Question

In organic chemistry, which reaction mechanisms permit the loss of a Hydride, and why?

Answer 1

Answer: Chichibabin reaction, to regain the aromaticity of benzene ring lost during nucleophile attack of amide ion.

In the first step of the reaction, amide ion attacks the ring carbon adjacent to the ring nitrogen, resulting in the formation of σ-complex. This is accompanied by the loss of aromaticity of benzene ring since the carbon under attack becomes sp3 hybridized. The hydride ion is then eliminated from the intermediate which initiates a series of shifting of electron pairs leading to the regain of aromaticity, the driving force behind the loss of hydride ion.

Please see details in the mechanism below: