A. Collaborative studies with C. L. Khetrapal and others at the Indian Institute of Science use nuclear magnetic resonance (NMR) methods to study molecules oriented in liquid crystals. Because the spectra rapidly become very complex with increasing numbers of interacting hydrogen atoms, only small or highly symmetric molecules have been studied. We are exploring a new method to use solid-state NMR spinning techniques to extend the range of applicability of the method. B. We are exploring the mechanism and potential applications of the effect of isotopic substitution on NMR chemical shifts, as shown in carbon-13 nuclei up to 10 bonds away from the site of substitution. Ab initio quantum mechanical calculations show that these effects correlate with electron density variations on the carbon atoms caused by the small difference in bond lengths of C-H and C-D bonds.
