Relationship between basicity and nucleophilicity

The empirical concepts of basicity and nucleophilicity are related but not strictly proportional. Hence, the aim of this study is to help in elucidating the range where both concepts are directly proportional. To do this, the relationship between a recently introduced nucleophilicity index and the proton affinity (PA) of several families of bases has been studied. A good correlation between the PA and the nucleophilicity index using HF and HCN as electrophilic partner has been found. Our studies show that the correlation exists only when the interaction is soft-soft in character and for strong bases with weak acids. However, the relationship is not only valid for exothermic reactions as it has been previously postulated but also for endothermic reactions. Copyright (D 2007 John Wiley & Sons, Ltd.