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21.
Anna B. DenisovaVyacheslav Ya. Sosnovskikh Wim Dehaen Suzanne ToppetLuc Van Meervelt Vasiliy A. Bakulev 《Journal of fluorine chemistry》2002,115(2):183-192
Reaction of 2-hydrazinothiazoles 1 with 1-thienyl- and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c. 相似文献
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23.
Summary This paper proposes an optimization model for gas-solid chromatographic separations in a non-linear programming form and an approximate equation of the plate height for the model. A computer-modified mapping procedure is also described for searching the optimum separation conditions. Just five experiments and about 20 minutes of the computer time are needed to establish the optima of column temperature and of the carrier gas linear velocity. The relative deviation between the predicted and the experimental values was found to be within 20% for the plate heights, and within 1.5% for the retention times. 相似文献
24.
INTRODUCTIONThe wicking technique has been used to determine the surface energy components of solids[1-7]. Generally, thereare two wicking processes in practice, i.e. thin layer wicking and column wicking. A comparison of the twowicking techniques made by van Oss et al.[2], shows that column wicking has a problem of showing differentpacking density due to some kinds of powder materials, i.e. clay can not give good repacking reproducibility[2].But thin layer wicking has a problem in sample… 相似文献
25.
O. Nilsson 《Journal of separation science》1979,2(12):720-722
Kaiser's “abt” concept rests on the experimental establishment of a linear relation between band width at half height, b0.5, and capacity ratio, k, according to His column specification quantity, hreal, is dependent on the square of the slope a, obtained from a linear regression analysis based on this relation. It is shown in the present paper that an improvement of the experimental conditions leading to a lower extra-column contribution to band broadening, b, introduces a tendency towards a negative curvature in the plot at low k values. The mean slope increases, and an uncritical linear regression would yield an hreal-value which is higher than before and which would be in the opposite direction to the requirements of a reliable column specification. Generally the linear regression analysis has to be moved to higher k regions in cases of curvature, especially as it is also shown that hreal is an estimation of the traditional HETP value, H∞, that would be obtained when k approaches infinity. This theoretically expected relation is a strong motivation for the use of hreal as a column specification, since the b0.5-value associated with H∞ is expected to be practically independent of b. 相似文献
26.
Summary A new index of performance of the chromatographic separation between two adjacent peaks, the discrimination factor, d0, is defined. It is normalized between 0 and 1 and is directly and easily determined from the chromatogram. It does not depend
on any assumption regarding peak shape, except that the peak profiles of individual sample components have a single mode.
Its value depends on the relative heights of the two peaks as well as on their separation.
The separation power of a chromatographic system is classically measured by its peak capacity, defined on the basis of constant
resolution between adjacent peaks. A previously developed statistical theory of the composition of mixtures makes it possible
to extend the concept of peak capacity by taking into account the peak height distribution in typical average chromatograms.
A new parameter, the effective peak capacity, is defined for this purpose on the basis of a constant discrimination factor
between adjacent peaks. It allows to take into account the distribution of peak heights in statistical theories of the evaluation
of complex chromatograms and in the measurement of the limit of determination in quantitative analysis.
The characteristics of the two new parameters, the discrimination factor and effective peak capacity, are discussed and compared
with those of their classical homologs, resolution and peak capacity, in the case of gaussian component peaks of equal widths. 相似文献
27.
The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλmax60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides. 相似文献
28.
周后型 《西南师范大学学报(自然科学版)》1996,(2)
证明了定理设G是一个有限群,p是一个素数,P是G的一个Sylowp-群.那么,G的每一个非线性不可约特征标的次数被p整除当且仅当G有正规p-补,使得Or(G)∩CG(P)为Abel群并且|G:G″|=|P:P′|·|Or′(G)∩CG(P)|还研究了当G有正规p-补时,G的全体线性特征标是如何分配在具有最高亏数的p-块中的. 相似文献
29.
应用数理统计方法,通过建拱坝数据库,确定拱坝体型厚高比,最小体积,最大柔度三个参数的统计模型,并对数座拱坝进行检验,得到比较一致的结果,提供的三个参数可拱设计人员在拟定拱坝体型几何参数和进行型优化设计时参考,并为宏观判断大坝安全性提供对比资料。 相似文献
30.
GUO Junjian FANG Wendong FANG Guohong CHEN Haiying 《科学通报(英文版)》2006,51(B12):1-8
11-year satellite altimeter sea surface height (SSH) anomaly data from January 1993 to December 2003 are used to present the dominant spatial patterns and temporal variations of the South China Sea (SCS) surface circulation through Empirical Orthogonal Function (EOF) analysis. The first three EOF modes show the obvious seasonal variations of SSH in the SCS. EOF mode one is generally characterized by a basin-wide circulation. Mode two describes the double-cell basin scale circulation structure. The two cells were located off west of the Luzon Island and southeast of Vietnam, respectively. EOF mode three presents the mesoscale eddy structure in the western SCS, which develops into a strong cyclonic eddy rapidly from July to September. EOF mode one and mode three are also embedded with interannual signals, indicating that the SCS surface circulation variation is influenced by El Nino events prominently. The strong El Nino of 1997/98 obviously changed the SCS circulation structure. This study also shows that there existed a series of mesoscale eddies in the western SCS, and their temporal variation indicates intra-seasonal and interannual signals. 相似文献