Ab initio studies of the strongest type of hydrogen bond: carboxylic acid–fluoride systems

Abstract

Ab initio LCAO–MO–SCF calculations have been performed on the acetic acid–fluoride system and the strength of the hydrogen bond, MeCO₂H ⋯ F^–, is found to be as strong as that previously reported for the formic acid–fluoride system. The implications of this and its relationship to other physical parameters of these hydrogen bonds are discussed. The carboxylic acid–fluoride systems are capable of forming esters with simple alkyl halides. The enhanced nucleophilicity of RCO₂H has been shown to be due to the increased negative charge of the hydroxy oxygen atom induced by the formation of the very strong hydrogen bond to the fluoride ion.