Question

Identify the major product obtained when 2-Bromobutane is heated with alcoholic KOH.

• A. But-2-ene
• B. But-1-ene
• C. Propene and methane
• D. Ethene

Hint:

Alcoholic KOH causes dehydrohalogenation, and the more substituted alkene is the major product (Saytzeff rule).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Heating an alkyl halide with alcoholic KOH removes HBr and forms an alkene by beta elimination.

Step 2: Possible alkenes
In 2-bromobutane, a beta hydrogen can be removed from \(\text{C-1}\) to give but-1-ene, or from \(\text{C-3}\) to give but-2-ene.

Step 3: Saytzeff rule
The more substituted, and therefore more stable, alkene is formed as the major product. But-2-ene is disubstituted and but-1-ene is monosubstituted.

Step 4: Compare the options
Propene with methane and ethene are not formed, so but-2-ene is the major product.

Final Answer:
The major product is but-2-ene. \[ \boxed{\text{(A) }\text{But-2-ene}} \]