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Reaction of oxiranes with alkali metals in aprotic solvents yields a variety of products depending on the nature of the metal and the structure of the oxirane. Deoxygenation to olefins is the major reaction in case of lithium. Rearrangement to carbonyl compounds, reduction to alcohols and formation of dimeric products occur when oxiranes are treated with sodium. All the reactions could be rationalised by a mechanism involving an initial single electron transfer leading to the formation of a radical-anion intermediate.  相似文献   
2.
Mono-, di-, tri- and tetra-substituted epoxides undergo facile deoxygenation yielding olefins when treated with lithium in tetrahydrofuran. Aliphatic epoxides yield olefins with the same stereochemistry as the parent compound.  相似文献   
3.
tert-Beta-bromo alcohols, derived from simple monoterpene hydrocarbons, react with zinc sulfide in dimethyl sulfoxide to afford saturated ketones as the major and hydroxy ketones as the minor products. The reaction involves initial nucleophilic attack by DMSO on the carbon attached to the halogen, which is assisted by electrophilic zinc sulfide. Subsequent Kornblum type oxidation yields the alpha-hydroxy ketone. On the other hand, abstraction of proton beta to the hydroxyl group followed by an attack of the neighboring hydroxyl moiety on the sulfur of the dimethylsulfoxonium intermediate and its subsequent collapse yields an enol, which tautomerizes to a saturated ketone. The latter pathway is predominantly followed.  相似文献   
4.
The study details the investigations on the ability of Lactobacillus plantarum CFR 2194, an isolate from kanjika, a rice-based ayurvedic fermented product, to produce biosurfactant. Surfactant production, as a function of fermentation time, indicates that the maximum production occurred at 72 h under stationary conditions. Isolation, partial purification, and characterization of the biosurfactant produced have been carried out, and Fourier transform infrared spectroscopy (FTIR) spectra demonstrated that biosurfactants were constituted by protein and polysaccharide fractions, i.e., possessed the structure typical of glycoprotein, which is affected by the medium composition and the phase of growth of the biosurfactant-synthesizing strain. Critical micelle concentration (cmc) of the biosurfactant was found to be 6 g l?1. The emulsification index (EI), emulsification activity (EA), and emulsion stability (ES) values of the biosurfactant have confirmed its emulsification property. Aqueous fractions of the produced biosurfactant exhibited a significant antimicrobial activity against the food-borne pathogenic species: Escherichia coli ATCC 31705, E. coli MTCC 108, Salmonella typhi, Yersinia enterocolitica MTCC 859, and Staphylococcus aureus F 722. More importantly, the biosurfactant from L. plantarum showed antiadhesive property against above food-borne pathogens. The results thus indicate the potential for developing strategies to prevent microbial colonization of food contact surfaces and health-care prosthesis using these biosurfactants.  相似文献   
5.
Morellic and isomorellic acids (2 and 3), present in the seed coat as well as resinous exudate of Garcinia morella Desr., are geometric isomers and structurally related to morellin (1), the major chromenoxanthone pigment. Both form crystalline complexes with pyridine and afford guttiferic acid (7), a novel skeletal rearrangement product, when heated with mild alkali. Structure of the latter has been deduced mainly by a comparative study of 1H and 13C NMR spectra of methyl morellate (5), methyl-O-methyl morellate (6), guttiferic acid (7) and dimethyl guttiferate (8).  相似文献   
6.
Tertiary alkyl halides undergo facile substitution reactions under solvolytic conditions in presence of zinc ions yielding alcohols, ethers and esters.  相似文献   
7.
N-heterocyclic carbenes (NHCs) have been established to be effective organocatalysts for facilitating the benzoin condensation and many other reactions. These reactions involve the formation of a Breslow intermediate (BI), which exhibits umpolung chemistry. To facilitate organocatalysis, several new cyclic carbenes are being introduced, four-membered NHCs are of special interest. Whether these NHCs can exhibit catalytic influence or not, can be evaluated by exploring the potential energy surface (PES) of the benzoin condensation reaction. Quantum chemical analysis has been carried out to compare the PES of these four-membered NHCs with that of standard five-membered NHCs to explore their catalytic ability. The barrier for the first step of the reaction for the formation of BI is comparable in all the cases. But the barrier for the second step of the reaction leading to the benzoin formation from BI is estimated to be very high for the four membered NHCs. These results indicate that the probability of identifying and isolating the BI is very high in comparison to the completion of benzoin condensation reaction in the case of the four-membered NHCs.  相似文献   
8.
Reaction of allylic, benzylic and tertiary alkyl halides with zinc oxide in protic solvents leads to the formation of the corresponding alcohol, ethers and esters in good yields. The scope and limitations of this reaction have been examined. The possible involvement of ion quadruplets in the reaction is suggested.  相似文献   
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