Proton chemical shifts of hydrogen bonded complexes of acetic acid. Electric field calculations for the monomer–dimer shift and for complexes with fluoride or acetate anions

Abstract

The permanent electric moments and the mutual polarisation of two acetic acid molecules in the dimer configuration are sufficient to account for the gas phase 1H association shift of the hydroxyl proton. A cyclic trimer configuration has a larger association shift than a dimer and such a component may account for the measured chemical shift of liquid acetic acid being low field of the probable dimer shift. The calculated shift of the hydroxyl proton hydrogen bonded to fluoride or acetate anions is much larger than the measured shift and this is rationalised in terms of the interaction of the anions with pairs of associated molecules and not simply with monomer acid.