Question

Identify the major product of dehydrohalogenation of \(\text{CH}_3\text{-CH}_2\text{-CH(Br)-CH}_3\).

• A. \(\text{CH}_3\text{-CH}_2\text{-CH=CH}_2\)
• B. \(\text{H}_3\text{C-CH=CH-CH}_3\)
• C. \(\text{CH}_3\text{-(CH}_2)_2\text{CH}_3\)
• D. \(\text{CH}_3\text{-(CH}_2)_2\text{CHO}\)

Hint:

By Saytzeff's rule the more substituted alkene, but-2-ene, is the major product.

Answer 1

The Correct Option is B

Step 1: Think about alkene stability:
Alkyl groups stabilise a double bond by hyperconjugation. More alkyl groups on the C=C carbons mean a more stable alkene.

Step 2: Count the substituents:
Product A has 1 alkyl group on the double bond carbons, product B has 2 (one methyl on each carbon). The path through the more stable alkene is faster.

Step 3: Pick:
$\text{H}_3\text{C-CH=CH-CH}_3$, option B.

Final Answer:
The more substituted alkene, but-2-ene, is favoured. \[ \boxed{\text{(B) }\text{H}_3\text{C-CH=CH-CH}_3} \]