New deuterium isotope effects on C and F chemical shifts across intramolecular hydrogen bonds of non-resonance assisted systems

A series of thioanilides and corresponding anilides, some of which contain fluorinated phenyl rings, have been synthesized as model compounds. They all contain rather strong intramolecular hydrogen bonds, the strength of which varies. Deuterium isotope effects on ¹⁹F and ¹³C chemical shifts due to deuteriation at the NH proton show interesting new long-range isotope effects on chemical shifts that may be related to the existence of an intramolecular hydrogen bond and to transmission of the isotope effect due to an electric field effect. Deuterium isotope effects on chemical shifts report on variations in hydrogen bonding, for example, as a function of changes in substituents or temperature. Deuteriation leads to a strengthening of the hydrogen bond.