Variable Composition of the Chlorine and Ethylene Oxide Clathrate Hydrates

The infrared spectra of characterized samples of ethylene oxide hydrate made from 100% H 2 0 , 99.7% D 2 0 , and several dilute isotopic solutions, are presented between 4000 and 360 cm-I. The similarity between the absorption by the watcr ~nolecules in the hydrate and in ice I is discussed. The frequency and halfwidth of tlie O H and O D stretching modes of isolated HDO molecules in tlie hydrate are related to those in the disordered ice phases; the frequencies correlate rather well with the weighted-mean hydrogen bond lengths in these phases.The ethylene oxide vibrations show sharp, single-line absorption. The only exceptions are the ringbreathing mode which appears as a doi~blet, separated by 2 cni-', with m~~c h weaker absorption about 13 cm-' away on either side, and the ring deformation modes which interact with the vK(H20) niodes. The possible causes of this behavior are disci~ssed, but no firm conclusions can be drawn. The sharpness of tlie absorption by enclathrated ctliylene oxide, compared to that by liquid ethylene oxide, is brietly discussed in the light of modern theories of bandshapes in liquids. dans l'hydrate ont ete reliees a celles des phases dCsordonnCes de la glace ; la correlation dcs frtqi~ences est plut8t bonne avec la nioyenne pondCrCe dcs liaisons hydrogcne dans ces phases. Les vibrations de

Section: Absorption B J~ the Ethylene Oxidementioning

confidence: 77%

“….46H20, judging from the conditions of preparation (1, 8). No changes in the relative intensities were observed for different samples, but the experimental difficulties made the sensitivity S L I C~ that the possibility of observing an effect in the samples available was marginal.…”

Section: Results and Assignmentmentioning

confidence: 99%

The Infrared Spectrum of Ethylene Oxide Clathrate Hydrate at 100°K between 4000 and 360 cm⁻¹

Bertie¹,

Othen²

1973

“…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 of ethylene oxide hydrate, there appears to be no accurate information about the degree of occupancy of the cages or the heat of formation of these hydrates.…”

mentioning

confidence: 85%

Composition of Tetrahydrofuran Hydrate and the Effect of Pressure on the Decomposition

Gough¹,

Davidson²

1971

152

103

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...

“…The upper limit to the size of molecules which form each structure roughly agrees with the "free diameter" of the larger cage obtained by subtracting the van der Waals radius of the water molecule (1.45 A) from the appropriate "average distance to center" given in Table 1. Complete occupancy of the smaller cages is approached for molecules less than about 5.0 A in diameter, although partial occupancy is possible for somewhat larger molecules like chlorine and ethylene oxide (13). The larger cages of each structure seem generally to be almost completely occupied.…”

Section: Introductionmentioning

confidence: 91%

The Motion of Guest Molecules in Clathrate Hydrates

Davidson¹

1971

The reorientation of molecules encaged in hydrates of structures I and I1 is controlled mainly by the cage geometry and the electrostatic fields of the water molecules. Departure from spherical symmetry of the short-range interactions between the guest molecule and the water molecules which form the cages leads to preferred orientations which become increasingly occupied at low temperatures. A modified Lemard-Jones potential energy calculation shows the preferred positions of C1, to lie offcenter and close to the equatorial plane of the tetrakaidecahedral cage with the C1 atoms near the axial planes of symmetry. In an attempt to account for the remarkable reorientational freedom of polar guest molecules, the electrostatic fields of the water molecules are treated in detail. It is shown that the geometry of the cages causes the sum of the fields of the cage water dipoles to almost vanish at points near the cage center, but that this is not true of the resultant quadrupolar fields. It is suggested that the quadrupolar fields are also relatively small because the hydrogen bonding to four neighbors considerably reduces the quadrupole moment of the water molecule. The orientational disorder of the water molecules results in a wide distribution of resultant electrostatic fields in different cages. This appears to be the origin of the great width of the dielectric absorption observed at low temperatures in tetrahydrofuran hydrate and of the wide temperature range of variation of the proton magnetic resonance (p.m.r.) line width in tetrahydrofuran deuterate.La rdorientation des mol6cules encagkes dans des hydrates de structures I et I1 est principalement contrBlde par la gComCtrie de la cage et les champs electrostatiques des molCcules d'eau. L'ecart a la symktrie sphkrique des interactions a courte distance entre les molbules d'eau qui forment les cages et la molbule qui y est emprisonnee conduit a des orientations prefkrentielles qui deviennent plus frdquentes a basse temperature. Un calcul d'knergie potentiel de Lennard-Jones modifid montre que les positions preferentielles de CI, sont decentrkes et proches du plan equatorial de la cage tetrakaidecahedrale avec les atomes de C1 proches des plans axiaux de symetrie. Dans une tentative de rendre compte de la liberte remarquable de reorientation des molbules polaires emprisomCes, les champs dlectrostatiques des mol6cules d'eau sont trait& en detail. On montre que la gkomktrie des cages entrainent la somme des champs dus aux dipBles aqueux de la cage a presque s'annuler en des points proches du centre de la cage, mais ceci n'est pas vrai des champs quadrupolaires resultants. On suggere que les champs quadrupolaires sont aussi relativement petits parce que la liaison hydrogene avec quatre voisins reduit considerablement le moment quadrupolaire de la molCcule d'eau. Le desordre d'orientatlon des mol6cules d'eau entraine une distribution Btendue des champs Blectrostatiques resultant dans les differentes cages. Ceci apparait etre a I'origine de la grande largeur d'absorption...