Parametrization of Substituents: Effects of Fluorine and Other Heteroatoms on OH, NH, and CH Acidities

Fluorine, the heterosubstituent par excellence, which can have a stronger impact on the reactivity in its vicinity than any other element, may serve as a crucial test of any model of the origin and transmission of electronic effects. To what extent fluoro substituents in organic compounds (A−H) increase their kinetic proton mobility (H/D and H/metal (M) exchange) and thermodynamic acidity in aqueous media and in the gas phase (see below) depends on many factors such as induction, resonance, polarization, hyperconjugation, and dipolar interactions.