Question

The correct order for acid strength of compounds CH ≡ CH, CH₃ – C ≡ CH and CH₂ = CH₂ is as follows: 
1. CH₃ – C ≡ CH > CH₂ = CH₂ > HC ≡ CH
2. CH₃ – C ≡ CH > CH ≡ CH > CH₂ = CH₂
3. HC ≡ CH > CH₃ – C ≡ CH > CH₂ = CH₂
4. CH ≡ CH > CH₂ = CH₂ > CH₃ – C ≡ CH

Answer 1

Correct Answer - Option 3 : HC ≡ CH > CH₃ – C ≡ CH > CH₂ = CH₂

Concept:

Ethane (H₂C=CH₂) is a sp² -hybridized and ethyne (HC ≡ CH) is sp- hybridized. In ethane, the sp -hybridised carbon atom possesses maximum s-character and hence, maximum electronegativity. Due to which, it attracts the shared electron pair of C–H bond to a greater extend and makes the removal of proton easier. Hence, alkyne is much more acidic than alkene. Hence, the correct order of acidic strength is:

HC≡CH>H₃ C-C≡CH>CH₂=CH₂