Kinetic Studies of Bimolecular Nucleophilic Substitution. II. Structural Effects of Alkyl Halides on the Rate of SN2 Reactions —A Reinvestigation of the Linear Free-Energy Relationships for the Structural Variation of the Alkyl Groups

Abstract

Abstract The linear free-energy relationships have been examined for 35 SN2 reaction series, including 4 series of the SN2 reactions of alkyl bromides which rates were measured in these laboratories. These results have then been treated using the equation, log(k⁄k0)=rα, where α is a structural constant for methyl, ethyl, n-propyl, n-butyl, i-propyl, i-butyl, and neopentyl groups and where r is a reaction constant. The α values have been estimated as the arithmetic means of the logkSN2 values of the reaction series examined for each alkyl. The correlation coefficients for r’s are greater than 0.960 for all of the reaction series except two. The inapplicability of Taft’s polar and steric substituent constants (σ* and Es) to the SN2 reactivity of these alkyl groups has been discussed.