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71.
Mandeep Thakur 《Tetrahedron》2008,64(22):5168-5173
1,4-Biradicals generated in the Norrish type-II reactions of 3-propargyloxy-2-arylchromones lead to cyclic products involving the 2-aryl group. The formation and distribution of products varied with the nature of 2-aryl group. 相似文献
72.
73.
A high-resolution diode laser spectrum of the 882-cm?1 band of s-tetrazine has been obtained. A complete rotational analysis of this band, incorporating quartic and sextic centrifugal distortion coefficients, has been carried out. The rotational constants A, B, and C have been determined with an accuracy better than 10?5 cm?1. The analysis has shown the band to be A-type and, on this basis, the vibrational assignment of this band has been revised from ν12 to ν14. 相似文献
74.
A simple, accurate and reliable titrimetric method is described for the determination of thiophanate-methyl, an important commercial fungicide. The method is based on its direct titration at room temperature with ammonium hexanitratocerate(IV) in sulphuric acid medium in the presence of potassium iodate as catalyst. The method permits detection of the end-point visually, potentiometrically or spectrophotometrically. The proposed method is recommended for routine determination of the fungicide in its commercial formulations. 相似文献
75.
Lakshman S Thakur 《Journal of Mathematical Analysis and Applications》1980,75(2):486-494
Computable lower and upper bounds on the optimal and dual optimal solutions of a nonlinear, convex separable program are obtained from its piecewise linear approximation. They provide traditional error and sensitivity measures and are shown to be attainable for some problems. In addition, the bounds on the solution can be used to develop an efficient solution approach for such programs, and the dual bounds enable us to determine a subdivision interval which insures the objective function accuracy of a prespecified level. A generalization of the bounds to certain separable, but nonconvex, programs is given and some numerical examples are included. 相似文献
76.
Paristerone, a novel phytoecdysone has been isolated from the tubers of P. polyphylla and its structure and stereochemistry has been established as 2α, 3β, 14α, 20(R), 22(r), 25-hexahydroxy-5β-chloest-7-en-6-one (2-epiecdysterone) on the basis of chemical and physical evidence. 相似文献
77.
A cathode-ray polarographic method has been developed for the determination of microgram quantities of gadolinium with the use of an azo-dye, Solochrome Violet RS. Disadvantages in the use of 0sd1M potassium chloride, commonly recommended as electrolyte for the polarographic determination of rare earths, have been demonstrated. The influence of pH, temperature, ligand concentration and purity, and the stability of the complex, have been investigated for the optimum performance of the method. The linear range is 0.5-12 mug/ml of gadolinium. Interferences by some lanthanides and other cations have been examined. 相似文献
78.
Asymptotic behavior of the pion form factors has been discussed treating pion as a bound state of the elementary nucleon and antinucleon system. The matrix-element of the electromagnetic current is written in terms of the Bethe-Salpeter amplitude for the nucleon-antinucleon bound system. Using suitable approximations the Bethe-Salpeter equation for nucleon-antinucleon bound state with nucleons as Dirac spinors has been solved and the corresponding off-shell pion form factors are determined. The form factors are strongly interaction dependent. For coupling the form factors vanish asymptotically like t?1 and for the form factors still vanish but less rapidly than t?1. 相似文献
79.
Laser flash photolysis and an external magnetic field have been used for the study of the interaction of 4-nitroquinoline-1-oxide (4NQO) with some indole derivatives, amino acids, tyrosine and tryptophan, and model proteins, lysozyme and bovine serum albumin. In an aprotic medium, photoinduced electron transfer (PET) from indoles to 4NQO is accompanied by proton transfer from the indole moieties irrespective of the substitution at the N-1 position. For 1,2-dimethylindole, however, proton abstraction is hindered possibly due to steric effects. In a protic medium, obviously proton transfer is possible from the medium and is the dominating reaction following PET. The effect of an external magnetic field is very small for all the systems studied. This is attributed to a competition between geminate proton abstraction by the 4NQO radical anion from the partner radical cation and escape of the 4NQO radical anion to the medium followed by proton transfer. The latter process is more predominant, and the former one, which produces a small population of geminate spin-correlated radical pairs, leads to a minor field effect. Another interesting observation is the affinity of 4NQO toward the tryptophan residues in a protein environment. It is seen that PET takes place preferably from the tryptophan residues rather than from the tyrosine residues. 相似文献
80.
Agostic interactions and weak hydrogen bonds to metal acceptors, M, are chemically and geometrically distinct, and this distinction must be maintained in the classification of new C-H...M interactions. 相似文献