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Friedrich Hammerschmidt 《Monatshefte für Chemie / Chemical Monthly》1991,122(5):389-398
Summary Racemic methyl O-benzyllactate was reduced to the alcohol, transformed into the bromide and reacted with triethylphosphite to give the diethylphosphonate. Removal of protecting groups afforded a phosphonic acid which was purified as its cyclohexylammonium salt. (S)-Ethyl and (R)-isobutyl O-benzyllactate were reduced with LiAlD4 to the corresponding dideuteriated alcohols, which were transformed in the same way as the racemic compound into the chiral (2-hydroxy-[1,1-2H2]propyl)phosphonic acids. The optical purity of alcohols (S)- and (R)-6 b was determined by derivatisation with (+)-MTPA-Cl and1H-NMR-spectroscopy to be 98%. Exchange of the carbonyl-16-oxygen atom of 2-oxopropylphosphonate for oxygen-18 from H2
18O, reduction with NaBH4, deprotection and addition of cyclohexylamine yielded the salt (±)-18 of (2-[18O]hydroxypropyl)phosphonic acid. 相似文献
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Davies SG Rodriguez-Solla H Tamayo JA Cowley AR Concellon C Garner AC Parkes AL Smith AD 《Organic & biomolecular chemistry》2005,3(8):1435-1447
The highly diastereoselective samarium diiodide and D(2)O-promoted conjugate reduction of homochiral (E)- and (Z)-benzylidene and isobutylidene diketopiperazines (E)-5,7 and (Z)-6,8 has been demonstrated. This methodology allows the asymmetric synthesis of methyl (2S,3R)-dideuteriophenylalanine 27 in > or = 95% de and >98% ee, and (2S,3R)- or (2S,3S)-dideuterioleucine-(S)-phenylalanine dipeptides 37 and 38 in moderate de, 66% and 74% respectively. A mechanism is proposed to account for this process. 相似文献
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J. D. Owen 《Acta Crystallographica. Section C, Structural Chemistry》1984,40(2):246-248
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《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1988,44(9):883-887
Electronic excitation in H2O, H2S, H2Se and H2Te molecules has been studied by the EELS technique. Spectra of H2S and H2Se are remarkably similar with the 1b1-nd transition most intense. The intensity of the first transition 1b1-nsa1 decreases through H2O to H2Se and this transition is absent in H2Te. Transitions observed by EELS have been compared with optical absorption studies. A correlation diagram of the occupied and the excited states has been provided for these four molecules by making use of UVPES and EELS. 相似文献
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Absorption of oxygen molecules by water clusters with sizes of 10 ≤ i ≤ 50 is studied by the molecular dynamics method using the modified TIP4P model. It is revealed that the total dipole moment
of the clusters nonmonotonically increases with their sizes. Absorption of O2 molecules tends to raise the static permittivity of the ultradispersed medium formed by the clusters. The real and imaginary
parts of the permittivity of water clusters with absorbed O2 molecules are aperiodic functions of frequency. The permittivity components turn out to be nonmonotonic functions of cluster
sizes. The IR absorption and reflectance spectra are calculated for clusters of pure water and aggregates with absorbed O2 molecules. After the addition of oxygen molecules, the absorption coefficient of the clusters decreases, while the reflection
coefficient increases. It is concluded that the capture of oxygen molecules by atmospheric moisture may reduce the greenhouse
effect.
Original Russian Text ? A.E. Galashev, V.N. Chukanov, O.A. Galasheva, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68,
No. 2, pp. 155–160. 相似文献