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Ahmad S. Shawali Nagwa M. S. Harb Khadiga O. Badahdah 《Journal of heterocyclic chemistry》1985,22(5):1397-1403
The spectra (1H nmr, ir and uv) of a series of 3-arylazo-4-hydroxycoumarins 1a-m indicate that such compounds exist predominantly in the keto hydrazone form 1A both in solid state and in solution. The acid dissociation constants of the series studied were determined spectrophotometrically in 80 vol% ethanol-water mixture at 27° and ionic strength of 0.1. The results of the correlations of these constants by Hammett and Yukawa-Tsuno equations exclude the presence of the hydroxyazo form 1B in equilibrium with 1A in agreement with the spectral data. Also, the HMO method has been used to study tautomerism in such compounds. The results are also in full agreement with both the spectral and linear free energy correlations, the hydrazone form 1A being the most stable. It is further shown that both the intermolecular and intramolecular hydrogen bonding favor the hydrazone tautomer. 相似文献
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E.H. Huntington C.C. Harb T.C. Ralph H.-A. Bachor D.E. McClelland 《Applied physics. B, Lasers and optics》1997,64(5):507-514
Received: 14 June 1996/Revised version: 6 November 1996 相似文献
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Using an ab initio method, the potential energy has been calculated for the 29 lowest molecular states of symmetries 2Σ+, 2Π, 2Δ for the molecular ion RbH+. The calculation is based on nonempirical pseudopotentials and parameterized ?‐dependent polarization potentials. Gaussian basis sets have been used for both atoms. The spectroscopic constants for 18 electronic sates have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. Through the canonical functions approach the eigenvalue Ev, the abscissas of the corresponding turning points (Rmin and Rmax) and the rotational constants Bv have been calculated up to 24 vibrational levels for the considered bound states. The comparison of the present results with those available in literature shows a very good agreement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
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Harb HY Collins KD Garcia Altur JV Bowker S Campbell L Procter DJ 《Organic letters》2010,12(23):5446-5449
The use of a silicon stereocontrol element in cyclobutanol and cyclopentanol-forming cyclizations mediated by SmI(2) results in excellent diastereocontrol. The C-Si bond in the products of cyclization provides a versatile handle for further manipulation. An asymmetric route to cyclization substrates involving copper-catalyzed silyl transfer has also been developed. 相似文献
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We consider the problem of measurement of optical transverse profile parameters and their conjugate variable. Using multimode analysis, we introduce the concept of detection noise modes. For Gaussian beams, displacement and tilt are a pair of transverse-profile conjugate variables. We experimentally demonstrate the optimal encoding and detection of these variables with a spatial homodyning scheme. Using higher-order spatial mode squeezing, we show the sub-shot-noise measurements for the displacement and tilt of a Gaussian beam. 相似文献
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Several new pyrazolo[3,4-d]pyrimidine, pyrazolo[3,4-e][1,4]diazepine, pyrazolo[3,4-d][1,2,3]triazine and pyrolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives were prepared by the reaction of the corresponding 5-amino-pyrazole-4-carbonitrile derivative with different organic reagents under different reaction conditions. Using IR, 1H NMR, and mass spectra we have characterized all new compounds. 相似文献
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Harb W Ruiz-López MF Coutrot F Grison C Coutrot P 《Journal of the American Chemical Society》2004,126(22):6996-7008
Experimental diastereoselectivities for the stereocontrolled reduction of glycosyl alpha-ketoesters into the corresponding alpha-hydroxyesters have recently been reported with unexpected results. The process is catalyzed by a chiral oxazaborolidine derivative (the so-called CBS catalyst) and represents the key step in the synthesis of glycosyl alpha-amino acids synthons, a class of compounds that allow preparation of natural glycopeptides analogues exhibiting potential therapeutic relevance. Good to very good diastereomeric excesses have been obtained for a series of reactions with different glucidic derivatives, but surprisingly, the major product obtained does not correspond to that predicted by using Corey's model. In the present work, we carry out a theoretical investigation of these reactions at the density functional level. Separated effects from the catalyst and from the glucidic derivative have been computed to rationalize the observed diastereoselectivities and the double asymmetric induction. 相似文献
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赵乃良 《高校应用数学学报(A辑)》1996,(1):91-96
Nira Dyn等提出的四点插值法是一种典型的自由曲线离散造型方法,但该方法不能控制插值点的切向。本文利用薄板样很可能 量的极小化原理给出了具有切向控制的四点分插值条件。用户可以方便地交互控制任一插值点的切向,使得四点插值法更为有效和实用。 相似文献