themselves. On cannot yet exclude the possibility that the energy of the transition state for direct S-inversion may be lower than those for reactions k1-4. A B3LYP+GD3+BJ/Def2-TZVPP/SCRF=dichloromethane model (Figure ) shows DG is 30.5 kcal/mol higher than the resulting exo-TS and 20.0 kcal/mol higher than the transition state for initial proton abstraction. Hence for both possibilities we infer that kinv << k1-k4. The rate of this isomerisation is therefore insignificant compared to the subsequent intramolecular hydrogen transfers, and only the rate model assuming forbidden inversion 9 was investigated further (see eqn. 1).