Substituent Effects on the 2-Phenylethyl Acetolyses Destabilized by a CF₃ Group

Abstract

The substituent effects on the acetolysis of α-CF₃-phenylethyl triflate (1) and β-CF₃-phenylethyl nosylate (2) were analyzed with LArSR equation, resulting ρ=-3.43, r⁺=0.67 and ρ=-3.20, r⁺=0.75, respectively. These exalted r⁺ values compared to that for the k_Δ acetolysis of 2-phenylethyl tosylate (r⁺=0.63) is considered due to the destabilization of the positive charge in the transition state by the adjacent α- or β-CF₃ group. The r⁺ value for the acetolysis of 1, however, is smaller than that for the acetolysis of 2 in spite of the stronger destabilization of positive charge in the transition state of the acetolysis of 1 by the α-CF₃ group. The differences in the r⁺ value is considered to be resulted from the difference in the transition state structures of the two k_Δ acetolyses.