Nitrogen nuclear magnetic resonance spectroscopy. Part 7. Extension of the nuclear magnetic resonance–ultraviolet correlation in nitroso-compounds to cover two-co-ordinate nitrogen in the other groupings with oxygen and carbon, and comparison with three-co-ordinate nitrogen in planar groupings (azoxy, etc.)

Abstract

The δ–λ correlation [of the ¹⁴N chemical shift δ with the reciprocal energy of the (n→π*) long wavelength electronic absorption] previously demonstrated for nitroso-compounds (etc.) X–NO (where X is alkyl, aryl, N, O, halogen, sulphur) is now extended to cover two co-ordinate nitrogen in N–N–NO₂, CN–O, –NN–O. –NN–F, CN–N–C, CN–O, O–NN–O, and C–NN–C groupings. For the related planar groups with three-co-ordinate nitrogen the δ-λ correlation is less good but still evident, even though the long wavelength transitions are not magnetically active; perhaps their energies vary in parallel with those of the relevant excitations (e.g. σ→π*). Perfluorination of alkyl or aryl groups attached to unsaturated nitrogen shifts the resonance upfield by ca. 20 p.p.m. (or rather more, at very low field).