Homolytic substitution in aromatic heterocycles

Abstract

A radical is a species with an unpaired electron. The classical research papers of Gomberg1 on the triphenylmethyl radical (I) (reaction 1 and 2), and the study by Lund and [diagram] Bodenstein 2 (1906) of the H₂ an Br₂ hain reaction, mark thebeginning of organic free-radical chemistry. Radical kinetics openedup with the radical-mirror removal experiments of Paneth et. al. 3 (1929) (reaction 3) and others. 4. [diagram] (3) The pyrolysis of tetramethyl lead (900--1200°K; 1 s, residence in quartz furnace) produced species (methyl radicals) which were capable of removing mirrors of lead, antimony and zinc. The rates and products observed made possible the first measurements of radical concentration and of radical reactivity.The Rice-HerzfieId mechanisms 5 (1934) gave a detailed scheme of elementary radical reactions to account for the rates and products of complex pyrolysis reactions.