13C-spin-lattice relaxation behavior of acetonitrile and acetone

Spin‐lattice relaxation times of all carbon atoms in acetonitrile and acetone were measured at various temperatures. Spin‐rotation coupling constants of acetonitrile were determined, and for the methyl carbon atom the following values were found: $c_{\perp }\text{=4.5\hspace{0.17em}}\mathrm{kHz}$ , c_‖= −39 kHz. Considerable contributions of anisotropic‐chemical shift relaxation to the nitrile carbon relaxation was detected at lower temperatures with a chemical shift anisotropy of Δσ≈450 ppm. The relaxation behavior of acetone was also studied in aqueous mixtures. Existence of microheterogeneities in the acetone rich concentration range has been concluded from the carbonyl relaxation in D₂O, where a considerable contribution from intermolecular proton‐carbon interaction was found.