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41.
Lori A. Nock Judah M. Goldwasser Horst G. Adolph 《Journal of polymer science. Part A, Polymer chemistry》1991,29(8):1133-1149
Polyformals of fluoro-, nitramine-, and C-nitrodiols show widely differing properties with respect to glass transition temperature, melting transition, and solubility. Polymers with desirable combinations of these properties, e.g., low Tg, high nitro content, and good solubility in polar solvents, were expected to result from acid-promoted copolycondensation of appropriate mixtures of diols with formaldehyde. A series of such condensations were carried out and the polymers obtained from binary mixtures of fluoro- and nitrodiols, different nitrodiols, and fluoro- or nitrodiols and carboranediols, were characterized by GPC, 1H-NMR, and DSC analysis. 相似文献
42.
43.
N(alpha)-Methylamino acid containing peptides exhibit interesting therapeutic profiles and are increasingly recognized as potentially useful therapeutics. Unfortunately, their synthesis is hampered by the high price and unavaibility of many N(alpha)-methylamino acids. An efficient and practical preparation of N(alpha)-methyl-N(alpha)-(o-nitrobenzenesulfonyl)-alpha-amino acids without extensive purification is described. The procedure is based on the well-known N-alkylation of N(alpha)-arylsulfonylamino esters which was improved by using dimethyl sulfate and DBU as base. Ester cleavage is efficiently achieved by using an S(N)2-type saponification with lithium iodide, avoiding racemization observed with lithium hydroxide hydrolysis. Compatibility of the synthesized N(alpha)-methylamino acids with Fmoc solid-phase peptide synthesis is demonstrated by using normal coupling conditions to efficiently prepare N-methyl dipeptides. The described procedure allows the preparation of N(alpha)-methylamino acids in a very short period of time and a rapid synthesis of N-methyl peptides using Fmoc solid-phase peptide synthesis. 相似文献
44.
The high pressure behaviour of InI is studied by DFT‐calculations and compared with experimental data. The existence of a 5s2 electron pair in In+ represents an unfavourable bonding situation for high symmetry structures because of effective closed shell repulsion. Since cations with a ns2 electron pair are highly polarizable and the electronic situation is more favourable in the low symmetry structure InI prefers a TlI‐type structure at ambient pressure. A pressure induced transition to the more densely packed high symmetry CsCl‐type structure takes place at about 19 GPa according to our calculations. At ambient pressure the interactions are predominantly ionic. However with increasing pressure the distances between In+ cations in the TlI‐type structure diminish drastically, mainly due to the changing space requirement of the lone electron pair. Apart from ionic interactions further bonding interactions between the In+ cations occur. At elevated pressure the electron localization function (ELF) as well as the band structure diagrams suggest metallic bonding between the In+ within the zigzag chain, i. e. increasing bonding interactions between the In+ cations due to the electron pair and its s‐p‐mixing. At ambient pressure In‐In interactions are rather weak and the space requirement of the lone electron pair mainly determines the characteristic arrangement of the ions. At elevated pressure the In‐In interactions become stronger and stabilise themselves additionally the specific structural arrangement. 相似文献
45.
The valence ionization potentials (IP's) of cyclopentadiene and 1-sila-cyclopentadiene-(2,4) are studied by an ab initio many-body approach which includes the effect of electron correlation and reorganization beyond the Hartree-Fock approximation. The Hartree-Fock approximation gives the correct ordering of the IP's for cyclopentadiene but this ordering does not agree with the results of the previous experimental and theoretical studies. The ordering is 1a2(π), 2b1(π), 4b2, 6a1, 5a1, 3b2, 1b1 (π), 4a1, 2b2, 3a1. For sila-cyclopentadiene the ordering of the IP's is: 1a2(π), 4b2, 2b1(π), 6a1, 1b1(π), 5a1, 3b2, 4a1, 3a1, 2b2. The Hartree-Fock approximation is found to be incorrect with respect to the ordering of the 4b2 and 2b1(π) IP's. A number of one-electron properties are calculated in the one-particle approximation and compared with the available experimental data. 相似文献
46.
Ab initio molecular orbital structures and energies of B2F4, B2Cl4, N2O4, and C2O have been calculated for both perpendicular D2d and planar D2h rotamers. The experimental trend toward greater preference for the D2d forms in going from B2F4 to B2Cl4 is reproduced. N2O4 favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B2F4, hyperconjugation for B2Cl4, lone-pair interactions for N2O4, and electrostatic repulsions for C2O. 相似文献
47.
At low temperatures, the broad excimer fluorescence band of α-perylene crystals is replaced by a weakly structured emission at higher energy. This emission originates from a new crystal state (Y-state) which is populated independently of the high temperature excimer (E-state). Due to the temperature dependence of its first order decay rate and due to the thermally activated formation of the E-state, the Y-emission grows rapidly at temperatures below 90 K. The Y-emission differs from the fluorescence of the monomeric β-perylene at 5.5 K by its Stokes shift of 1300 cm?1, the lack of vibronic structure, the long first order decay time of 40 ns and the absence of bimolecular annihilation indicating a localized state. The Y-state is attributed to a less relaxed pair state formed upon contraction of the dimeric crystal lattice. 相似文献
48.
49.
Max Ziegler und Horst Winkler 《Fresenius' Journal of Analytical Chemistry》1959,166(4):241-242
Zusammenfassung Durch die Anwendung eines H2S-haltigen Laufmittels werden die Ionen Cu2+, Pb2+, Bi3+ und Hg2+ am Startpunkt des Chromatogramms als Sulfide fixiert, während Cd2+ nach kurzer Laufzeit in scharf begrenzter Zone als Sulfid im Chromatogramm nachgewiesen wird. Als Arbeitsgefäße dienen Reagensgläser. Die Spezifitäten liegen für 5 g Cd bei Cd2+Cu2+=12000, Cd2+Pb2+=12000, Cd2+Bi3+=12000, Cd2+Hg2+=1100.Herrn Prof. Dr. O. Glemser, Direktor des Anorganisch-chemischen Insituts der Universität Göttingen, danken wir für Unterstützung der Arbeit. 相似文献
50.
David T. Connor Patricia A. Young Maximillian Von Strandtmann 《Journal of heterocyclic chemistry》1977,14(1):139-141
The reaction of 2-picoline N-Oxide anion with o-substituted henzoates and isatoic anhydrides to give synthetically useful l-(2-methoxyphenyl)-2-(2-pyridinyl)ethanone N-oxides, I-(2-hydroxy-phenyJ)-2-(2-pyridinyl)ethanone N-oxides and I -(2-arninopheny])-2-(2-pyridinyl)ethanone N-oxides is described. 相似文献