Electron Paramagnetic Resonance Studies of Molecular Orientation and Nuclear Exchange in Single Crystals of Morpholine N-Oxide

摘要

Low temperature -150C EPR spectra of the nitroxide generated photolytically in a single crystal of N-nitromorpholine are complicated by the presence of two magnetically distinct orientations of the N-0 bond within the crystal. As the temperature is raised, the spectra are further complicated by motional effects. Since at -150C the molecule is essentially frozen in the crystal lattice with respect to the time of the EPR interaction, and since the nitrogen coupling tnesor is markedly anisotropic, the observed EPR spectrum varies widely as the orientation of the applied field changes. The anisotropy of the nitrogen coupling tensor made it possible to unequivocally determine the orientation of the crystal with respect to the applied magnetic field. It was possible to determine the angle between the two orientations of the N-0 bond in the crystal and also to determine the energy barrier to exchange. (Author)