Alkyl halide 2 cont:

Cyclohexyl bromide 1 exists mainly with the bromide equatorial (1e). In the Newman projection of 1e both of the b-hydrogens (H_e and H_a) form a 60° dihedral angle with the C-Br bond, less than the ideal 180° required for anti-elimination. In the chair conformation of 1 having the C-Br bond axial (1a), there are two b-hydrogens (b and b') that are anti (180°) to the C-Br bond. Elimination occurs through the less stable (1a) chair conformation. As HBr is eliminated by the base, the sp³ hybridized carbons become sp² hybridized. The transition state requires alignment of the C-H and C-Br bonds so that they are perfectly disposed to form the new p-bond. Draw an energy diagram for this reaction.