Predicting the quality of leaving groups in organic chemistry: Tests against experimental data

Guided by experimentally observed solvolysis rates, 66 different reactivity indicators for predicting the quality of organic leaving groups are tested. None of these indicators is completely satisfactory. Most of the proposed indicators work well when the leaving group is a halogen, but poorly in the other cases (carboxylates, sulphates, phosphinates). This suggests that it is very difficult to devise simple reactivity indicators for the intrinsic quality of a leaving group, and supports recent work on molecule-dependent models for nucleofugality.