Abstract:
The addition of halogens to unsaturated compounds according to the equation X₂ + A=B → AX.BX has been gradually accepted to occur by an ionic mechanism. T. M. Lowry early made the suggestion that the reactivity of double bonds was caused by the development of polarisation such as CH₂(+)-CH₂(-) while the halogen molecule dissociated into ions which reacted with this. Activation of the ethylenic compound would take place by means of some catalyst in the gas, liquid, or solid phase. As will be seen, the environment of the double link determines the mode of this polarisation and the ease or tardiness with which it takes place. The molecule of every halogen has an appreciable permanent dipole moment - that of iodine being the greatest. Not only is liquid iodine an ionising solvent, but also iodine in certain ionising solvents has been found to conduct electricity, demonstrating actual ionic dissociation of the molecule.
