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11.
13C- and 1H-NMR. spectra of ortho-benzoquinone 1 and its methyl derivatives have been analysed. By means of heteronuclear double resonance experiments it is shown that assignments given in the literature for the olefinic carbon resonances of 1 and of a series of substituted ortho-benzoquinones have to be inverted. 13C-carbonyl frequencies of various six-membered cyclic ketones are presented. 相似文献
12.
Jean Ravez Re´gnault Von Der Mu¨hll Paul Hagenmuller 《Journal of solid state chemistry》1975,14(1):20-24
Au sein d'un re´seau de type BaFeF5 des chai?nes d'octae`dres fluore´sa`sommets communs peuvent disparai?tre en donnant naissance a des canaux dont l'occupation partielle ou totale par des files de cations Sr2+ et de couples d'anions F?, conduit respectivement aux phases Sr3(FeF6)2 ou Sr5T3F19 (T = Cr, Co, Ga). Une discussion cristallochimique permet d'expliquer l'existence d'un domaine de solutions solides au sein du diagramme ternaire SrF2BaF2FeF3. 相似文献
13.
The cyclodehydration of N-[heleroarylcarbamoyl)methyl]benzamides was found to yield 5-(heteroarylamino)oxazoles 相似文献
14.
15.
Yan B Collins N Wheatley J Irving M Leopold K Chan C Shornikov A Fang L Lee A Stock M Zhao J 《Journal of combinatorial chemistry》2004,6(2):255-261
We have developed a high-throughput purification system to purify combinatorial libraries at a 50-100-mg scale with a throughput of 250 samples/instrument/day. We applied an accelerated retention window method to shorten the purification time and targeted one fraction per injection to simplify data tracking, lower QC workload, and simplify the postpurification processing. First, we determined the accurate retention time and peak height for all compounds using an eight-channel parallel LC/UV/MS system, and calculated the specific preparative HPLC conditions for individual compounds. The preparative HPLC conditions include the compound-specific gradient segment for individual compounds with a fixed gradient slope and the compound-specific UV or ELSD threshold for triggering a fraction collection device. A unique solvent composition or solvent strength was programmed for each compound in the preparative HPLC in order to elute all compounds at the same target time. Considering the possible deviation of the predicted retention time, a 1-min window around the target time was set to collect peaks above a threshold based on UV or ELSD detection. Dual column preparative instruments were used to maximize throughput. We have purified more than 500 000 druglike compounds using this system in the past 3 years. We report various components of this high-throughput purification system and some of our purification results. 相似文献
16.
R.E. Benner K.U. Von Raben K.C. Lee J.F. Owen R.K. Chang B.L. Laude 《Chemical physics letters》1983,96(1):65-69
Raman scattering from Pt(CN)42? adsorbed on Pt colloids (average diameter of 16 A) is compared with the Raman signal from the same amount of Pt(CN)42? in solution. The wavelength dependence of the adsorbate Raman intensity is measured from 308 to 647 nm and compared with a Lorenz/Mie calculation of the enhancement factor for the electromagnetic field intensity on the surface of a Pt sphere as a function of sphere radius and incident wavelength. 相似文献
17.
Microchimica Acta - Eine empfindliche spektrophotometrische Methode zur Bestimmung von Kupfer mit Salicyls~iure wurde beschrieben (Molarextinktion ε = 2,4 · 9 105). Die nachweisbaren... 相似文献
18.
The valence ionization potentials (IP's) of cyclopentadiene and 1-sila-cyclopentadiene-(2,4) are studied by an ab initio many-body approach which includes the effect of electron correlation and reorganization beyond the Hartree-Fock approximation. The Hartree-Fock approximation gives the correct ordering of the IP's for cyclopentadiene but this ordering does not agree with the results of the previous experimental and theoretical studies. The ordering is 1a2(π), 2b1(π), 4b2, 6a1, 5a1, 3b2, 1b1 (π), 4a1, 2b2, 3a1. For sila-cyclopentadiene the ordering of the IP's is: 1a2(π), 4b2, 2b1(π), 6a1, 1b1(π), 5a1, 3b2, 4a1, 3a1, 2b2. The Hartree-Fock approximation is found to be incorrect with respect to the ordering of the 4b2 and 2b1(π) IP's. A number of one-electron properties are calculated in the one-particle approximation and compared with the available experimental data. 相似文献
19.
Ab initio molecular orbital structures and energies of B2F4, B2Cl4, N2O4, and C2O have been calculated for both perpendicular D2d and planar D2h rotamers. The experimental trend toward greater preference for the D2d forms in going from B2F4 to B2Cl4 is reproduced. N2O4 favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B2F4, hyperconjugation for B2Cl4, lone-pair interactions for N2O4, and electrostatic repulsions for C2O. 相似文献
20.
At low temperatures, the broad excimer fluorescence band of α-perylene crystals is replaced by a weakly structured emission at higher energy. This emission originates from a new crystal state (Y-state) which is populated independently of the high temperature excimer (E-state). Due to the temperature dependence of its first order decay rate and due to the thermally activated formation of the E-state, the Y-emission grows rapidly at temperatures below 90 K. The Y-emission differs from the fluorescence of the monomeric β-perylene at 5.5 K by its Stokes shift of 1300 cm?1, the lack of vibronic structure, the long first order decay time of 40 ns and the absence of bimolecular annihilation indicating a localized state. The Y-state is attributed to a less relaxed pair state formed upon contraction of the dimeric crystal lattice. 相似文献