Impact of Electronic Effects on the Nucleofugality of Leaving Groups

A short review of the development of nucleofugality and electrofugality scales based on solvolysis rates of benzhydryl derivatives is presented. Accordingly, the rate of the heterolytic step in the SN1 displacement reaction and the leaving group ability (nucleofugality) in a given solvent are related with the special linear free-energy relationship (LFER) equation: log k = s(f) (N-f + E-f). The impact of electronic effects in the leaving group (nucleofuge) on the overall S(N)1 reactivity of the substrate is given. The importance of inductivity, resonance, polarity and field effects in the leaving group moiety in the transition state is analyzed. Also, the effect of the negative hyperconjugation and the influence of other electronic effects in the leaving group on the height of the reaction intrinsic barrier are considered. 1 Introduction 2 Development of the Nucleofugality Scale 3 Inductive and Resonance Effects 4 Negative Hyperconjugation 5 Intrinsic Barrier 6 Conclusions