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61.
[reaction: see text] The title reactions, in 44 wt % ethanol-water at 25.0 degrees C, exhibit slightly curved Br?nsted-type plots (log kN versus pKa of amines) with slopes beta1 = 0.1-0.44 (at high pKa) and beta2 ca. 0.7 (at low pKa). The magnitude of some of these slopes, together with the fact that the curvature center (pKa(0) = 9.5-10.8) does not change with the electronic effects of the benzoyl substituent, suggests that these reactions are not stepwise, but concerted. 相似文献
62.
Geciane Toniazzo Débora de Oliveira Cláudio Dariva Enrique Guillermo Oestreicher Octávio A. C. Antunes 《Applied biochemistry and biotechnology》2005,123(1-3):837-844
The main objective of this work was to investigate the biotransformations of (−)α-pinene, (−)β-pinene, and (+) limonene by
Aspergillus niger ATCC 9642. The culture conditions involved—concentration of cosolvent (EtOH), substrate applied, and sequential addition
of substrates—were investigated. Adaptation of the precultures with small amounts of substrate was also studied. The experiments
were performed in conical flasks with liquid cultures. This strain of A. niger was able to convert only (−)β-pinene into α-terpineol. An optimum conversion of (−)β-pinene into α-terpineol of about 4%
was obtained when the substrate was applied as a diluted solution in EtOH and sequential addition of substrate was used. 相似文献
63.
Enantioselective addition of aryllithium reagents to aromatic imines mediated by 1,2-diamine ligands
A variety of optically enriched amines have been obtained by addition of aryllithium reagents to aromatic imines using N,N′-tetramethylcyclohexane-1,2-diamine as chiral ligands. Enantiomeric excesses up to 90% could be obtained. 相似文献
64.
[reaction: see text] The temperature dependence of the dissociation of dimers formed from highly stabilized carbon-centered radicals has been examined. Analysis of the data yields the bond dissociation energy (BDE) for the central head-to-head C-C bond in these compounds. For example, for the dimer derived from 3-phenyl-2-coumaranone, BDE is 23.6 kcal/mol and the C-C bond length 1.596 A, a rather long value for a sigma bond. 相似文献
65.
The infrared and laser-Raman spectra of crystalline Mg3(VO4)2 are reported and a factor group analysis for the full lattice is presented to support the discussion. The 1,000 to 600 cm?1 region of the spectrum is essentially related to internal (stretching) modes of the greatly distorted VO4 tetrahedra, whereas the bands in the low frequency region must be assigned to complex vibrations originating in the interaction of the bending vibrations of the tetrahedral groups with the external modes. 相似文献
66.
Blanco JM Caamaño O Fernández F Rodríguez-Borges JE Balzarini J de Clercq E 《Chemical & pharmaceutical bulletin》2003,51(9):1060-1063
Six new carbocyclic nucleosides were prepared by constructing a purine base (in compounds 9-11) or pyrimidine base (in 6-8) on the amino groups of (+/-)-(1 beta,2 alpha,4 beta)-4-amino-1,2-cyclopentanedimethanol (4) and (+/-)-(1 beta,3 alpha,4 beta)-4-amino-1,3-cyclopentanedimethanol (5), and their activities against a variety of viruses and tumour cell lines were determined. 相似文献
67.
The infrared andRaman spectra of the tittle compound have been recorded and an assignment for the internal vibrations of the H2S2I2O
14
4–
polyanion is proposed. The thermal behaviour was investigated using TG-, DTA-, IR- and X-ray methods; it is shown that the polyanion breaks down after the release of one mole of H2O, generating a mixture of -K2SO4 and I2O5. 相似文献
68.
Cabaleiro-Lago EM Rodríguez-Otero J Varela-Varela SM Peña-Gallego A Hermida-Ramón JM 《The Journal of organic chemistry》2005,70(10):3921-3928
[reactions: see text] Electrocyclization reactions of (3Z)-1,3,5-hexatrienone and nitrogen derivatives were studied by performing density functional theory (DFT) calculations together with the 6-31+G* basis set. Reactants, products, and transition states for each reaction were localized and the IRC connecting reactants and products was also obtained. Magnetic properties were evaluated along the reaction path to elucidate the characteristics of the reactions studied. As obtained from the calculations, electrocyclization of (3Z)-1,3,5-hexatrienone is a pericyclic process, as indicated by a variety of indexes, such as Nucleus Independent Chemical Shift (NICS), anisotropy of the magnetic susceptibility, or anisotropy of the current-induced density (ACID). This reaction presents characteristics of pericyclic reactions despite the activation energy lowering relative to the electrocyclization of (4Z)-1,2,4,6-heptatetraene, and the relatively small NICS values observed in the transition state. Magnetic properties indicate that an enhancement of the aromaticity relative to reactants and products occurs revealing the absence of orbital disconnections on the cyclic loop of interacting orbitals. Only two reactions among those studied exhibit pseudopericyclic character due to the in-plane attack of the lone pair on nitrogen. In these cases, the reactions showed no barrier for the electrocyclization process, and no aromaticity enhancement was observed. 相似文献
69.
Frank W. Vergeer Taasje Mahabiersing Enrique Lozano Diz Georg Süss-Fink František Hartl 《Journal of Cluster Science》2004,15(1):47-59
Electrochemical and photochemical properties of the tetrahedral cluster [Ru3Ir(
3-H)(CO)13] were studied in order to prove whether the previously established thermal conversion of this cluster into the hydrogenated derivative [Ru3Ir(-H)3(CO)12] also occurs by means of redox or photochemical activation. Two-electron reduction of [Ru3Ir(
3-H)(CO)13] results in the loss of CO and concomitant formation of the dianion [Ru3Ir(
3-H)(CO)12]2–. The latter reduction product is stable in CH2Cl2 at low temperatures but becomes partly protonated above 283K into the anion [Ru3Ir(-H)2(CO)12]– by traces of water. The dianion [Ru3Ir(
3-H)(CO)12]2– is also the product of the electrochemical reduction of [Ru3Ir(-H)3(CO)12] accompanied by the loss of H2. Stepwise deprotonation of [Ru3Ir(-H)3(CO)12] with Et4NOH yields [Ru3Ir(-H)2(CO)12]– and [Ru3Ir(
3-H)(CO)12]2–. Reverse protonation of the anionic clusters can be achieved, e.g., with trifluoromethylsulfonic acid. Thus, the electrochemical conversion of [Ru3Ir(
3-H)(CO)13] into [Ru3Ir(-H)3(CO)12] is feasible, demanding separate two-electron reduction and protonation steps. Irradiation into the visible absorption band of [Ru3Ir(
3-H)(CO)13] in hexane does not induce any significant photochemical conversion. Irradiation of this cluster in the presence of CO with
irr>340nm, however, triggers its efficient photofragmentation into reactive unsaturated ruthenium and iridium carbonyl fragments. These fragments are either stabilised by dissolved CO or undergo reclusterification to give homonuclear clusters. Most importantly, in H2-saturated hexane, [Ru3Ir(
3-H)(CO)13] converts selectively into the [Ru3Ir(-H)3(CO)12] photoproduct. This conversion is particularly efficient at
irr
>340nm. 相似文献
70.
Prof. Dr. Enrique J. Baran Irma L. Botto 《Monatshefte für Chemie / Chemical Monthly》1977,108(4):781-790
The infrared spectra of the title compounds, as well as that of the structurally related mineral meta-autunite, [Ca(UO2)2(PO4)2·n H2O], are reported and discussed using the available crystallographic data. The results can be considered as representative for the full group of the so-called torbernite-minerals. 相似文献