Directive Effects in Gas-Phase Radical Addition Reactions

The solvent plays a major part in determining the course of most reactions in solution. The electron displacements accounted for by the electronic theory may be more important in the effect they have on the solvation of the transition state than any supposed “resonance stabilization.” In this context, the chapter investigates the reactions in the gas phase, free from the complications of the solvent, and determines the the extent to which the substituent effects established in solution and rationalized by the electronic theory, are effective in the gas phase. These activation parameters are in principle capable of complete interpretation using existing theory, whereas activation parameters determined in solution are very difficult to interpret because the extent of solvation, and the very structure of the solvent, changes with changing temperature. It is anticipated that kinetic study of radical reactions in the gas phase would provide the vital bridge connecting the qualitative pictorial theories of the organic chemist with semi-quantitative models of the theoretical chemist.