Intrinsic deuterium isotope effects on NMR chemical shifts of hydrogen bonded systems

effects on chemical shift of hydrogen bonded compounds in solution. For recent more complete reviews see [7, 8, 25] and for isotope effects primarily on intermolecular hydrogen bonding and in the solid state the papers by the Limbach group [3, 4, 33, 34]. The paper will concentrate on intrinsic isotope effects and not so much on equilibrium ones. The review will also concentrate on situations with rigid molecules. Deuterium isotope effects on chemical shifts are easily measured provided the deuterium is not exchanging at the NMR time scale. An example is given in Fig. 1. The main reason for obtaining a different chemical shift in the isotope substituted compounds can clearly be related to the shape of the potential well and the different zero point energy of XH and XD bonds (see Fig. 2). A prerequisite for obtaining an isotope effect is an asymmetric potential. The isotope effect on chemical shifts is a ground state property. For many of the situations encountered only the zero point energy level is appreciably populated. However, if other levels are populated then the effect will also take into account the different populations of the protio and the deuterio species [15].