14N chemical shifts in linear triatomic species

Abstract

Calculations of chemical shifts in azide and NCO– ions, and their hydracids have been performed using procedures developed by Karplus and Pople. A single value of the mean excitation energy has been used for an isoelectronic species and applied to all nuclei irrespective of position or type, the value of the excitation energy being selected to produce a fit with one of the observed values of chemical shift or of chemical shift difference. The values of energy obtained are plausible; calculated shifts are consistent with experimental values. Where possible localized diamagnetic shifts have been included in an attempt to test their significance, and the validity of their incorporation in the manner described by Grinter and Mason. The conclusions are that the absolute scale of 14N chemical shifts developed by these authors is not consistent with a single value of excitation energy in the azide ion, but that if differences in diamagnetic terms are used to give corrected values of the paramagnetic shifts, consistency with experiment is obtained.