DISCRETE SECONDARY ISOTOPE EFFECTS IN ZERO-FIELD NMR - THEIR RELATIONSHIP TO HALIDE ION COORDINATION

Zero-field magnetic resonance spectra of halogen nuclei in amine and a mino acid hydrohalides, partially deuterated at the exchangeable posit ions, show multiple spectral lines, each one corresponding to a partic ular pattern of deuteron replacement in the coordinating protonated gr oups, We have analyzed this isotope perturbation using two-dimensional I-127 zero-field NMR spectroscopy (NQ-COSY). The principal values of the electric field gradient tenser for each isotopomer are obtained fr om the corresponding resonance frequencies of two connected transition s. The difference between the electric field gradient tenser for isoto pomers differing by a single isotope substitution is treated as an axi ally symmetric perturbation along the hydrogen bond between the substi tuted proton and the halide: under this assumption, we have determined the orientation of the electric field gradient tenser principal axis system.