How many stereoisomers does 1,3,5-trimethylcyclohexane have? (Configurational isomers only.)

Answer: D

Enumerate up/down arrangements of the three methyls on a planar ring: all on one face (cis,cis) or two on one face and one on the other (cis,trans). Every other arrangement is related by a rotation or flip of the ring. Both resulting isomers have a mirror plane, so there are 2 stereoisomers, both achiral (the

2^{3} = 8

rule fails because of symmetry).

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