Question

Predict the elimination products of the following reactions and label the major products.

1. Cis-1-bromo-2-methylcyclohexane +in
2. Trans-1-bromo-2-methylcyclohexane +in

Short answer

a.

Major Minor

b.

Major

Step-by-step solution

Explanation of part (a)

For E2 elimination to occur, the hydrogen and leaving group, bromine must have trans-diaxial orientation. The cis-isomer has methyl in equatorial position, the NaOCH₃ can remove a hydrogen from either C-2 or C-6, giving a mixture of alkenes where the most highly substituted isomer is the major product (Zaitsev product).

Major Minor

Explanation of part (b)

Trans-isomer has methyl in the axial position at carbon-2, so no elimination can occur at C-2. The only possible orientation for elimination reaction to occur is toward C-6. Thus, only one alkene is possible which is not more substituted.

Major