Question

Cyclopentadiene is much more acidic than cyclopentane. The reason is that:

• A. Cyclopentadiene has conjugated double bonds
• B. Cyclopentadiene has both $s{p}^2$ and $s{p}^3$ hybridized carbon atoms
• C. Cyclopentadiene is a strain-free cyclic system
• D. Cyclopentadiene ion, the conjugate base of cyclopentadiene, is an aromatic species and hence has higher stability

Answer 1

Answer: (D)

Cyclopentadiene ion, the conjugate base of cyclopentadiene, is an aromatic species and hence has higher stability

Cyclopentadiene is more acidic than cyclopentane because it has conjugated double bonds.

When cyclopenta$-1,3-$diene loses a $H+$ ion from the $5th$ carbon, the resulting carboanion is aromatic because of its structure: its cyclic, planar, has a delocalised conjugated pi system which has$4n+2$ pi electrons, so it's aromatic. Aromaticity gives stability to the structure, so the formation of the carbanion is favourable and the position of the equilibrium for the reaction is to the right, thus cyclopentadiene is acidic.