Visual inspection of the transition state structure of TS3 with the catalyst M10 reveals that the catalyst is forming a hydrogen bond between the secondary amine moiety of the catalyst and the carbonyl moiety of the reactant as shown in Figure . The hydrogen bond helps to stabilise the negative charge that is built up due to the abstraction of the proton by a methoxy anion. When the secondary amine moiety of the catalyst is replaced with a CH 2 group the activation energy increases by 4.09 kcal • mol -1 since no stabilising hydrogen bond can be formed.