In the following compound, Br ionises as (a) $B r^{-}$ or (b) $B r^{+}$ . Classify the ring cation formed on ionisation as aromatic, anti-aromatic or non-aromatic. (assume the ring is planar)

Question

In the following compound, Br ionises as (a) B r − or (b) B r + . Classify the ring cation formed on ionisation as aromatic, anti-aromatic or non-aromatic. (assume the ring is planar)

TestHub · Accepted Answer

Br leaves as B r − because the heptatrienyl (tropylium) cation formed has 6 π electrons (3 C=C) with an empty p orbital on the s p 2 carbon, so it is aromatic. Loss of B r + would give a carbanion with 8 π electrons, which is not stable.

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