Isomerization of substituted biphenyls by superacid. A remarkable confluence of experiment and theory.

Acid-catalyzed isomerization of dimethylbiphenyls is determined by the relative stability of intermediate carbocations, rather than the neutral products, and may be predicted by a simple semiempirical method (AM1). A general kinetic model for such isomerizations is suggested in which the rearrangement of an intermediate cation is the rate-limiting step. Control of regiochemistry of dialkylbiphenyls provides a useful entry into high-purity monomers for high-polymer synthesis.