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1Author    RaphaelJ F Berger3, MichaelA. Schmidt3, Jonas Juséliusb, Dage Sundholmb, Peter Sirsch3, Hubert Schmidbaur3Requires cookie*
 Title    Tetraberyllium-?74-oxo-hexa(arylcarboxylates)  
 Abstract    Tetraberyllium-oxo-hexabenzoate and -hexa(mesitylcarboxylate) were prepared from ben­ zoic / mesitylcarboxylic acid and freshly precipitated beryllium hydroxide in a tetrahy-drofuran / water two-phase system. The crystal structure of the benzoate was deter­ mined from Be4 0 (0 C0 Ph)6 (CöH6)3 , and that of the mesitylcarboxylate from the phase Be4 0 (0 C0 Mes)6 (CCl4). The two clusters have the /i4-oxo cage structure also detected for the acetate and nitrate complexes, and for the related hexacarbonato hexaanion. The high symmetry of the cluster allows the observation of 9Be and l70 signals in the solution NMR spectra. The terminal atoms of the rigid carboxylate groups may be expected to lie at the vertices of large octahedra enclosing the cluster molecules. The axes of the six aryl groups would thus coincide with the axes of the cartesian coordinates with the /j 4 oxygen atom at the origin. This disposition suggests a connectivity suitable for cubic lattices if p-difunctional arene-dicarb-oxylate anions are employed instead of aryl-monocarboxylate anions. However, the new results show that significant deviations of the 0 Be2 0 2 C-Ar six-membered rings from planarity cause major deviations from octahedral symmetry and therefore no connectivity in cubic symmetry is to be expected. Fragmentation of the Be4 0 (0 C0 R)6 clusters upon ionization in a mass spectrometer leads predominantly to cations [Be3 0 (0 C0 R)3]+ which can be assigned a planar, highly symmet­ rical tricyclic core structure of D,^ symmetry. Quantum chemical calculations confirm dis­ crete energy minima for these cations and show that their stability is largely due to the favourable arrangement of alternating charges of neighbouring core atoms. The high polar­ ity of Be-O bonds rules out any significant contributions from aromaticity. The reactions of Be(OH)2 with 4 -HS-C6H4 -COOH and HS(CH2)2COOH give the corresponding cluster com­ pounds Be4 0 (0 C0 RSH)ö, [R = C6 H4 , (CH2 h] with six terminal mercapto functions. 
  Reference    Z. Naturforsch. 56b, 979—989 (2001); received June 26 2001 
  Published    2001 
  Keywords    Beryllium Chemistry, Beryllium Carboxylates, Quantum Chemical Calculations 
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 TEI-XML for    default:Reihe_B/56/ZNB-2001-56b-0979.pdf 
 Identifier    ZNB-2001-56b-0979 
 Volume    56 
2Author    Janina Kuczera3, Henryk Chojnackib, TeresaE. Kral3, Stanislaw Przestalski3Requires cookie*
 Title    Effect of Amphiphilic Cationic Compounds on Calcium Ion Desorption from Lecithin Liposome Membranes. Kinetic Studies and Quantum Chemical Calculations  
 Abstract    The effect o f four amphiphilic cationic compounds that differ in their polar head properties on the kinetics of calcium ion desorption from unilamellar lecithin liposom e membranes has been studied. The compounds under investigation were: N-benzyl-N,N-dimethyl-N-tetradecy-lammonium chloride (B D T A), N-methyl-N-tetradecylmorpholinium bromide (M TM), N-methyl-N-dodecyloxym ethylenem orpholinium chloride (M D O M) and N,N,N-trimethyl-N-te-tradecylammonium bromide (TM TA). Kinetic constants were determined using the three-compartmental analysis for isotopic labels. For the above m entioned compounds electronic structure calculations were performed and point charges and dipole m om ents of the molecules determined by using quantum chemis­ try methods. It was found that the rate of desorption increases with increasing concentration of the compounds studied, and effectiveness of the compounds follows the sequence: BDTA >M TM >TM TA >M DO M . For dipole moments the sequence obtained is somewhat different, namely: BDTA>M TM >M DO M >TM TA. Apparently, the differences in the effec­ tiveness of action of the compounds in the calcium desorption process follow not only from the values of dipole m om ents o f their polar heads but also from the values of point charges on som e atoms and from steric properties. 
  Reference    Z. Naturforsch. 51c, 219 (1996); received November 7 1995/January 3 1996 
  Published    1996 
  Keywords    Cationic Amphiphiles, Liposom es, Calcium Ion Desorption, Quantum Chemical Calculations 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0219.pdf 
 Identifier    ZNC-1996-51c-0219 
 Volume    51 
3Author    H. Bocka, J. M. Eureta, J. W. Bats3, Z. HavlasbRequires cookie*
 Title    Strukturen sterisch überfüllter Moleküle, 39 [1,2] Einkristall-und Gasphasen-Strukturen von l,4-Bis(trimethylsiloxy)benzol Structures of Sterically Overcrowded Molecules 39 [1,2] Single Crystal and Gas Phase Structures o f l,4-Bis(trimethylsiloxy)benzene  
 Abstract    l,4-Bis(trim ethylsiloxy)benzene has been crystallized both by vacuum sublimation and from «-heptane solution, which each yielded colourless plates with identical monoclinic unit cell dim ensions (P 2 Jn, Z = 4). The conform ation o f C[ symmetry shows the two (H 3C)3SiO-substituents to be conrotationally twisted around the 0 -(C 6H4) -0 axis by dihedral angles o f ± 60°. According to the photoelectron spectroscopic ionisation pattern and its K oopm ans' as­ signment, IEV" = -e f MI, by AM 1 eigenvalues, the gas phase structure should also be o f C, symmetry. The results o f geometry-optimized M N D O , A M I or P M 3 calculations for the monosubstituted derivative H 5C6-O S i(C H 3)3 are compared with respect to the quality o f their fit to the measured data. Ausgangspunkt: Molekülkonformationen sterisch überfüllter 1,4-Benzol-Derivate 
  Reference    Z. Naturforsch. 49b, 288—2 (1994); eingegangen am 1. Oktober 1993 
  Published    1994 
  Keywords    Sterically Overcrowded Organosilicon M olecules, Single Crystal Structure, Photoelectron Spectroscopy, Quantum Chemical Calculations 
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 TEI-XML for    default:Reihe_B/49/ZNB-1994-49b-0288.pdf 
 Identifier    ZNB-1994-49b-0288 
 Volume    49