THEORETICAL STUDIES ON THE REACTIONS OF SUBSTITUTED PHENOLATE ANIONS WITH FORMATE ESTERS

摘要

Semiempirical MO (PM3) studies are reported on the reactions of 18 substituted phenolate anions with m-(MNPF), p-(PNPF) and 3,4-dinitrophenyl formates (DNPF). The mechanistic change from rate-limiting formation to breakdown of the anionic intermediate (T~-) can occur in the gas phase, especially for MNPF, at approximately an equal proton affinity (PA) of the nucleophile and leaving group phenolates, i.e. ΔPA = 0 as the PA of the phenolate anion is decreased. In solution, however, owing to the low stability of T~- and a greater stabilization by solvation of the transition state for the breakdown step (TS2), all three formate esters are predicted to proceed by a concerted mechanism, which is in agreement with the experimental results. The low stability of T~- can be ascribed to the relatively high electron affinity of the phenolate anions.