Question

Predict the alkene formed by dehydrohalogenation of 1-Bromo-1-methylcyclohexane.

Hint:

Zaitsev's rule: Elimination gives the more substituted (more stable) alkene as the major product.

Answer 1

Step 1: Reaction type and Zaitsev's rule.
Dehydrohalogenation is an elimination reaction. Zaitsev's rule: the major product is the more substituted (more stable) alkene.
Step 2: Structure of 1-bromo-1-methylcyclohexane.
Bromine is on C-1, which also carries a methyl group. Elimination can produce either methylenecyclohexane (exocyclic $=CH_2$, disubstituted) or 1-methylcyclohex-1-ene (endocyclic double bond, trisubstituted).
Step 3: Stability comparison.
The endocyclic double bond in 1-methylcyclohex-1-ene is trisubstituted and more stable (more hyperconjugation) than the exocyclic disubstituted methylenecyclohexane.
Step 4: Major product.
By Zaitsev's rule, the major product is 1-methylcyclohex-1-ene (more substituted endocyclic alkene).