Table of Contents

Abstract: n/a

Abstract: Solid state ¹⁵N NMR chemical shift measurements have been performed on a series of nitro- and amino-substituted nitrogen-containing heterocycles that are of interest as potential new insensitive explosives. Due to low solubilities, many of these compounds are not amenable to study by solution state methods. Theoretical calculations of 15N chemical shift parameters have been performed on the structures of interest and are reported herein. The calculated and experimental values are in good agreement. The use of a model that includes intermolecular effects and allows the proton positions of the nearest neighbors to be optimized leads to the best agreement between calculated and experimental values. The theoretical models accurately predict the effects of nitro and amino substituents on ringnitrogen chemical shifts, explaining a seeming reversal in trend that is noted in the pyridine and pyridine-1-oxide chemical shifts of the highly substituted compounds.

Abstract: Recent ab initio calculations of cobalt NMR shielding show that DFT-GIAO calculations using hybrid functionals are found to reproduce experimental values well. This method is used to calculate the variation of the cobalt NMR shielding tensor of sqaure pyramidal nitrosyl complexes with respect to the CoNO geometry and to differing basal ligands. The isotropic shielding is shown to have a large negative derivative with respect to CoX distance where X is a ligating atom.; the derivative with respect to NO distance is smaller but still significant. The zz component where z is along the CoN(NO) bond is more sensitive to the basal ligands but the other two principal components are sensitive to the CoNO geometry.

Abstract: Ring formation in phosphate systems is expected to influence both the magnitude and orientation of the phosphorus (³¹P) nuclear magnetic resonance (NMR) chemical shielding anisotropy (CSA) tensor. Ab initio calculations of the ³¹P CSA tensor in both cyclic and acyclic phosphate clusters were performed as a function of the number of phosphate tetrahedral in the system. The calculation of the ³¹P CSA tensors employed the GAUSSIAN 98 implementation of the gauge-including atomic orbital (GIAO) method at the Hartree-Fock (HF) level. It is shown that both the ³¹P CSA tensor anisotropy, and the isotropic chemical shielding can be used for the identification of cyclic phosphates. The differences between the ³¹P CSA tensor in acyclic and cyclic phosphate systems become less pronounced with increasing number of phosphate groups within the ring. The orientation of the principal components for the ³¹P CSA tensor shows some variation due to cyclization, most notably with the smaller, highly strained ring systems.

Abstract: NMR chemical shifts of the amide proton of a supermolecule, an Nmethylacetamide hydrogen-bonded with a formamide, were calculated as functions of hydrogen-bond length RN…O and hydrogen-bond angles by FPT-GIAO method within the framework of HF/STO 6-31⁺⁺G(d,p) ab initio MO method. The calculations explained reasonably the experimental data reported previously that the isotropic proton chemical shifts move downfield with a decrease in R_N…O. Further, the behavior of proton chemical shift tensor components depending on the hydrogen-bond length and hydrogen-bond angle was discussed.

Abstract: A theory for the calculation of self-energy corrections to the nuclear magnetic parameters is given in this paper. It is based on the S-matrix formulation of bound-state quantum electrodynamics (QED). Explicit expressions for the various terms of the S-matrix are given. The interpretation of the self-energy, one- and two-vertex terms and some perspective for possible future developments are discussed.