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《Tetrahedron》1987,43(22):5375-5380
Photochemical reactions of hydroxamic acids have been studied. The intermediacy of a RCONH radical is postulated, based on oxidations achieved with DCA under photochemical conditions.  相似文献   

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Braslau R  Axon JR  Lee B 《Organic letters》2000,2(10):1399-1401
[process--see text] A novel chemical ligation process is described that results in the construction of N-hydroxy peptides.  相似文献   

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The relatively strong acidity of hydroxamic acids was analyzed by means of isodesmic reactions in which this acid or its anion is formed from simpler precursors. Acidity of amides was analyzed in the same way. Energies of all compounds involved in the reactions were calculated at the B3LYP/AUG-cc-pVTZ//B3LYP/6-311 + G(d,p) level; at this level a good agreement was reached with the sparse experimental data. Interpretation of the results was the same as in the recent discussion of the acidity of carboxylic acids, and the conclusions were similar: both amides and hydroxamic acids are stabilized with respect to simpler reference molecules of amines or N-alkylhydroxylamines, respectively. However, their anions are stabilized still more and are responsible for the acidity. This effect is stronger in hydroxamic acids or amides than in carboxylic acids. The problem of whether it is due to resonance depends on the definition of this term. Semiquantitative comparison suggests that resonance in hydroxamic acids is more important than in amides and still more than in carboxylic acids. The stronger acidity of hydroxamic acids compared to amides is due to the destabilizing inductive effect of the hydroxyl group in the acid molecule, not to any effect in the anion.  相似文献   

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Stamey TW  Christian R 《Talanta》1966,13(1):144-151
Benzohydroxamic acid is titrated with 0.1M tetrabutyl-anunonium hydroxide in nine non-aqueous solvents with three different indicating electrodes. The best results are obtained using dimethylformamide as solvent and platinum-platinum electrodes. Four monoprotic and three diprotic hydroxamie acids and iron(III) benzohydroxamate have been successfully titrated with this system. The effect of quantitative additions of carbon dioxide to the titrant on its apparent molarity are found to be dependent on the amount added, the strength and sample size of acid titrated and the solvent used.  相似文献   

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Antimicrobial activity of hydroxamic acids   总被引:2,自引:0,他引:2  
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The first O-glycosylation of hydroxamic acids is reported. This process involves the use of glycosyl N-phenyl trifluoroacetimidates as glycosyl donors in the presence TMSOTf and 4 A molecular sieves in dichloromethane. Under such conditions, a wide range of new glycosyl donors including glucosyl, galactosyl, mannosyl, glucuronyl, and ribosyl hydroxamates were prepared in good to high yields. This procedure appears to be an advantageous alternative for the synthesis of glycosyl hydroxamates of biological interest.  相似文献   

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Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The 1H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation.  相似文献   

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The 4s and 5s Rydberg excited states of NaAr(n)* clusters are investigated using a pseudopotential quantum-classical method. While NaAr(n) clusters in their ground state are known to be weakly bound van der Waals complexes with Na lying at the surface of the argon cluster, isomers in 4s or 5s electronically excited states of small NaAr(n)* clusters (n< or =10) are found to be stable versus dissociation. The relationship between electronic excitation and cluster geometry is analyzed as a function of cluster size. For both 4s and 5s states, the stable exciplex isomers essentially appear as sodium-centered structures with similar topologies, converging towards those of the related NaAr(n)+ positive ions when the excitation level is increased. This is consistent with a Rydberg-type picture for the electronically excited cluster, described by a central sodium ion solvated by an argon shell, and an outer diffuse electron orbiting around this NaAr(n)+ cluster core.  相似文献   

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The conformational preferences of a few hydroxamic acids are investigated by the density functional B3LYP/6-311++G**//B3LYP16-31G* and semiempirical AM1 and PM3 methods in this work. It is found that both semiempirical methods give satisfactory results in comparison with sophisticated DFT and ab initio calculations, except for the activation barriers, which are overestimated. Of the two semiempirical methods, while the PM3 method gives better results for relative stabilities, AM1 geometries are in slightly better agreement with the experiments. The keto forms are found to be most stable and the reaction pathways for the interconversion between the keto and enol forms have been deduced. The effect of solvation on the reaction has also been investigated, as has the effect of methyl substitution at the carbon and nitrogen atoms. All the investigated acids exhibit N-acid behavior.  相似文献   

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A new calixarene hydroxamic acid, 5,11,17,23-tetra-(N-p-chlorophenyl hydroxamate c-phenyl-25,26,27,28-tetrahydroxycalix[4]arene (CPCHA) was synthesized and used for the extraction and spectrophotometric determination of uranium(VI). The molar absorptivity of the uranium(VI)-CPCHA-thiocyanate complex was 9.9·103 1·mol–1·cm–1 at 436 nm. The system obeyed Beer's law in the range of 1.78–23.1 ppm of uranium. The uranium(VI)-hydroxamate-ethyl acetate complex was directly aspirated for graphite furnace atomic absorption spectrometry measurements (GFAAS) which increased the sensitivity by about a factor of fifty. Uranium was determined in various standard and environmental samples.  相似文献   

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The structure of CuII complexes with hydroxamic acids Cu[R1N(O)−(O)CR2]2, where R1=Ph, R2=Me; R1=Me, R2=Ph, was studied by ESR spectroscopy. In toluene solutions and low-temperature glasses, the complexes exist as two forms, which were identified ascis-andtrans-isomers. The proportions of the isomers were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 726–729, April, 1999.  相似文献   

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《中国化学快报》2021,32(8):2551-2554
Ynamides are electron-rich alkynes with unique reactivities and act as flexible building blocks in organic synthesis. Therefore, the investigation for transformation of ynamides with exceptional selectivity and efficiency is attractive and interesting. Herein, we report an oxoarylation of ynamides with N-aryl hydroxamic acids. In the presence of catalytic Cu(OTf)2, both the terminal and internal ynamides could undergo an addition/[3,3] sigmatropic rearrangement cascade with N-aryl hydroxamic acids to achieve oxoarylation, along with providing selective entry to (ortho-amino)arylacetamides and oxindoles. Moreover, deuterium-labelling reaction and gram-scale reaction were conducted to probe the mechanism and showcase the scalability.  相似文献   

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A convenient method was developed for obtaining 2-N-hydroxy-3-keto-1-phenyl-1,3-dihydropyrrolo[3,4-b]indoles by reaction of indole-2-hydroxamic acid with substituted benzaldehydes. Complex compounds of trivalent iron salts with cyclic hydroxamic acids were isolated.Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 227–229, February, 1985.  相似文献   

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