Infrared spectra of partially deuterated hydrates yield the fundamental frequencies of isotopically dilute H,O, D,O, and HDO molecules. Isotopic dilution eliminates vibrational coupling arid allows the determination of the total number of crystallographicaily distinct n'ater molecules in the crystal. It also yields the number of distinct symmetric (Cz,) and asymmetric (C,) ~vater molecules. The results for gypsum show that all the water lllolecules are equivalent and that they are asymmetric, in agreement with crystallographic results. The extent of asymmetry is measured by the difference bet~veec the two O H stretching frequencies of H D O molecules, which is 90 c m ' . This corresponds to an estimated difference of 0.02 A in the 0 . . . O distances of the two hydrogen bonds. The spectra of partially deuterated gypsum show clearly that spectral features previous!y explained by the presence of two sets of distinct water n~olecules or by proton tunnelling, are in fact due to vibrational coupling.Canadian Journal of Chemistry, 47, 1361 (1969) The crystal structure of gypsum has been reported to have the space-group sj~minetry C2/c (12/c) -CZh6, with four CaS04.2H20 per unit ceil (1, 2). The oxygen atoms Ow of the water molecule have been placed in the S( f ) equipoint, which has a site syillmetry 1 -C , (3). The 16 hydrogen atoms must then belong to two non-equivalent sets SH, + 8H2. As a consequence there are 8 symmetrically equivalent water molecules in the unit cell. but the two O.,,-H distances in each water molecule are nonequivalent and thus, a t least in principle, of different length. This asymmetry is connected with the existence of hydrogen bonds between the water molecule and the oxygen atoms 0, of two SO, groups (Fig. I); the sulfate groups are related by a center of symmetry, but the two 0, atoms that are engaged in the hydrogen bonding are not,The extent of the asymmetry has never been estimated with confidence. An attempt to locate the hydrogen atoms by the most direct method, neutron diffraction, has resulted in these interatomic distances (2) VOL. 47, 1969 extent, or even confirm the existence, of the asymmetry. The number of normal vibrations and their activities in the i.r. and Raman spectra are the same for an unperturbed (C,,) and a perturbed (C,) water molecule. Raman and i.r. intensities of undeuterated gypsum are of equally little help. If a n unperturbed water molecule is assumed, as was done by Cabannes et al. (4) in their analysis of the Raman spectrum, and by Hass and Sutherland (5) in their analysis of the i.r. spectrum, gross discrepancies arise between the expected and the observed intensities of the fundamental bands. Whether these discrepancies are due to an unrealistic model or to the contributions of combination modes to the intensities of the fundamentals, is difficult to decide. When, however, the H,Q molecule in the crystal is replaced by HDO, the existing perturbation from the C,, symmetry caused by asymmetric environment leads to the doubling of all three fundamenta...

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The azido functionality is one of the progenetorial groups for the synthesis of nitrogen-containing organic compounds.2 In polycyclic bridgehead compounds such (1) Synthetic Methods and &actions. 125. For part 124, see: Olah, (2) The Chemistry of the Azide Group; Patai, S , Ed.; Wiley Inter-G. A.; Husain, A.; Singh, B. P. SyntheSi8 1985, 703. science: New York, 1971.

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We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C8C1Im][PF6] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG2)2Im]I in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of [C8C1Im][PF6] and the PEG chains of [(mPEG2)2Im]I are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low [C8C1Im][PF6] contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy.

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2-methylthio-2-imidazoline and 2-methylthio-1,4,5,6-tetrahydro-2-pyrimidine amidated 2-chloro-3-pyridine- and 2-chloro-3-pyrazinecarbonyl chlorides. The products reacted with aromatic amines forming a series of tricyclic, linearly fused N-aryl pyrimidones. Included among these pyrimidones were 10-aryl-2,3-dihydroimidazo[1,2-a]pyrido[2,3-d]pyrimidin-5(10H)-ones, 11-aryl-2,3,4,11-tetrahydropyrido-[2,3-d]pyrimido[1,2-a]pyrimidin-6(6H)-ones, 10-aryl-2,3-dihydroimidazo[1,2-a]pyrazino[2,3-d]pyrimidin-5(10H)-ones and 11-aryl-2,3,4,11-tetrahydropyrimido-[1,2-a]pyrazino[2,3-d]pyrimidin-6(6H)-ones. 4,5,6,7-Tetrahydro-2-(mythylthio)-1H-1,3-diazepine amidated the ethyl hydrogen carbonate of 2-(phenylamino)-3-pyridinecarboxylic acid, forming 12-phenyl-2,3,4,5-tetrahydropyrido[2',3':4,5]pyrimido[1,2-a][1,3]diazepine-7(12H)-one. A single crystal X-ray analysis and an unambiguous synthesis established the structure of the linearly fused isomer 10-phenyl-2,3-dihydroimidazo[1,2-a]pyrido[2,3-d]pyrimidin-5(10H)-one.