Question

Cyclopentadiene has a $p{K}_a=15$, cyclopentane has a $p{K}_a>50$. This is because :

• A. Cyclopentadiene is particularly unstabe
• B. Cyclopentadiene contains no lone pairs
• C. Cyclopentadiene is a $4\pi$ anti-aromatic compound
• D. Cyclopentadiene is a $4\pi$ non-aromatic compound and after deprotonation it is aromatic

Answer 1

The correct option is D Cyclopentadiene is a $4\pi$ non-aromatic compound and after deprotonation it is aromatic

Since after deprotonation cyclopentadiene becomes stable by aromaticity, So, it will definitely have a higher acidic strength than that of cyclopentane and consequently lower pKa value.
Further, no such stability factor has a role in the case of cyclopentane so it has lower acidic strength comparatively.