Methyl group tunneling effects on 1H NMR line shapes of solids at low temperatures

Methyl group tunneling side bands have been observed in the proton NMR line shapes of solid dimethyl ether, propane, propane-2, 2d2, and dimethyl sulfide at low temperatures. The line shape theory after Apaydin and Clough was used to derive tunneling frequencies. Assuming a threefold, sinusoidal potential barrier for methyl group rotation, application of the Hecht and Dennison relation yields barrier heights of 3.85, 3.58, 3.60, and 3.51 kcal/mole, respectively, for dimethyl ether, propane, propane-2, 2d2, and dimethyl sulfide.