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951.
Christoph Rüchardt Hans-Dieter Beckhaus 《Angewandte Chemie (International ed. in English)》1985,24(7):529-538
The chemist is accustomed to deriving structures and preferred conformations of organic compounds from rigid molecular models and standard values for bond lengths, bond angles, and torsional profiles. In the case of strained compounds, this rigid structural model has to be abandoned and replaced by a flexible one which takes individual conditions of strain into consideration. It is shown, on the basis of new experimental structure data, that the force field method is suitable and highly reliable for the calculation of structural parameters and preferred conformations of strained compounds. It is, therefore, capable of replacing the rigid molecular model. Furthermore, the systematic analysis of strain induced angle and bond deformation gives a new pivot for the development of a qualitative discussion of deformation in strained molecules and hence for improved conformational analysis. — In the course of this work we were able to isolate two rotamers of D,L -3,4-di(1-adamantyl)-2,2,5,5-tetramethylhexane; this is the first isolation of a rotamer pair of an aliphatic hydrocarbon. 相似文献
952.
B. Tabbert M. Beau H. Günther W. Häußler C. Hönninger K. Meyer B. Plagemann G. zu Putlitz 《Zeitschrift für Physik B Condensed Matter》1995,97(3):425-432
Optical spectra of atomic impurities in liquid helium have been investigated. Comparison is made between the wavelength of the free atomic and ionic lines and those in the liquid helium matrix. Simultaneously, the line width and a possible asymmetry is recorded. Presence and absence of radiative transitions depend on the species of the atom implanted in the quantum fluid. The absence of any optical transitions from states lying as low as 1,8 eV below the ionization limit will be explained in this paper. 相似文献
953.
Gerd Meyer 《无机化学与普通化学杂志》2003,629(10):1641-1642
954.
Katharina Gibson Markus Strbele Bjrn Blaschkowski Jochen Glaser Martina Weisser Radhakrishnan Srinivasan Heinz‐Jürgen Kolb Hans‐Jürgen Meyer 《无机化学与普通化学杂志》2003,629(10):1863-1870
Solid state metathesis reactions have been studied in fused silica tubes, by differential thermal analysis, and by X‐ray powder diffraction. A selection of reactions between metal (La, Nb, and Ni) chlorides and lithium nitride or lithium acetylide were investigated to get more insight into reaction pathways and intermediate reaction stages that may be adopted on course of the formation of metal nitrides or carbides. Intermediate compounds are considered to be important because they can control the reactivity of a system. Such compounds were traced by changing the molar ratios of reaction partners away from the salt‐balanced binary metal nitride or carbide target compositions. New preparative perspectives are discovered when metal chlorides were reacted with lithium nitridoborate or lithium cyanamide. Due to their reductive nature towards several d‐block metal chlorides, (BN2)3‐ and (CN2)2‐ react to form metals or metal nitrides plus X‐ray amorphous BN, and probably C3N4. With lanthanum chloride they can react to form nitridoborates and nitridocarbonates. The metathesis reaction between lithium cyanamide and cyanuric chloride (C3N3Cl3) instead of metal chloride was studied for the synthesis of C3N4. 相似文献
955.
Colourless needles of mercurous dimethylglyoximato nitrate, Hg2(Dmg)2(NO3)2, grow from a diluted nitric acid solution of mercurous nitrate and dimethylglyoxime. The crystal structure (triclinic, P1¯, a = 728.50(13), b = 1066.8(2), c = 1167.9(2) pm, α = 93.78(2)°, β = 94.16(2)°, γ = 98.61(2)°, Rall = 0, 0726) contains the cations [Hg2(Dmg)2]2+ and “non‐coordinating” (NO3)— anions. In the cation, two neutral dimethylglyoxime molecules coordinate bidentately with Hg—N distances in the narrow range of 236 to 239 pm to the mercurous ion, Hg22+, which exhibits a Hg—Hg bond distance of 252.23(8) pm). 相似文献
956.
G. Vanden Berghe H. De Meyer M. Van Daele 《International Journal of Theoretical Physics》1995,34(9):1931-1937
An infinite set of exact solutions for the three-dimensional Schrödinger equation with the interactionsar 2+br4+cr6 andr 2+λr2/(1+gr 2) is presented. The conditions under which these solutions can occur are given. Some previously published errors are corrected. 相似文献
957.
Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν1 = 120 (100) cm?1, ν2 = 280 (210) cm?1, ν3 = 360 (160) cm?1 and B = 0.0194 (0.0196) cm?1 for IHI (IDI). A detailed discussion of the dependence of ν1, ν2 and B on ν3, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I2 and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule. 相似文献
958.
We have measured the rheological properties of two cholesterol derivatives (cholesteryl myristate and cholesteryl nonanoate) in the vicinity of their cholesteric-smecticA transitions. The results for the two compounds differ qualitatively, and are in agreement with results based on optical observations of new defects in cholesteryl nonanoate showing that this material, traditionally considered as a typical cholesteric, in fact exhibits a TGBA phase between the cholesteric and smectic A phases. 相似文献
959.
Thomas Meyer Pierre -A. Nicati Philippe A. Robert Dimitris Varelas Hans -G. Limberger René P. Salathé 《Optical Review》1997,4(1):A53-A55
This paper presents a new method for writing and erasing a birefringence in optical fibers by polarized ultra violet side-exposure.
This experiment gives new insight into the origin of the induced birefringence and some applications are outlined. 相似文献
960.
Periodica Mathematica Hungarica - 相似文献