Charge distributions and chemical effects. XXXVIII. Correlations between nuclear magnetic resonance shifts and electronic charges of nitrogen atoms

Abstract

Correlations between nuclear magnetic resonance shifts and atomic charges of nitrogen in selected alkylamines, nitroalkanes, isonitriles, and azines consistently follow the general trends observed for carbon and oxygen nuclei. In azines, any increase in total electronic population on nitrogen, resulting from a gain in π charge prevailing over a concurrent loss of σ electrons, is accompanied by an upfield resonance shift—as found for aromatic and ethylenic carbon and carbonyl oxygen atoms. On the other hand, any gain in total charge dictated by that of σ populations translates into a downfield 15N shift, which is the trend exhibited by alkylamines, nitroalkanes, and isonitriles—a situation encountered earlier with sp3-hybridized carbon, carbonyl carbon, and dialkyl ether oxygen atoms.