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31.
32.
A series of four new azulene-1,5-diol diastereomers were prepared and found to exhibit large differences (ΔRf 0.22–0.46) in silica TLC mobilities despite having stereocenters four bonds apart. The stereoisomers were identified by X-ray crystallography, and in all cases the RR/SS diastereomers were less strongly retained than the RS/SR diastereomers. The crystal structures suggested that this is due to a conformational preference for the CF3 groups to be nearly perpendicular to the plane of the azulene ring, which caused the dihedral angle between the OH groups to be larger (in the RR/SS diastereomers) or smaller (in the RS/SR diastereomers). The smaller dihedral angles allow the RS/SR diastereomers to simultaneously bind to a silica surface and thus be more strongly retained. Two similar benzene derivatives and several cycloalkanediols with more proximate stereocenters showed little or no difference in mobilities between diastereomers, though the NMR differences were greater. Thus, the azulene ring is an important factor in enforcing the conformational preferences, either through steric interactions with the 4/8 substituents (H or methyl) or its significant dipole moment, or both. 相似文献
33.
Numerical Algorithms - We will refer to the paper “Convergence rates for Kaczmarz-type algorithms”, published in Numerical Algorithms, 79(1)(2018), 1-17. It was observed by Dr. Mokhtar... 相似文献
34.
Chae Bin Kim Dustin W. Janes Dana L. McGuffin Christopher J. Ellison 《Journal of Polymer Science.Polymer Physics》2014,52(18):1195-1202
The Marangoni effect describes how fluid flows in response to gradients in surface energy. This phenomenon could be broadly harnessed to pattern the surface topography of polymer films if generalizable techniques for programming surface energy gradients existed. Here, a near UV–visible light (NUV–vis) photosensitizer, 9,10‐dibromo‐anthracene (DBA), was doped into thin films of a model polymer, poly(isobutyl methacrylate). After exposure to light through a photomask and heating above the glass transition, thermolysis of photo‐oxidized DBA and grafting to the polymer promoted flow of the film material into the exposed regions. This mechanism did not significantly alter the molecular weight of PiBMA or the film's glass transition temperature, but resulted in an increase in film surface energy as indicated by a decrease in water contact angle. Film height variations of 580 nm were produced using a mask with 12.5 μm features; a mask with 800 nm features was also employed to generate topographic features of corresponding width without expensive contacting equipment. Due to the broad absorbance spectra of DBA, highly accessible and/or unconventional light sources may be employed in this process; this advantage was demonstrated by patterning with sunlight. The nonspecific radical‐mediated nature of the DBA grafting reaction makes this a promising approach for many classes of polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1195–1202 相似文献
35.
The syntheses of boronates derived from the reaction of dioxaborolanes and dioxaborinanes with either organolithium or organomagnesium reagents are investigated along with their subsequent use in the palladium cross coupling reaction. The intrinsic stability of these cyclic esters contributes to their facile reaction with both lithium and magnesium nucleophiles at mild and safe conditions. We have found that many of the reactions proceed at room temperature which is a significant improvement over the traditional routes which require cryogenic temperatures. The scope of these reactions and their practical application to large scale process synthesis is described. 相似文献
36.
Dumitru Popa 《Archiv der Mathematik》2014,103(3):291-300
We use the Maurey–Rosenthal factorization theorem to give a characterization of almost summing and multiple almost summing multilinear operators on a cartesian product of l p spaces. As applications we give the necessary and sufficient conditions for the multiplication operator on l p spaces be almost summing and multiple almost summing. 相似文献
37.
38.
O.M. Lyulin V.I. Perevalov H. Tran J.-Y. Mandin V. Dana L. Rgalia-Jarlot X. Thomas D. Dcatoire 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(17):1815-1824
Using the Fourier transform spectra of the acetylene molecule recorded near 1.5-μm, the intensities of 111 lines belonging to seven hot bands of the main isotopologue 12C2H2 have been retrieved by means of a multispectrum fitting procedure. Considering the density of lines in the spectra, and the fact that the measured bands are the weakest observed, the accuracy of the measurements is around 10%. At first stage, an empirical treatment of these data has been performed, leading to the vibrational transition dipole moment squared and some Herman–Wallis coefficients. Then the measured line intensities of this work and collected ones from the literature have been treated simultaneously within the framework of the effective operator approach. 相似文献
39.
Gheorghe Ilia Adriana Popa Smaranda Iliescu Alina Bora Gheorghe Dehelean Aurelia Pascariu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1513-1519
Some mixed phosphites having two different alkyl chain were obtained as forerunners for mixed phosphates Mixed dialkyl phosphates were obtained in good yields (40-80%) by phase transfer catalysis in liquid-liquid sistem, starting from different dialkyl phosphites and aliphatic alcohols. The reaction conditions were optimized in order to obtain good yields in phosphites and phosphates respectively. Compounds were analyzed by IR, P 31 -NMR. 相似文献
40.
In the present paper, the reaction of chemical immobilization of catalase on a crosslinked macromolecular carrier of a polysaccharide structure (gellan) is studied. The influence of some reaction parameters (enzyme/carrier, activator/carrier ratios, duration) on the activity of enzymatic products is analyzed. The kinetics of the biocatalytic process, stability under different pH and temperature conditions, and the inhibitors effect were studied for the immobilized enzymes. 相似文献