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31.
32.
Vinylversatate-10 (VV10)1 has successfully been used to synthesise a large number of lower vinyl esters by transvinylation in presence of mercuric acetate and sulfuric acid. The synthesis of vinylhalo esters proceeds with more difficulty. It has been observed that neither Hg(OAc)2 nor H2SO4 alone is capable of initiating the transvinylation. Furthermore, it has been found that a molar ratio 2:1 of VV10 to carboxylic acid is sufficient to drive the reaction to the right by continuous distillation of the vinyl ester formed, and as a result a high yield of vinyl ester is obtained. A mechanism for this reaction and for the formation of side products has been proposed. 相似文献
33.
Simultaneous
measurement of gamma-rays and neutron fluences</p>
using
a HPGE detector</o:p></p>
</p>
Z. B. Alfassi T. Zlatin U. German 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):237-241
Summary A
simultaneous determination of gamma and neutron fluences in a mixed neutron +
gamma field can be achieved by gamma-ray spectrometry, optimizing the
moderator-converter-detector assembly and measuring both the direct gamma-lines
and the neutron induced prompt gammas. For the prompt gamma-lines a combination
of high efficiency and low background is the goal, and it can be best achieved
if the gamma-energy is in the range above about 1 MeV up to 2.5 MeV. The
optimal moderator-converter thickness can be determined experimentally. Most
converter elements produce gamma-rays in the low energy range. If chlorine is
used as a converter, the 1164.7 keV peak and the 1950-1960 keV peaks seems to
be a good choice. A very practical material containing chlorine is PVC. It is
an efficient moderator, it is solid, common, and can be handled easily.</p>
</p> 相似文献
34.
V. M. Rogovik N. I. Delyagina A. F. Aérov V. F. Cherstkov S. R. Sterlin L. S. German 《Russian Chemical Bulletin》1992,41(3):561-565
Fluorine-containing ,-fluorosulfatocarbonyl compounds interact with halides of alkali metals with the formation of -halogeno--dicarbonyl derivatives.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 177813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 715–719, March, 1992. 相似文献
35.
36.
P. Molina Ma. J. Vilaplana P. L. Andreu J. Mller 《Journal of heterocyclic chemistry》1987,24(5):1281-1284
N-Aryl-N-(α-phenylphenacyl)oxamoyl chlorides react with N3-arylsubstituted amidrazones to give functionalized 1,2,4-triazoles which undergo ring-closure by the action of thionyl chloride to give 1,2,4-triazolo[1,5-a]-pyrazinium chlorides in excellent yields. 相似文献
37.
Conclusions The isomerization of perfluoro-1-pentene by CsF in polar aprotic solvents leads to a mixture of trans- and cis-perfluoro-2-pentene in an isomer ratio of 61.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2646–2647, November, 1981. 相似文献
38.
Pedro Molina Angeles Lorenzo Rosa Ma Claramunt José Elguero 《Tetrahedron letters》1984,25(47):5427-5428
A number of mesoionic compounds derivatives of the bicyclic system 1,2,4-triazolo(4,3-b)-1,2,4-triazole have been prepared from 4-amino-1-methyl-3,5-bis(methylthio)-1,2,4-triazolium iodide and aryl isothiocyanates. 相似文献
39.
Pablo A. Molina R. Steven Sikorski Jan H. Jensen 《Theoretical chemistry accounts》2003,109(3):100-107
The relationship between hydrogen bonding and NMR chemical shifts in the catalytic triad of low-pH α-chymotrypsin is investigated
by combined use of the effective fragment potential [(2001) J Phys Chem A 105:293] and ONIOM–NMR [(2000) Chem Phys Lett 317:589] methods. Our study shows that while the His57 Nδ1−H bond is stretched by a relatively modest amount (to about 1.060 ?) this lengthening, combined with the polarization due
to the molecular environment, is sufficient to explain the experimentally observed chemical shifts of 18.2 ppm. Furthermore,
the unusual down-field shift of Hɛ1 (9.2 ppm) observed experimentally is reproduced and shown to be induced by interactions with the C=O group of Ser214 as previously
postulated. The free-energy cost of moving Hδ1 from His57 to Asp102 is predicted to be 5.5 kcal/mol.
Received: 26 September 2001 / Accepted: 6 September 2002 / Published online: 21 January 2003
Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American
Chemical Society, 2001
Correspondence to: J. H. Jensen e-mail: jan-jensen@uiowa.edu
Acknowledgements. This work was supported by a Research Innovation Award from the Research Corporation and a type G starter grant from the
Petroleum Research Fund. The calculations were performed on IBM RS/6000 workstations obtained through a CRIF grant from the
NSF (CHE-9974502) and on supercomputers at the National Center for Supercomputer Applications at Urbana-Champaign. The authors
are indebted to Visvaldas Kairys for help with the CHARMM program, and to Daniel Quinn for many helpful discussions. 相似文献
40.
S. D. Chepik V. F. Cherstkov E. I. Mysov A. F. Aérov M. V. Galakhov S. R. Sterlin L. S. German 《Russian Chemical Bulletin》1991,40(11):2285-2291
An unusual electrophilic cyclization of fluorine-containing carbonyl compounds and -oxides was discovered. Upon the action of SbF5, perfluorinated ketones, diketones, and -oxides isomerize to oxolanes. This reaction proceeds with the obligatory participation of the terminal CF3 group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2611–2618, November, 1991. 相似文献