Negative fluorine hyperconjugation. A theoretical re-examination

Abstract

Molecular orbital ab initio calculations show that the small changes in hydrocarbon acidities or in the rates of nucleophilic substitution reactions, which are found whan a β-F is substituted by a β-CF₃ group, do not reflect absence of fluorine hyperconjugation, but result from the stronger inductive effect of the CF₃ group relative to F, which compensates for its poorer hyperconjugation.