Transition state analysis. I. Correlation between solvent stretching frequencies and C vs. O product ratios in alkylation of ambient anions. A new explanation for the observed product ratios

A new explanation is presented for the O to C product ratios observed in alkylation reactions of ethyl acetoacetate and related enolic and phenolic compounds, based on a Hammond postulate analysis of the nature of the transition states involved. The explanation not only covers the effects of solvent and the nature of the metal cation, but also encompasses the previously unexplained effect of the alkyl halide structure. From the latter effect, ground state interaction between solvent and alkyl halide is predicted. Evidence consistent with this interaction is found in linear free energy relationships between the ΔΔG‡ (C vs. O) values for various alkyl halides and the stretching frequency of the solvent (S=O of DMSO; P=O of HMPA) when measured as alkyl halide solutions.