Is 1,2-dimethylcyclohexane a meso compound?

1 Answer
Jun 2, 2015

Only the cis isomer of 1,2-dimethylcyclohexane is a meso compound.

A meso compound must have at least two chiral centres but still be optically inactive because of an internal plane of symmetry.

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We see that the cis isomer has chiral carbons at #"C-1"# and #"C-2"#.

It also has a plane of symmetry passing through the mid-points of the 1,2 and 4,5 bonds

So the cis isomer is a meso compound.

In the trans isomer, one of the bonds is dashed.

The mirror plane vanishes, so the trans isomer exists as a pair of enantiomers.