Nuclear Quadrupole Coupling in 5-Membered Ring Oxygen and Sulphur Heterocyclic Compounds; Studies by Nuclear Quadrupole Resonance and Ab Initio Molecular Orbital Calculations

Abstract

Abstract The 14N nuclear quadrupole resonance spectra for the compounds 2a, b, 3b, 4b, 5a, b, 6b have been obtained at 77 K and the asymmetry parameter and coupling constants extracted. A comparison of these with microwave spectral results, shows that small but systematic differences occur between the solid and gaseous states. There is a high level of agreement for the observed coupling constants from NQR or MW spectra and the ab initio calculations in both magnitude and direction. This enables us to extract further principal axis data from the observed microwave spectra, and to predict with some confidence the axes and coupling magnitudes for other members of the series where incomplete determinations are available. Variations in coupling constants with structure are discussed