Chirality in Mobile Systems Consider cis-1,2-dibromocyclohexane If the ring was flat and planar,then an internal plane of symmetry would exist,and this molecule would therefore be achiral H B But the ring is not planar,it is puckered into a chair conformation,with one Br axial,and one equatorial. These mirror images are non-superimposable. BUT,this does not mean that cis-1.2-dibromocyclohexane is chiral: A molecule cannot be optically active if its chiral conformations are in equilibrium with their mirror images. Cis-1,2-dibromocyclohexane exists as a racemic mixture,but cannot be enriched to be optically active because the conformational equilibrium will racemise the mixture. Ch05 Stereochemistry (landscape) Page 13 Ch05 Stereochemistry (landscape) Page 13 Chirality in Mobile Systems Consider cis-1,2-dibromocyclohexane. If the ring was flat and planar, then an internal plane of symmetry would exist, and this molecule would therefore be achiral. But the ring is not planar, it is puckered into a chair conformation, with one Br axial, and one equatorial. These mirror images are non-superimposable. BUT, this does not mean that cis-1,2-dibromocyclohexane is chiral: A molecule cannot be optically active if its chiral conformations are in equilibrium with their mirror images. Cis-1,2-dibromocyclohexane exists as a racemic mixture, but cannot be enriched to be optically active because the conformational equilibrium will racemise the mixture