Question

Identify the product X in the following reaction.

• A. 2,3-dimethyl-2-butene
• B. 3,2-diethyl butene
• C. 3,3-dimethyl-1-butene
• D. 2,2-diethyl butene

Hint:

The carbocation rearranges by a methyl shift to a more stable tertiary cation before losing H+.

Answer 1

The Correct Option is A

Step 1: Skeleton
The carbon chain is four carbons with two methyls on C3 and OH on C2. Dehydration under acid goes through an E1 pathway.

Step 2: Stability argument
Secondary cation to tertiary cation by 1,2-methyl shift is energetically favoured. The tertiary cation then forms the tetrasubstituted alkene, which is the most stable alkene.

Step 3: Result
The product is 2,3-dimethylbut-2-ene, option (A).

Final Answer:
2,3-dimethyl-2-butene. \[ \boxed{\text{(A)}\ \text{2,3-dimethyl-2-butene}} \]