Impact of fluorine substituents on the rates of nucleophilic aliphatic substitution and β-elimination

Article abstract of DOI:10.1016/j.jfluchem.2011.10.008

A measure of the quantitative effect of proximate fluorine substituents on the rates of S_N2 and E2 reactions has been obtained through a study mainly of reactions of fluorinated n-alkyl bromides with weak base, strong nucleophile azide ion and strong base/nucleophile methoxide ion in the protic solvent methanol and the aprotic solvent, DMSO. The order of reactivity for S_N2 reactions of azide in methanol at 50 °C was found to be: n-alkyl-Br > n-alkyl-CHFBr > n-perfluoroalkyl-CH₂CH ₂Br n-perfluoroalkyl-CH₂Br > n-alkyl-CF₂Br. Approximate relative rates of reaction were: 1, 0.20, 0.12, 1 × 10 ^-4, <7.7 × 10^-5. The order of reactivity for E2 reactions was found to be: n-perfluoroalkyl-CH₂CH₂Br n-alkyl-CF₂Br > n-alkyl-CHFBr > n-alkyl-Br. The approximate relative rates for reaction of methoxide in methanol at 50 °C were: 1100, 4.4, 1.9, 1.