CONFORMATIONS OF NORMAL-ALKANES IN UREA INCLUSION ADDUCTS

Urea inclusion adducts of several specifically deuterated n-alkanes were prepared and their infrared and Raman spectra recorded. The Raman spectra are used to monitor the integrity of the adducts. The conformation-sensitive CD2 rocking bands in the infrared spectra demonstrate that the conformation of the included n-alkane molecules is planar (all trans) and that, if any, the nonplanar gauche conformers are present at concentrations below 3%. It is also demonstrated that mechanical agitation induces decomposition of the urea inclusion adducts thereby producing free urea and nonincluded n-alkane. These results refute recent claims of extensive conformational disorder (gauche bond concentrations of over 20%) in n-alkane molecules in urea inclusion adducts.