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: Read the structure
The figure shows \((CH_3)_3C-CH(OH)-CH_3\), which is 3,3-dimethylbutan-2-ol, treated with \(H_2SO_4\). The alcohol is secondary and has a quaternary neighbouring carbon.

Step 2: Form the carbocation
Protonation and loss of water give a secondary carbocation at C2. It is next to the \(C(CH_3)_3\) carbon.

Step 3: Methyl shift
A methyl group moves from the neighbouring carbon to the cationic carbon. This gives a tertiary cation \((CH_3)_2C^+-CH(CH_3)_2\), which is more stable.

Step 4: Lose a proton
Loss of a proton from the carbon next to the cation follows Zaitsev's rule and gives the more substituted alkene \((CH_3)_2C=C(CH_3)_2\), which is 2,3-dimethyl-2-butene.

Step 5: Other options
3,3-dimethyl-1-butene would be the direct non-rearranged, less substituted product, so it is minor.

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