High-Resolution 13C NMR Study of Solid π-π Molecular Complexes Using “Magic Angle” Spinning Techniques

Abstract

With the use of cross-polarization, high-power decoupling, and “magic-angle” spinning techniques, high-resolution 13C NMR spectra have been obtained for the solid crystalline π-π molecular complexes of the donor molecule hexamethylbenzene with a series of acceptor molecules. Small shifts were found for the aromatic carbon resonance of the hexamethylbenzene moiety in the complexes compared to that for solid hexamethylbenzene itself. The shifts were roughly proportional to the electron affinities of the acceptor molecules, indicating a small degree of electron transfer in the ground state for these compounds. With the use of chemical shift'charge density relationships determined from solution NMR studies, the degree of electron transfer was estimated at <10% for the complexes studied. © 1981, American Chemical Society. All rights reserved.