A Clathrate Hydrate of Cyclobutanone: Dielectric Relaxation of the Host and Guest Molecules

Abstract

A low-frequency dielectric study of (CH 2 ) 3 CO•17H 2 O shows a water absorption region characteristic of a structure II clathrate hydrate which melts congruently at 0.0 °C. The relatively low Arrhenius energy of 6.5 kcal mol –1 is similar to that of acetone hydrate, for which new results are given. At low temperatures reorientation of encaged cyclobutanone molecules gives a very broad absorption region and a contribution to the static permittivity which falls with decrease of temperature. These properties are attributed to the effects of the electrostatic fields of the orientationally-disordered water molecules, which form the cages. Such fields distort the tetrahedral symmetry of the cages to an extent which varies greatly from cage to cage. The high permittivity (~3.6) at 4.2 °K probably arises from rotational oscillations at frequencies near 20 cm −1 of the guest molecules in shallow potential minima. This enhancement of polarizability removes the difficulty previously noted in the applicability of the Onsager cavity model to structure II hydrates. The dipole moment of cyclobutanone in cyclohexane solution was found to be 2.78 ± 0.02 D.