Spin-Density Distributions in Conjugated Ligands of Paramagnetic Chelates from NMR Contact Interaction Shifts

Abstract

Electron‐spin‐density distributions in a variety of π systems have been obtained from proton‐contact interaction shifts in paramagneticnickel II chelates of N,N′‐disubstituted aminotroponeimines. The results have furnished a great deal of new information regarding the detailed manner in which π electrons are distributed via conjugative effects. Spin‐density distributions in these systems calculated by the valence‐bond scheme are shown to be in quite good general agreement with experimental determinations. Effects attributable to hyperconjugation have been observed and the conjugating abilities of linking groups C=C, N=N, NH, O, S, and SO2 have been assessed. It is shown also that metal‐ligand π‐bond formation results in transfer of 0.1 of an unpaired electron from nickel to the π system of each of the ligands of these bischelates.