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排序方式: 共有315条查询结果,搜索用时 31 毫秒
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Bond IA Budding E Conway MJ Fenton KB Fujii H Fujii Z Fujimoto M Hasegawa H Hayashida N Honda M Hotta N Humble JE Kabe S Kasahara K Kifune T Masaike A Matsubara Y Mitsui K Miura Y Mori M Murakami K Muraki Y Nagano M Nakamura K Nakamura T Norris PM Ohashi Y Okada A Saito T Sakata M Sato H Shibata S Shima M Storey JR Tanimori T Teshima M Torii S Uchino K Watase Y Woodhams MD Yamamoto Y Yock PC Yuda T 《Physical review letters》1988,61(20):2292-2295
3.
Paterno-Buchi coupling, photochemical [2 + 2] cycloaddition, of carbonyl compounds 2a-f with 2-siloxyfurans 1a-d has been investigated in detail. The stereoselective formations of exo-oxetanes 3 and 4 were observed in high yields. The regioselectivity (double-bond selection, 3 vs 4) was found to be largely dependent upon the carbonyls, the substituents at the furan ring, and the excited state of the carbonyls (singlet vs triplet). The photoreaction of aldehydes 2a-c gave bicyclic exo-oxetanes 3 and 4 at regio-random, independent upon their excited states and the substituents at furan ring. However, the photoreaction of the triplet state of ketones 2d-f was found to give regioselectively exo-oxetanes 4, except for the 4-methyl-2-siloxyfurane 1d case. The singlet-excited state of acetone 2f gave both oxetanes 3 and 4 at regio-random. For the singlet-state photochemistry, the approach direction of the electrophilic oxygen of the excited carbonyls to the furan ring is proposed to be an important factor for the exo-stereoselection. The Griesbeck model can rationalize the regio- and exo-selective formation of oxetanes in the triplet-state photoreaction. 相似文献
4.
Allen WH Bond IA Budding E Conway MJ Daniel A Fenton KB Fujii H Fujii Z Hayashida N Hibino K Honda M Humble JE Kabe S Kasahara K Kifune T Lythe GD Masaike A Matsubara Y Mitsui K Miura Y Mori M Muraki Y Nagano M Nakamura T Nishizawa M Morris PM Ogio S Saito T Sakata M Sato H Shimizu HM Spencer M Storey JR Tanimori T Teshima M Torii S Wadsworth A Watase Y Woodhams MD Yamamoto Y Yock PC Yuda T 《Physical review D: Particles and fields》1993,48(2):466-478
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New ring-opening reaction of thiazoline-azetidinones 1 to dithioazetidinones 2 was achieved with 2-benzothiazolyl disulfide in aqueous acidic media and its potentiality for the preparation of a variety of cephalosporins 3 from various thiazoline-azetidinones 1 is demonstrated. 相似文献
7.
The nu(C=O) Raman band frequencies of acetone have been analyzed to separate the contributions of the environmental effect and the vibrational coupling to the gas-to-liquid frequency shifts of this band and to elucidate the changes in these two contributions upon dilution in DMSO. We have measured the frequencies of the nu((12)C=O) band in acetone/DMSO binary mixtures, the nu((13)C=O) band of the acetone-(13)C=O present as a natural abundance isotopic impurity in these mixtures, and both the nu((12)C=O) and nu((13)C=O) bands in the acetone-(12)C=O/acetone-(13)C=O isotopic mixtures at infinite dilution. These frequencies are compared with those of the nu((12)C=O) band in the acetone/CCl(4) binary mixtures measured previously. We have found the following three points: (i) The negative environmental contribution for the nu((12)C=O) oscillator of acetone completely surrounded by DMSO is reduced in magnitude by +5.5 cm(-1) and +7.8 cm(-1) upon the complete substitution of DMSO with acetone and CCl(4) molecules, respectively, indicating the progressive reduction of the attractive forces exerted by the environment on the nu((12)C=O) mode of acetone. (ii) In DMSO and other solvents, the contribution of the vibrational coupling to the frequency of the isotropic Raman nu((12)C=O) band of acetone becomes progressively more negative with increasing acetone concentration up to a value of -5.5 cm(-1), while the contribution to the frequency of the anisotropic Raman band remains approximately unchanged. The only difference resides in the curvatures of the concentration dependencies of these contributions which depend on the relative solute/solvent polarity. (iii) The noncoincidence effect (separation between the anisotropic and isotropic Raman band frequencies) of the nu(C=O) mode in the acetone/DMSO mixtures exhibits a downward (concave) curvature, in contrast to that in the acetone/CCl(4) mixtures, which shows an upward (convex) curvature. This result is supported by MD simulations and by theoretical predictions and is interpreted as arising from the reduction and enhancement of the short-range orientational order of acetone in the acetone/DMSO and acetone/CCl(4) mixtures, respectively. 相似文献
8.
Absorption and photoluminescence (PL) spectra, PL quantum efficiency, and PL lifetime have been investigated on bis(8-hydroxyquinoline)
zinc (Znq2) and magnesium (Mgq2) in solutions and powder. Znq2 and Mgq2 have the lowest-energy absorption band at 376 and 396 nm in acetonitrile solution, respectively, and emission band with peak
at 555 and 480 nm. The PL quantum efficiency is 0.03 and 0.45 for Znq2 and Mgq2 in the solution, respectively, while 0.45 and 0.36 in powder. Unlike the case of powders, two PL lifetimes are obtained in
solutions. The longer lifetime is attributed to molecule having interaction with its neighboring molecule, while the shorter
one to the isolated single molecule. 相似文献
9.
Prof. Dr. Junfeng Yang Yuto Mori Prof. Masahiro Yamanaka Prof. Naohiko Yoshikai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8302-8307
A simple cobalt-diphosphine catalyst has been found to efficiently promote intramolecular cyclization of ortho-cyclopropylvinyl- and cyclopropylidenemethyl-substituted benzaldehydes into benzocyclooctadienone and benzocycloheptadienone derivatives, respectively. This ring-opening hydroacylation likely involves aldehyde C−H oxidative addition, olefin insertion, cyclopropane cleavage by β-carbon elimination, and C−C bond-forming reductive elimination, as was supported by mechanistic experiments and DFT calculations. 相似文献
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