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971.
Acetonitrile and [D3]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH3CN 2252 cm?1, CD3CN 2262 cm?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD3CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell. 相似文献
972.
Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol. 相似文献
973.
Frank Gahlmann Michael Sch fer Sylvia Magull 《Journal of organometallic chemistry》1992,440(3):263-275
The reaction of iPr2InCl (1) with KF and 15-crown-5 in acetonitrile at room temperature leads to the toluene-soluble crown ether salt [K(15-crown-5)2][iPr2InCl2] (2) and to the MeCN-soluble diorganoindium fluoride iPr2InF (3). Pure 3 can be isolated, when the reaction is carried out with KF but without crown ether at −15°C. Crystals of 1 und 2, suitable for X-ray structure determinations, were obtained when 1 and 2 were recrystallized from toluene. 1 exists as infinite chains of the monomeric unit iPr2InCl, while the unit cell of 2 contains separate ions. 相似文献
974.
Roland Boese Dieter Bläser Michael Nussbaumer Tadeusz Marek Krygowski 《Structural chemistry》1992,3(5):363-368
The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects. 相似文献
975.
α-(α'-Bromobenzyl)chalcone ( 3 ) reacts with primary amines (t-butyl, isopropyl,cyclohexyl) to give α-(α'-alkylaminobenzyl)chalcones ( 4, 5 and 6 ). When these allylic amines are treated with hydrogen bromide followed by reaction with base, they produce l-alkyl-2,4-diphenyl-3-benzoyl-azetidines ( 7,8 and 9 ). These azetidines were readily converted to their 3-deuterio derivatives ( 10 , 11 and 12 ) by treatment with sodium methoxide in deuteriomethanol. The configurations were assigned primarily by pmr spectra and mass spectra in reference to analogous compounds. 相似文献
976.
Jens Hartig Andreas Schnepf L. Jos de Jongh David Bono Hansgeorg Schnöckel Prof. Dr. 《无机化学与普通化学杂志》2007,633(1):63-76
Towards the Understanding of the Unexpected Properties of the Metalloid Cluster Compound [Ga84(N(SiMe3)2)20][Li6Br2(THF)20]·2Toluol In several short communications we have recently reported on the electrical and superconducting properties of the crystalline title compound 1 which contains anionic Ga84R20‐moieties. Here we present a collection of these results, complemented and interpreted by using DFT‐calculations on model clusters (Ga84(NH2)20?). These calculations allow a) a first insight into the dynamics of the Ga84‐moieties (e.g. a rotation of the central Ga2‐dumbbell) and thus an explanation of the temperature‐dependent Ga‐NMR‐spectra described recently, and b) estimations on the lattice energy of 1 and its resulting unexpected energetic stabilization compared to metallic gallium. A possible contribution of the cations in the electrical conduction mechanism of 1 can also be made feasible with model calculations. The basis for all the results presented is to be found in the “perfect” arrangement of nanoscopic Ga84‐clusters in the crystal. This theoretically predicted condition for superconductivity in a “chain” of identical metal cluster molecules is a requirement which can hardly be realized by means of physical fabrication methods. Therefore, on the one hand the results presented here make for some disillusionment in the field of nanoscience, but on the other hand, especially in the field of synthetic chemistry, they present rewarding challenges for fundamental work in the future. 相似文献
977.
Sun G Kappl M Pakula T Kremer K Butt HJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8030-8034
Forces across polymer melts are poorly understood despite their importance for adhesion and fabricating composite materials. Using an atomic force microscope (AFM), this interaction was measured for poly(dimethyl siloxane) (PDMS). The structure of the polymer at the surface changed during the first approximately 10 h. Afterward, short-range attractive forces were observed with short-chain PDMS (M(w) = 4200 g/mol). Using PDMS with a molecular weight (M(w) = 18 000 g/mol) above the entanglement limit, we measured a monotonically decaying repulsive force, which indicates that a quasi-immobilized layer had formed at the solid surface. Due to the small radius of curvature of the tip, forces could be measured in equilibrium. 相似文献
978.
Kumar K Michalik D Garcia Castro I Tillack A Zapf A Arlt M Heinrich T Böttcher H Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(3):746-757
A practical route for the synthesis of new biologically active 5-HT(2 A) receptor antagonists has been developed. In only three catalytic steps, this class of central nervous system (CNS) active compounds can be synthesized efficiently with high diversity. As the initial step, an anti-Markovnikov addition of amines to styrenes provides an easy route to N-(arylalkyl)piperazines, which constitute the core structure of the active molecules. Here, base-catalyzed hydroamination reactions of styrenes with benzylated piperazine proceeded in high yield even at room temperature. After catalytic debenzylation, the free amines were successfully carbonylated with different aromatic and heteroaromatic halides and carbon monoxide to yield the desired compounds in good to excellent yields. The two key reactions, base-catalyzed hydroamination of styrenes and palladium-catalyzed aminocarbonylation of haloarenes/heterocycles, showed tolerance towards various functional groups, thereby demonstrating the potential to synthesize a wide variety of new derivatives of this promising class of pharmaceuticals. 相似文献
979.
Soonam Park Feng Liao John M. Larson Steven L. Girshick Michael R. Zachariah 《Plasma Chemistry and Plasma Processing》2004,24(3):353-372
A molecular beam mass spectrometry system for in situ measurement of the concentration of gas phase species including radicals impinging on a substrate during thermal plasma chemical vapor deposition (TPCVD) has been designed and constructed. Dynamically controlled substrate temperature was achieved using a variable thermal contact resistance method via a backside flow of an argon/helium mixture. A high quality molecular beam with beamtobackground signal greater than 20 was obtained under film growth conditions by sampling through a small nozzle (75 m) in the center of the substrate. Mass discrimination effects were accounted for in order to quantify the species measurements. We demonstrate that this system has a minimum detection limit of under 100 ppb. Quantitative measurements of hydrocarbon species (H, H2, C, CH3, CH4, C2H2, C2H4) using Ar/H2/CH4 mixtures and silicon species (Si, SiH, SiH2, SiCl, SiCl2, Cl, HCl) using Ar/H2/SiCl4 mixtures were obtained under thermal plasma chemical vapor deposition conditions. 相似文献
980.
Michael R. Buchmeiser 《Monatshefte für Chemie / Chemical Monthly》2003,134(3):327-342
Summary. The metathesis polymerization, respectively cyclopolymerization, of 1-alkynes and 1,6-heptadiynes using well-defined group
VIA transition metal initiators is summarized. For purposes of comparison, selected quaternary catalytic systems used as alternatives
as well as the properties of the resulting materials will be presented. Special consideration is given to the mechanistic
advancements that have been made during the last decade, which allow the tailor-made synthesis of conjugated materials with
interesting optical and electronic properties.
E-mail: michael.r.buchmeiser@uibk.ac.at
Received November 20, 2002; accepted November 21, 2002 相似文献