Interpretation of Solid State Deuterium NMR Spectroscopic Parameters.

Abstract

Solid-state deuterium NMR spectroscopic parameters including the deuterium quadrupole coupling constant and asymmetry parameter are interpreted in both theoretical and experimental aspects. Ab initio molecular orbital calculations were performed on the alkali metal hydrides, toluene, thymine, acetic acid dimer, and phenylacetic acid molecules with different conformations. In the alkali metal hydrides, the electric field gradient at the hydrogen atom site was calculated in three model systems: terminal metal hydride, bridging metal hydride, and dihydrogen adducts. The effect of metal hydride geometry on the deuterium quadrupole coupling constant was examined. The results can be used in the assignment and interpretation of solid-state deuterium NMR spectra of metal-hydrogen bonds in organometallic complexes. In the carbon-bound deuterium system, the orientation of the C-$\sp2$H bond vector in different conformers was varied with respect to either (or both, in the case of phenylacetic acid molecule) the phenyl ring or the carboxylic acid group. The correlation between the calculated NMR parameters and the conformational change was found, and fitted into a Karplus-type equations. The deuterium quadrupole coupling constant obtained from ADLF spectroscopy and the torsion angels from X-ray structural data for substituted arylacetic acids were used to obtain the coefficient values in the Karplus-type equation. The application of the Karplus-type equation to measure the solid-state local structural effect in substituted arylacetic acids is discussed in detail.