Question

The correct order of acidic nature of the following alkynes is:
I. \( \text{C}_2\text{H}_2 \)
II. \( (\text{CH}_3)_2\text{C}_2 \)
III. \( (\text{CH}_3)\text{C}_2\text{H} \)

• A. I<III<II
• B. II<III<I
• C. III<II<I
• D. II<I<III

Hint:

Terminal alkynes are more acidic than internal ones due to acidic hydrogen on sp-carbon.

Answer 1

The Correct Option is B

Acidity of alkynes depends on:
- s-character of the hybrid orbital
- Electron-withdrawing groups
- Less substituted terminal alkynes are more acidic
Order of acidity: - \( \text{C}_2\text{H}_2 \): terminal, no substitution → most acidic
- \( (\text{CH}_3)\text{C}_2\text{H} \): terminal with 1 methyl → less acidic
- \( (\text{CH}_3)_2\text{C}_2 \): internal alkyne → no acidic H → least acidic
\[ \Rightarrow (\text{CH}_3)_2\text{C}_2<(\text{CH}_3)\text{C}_2\text{H}<\text{C}_2\text{H}_2 \]