Abstract:
The advance of the electronic theory, as applied to organic chemistry, has made possible the modern concept of the mechanism of halogen addition to unsaturated compounds. Halogen addition was believed to be a simple process but is actually one of great complexity. Lapworth (J.C.S. 1922, 422) developed the theory of alternate charges governed by a key atom or group, basing his evidence on the cyanhydrin reaction. Lewis (J.A.C.S. 1916, 762) had shown previously that the sharing of the electron pair of a covalent link is such that there is no permanent polarisation in a compound as CH₃-CH₃; but there is this effect in a molecule like CH₃-Cl. Lowry (J.C.S. 1923, 822) extended this idea by suggesting an electromeric change in the ethylenic system which preceded any reaction involving the double bond.
