The molecular behavior of selectively deuterated n-hexadecane in the urea inclusion compound is studied between 100 and 290 K by means of dynamic H-2 NMR spectroscopy employing line shape studies and spin-spin and spin-lattice relaxation experiments. Particular emphasis is given to the changes of the guest molecule behavior close to a solid-solid phase transition occurring at lower temperatures which is accompanied by a distortion of the urea lattice; It is demonstrated that spin-lattice relaxation experiments are of particular help for the evaluation of the chain dynamics in such systems. A comprehensive computer analysis of the available experimental data could provide a detailed picture of the hexadecane chains in the low-temperature phase and above the solid-solid phase transition. In the low-temperature phase the alkyl chains are found to undergo fast but restricted rotational motions (rate constant ca. 10(7) s(-1)). In addition, intramolecular trans-gauche isomerizations and methyl group rotation contribute to the spin relaxation of the alkane chain ends. In the high-temperature phase the alkyl chains rotate rapidly (rate constant ca. 10(10) s(-1)) and almost unrestricted around the channel long axis, giving rise to a dynamic (rotational) disorder of the embedded alkyl chains. It therefore is concluded that the phase transition can be assigned to a (dynamic) order-disorder transition. The alkane chains furthermore are found to be perfectly aligned with respect to the urea channel long axis. At the same time, they exhibit an internal flexibility gradient toward the chain ends. The conformational order significantly is altered at the phase transition. Thus, the trans population in the low-temperature phase is given by p(t) = 0.7 while in the high-temperature phase a value of p(t) = 0.95 has beer! derived.