Activation parameters for the cyclisation of bis-sulphonyl-stabilised carbanions to bis-sulphonylcycloalkanes have been determined; cyclopropanes form nearly a million-fold faster than cyclobutanes and ring strain is a negligible factor in determining reactivity. ... The effect of structure on intramolecular nucleophilic substitu- tion has been studied systematically by several groups of workers for more than 50 years' but for carbocycle formation, however, few general conclusions have been ...