Which of the following compounds will undergo E2 elimination at the fastest rate?

• A. I
• B. II
• C. Both will proceed at equal rates.

Answer: (B)

Verified step by step guidance

1. Identify the type of elimination reaction: E2 elimination is a bimolecular process where the base removes a proton from the β-carbon, and the leaving group departs simultaneously, forming a double bond.
2. Examine the structure of compound I: It is a secondary alkyl bromide, which is a good candidate for E2 elimination due to the presence of a β-hydrogen and a good leaving group (Br).
3. Examine the structure of compound II: It is also a secondary alkyl bromide, but it has an additional double bond in conjugation with the leaving group, which can stabilize the transition state and potentially increase the rate of elimination.
4. Consider the factors affecting E2 elimination rate: The presence of a conjugated system in compound II can stabilize the transition state through resonance, making the elimination faster compared to compound I.
5. Conclude which compound undergoes E2 elimination faster: Compound II, due to the stabilization provided by the conjugated double bond, will undergo E2 elimination at a faster rate than compound I.