Molecular dynamics of paraffins in the n-alkane/urea clathrate

Abstract

Simulations of the molecular dynamics of n‐C_NH_2N+2 in the n‐alkane/urea clathrate have been performed for N=13,23,33, for a period of 1 ns. Parallel simulations were performed starting from conformations in which all CH₂–CH₂ bonds were in the trans conformation, and starting from a conformation in which one of the terminal CH₂–CH₂ bonds was in a gauche conformation. These simulations suggest less than 3% of the terminal CH₂–CH₂ bonds would be in a gauche state at equilibrium. The gauche content is much smaller at the CH₂–CH₂ bonds further removed from the ends of the chain. No significant differences are seen in the simulations performed with n‐alkanes with N=13,23,33. The mobility of the C–H bond vectors about the axis defined by the channel is greater at the ends than in the middle of the chain. The angular distribution is nearly randomized in 1 ns for the C–H vector in a methyl group, but a longer time scale would be required for randomization of this distribution for the C–H vector bonded to the central methylene group in C₃₃H₆₈.