Anisotropic reorientation of planar molecules measured by nuclear relaxation in strongly coupled spin systems

Abstract

In this paper we describe the use of nuclear magnetic relaxation in strongly coupled spin systems for determining all three rotational diffusion constants of rigid, planar molecules with C_2v symmetry. The complete evaluation of the motional parameters rests on the accurate measurement of the cross‐correlation terms relating the reorientation of two proton–proton internuclear vectors. This term, as well as more familiar auto correlation terms, may be extracted from an analysis of the recovery of individual lines in the strongly coupled proton spin system following a nonselective 180° pulse. The principles, procedure, and practical considerations of this approach to studies of anisotropic motion are illustrated for the AB₂ spin systems of 1,2,3‐trichlorobenzene, 2,6‐dichloroanisole, and 2,6‐dichlorophenol‐0‐d.