Relationships of the 15N nuclear magnetic resonance chemical shift and the 15N–1H spin coupling constant to the infrared stretching frequency of the amino group in saturated primary amines and anilines

Abstract

The amino group stretching frequency (ν_NH) and the ¹⁵N chemical shift (δ¹⁵N) were measured for saturated primary amines. A good linear relationship was found between them, with the slope being the opposite of that found in substituted anilines. A linear relationship was also found for substituted anilines between ν_NH and the ¹⁵N–¹H spin coupling constant (¹J_¹⁵N,¹H). CNDO/2 calculations were done for representative molecules to obtain the NH stretching frequency, the local paramagnetic term of ¹⁵N, and the nitrogen 2s–hydrogen 1s bond order, on the basis of which the characteristic behaviour found for the i.r. and n.m.r. parameters was interpreted.