The structure of the carboxyl group. I. The investigation of formic acid by the diffraction of electrons

Abstract

The electronic structure of a carboxylic acid has been ordinarily written as [diagram]. It has been recognized,(1) however, that the structure O:- R:C::O+:H also may make a significant contribution to the normal state of the molecule, and the existence of such resonance of the double bond between the two oxygen atoms has been supported by thermochemical data,(2) the resonance energy being 1.20 v.e. for the carboxyl group in acids and in esters. During the investigation reported in this paper we have verified the resonating structure by the determination of interatomic distances in formic acid, and have also shown that in the dimer of formic acid the molecules are joined together by hydrogen bonds between the oxygen atoms of the carboxyl groups.