A 2H NMR study of molecular motions of nonadecane-<i>d</i>40 in a urea inclusion adducta)

Abstract

The 3H NMR spectrum of nonadecane-d40 included in a urea adduct has been recorded at several temperatures in the range 145–273 K. This inclusion adduct is found to undergo a phase change in the range 160–170 K. In the high temperature phase the spectra indicate that the included alkane molecules are freely rotating. The amplitude of rotation is greatly diminished in the low temperature phase; however, the spectra are not those characteristic of the 2H NMR rigid limit. We also present direct evidence that the chain segments next to and including the methyl groups are undergoing motions of greater amplitude than those corresponding to free chain rotation.