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91.
Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon
bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally,
in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous
in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and
the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration
and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization
by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon
coupling in the monomer lattice. This reaction seems to be phonon-mediated. 相似文献
92.
S. L. Prunty 《International Journal of Infrared and Millimeter Waves》1985,6(6):471-479
This paper presents a simple theory based on the diffraction integral approach for calculating the coupling efficiency in waveguide lasers which employ plane or spherical mirrors. The results obtained differ only slightly from a full rigorous approach, due to the fact that only less than one percent of the beam energy lies outside the waveguide aperture. The infinite aperture approximation employed here leads to an explicit compact formula for the coupling efficiency, whereas exact calculations lead to expressions requiring numerical integration for their evaluation. 相似文献
93.
The application of solid layer crystallization techniques in industry is arousing ever more interest. One reason is the increasing demand for ultrapure products, and another is the energysaving potential of this separation technology.This article examines solid layer melt crystallization as concerns its purification efficiency. The crystallization process was carried out in two different modes, whereby the process parameters were varied and post-crystallization treatments were additionally applied. The experimental results were used as the basis for a mathematical fit of a semi-empirical expression which predicts the purification efficiency. It was used for a design of different multistage plants, which operate with different crystallization strategies. One result is that a comparable product quality is attainable with a simple process technique in combination with post-crystallization treatments, instead of a more complicated and therefore more expensive process technique.The authors wish to acknowledge support by the EU (JOULE program), which helped attainment of some results presented here. 相似文献
94.
《Tetrahedron》2004,60(3):529-534
Cyclodextrin glucosyltransferase (CGTase) from Thermoanaerobacter sp. was covalently immobilized on Eupergit C and used for the synthesis of maltooligosyl fructofuranosides employing soluble starch as donor and sucrose as acceptor. Using a weight ratio starch-sucrose of 1:2, the conversion of starch into acceptor products catalyzed by soluble and immobilized CGTases was higher than 80% in 48 h. Under these conditions, the reaction was selective for the formation of maltosyl fructofuranoside. 相似文献
95.
96.
Circular high-performance thin-layer chromatography (HPTLC) has been used to differentiate a series of twelve tricyclic neuroleptics, using both normal phase and reverse phase procedures. The use of normal phase systems also allows the resolution of geometric isomers of chlorprothixene, clopenthixol and flupenthixol. Thirteen sulphonamides and Trirnethoprim may also be distinguished using HPTLC. 相似文献
97.
We provide a quick elementary solution of the mean spherical model in a random external field. This also allows an immediate proof of the self-averaging property of the free energy. We calculate the free energy by means of the replica method, i.e., for any (not necessarily integer) replica numbern, and show that when a phase transition occurs the limits
andn 0 are not interchangeable. 相似文献
98.
Two types of directional couplers for transverse electric (TE) modes are described: short and multihole couplers, respectively. They selectively pick one mode out of a mode mixture in an overmoded circular waveguide system. Unwanted modes are either statistically kept at low level or are suppressed by destructive interference in the coupling waveguide. Mode selectivity and directivity in multihole couplers oscillate up and down with an increasing number of holes, finally reaching a minimum of approximately 20 dB, unless there are competing modes with rational fractions of the beat wavelength. A multihole coupler for the TE02 mode (28 GHz, 63.4 mm waveguide diameter, 41 holes) and a length of 1.6 m shows a calculated directivity of 68 dB and suppresses the unwanted modes TE01 with 34 dB (24 dB), TE22 with 37 dB (45 dB), and further modes TEm (<5, m<6) with 17 dB to 34 dB in forward direction (figures in parentheses are for unwanted modes propagating in backward direction).A short directional coupler for the TE01 mode (28 GHz, 63.4 mm waveguide diameter) with 16 holes and a length of 230 mm shows a directivity of 55 to 100 dB between 27.9 and 28.1 GHz, suppressing the TE02 mode with 35 to 80 dB, the TE03 mode with 30 to 65 dB, and the TE22 mode with 30 to 70 dB. 相似文献
99.
Copper-catalyzed N-arylation of diazoles can be accomplished using air-stable CuI as a copper source and 1,10-phenanthroline in the presence of KF/Al2O3 as a base. This is a simple and efficient method for the coupling of aryl bromide with diazoles. Different functionalized aryl bromides were coupled with diazoles using this system. 相似文献
100.
María Fernanda Martínez-Esperón 《Tetrahedron》2006,62(16):3843-3855
N,N′-aryl- and N,N′-alkyl-buta-1,3-diyne-1,4-ditosylamides have been synthesized for the first time, in good to excellent yields, by copper-catalyzed dimerization of the corresponding N-aryl or N-alkyl tosylynamides. Negishi coupling of N-ethynylzinc tosylamides derivatives with (hetero)aryl iodides in the presence of Pd2dba3 and triphenylphosphine affords N-aryl and N-alkyl arylynamides in yields of up to 90%. Intramolecular [4+2] cycloaddition reactions of N-ethynylphenyl ynamides and arylynamides allow the synthesis of carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields. 相似文献