DIRECT DETERMINATION OF A MOLECULAR TORSIONAL ANGLE BY SOLID-STATE NMR

A solid-state NMR method for the determination of the torsional angle of a C-13-labelled H-C-C-H moiety is demonstrated. The method exploits the evolution of C-13 double-quantum coherence under the influence of magnetic fields from the neighbouring proton spins. The experiment op erates under magic-angle-spinning conditions, does not require molecul ar orientational order, is insensitive to shielding tensor orientation s, and has high sensitivity and resolution. Experimental demonstration s and numerical simulations are shown. We obtain a torsional angle res olution of approximate to +/-20 degrees in the neighbourhood of the ci s geometry and approximate to +/-10 degrees in the neighbourhood of th e trans geometry.