The decomposition temperature of the structure I1 clathrate hydrate of tetrahydrofuran has been followed to pressures above 3 kbars, where the hydrate is found to decompose incongruently in the regions of stability of ices I11 and 11, with no evidence of formation of a denser hydrate. From measurements of liquid solution densities and of volume changes at hydrate decomposition the density of the hydrate was obtained. Comparison with the X-ray lattice dimension indicates that at least 98% of the large cages are occupied, the principal uncertainty being in the lattice parameter. A similar treatment is made of Tammann and Krige's data (23) for chloroform hydrate. Analysis of the results of 18 composition determinations of structure I1 hydrates shows no statistical evidence of departure from the ideal composition of 17 mol of water per mol of hydrate former.La temperature de dCcomposition du clathrate hydrate de structure I1 du tktrahydrofuranne a Ct C suivie jusqu'a des pressions superieures a 3 kbar; il a kt6 trouve que dans ces regions de stabilitk des glaces I11 et I1 l'hydrate se decompose d'une f a~o n aberrante sans preuve de formation d'un hydrate plus dense. A partir des mesures de densite des solutions liquides et des changements de volume a la dCcomposition de I'hydrate, il a Ct C possible d'obtenir la densite de l'hydrate. La comparaison avec la dimension du reseau obtenu par rayons X indique qu'au moins 98% des grandes cages sont occupees, ]'incertitude principale &ant dans le parametre retuculaire. A partir des donnCes de Tamman et Krige une analyse similaire est effectuee pour le chloroforme hydrate. Les analyses des resultats se rapportant a 18 determinations de composition d'hydrates ayant la structure I1 ne montrent aucune preuve statistique d'ecart par rapport la composition idkale de 17 mol d'eau par mole de gCnCrateur d'hydrate. Canadian Journal o f Chemistry, 49, 2691 (1971)Among the diverse molecules now known to therefore most easily distinguished from ice and form "gas hydrates" of von Stackelberg's has been chosen for further study. structures I and I1 (1) are a number of ethers and Tetrahydrofuran hydrate was first reported ketones which are distinguished from the classical by Palmer (10) who found from melting point us. gas-hydrate formers by their solubility in water concentration curves a composition of between and by the possibility of hydrogen bonding with 13 and 16 molecules of water per molecule of the host water molecules bf the clathrate struc-tetrahydrofuran (THF), with a probable formula tures. Ethylene oxide (2, 3) and trimethylene of THF.14H20. Erva (1 1) obtained a congruent oxide (4) form hydrates of type I. Structure I1 melting point of 4.38 "C at an approximate comhydrates are formed by dimethyl ether (I), by position of THF.16H20. Several nugatory irtrimethylene oxide, tetrahydrofuran, 2,5-dihydrofuran, propylene oxide, and 1,3-dioxolane (4, 5) and by acetone (6, 7) and cyclobutanone (5,8). With the exception of the study by Glew and Rath (9) of the variable composition o...

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Cubic ice Ic and hexagonal ice Ih were prepared in pressurizable dielectric cells at temperatures near − 110°C from the high-pressure ices II and IX. No differences were found between the dielectric properties of Ic and Ih. Freshly prepared samples exhibited longer relaxation times at low temperatures than those commonly found for samples of Ih prepared directly by freezing purified water. These long relaxation times became appreciably shorter with sample aging. These results are attributed to precipitation of impurities from ices II and IX, followed by their gradual reincorporation in the ice I lattice. At temperatures as high as − 50°C the isothermal sequence of transformations I→II→I is capable of producing a substantial degree of purification of ice I in terms of its dielectric relaxation time.

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Publication costs assisted by NRCC Dielectric measurements between 1.8 and 250°K are reported for the isostructural hydrates of tetrahydrofuran, trimethylene oxide, and acetone. The characteristic shape of the high-temperature absorption arising from reorientation of water molecules is better represented by two discrete relaxation times than by a continuous distribution of the Cole-Cole or Frohlich type. The activation volume for water reorientation, 4.4 ± 0.3 cm3 mol'1 for tetrahydrofuran hydrate at 211°K, is similar to values found in other disordered ices. At low temperatures, very broad absorption by the guest molecules and failure of the guest contribution to the permittivity to increase as 1/T show the perturbing effect of the variable (but relatively small) electrostatic fields of the orientationally disordered water molecules. Permittivities of 3.5 to 4.0 at 4°K for the three hydrates include large contributions from rotational oscillations of guest molecules at far-infrared frequencies. The relaxation rate of H2S in the small cages of the double hydrates exceeds 1 MHz at all temperatures down to 1.8°K.

The limiting high frequency permittivity ε∞ of hexagonal ice, measured using a coaxial three terminal dielectric cell designed to minimize errors arising from differential thermal contraction, varies from 3.093 ± 0.003 at 2 K to 3.15 ± 0.02 at 200 K. The result is discussed in relation to the translational lattice vibrations and a comparison is made with other ices.

Continuous-wave proton nmr spectra of the clathrate hydrates and/or deuteriohydrates of methane, ethane, propane, isobutane, and neopentane–D2S have been recorded down to 2 K. Between 50 and 200 K each H2O hydrate spectrum consists of a line 3 to 4 G wide from reorienting guest molecules and a broader band from rigid water molecules. Line shapes characteristic of non-rotating guests are obtained in D2O hydrates at low temperatures, except for methane which gives a narrow line to 2 K. Neopentane, shown for the first time to be capable of enclathration, exhibits a Resing effect and other features related to its tetrahedral symmetry. Low-temperature dielectric absorption from reorienting guest-molecule dipoles has been measured in H2S, propane, isobutane, and n-butane–H2S hydrates. For steric reasons n-butane is encaged as a gauche rather than the trans isomer. Average barriers to reorientation estimated from nmr and dielectric data are 1.2 kcal/mol for ethane in type I hydrate and 0.6, 1.2, 1.4, and 0.8 kcal/mol for propane, isobutane, n-butane, and neopentane in type II.

The dielectric relaxation of water in the structure I clathrate hydrates of argon and nitrogen was studied over a range of temperature and pressure. Hydrates were slowly grown at pressures of 1 to 2 kbar in a coaxial cell enclosed in a pressure vessel. The complex permittivity loci resemble circular arcs with static dielectric constants of -56 at 0 "C and high-frequency dielectric constants of 2.85 i-0.05. Relaxation near 0 "C is about as slow as in ice I, but activation energies and entropies are much smaller. Formation of Bjerrum defects probably takes place preferentially near the occasional sites at which argon and nitrogen molecules have replaced water molecules in the lattice. The much faster relaxations found previously in the isostructural hydrates of ethers arise from orientational defects induced in the water lattice by the encaged molecules, a small proportion of which may form hydrogen bonds with water. The effect of small gaps in series with samples showing circular-arc dispersion behavior was evaluated.Canadian Journal of Chemistry, 46, 1673Chemistry, 46, (1968 Dielectric relaxation associated with the reorientation of water molecules in ice (1, 2) and its high-pressure modifications (3, 4) has been previously studied. The gas, or clathrate, hydrates (5) are further examples of ices whose lattices consist of hydrogen-bonded four-coordinated water molecules. Stability is conferred upon these hydrates by the presence in the lattice cages of guest molecules, which typically seem to interact only weakly with the water molecules of the host lattice (5, 6).The earlier dielectric studies of the water relaxation in clathrate hydrates were mainly confined to hydrates of rather large water-soluble ethers and ketones, viz. those of acetone (7); ethylene oxide (8); tetrahydrofuran, 2,5-dihydrofuran, propylene oxide, and trimethylene oxide (9) ; 1,3-dioxolane (1 0) ; dimethyl ether and cyclobutanone (1 1). In these hydrates the relaxation rates were found to be several orders of magnitude faster than in ice I and the activation energies only about half as great. Although the shapes of the dispersion loci appeared to be characteristic of the lattice structure for the structure I1 hydrates (9-1 I), the relaxation rates depended somewhat on the nature of the guest molecules. Except for the structure I hydrate of ethylene oxide (12), the smaller cages of all these hydrates are essentially unoccupied. Moreover, all of these hydrate formers are capable of relatively strong interaction, i.e. of hydrogen bonding, with water molecules. It is known from microwave absorption measurements (6) 'Issued as NRCC No. 9962. that in ethylene oxide and tetrahydrofuran hydrates the rotation of the guest molecules is only slightly hindered, but this does not exclude the possibility that a guest molecule may occasionally hydrogen bond to a lattice water molecule. Since these factors mav well affect the details of the mechanism of relaxation of the water lattice, it is of considerable interest to examine the relaxation behavior o...