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'Hydrogen bonds' in keywords Facet   Publication Year 2000  [X]
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2000[X]
1Author    Nobuo Nakamura, Hirotsugo Masui, Takahiro UedaRequires cookie*
 Title    Effect of Intermolecular Hydrogen Bonding on the Nuclear Quadrupole Interaction in Imidazole and its Derivatives as Studied by ab initio Molecular Orbital Calculations  
 Abstract    Ab initio Hartree-Fock molecular orbital calculations were applied to the crystalline imidazole and its derivatives in order to examine systematically the effect of possible N-H---N type hydrogen bond-ing on the nuclear quadrupole interaction parameters in these materials. The nitrogen quadrupole coupling constant (QCC) and the asymmetry parameter (r?) of the electric field gradient (EFG) were found to depend strongly on the size of the molecular clusters, from single molecule, to dimer, trimer and to the infinite molecular chain, i.e., crystalline state, implying that the intermolecular N-H -N hydrogen bond affects significantly the electronic structure of imidazole molecule. A certain correla-tion between the QCC of l4 N and the N-H bond distance R was also found and interpreted on the basis of the molecular orbital theory. However, we found that the value of the calculated EFG at the hy-drogen position of the N-H group, or the corresponding QCC value of 2 H, increases drastically as /C* when R is shorter than about 0.1 nm, due probably to the inapplicability of the Gaussian basis sets to the very short chemical bond as revealed in the actual imidazole derivatives. We suggested that the ob-served N-H distances in imidazole derivatives should be re-examined. 
  Reference    Z. Naturforsch. 55a, 315—322 (2000); received August 26 1999 
  Published    2000 
  Keywords    Hydrogen Bond, Nuclear Quadrupole Interaction, Molecular Orbital, Imidazole 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0315.pdf 
 Identifier    ZNA-2000-55a-0315 
 Volume    55 
2Author    Taka-Aki Nihei, Shin'. Ichi, Ishimaru, Ryuichi IkedaRequires cookie*
 Title    C1 NQR Studies of Hydrogen Transfer in Crystalline /7-Chlorobenzoic Acid  
 Abstract    35 C1 NQR frequencies and spin-lattice relaxation times 7, Q were measured inp-ClC 6 H 4 C0 2 H(PCB A) and p-ClQF^CC^DtPCBA-d,) at 77-333 K. T lQ in PCB A gave a shallow minimum of 8.0 ms at ca. 110 K, which could be explained by a double proton transfer mechanism in the carboxylic acid dimer referring to *H NMR data giving a T 1H minimum at almost the same temperature. PCBA-d, showed temperature dependent NQR frequencies quite analogous to those in PCBA, whereas their r 1Q behavi-our was quite different in its minimum value and its temperature as well as temperature gradient. These results were explained by suppressed deuteron tunnelling and the Ubbelohde effect. 
  Reference    Z. Naturforsch. 55a, 355—358 (2000); received August 27 1999 
  Published    2000 
  Keywords    CI NQR, Hydrogen-Bond, Hydrogen-transfer, Tunneling 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0355.pdf 
 Identifier    ZNA-2000-55a-0355 
 Volume    55 
3Author    Maciej Kubicki3, Teresa Borowiak3, WieslawZ. AntkowiakbRequires cookie*
 Title    Hydrogen Bonds in "Carboxyoximes": the Case of Bomane Derivatives  
 Abstract    The tendency of forming mixed carboxyl-to-oxime hydrogen bonds was tested on the series of bomane derivatives: one with the acid function only (bomane-2-erajfo-carboxylic acid), one with the oxime function (2,2'-diethylthiobomane-3-oxime), and one with both oxime and carboxylic functions (bomane-2-oxime-3-endo-carboxylic acid). The crystal structures of these compounds were determined by means of X-ray diffraction. In bomane-2-^n^/o-carboxylic acid and 2,2'-diethylthiobom ane-3-oxime 'homogenic' hydrogen bonds were found, and these hydrogen bonds close eight-and six-membered rings, respectively. By contrast, in bomane-2-oxime-3-era/o-carboxylic acid 'heterogenic' hydrogen bonds between carboxylic and oxime bonds were found. This carboxylic-oxime, or 'carboxyoxime' system is almost always present in compounds which have both oxime and carboxylic groups; therefore it can be regarded as an element of supramolecular structures (synthon). The presence of such synthons can break the tendency of carboxylic acids and oximes towards crystallizing in centrosymmetric structures. 
  Reference    Z. Naturforsch. 55b, 677—684 (2000); received March 16 2000 
  Published    2000 
  Keywords    Bom ane Derivatives, Hydrogen Bonds, Supramolecular Synthons 
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 TEI-XML for    default:Reihe_B/55/ZNB-2000-55b-0677.pdf 
 Identifier    ZNB-2000-55b-0677 
 Volume    55 
4Author    Takahiro Ueda, Nobuo NakamuraRequires cookie*
 Title    Nature of Hydration Water in (±)-Tris(ethylenediamine)cobalt(III) Chloride Hydrate, (±)-[Co(en) 3 ]Cl 3 -/iH 2 0, as Studied by *H, 2 H, and 17 O Solid State NMR  
 Abstract    The static and dynamics properties of hydration water molecules in (±)-[Co(en) 3 ]Cl 3 were studied by means of 'H, 2 H, and ,7 0 solid state NMR. By 'H pulsed field gradient (PFG) NMR the apparent diffusion coefficient of mobile water through a micropore along the crystalline unique c-axis was found to be 1.0 x 10~ 9 m 2 s -1 . The 2 H NMR spectrum at 141 K consists of two components, one being a Pake doublet corresponding to a quadrupole coupling constant (QCC) of (226 ± 2) kHz and an asymmetry parameter of the electric field gradient 77 of 0.08 ± 0.01, and another being a Gaussian line with a linewidth of 3.5 kHz. The 17 0 NMR spectrum at 300 K also consists of a narrow Gaussian peak and a broad powder pattern with a second order quadrupole effect corresponding to QCC = (6.3 ± 0.5) MHz and 77 = 0.55±0.02. The broad and narrow components are assigned to water molecules accommodated at general 12g positions and special 2a and 2b positions in the trigonal lattice with space group Plcl. From the ratio of the populations at these positions their potential energy difference was estimated to be between (2.7 ±0.1) and (3.5 ± 0.1) kJmol -1 . The 2 H NMR spectrum at room temperature indicates a finite quadrupole interaction which is attributable to the rapid rotation of water molecule about the molecular C 2 -axis. When the water content exceeds 2.7, the QCC is reduced sharply to (5.0 ±0.1) kHz at 285 K, suggesting that there occurs rapid rotation of water and rapid exchange of 2 H between nonequivalent positions. 
  Reference    Z. Naturforsch. 55a, 362—368 (2000); received August 23 1999 
  Published    2000 
  Keywords    (±)-[Co(en) 3 ]Cl 3, Absorbed Water, Molecular Motion, Hydrogen Bond, Quadrupole Interaction 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0362.pdf 
 Identifier    ZNA-2000-55a-0362 
 Volume    55