Halogen Replacement in Covalent Halides

Abstract

PREPARATIVE experiments involving halogen substitution in mixed halides of silicon¹ have emphasized the need for obtaining some comparative measure of the ease of replacement of halogen atoms in these covalent halides. Since no such study appears to have received deliberate attention, we suggest a simple theoretical basis upon which suitable experiments for this purpose may be designed. Simplifying assumptions must necessarily be introduced into such a discussion, and we suggest that it will suffice to relate ease of replacement to bond strengths and electron affinities, and to steric factors amenable to simple geometrical treatment. Our discussion refers particularly to a displacement reaction of the type considered to proceed bimolecularly according to a Heitler–London mechanism.