Hydrocarbon A (pK about 14) is much more acidic than hydrocarbon B (pK about 22). Which statement explains this ?
(A)
(B)

Question

Hydrocarbon A (pK about 14) is much more acidic than hydrocarbon B (pK about 22). Which statement explains this ? (A) (B)

TestHub · Accepted Answer

A is the stronger acid because its conjugate base is more stable. In the anion of A, both five-membered rings can become aromatic cyclopentadienide rings. In the anion of B only the ring that lost H + is a cyclopentadienide, and further delocalisation of the charge into the seven-membered ring makes that ring anti-aromatic (8π), which destabilises the base.

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