The electron distribution at the nitrogen atom in substituted pyridines and related compounds as measured by their14N quadrupole coupling constants

Abstract

The measurements of ¹⁴N pure quadrupole resonance spectra of symmetrical azabenzenes and their analysis in terms of the electron distribution around the nitrogen atom has been extended to the two asymmetric diazabenzenes, pyrimidine and pyridazine, and to a variety of substituted pyridines. The coupling constants of unsymmetric compounds, i.e. compounds where the two nitrogen sigma bonds are not equivalent, cannot be analysed completely but yield values of the difference between the pi population and the average sigma population, including the lone-pair. Within these limits the electron distributions are in good agreement with those expected from simple molecular orbital theory. The results for the substituted pyridines show very strikingly the expected effect of substituents and the expected differences between the same substituent either ortho or para to the nitrogen atom on the one hand or meta on the other.