The influence of the nitro-group upon side-chain reactivity. Part VI. The d-orbital resonance stabilisation of α-bromo- and α-iodo-4-nitrobenzyl anions, retarding their α-elimination to 4-nitrophenylcarbene

Abstract

Although the α-proton extraction from 4-nitrobenzyl bromide or iodide by alkali in aqueous dioxan is much faster than that from the chloride (as proved by comparing the rates of interception of the halogenocarbanions on 4-nitrobenzaldehyde to form epoxides), yet the formed bromo- or iodo-carbanion (stabilised by d-orbital resonance) does not undergo the α-elimination of bromide or iodide ion to give the carbene as does the corresponding chlorocarbanion (the carbene subsequently changes to 4,4′-dinitrostilbene) but reverts to the original halide which undergoes two faster successive S_N2 halogen displacements by the alkali leading to the formation of 4,4′-dinitrodibenzyl ether. 3-Hydroxy-4-nitrobenzyl bromide gives one S_N2 displacement of the halogen forming the alcohol.