Cw-l,2-dibromocyclohexane

The preceding structure for cw-l,2-dibromocyclohexane suggests that the compound has a plane of symmetry. Cyclohexane, however, is not a planar hexagon—it exists preferentially in the chair conformation, and the chair conformer of ctT-l,2-dibromocyclohexane does not have a plane of symmetry. Only the much less stable boat conformer of cw-l,2-dibromocyclohexane has a plane of symmetry. Then, is ci5-l,2-dibromocyclohexane a meso compound The answer is yes. As long as any one conformer of a compound has a plane of symmetry, the compound will be achiral, and an achiral compound with two asymmetric carbons is a meso compound. 

Hydrogen bromide undergoes photoaddition to 1-bromocyclohexene to produce cw-l,2-dibromocyclohexane as the sole product. Studies of the photoaddition of HBr to other olefins indicate that essentially stereospecific trans addition occurs " ... 

But we know the ring is puckered into a chair conformation with one bromine atom axial and one equatorial. A chair conformation of cw-l,2-dibromocyclohexane and its mirror image are shown next. These two mirror-image structures are nonsuper-imposable. You may be able to see the difference more easily if you make models of these two conformations. 

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