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61.
Grilli S Lunazzi L Mazzanti A Pinamonti M Anderson JE Ramana CV Koranne PS Gurjar MK 《The Journal of organic chemistry》2002,67(18):6387-6394
Variable-temperature NMR studies of tetraethylmethane (1a), tetrapropylmethane (1b), tetrachloromethylmethane (1c), tetrabromomethylmethane (1d), tetracyclopropylmethylmethane (1e), and tetrabenzylmethane (1f) show a range of dynamic behavior. Separate signals for two types of conformation are observed for 1a, 1c, and 1d at low temperatures, with more than 95% of the molecules in a time-averaged D2d conformation, and the S4 conformation as the minor populated alternative. Compound 1e populates only S4-type conformations but equilibrates slowly between degenerate versions of these at low temperatures. Compounds 1b and 1f show a temperature-dependent spectrum but the low-temperature limit spectrum could not be observed. Ab initio calculations agree well with experiment on the conformational equilibria and suggest in particular that compounds 1b and 1f behave similarly to compounds 1a and 1e, respectively. A crystal structure of compound 1f is reported. 相似文献
62.
S. Naveen Priti Adlakha Chintan Dholakia Anamik Shah M. A. Sridhar J. Shashidhara Prasad 《Structural chemistry》2006,17(6):569-575
A novel dihydropyrimidine (DHPM) derivative bearing a carbamoyl moiety was synthesized by an efficient three-component Biginelli reaction and was characterized spectroscopically and finally confirmed by X-ray diffraction studies. The title compound C20H20N4O4 crystallizes in the monoclinic space group P21/c with cell parameters a=12.8970(12) Å, b=13.6210(11) Å, c=11.8420(13) Å, β=115.860(3)°, Z=4 and V=1872.0(3) Å3. The conformation of the dihydropyrimidine ring is unusual; it is planar instead of the usual boat-like conformation. The 3-nitrophenyl ring is orthogonal to the 3,4-DHPM ring. The carbonyl group is in an anti-clinal conformation. 相似文献
63.
Amar Maheshwari 《Pramana》1986,27(3):383-391
The complete expression of the five-dimensional Einstein-Hilbert action as an expansion in fields in the Appelquist-Chodos
parametrization of the Kaluza-Klein metric has been given in this paper. It is explicitly shown that a unitary gauge can be
fixed in which in each of the charge sectors the vector and the scalar fields are absorbed as Goldstone modes leaving behind
the Pauli-Fierz Lagrangian for massive charged spin-2 field. 相似文献
64.
The a.c. electroluminescent characteristics of ZnO:Cu, Sn powder phosphor have been investigated in audio frequency range.
A simple preparative method for this phosphor has been described. The detailed variation of light output during one cycle
of the applied sinusoidal voltage has been studied and discussed. In addition to the two primary peaks, the two secondary
peaks have also been observed in each cycle of the applied field. The voltage and frequency dependence of the time-averaged
electroluminescent brightness have been found to follow the Alfrey-Taylor relation over a wide range of frequencies. The constants
of this relation have been determined. The spectral energy distribution of this phosphor shows that the peak-shift depends
upon the a.c. frequency and is independent of the magnitude of applied field. 相似文献
65.
Summary A method is reported for the separation of 16 closely related 2-(1, 2-diphenylvinyl)-3-phenylbenzofuran and 2-(1, 2-diphenylvinyl)-1-phenylnaphtho[2,1-b] furan derivatives on thin-layers of silica gel-G. 相似文献
66.
S. N. Maheshwari 《Annali di Matematica Pura ed Applicata》1962,59(1):41-53
Summary Valiron [12] obtained very extensive generalisations ofBorel’s method. In this paper the author has consideredValiron summability. The results proved are equivalent toBorel’s for k=1. 相似文献
67.
Summary The determination of phenyl hydrazine is done by reaction with ammonium molybdate; the pink colour procedud is extracted inton-butanol. 100–1300g of phenyl hydrazine can be determined at 510 nm. The effect of time, temperature, ammonium molybdate concentration and interferences has been studied.
Zusammenfassung Die Bestimmung von Phenylhydrazin erfolgt auf der Grundlage seiner Reaktion mit Ammoniummolybdat. Die rosa Färbung wird mitn-Butanol extrahiert. 0,1–1,3 mg Phenylhydrazin können bei 510 nm gemessen werden. Der Einfluß der Reaktionszeit, der Temperatur, der Reagenskonzentration sowie auftretende Störungen wurden untersucht.相似文献
68.
The effect of neutral gas friction is considered on the Rayleigh-Taylor instability of a compressible plasma in the presence of Hall currents. The prevailing magnetic field is assumed to be uniform and horizontal. It is shown that the solution is characterized by a variational principle. Based on the variational principle the dispersion relation is derived for a composite plasma, confined between two horizontal planes at a finite distance, in which the density is stratified in the direction of gravity according to the exponential law. It is found that the effect of collisions with neutrals, Hall currents and compressibility of the medium have destabilizing influence as the wave number range which is stable in their absence, is rendered unstable by their presence. 相似文献
69.
Kanthimathi M Nair BU Maheshwari R Dhathathreyan A 《Journal of colloid and interface science》2004,276(1):125-131
The oxidation of benzaldehyde as a film on a solid surface by various substituted oxochromium(V) salen in solution has been studied by monitoring the change in contact angle of the oxidant at the film/liquid interface utilizing a Teflon cell of known hydrodynamics and controlled convection/diffusion. The kinetics of the redox reaction in bulk has been monitored by measuring the change in absorbance of the oxidant solution. The interfacial study permits analysis of adsorption of the oxidant followed by the oxidation of the substrate under pseudo-first-order conditions. A comparison of the independent surface-averaged kinetic data with those obtained in the solution phase oxidation reaction is made and a model is presented for the mechanism of the interfacial reaction. The kinetic investigation shows that the rate of oxidation is accelerated in the presence of an electron-withdrawing group and is faster at the solid/liquid interface compared to the bulk. The probable mechanism of the redox reaction is discussed. 相似文献
70.
An analytical and numerical study of backward wave oscillator (BWO) in linear regime is presented to get an insight into the
excitation of electromagnetic waves as a result of the interaction of the relativistic electron beam with a slow wave structure.
The effect of background plasma on the BWO instability is also presented. 相似文献