Solvent dependence of rotational anisotropy and molecular geometry as probed by NMR cross-relaxation rates

Abstract

A medium size and rigid molecule (2,3-naphto-1,3-dioxole) has been selected for this study because full anisotropic reorientation is expected and because its symmetry elements dictate the orientation of the rotation–diffusion tensor. NMR measurements include direct cross-relaxation rates (which yield the three rotation–diffusion coefficients by assuming the length of CH bonds) and remote cross-relaxation rates (which, by using these rotation–diffusion coefficients, yield distances between a given carbon and remote protons). Two different solvents have been used: carbon disulfide and dimethyl sulfoxide. In both solvents, the same type of reorientation anisotropy is observed although with different ratios of rotation–diffusion coefficient values, presumably due to specific intermolecular interactions undergone by the dioxole ring. This would also explain geometrical variations at the level of this moiety.