C_2# axis that maps the pendant methyl group. And, thus, for a fact, this structure can support #"RR"# and #"SS"# enantiomers.

![sigmaaldrich.com](useruploads.socratic.org)

For #"1,2-diethyl-1-methylcyclohexane"#, this generates 4 stereoisomers, because there are 2 chiral centres on the ring.

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