(Solved): 1,3-Cyclopentadiene \( \left(\mathrm{pK}_{\mathrm{a}}=16\right) \) is a much stronger acid than cyc ...

1,3-Cyclopentadiene \( \left(\mathrm{pK}_{\mathrm{a}}=16\right) \) is a much stronger acid than cyclopentane \( \left(\mathrm{pK}_{\mathrm{a}}=44\right) \). WHY? A. The pi electrons of 1,3-cyclopentadiene repel a hydrogen ion away from the molecule B. The conjugate base of 1,3-cyclopentadiene is a stable, aromatic species, while the conjugate base of cyclopentane is not aromatic and is much less stable. C. 1,3-cyclopentadiene (the acid) has resonance stability; cyclopentane does not. D. The shorter C-C bonds of 1,3-cyclopentadiene greatly augment its acid strength.