Low temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline uracil and thymine

The FTIR spectra of pure NH and isotopically diluted (NH/ND and ND/NH) polycrystalline uracil and thymine were measured in the range 4000-400 cm(-1) at temperatures from 300 to 10K. For the first time, the essentially narrow bands corresponding to the uncoupled stretching (nu(1)) and out of plane bending (nu(4)) NH proton modes of uracil and thymine were observed in the solid phase. It was found that in the nu(4) region the spectra reveal more details on the H-bond interactions present in both solids than in the nu(1) range. The frequencies of the various bands observed in both spectral regions were used for estimation of the H-bond energy, using empirical correlations between this property and both the red shift of nu(1) and the blue shift of nu(4) that occur upon crystallization due to the establishment of the H-bonds. The results are compared with known thermodynamic, structural and theoretical data. The IR data also suggest that the H-bond networks of both crystals contain, besides the two NH...O=C bonds revealed by X-ray experiments, additional types of H-bonds, which do not show long range periodicity and, thus, cannot be detected by the conventional structural methods. The assignment of some other bands in the spectra of both substances was also reviewed.     

The preparation and reactivity of metal-containing monomers. 54. Thermolysis of the acrylamide monomer [Co(CH2=CHCONH2)4(H2O)2](NO3)2

The kinetics and pathways of thermolysis of the Co(II) complex with acrylamide, [Co(CH₂=CHCONH₂)₄(H₂O)₂](NO₃)₂ (1) were studied. The rate of gas evolution is satisfactorily approximated by a first-order equation of autocatalysis. The composition of gaseous and solid products of thermolysis of 1 was studied by IR spectroscopy, mass spectrometry, and electronic microscopy. Thermal transformations of acrylamide complex 1 include three macro stages: dehydration, polymerization of the dehydrated monomer, and thermooxidative destruction of the resulting polymer.     

Crystal structures of low-symmetry cancrinite and cancrisilite varieties

The high-sodium variety of cancrinite [Si_6.3Al_5.7O₂₄][Na₂(H₂O)₂][Na_5.7(CO₃)_0.9(SO₄)_0.1(H₂O)_0.6] (Kovdor Massif, Kola Peninsula, Russia) and the calcium-containing variety of cancrisilite [Si_6.6Al_5.4O₂₄][(Na_1.2Ca_0.4)(H₂O)_1.6][Na₆(CO₃)_1.3(H₂O)_1.2] (Khibiny Massif, Kola Peninsula, Russia) are studied. The trigonal unit cell parameters of the crystal structures under investigation are as follows: a = 12.727(4) Å, c = 5.186(2) Å, and space group P3 for the former mineral and a = 12.607(4) Å, c = 5.111(1) Å, and space group P3 for the latter mineral. The reduced symmetry of the new varieties as compared to the symmetry of typical cancrinite and typical cancrisilite is associated with the specific features in the arrangement of the carbonate groups and water molecules in channels. This inference is confirmed by the IR spectroscopic data.     

Traces,dependency graphs and DNLC grammars

We point out the use of graph grammars for specifying (generating) languages of dependency graphs that arise in theoretical studies of concurrent systems.     

Solid-phase reaction of organometallic derivatives of nitrophenols,P-nitrothiophenol,andP-nitroaniline with bromides,according to the molecular spectroscopy data

The effect of the visualization of the reaction of bromide anion with PhHg- and PPh₃Auderivatives of phthalein has been extended to the organometallic derivatives (M=Hg, Au, Sn, Pb, Sb) of other classes of indicators: nitrophenols, nitrothiophenol, and 4-nitrobenzenesulfonylanilide. On the basis of the analysis of the electronic reflection spectra and the IR spectra it has been found that the changes occurring upon the reaction of these compounds with bromides are determined by the formation of complexes and/or anions and are more pronounced in the latter case. The character of the interaction depends on the dissociation ability of the M-X bonds (which was determined earlier while studying the reaction with DMSO), the ability to form complexes, and on the steric hindrance which has proved to be considerable in the solid-phase reaction (with Br^–).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1974–1977, November, 1993.