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951.
Solid-state 17O NMR spectra were obtained at 4.70, 11.75 and 19.60T for potassium hydrogen [17O(4)]dibenzoate (PHB) under both magic-angle spinning and stationary conditions. Spectral analyses yielded both the magnitude and orientation of the 17O chemical shift (CS) tensor and the electric field gradient (EFG) tensor for each of the two chemically distinct oxygen sites in PHB. For the oxygen site that is not involved in hydrogen bonding, the experimental 17O NMR tensors are: delta(iso)=287+/-2 ppm, delta(11)=470+/-5 ppm, delta(22)=380+/-5 ppm, delta(33)=10+/-5 ppm, C(Q)=8.30+/-0.02 MHz, eta(Q)=0.23+/-0.05, alpha=0+/-5 degrees, beta=90+/-5 degrees, and gamma=30+/-5 degrees. For the oxygen site in the short O...H...O hydrogen bond, the experimental 17O NMR tensors are: delta(iso)=213+/-2 ppm, delta(11)=370+/-5 ppm, delta(22)=190+/-5 ppm, delta(33)=80+/-5 ppm, C(Q)=5.90+/-0.02 MHz, eta(Q)=0.55+/-0.05, alpha=5+/-5 degrees, beta=90+/-5 degrees, and gamma=90+/-5 degrees. Extensive quantum mechanical calculations at both restricted Hartree-Fock and density functional theory levels were performed to investigate the effects of an effectively symmetrical O...H...O hydrogen bond on 17O CS and EFG tensors. 相似文献
952.
953.
Treatment of a mixture of a terminal alkyne and an aldehyde with CrCl(2) and a catalytic amount of NiCl(2) and triphenylphosphine in the presence of water in DMF at 25 degrees C gives a 1,2-disubstituted allylic alcohol regioselectively. 相似文献
954.
Takatori K Nakayama M Futaishi N Yamada S Hirayama S Kajiwara M 《Chemical & pharmaceutical bulletin》2003,51(4):455-457
Robinson annulation on alumina occurred efficiently on heating with microwave irradiation. 相似文献
955.
956.
Hideo Fujita Yasuo Deguchi Hiroaki Ohya-Nishiguchi Kazuhiko Ishizu 《Magnetic resonance in chemistry : MRC》1981,16(3):245-246
The ENDOR spectrum was obtained for the benzo[c]cinnoline anion radicalin 1,2-dimethoxyethane. The hfs constants of the protons correspond with those found by EPR spectroscopy, and also agree well with the qualitative tendency of the reported spin density distributions by HMO calculation. 相似文献
957.
Reaction of acetaldehyde with the trianion of 4,6-dimethylnonane-3,5,7-trione followed by acidification yielded a stereoisomeric mixture of stegobinone, the pheromone of Stegobium paniceum L. Acylation of the dianion derived from 4-methylheptane-3,5-dione with a mixed anhydride prepared from (2R, 3S)-3-hydroxy-2-methylbutanoic acid or its enantiomer led to (2S,3R,7RS)- or (2R, 3S, 7RS)-stegobinone. The natural pheromone possesses (2S,3R)-stereochemistry. 相似文献
958.
959.
Kazuhiko Seki Ulf O. Karlsson Rainer Engelhardt Ernst-Eckhard Koch Werner Schmidt 《Chemical physics》1984,91(3):459-470
Ultraviolet photoelectron spectra were measured of solid sexiphenyl with synchrotron radiation and of gaseous polyphenyls from biphenyl to sexiphenyl with a Hel light source. The similarity of the spectrum of the solid with the XPS spectrum of poly(p-phenylene) (PPP) shows the usefulness of sexiphenyl as a model compound of PPP. Examination of the fine structure observed in the low binding-energy region clearly shows how the electronic structure of the p-phenylenes evolves from that of benzene including the effects of deeper levels and of the non-planarity of the molecular geometry. The experimental E = E(k) energy band-dispersion relation of a PPP chain can be deduced by giving each energy level of the oligomers an appropriate k value. An extrapolation for the total bandwidth and the threshold photoemission energy of solid PPP yields 3.95 and 5.65 eV. respectively. 相似文献
960.
Gamma rays emitted in the decay of 147Nd have been studied using Ge(Li) detectors as singles and coincidence spectrometers. Four new γ-rays of 53.1, 81.15, 149.4 and 191.24 keV have been detected and all incorporated into the decay scheme. Angular correlation measurements for the 275–319, 275–411 and 272–408 keV cascades have yielded the following result: A2(275–319) = 0.006(2), A4(275–319) = 0.005(5), A2(215–411) = ?0.013(17), A4(275–411) = ?0.008(30), A2(272–408) = ?0.283(10) and A4(272?408) = 0.015(18). From these coefficients the E2/M1 mixing ratios of the 272 and 275 keV γ-transitions have been determined to be 0.10(3) and 0.107(7), respectively, and the spin of the 680.43 keV level to be . Theoretical calculations on the intermediate coupling model for harmonic and anharmonic potential functions have been carried out and better agreement with experiment has been obtained for the anharmonic potential function. 相似文献