14N nuclear quadrupole resonance (NQR) spectra of the NO functional group in a series of 4‐substituted pyridine 1‐oxides (R = H, CH3, C6H5, OCH3, OCH2C6H5, Cl, CN, NO2) and the natural abundance 17O NQR and nuclear magnetic resonance (NMR) solution spectra of a number of selected systems were obtained. The orientations of the principal axes of the 14N electric field gradient tensor (efg) in the NO group were determined using a Townes‐Dailey treatment of the NQR results, combined with a 13C cross‐polarization magic‐angle sample‐spinning NMR line shape analysis of carbons bonded directly to nitrogen. The major principal axis (Z) is coincident with the NO bond. The orientation of the principal (Z) axis of the 17O efg tensor also lies along the N‐O bond, as determined by Townes‐Dailey analysis. The NO π‐bond orders show considerable sensitivity to the nature of the para‐substituent, ranging from 0.17 to 0.31. 17O and 15N NMR chemical shifts parallel these changes in π‐bond order.
ASJC Scopus subject areas
- Materials Science(all)