Sensitivity of the H/D isotope shifts of the 13C nuclear shielding to the nitrogen lone pair delocalization in anilines and acetanilides

Abstract

AbstractTwo‐ and three‐bond deuterium isotope shifts (2Δ and 3Δ) of the 13C nuclear shielding were measured for a series of para‐substituted anilines and acetanilides, in which the amide NH or the amine NH2 hydrogens were partially exchanged with deuterium. The results show that when strong electron‐donating groups are present at the para position in acetanilides, the 2Δ(C‐1) isotope shifts are smaller than the 3Δ(C‐2,6) isotope shifts. Empirical correlations that relate 2Δ isotope shifts with 1H(NH), 13C(C‐ipso), 15N(NH2 or NH), 17O(CO) NMR chemical shifts and with 3Δ isotope shifts are presented. The results are interpreted in each series as depending on the characteristic nitrogen lone pair delocalization.