Rather, the interaction energy between the metal and the hydrocarbon fragment at the transition state is likely the key contributor to determining the kinetic barrier to -alkyl migration. This is more favourable for smaller ring sizes (3 vs 4) and for the more electropositive metal (Mg vs Zn). In combination, the analysis suggests the -alkyl migration at main group centres should become more favourable for systems in which the metal can polarise the hydrocarbon fragment, and the hydrocarbon fragment can best accommodate and delocalise the associated charge.