Machine scheme of additive calculation of physicochemical properties of paraffin hydrocarbons

Summary A machine scheme has been developed for the additive calculation of the physicochemical properties of alkanes necessary for mass calculation of the constants and as a supplementation to the automatic chemical information retrieval system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 11, pp. 1985–1988, November, 1964     

A Robust and Efficient Method for the Computation of Equilibrium Composition in Gaseous Mixtures

This paper presents in detail a robust, efficient and accurate methodology for the computation of equilibrium composition in gaseous mixtures. The methodology is founded on the concept of the chemical basis, which is defined and formalized using a powerful matricial approach. The method is specially designed to be general, thus providing basic thermodynamic data in several areas, such as combustion, plasma chemistry and, more generally speaking, computational fluid dynamics. The performance of the method is given in terms of CPU usage and the computed results are compared with those in the published literature. The method is shown to yield results of very high quality in terms of accuracy and smoothness.     

The synthesis of DL-1-(hexadecanoyloxy)methyl- and 1-O-hexadecanoyl-inositols as potential inhibitors of phospholipase C

The synthesis of racemic analogues of phosphatidylinositol (PI) and phosphatidylinositol 4,5-bisphosphate (PIP₂) starting from myo-inositol is described. Inositol derivatives with and without homologalion at C(l) and with and without ionic groups (phosphate or sulfate) at C(4) and C(5) were prepared as well as homologated derivatives with deoxy composition at C(2) and/or C(6). In all these compounds, palmitate ester groups were introduced in place of the diacylglyceryl group of PI or PIP₂.     

Contribution à l'étude du comportement de la catéchine en milieu alcalin

Contribution to the study of the behaviour of catechin in alkaline medium When catechin ( 1 ) is warmed with aqueous alkali it first undergoes rapid epimerisation. After some time a novel bridged carbocyclic enol, catechinic acid ( 3 ) separates out and may be isolated in excellent yield. Eventually catechinic acid isomerises to 2-(3′,4′-dihydroxyphenyl)-3,9-epoxy-6-oxo-bicyclo[3,3,1]-non-7-en-8,9-diol ( 4 ) via an open chain anion ( 5 ) which is also involved in the epimerisation of catechin. Assignments of structure are given and the equilibria observed are discussed.     

On the biological importance of the hydrogen bond breaking potency of fluorocarbons

Fluorocarbons containing higher halogens have the potency of breaking certain hydrogen bonds in solutions. The relative strength of this potency varies in the series F < Cl < Br < I and the presence of hydrogen atoms in the fluorocarbon increases it. There is a striking parallelism between the hydrogen bond breaking and the anaesthetic potency of these molecules. It is suggested that the breaking of hydrogen bonds is an important step in the mechanism of anaesthesia.     

Multiresidue method for simultaneous determination of ten quinolone antibacterial residues in multimatrix/multispecies animal tissues by liquid chromatography with fluorescence detection: single laboratory validation study

Quinolone antibacterials are veterinary drugs authorized for use in food animal production. The analysis of residual amounts of drugs in food from animal origin is important for quality control of products for consumers. For this purpose, Maximum Residue Limits (MRLs) have been set up by a European Union Council Regulation on Veterinary Drug Residues (No. 90/2377/EEC and subsequent), and 8 quinolones received MRLs at concentration levels depending on both the matrix and the animal species of interest. A method was developed for screening and confirming 10 quinolone residues (ciprofloxacin, danofloxacin, difloxacin, enrofloxacin, flumequine, marbofloxacin, nalidixic acid, norfloxacin, oxolinic acid, sarafloxacin) in a wide variety of matrixes of different animal species. It involves extraction of the residues from the biological tissues/fluids by acidic aqueous solution, centrifugation and filtration prior to injection on a C18 narrow-bore column, and detection through a 3-step-mode fluorescence detector. The method was validated during a 2-week study for a set of 8 species-matrixes (i.e., bovine raw milk, bovine muscle, porcine muscle, porcine kidney, porcine liver, fish flesh and skin, poultry muscle, whole egg). Residues were quantified down to 15 microg/kg with limits of detection and quantitation ranging from 4 to 11 and 13 to 36 microg/kg, respectively, which are sufficient compared to the wide range of MRLs set for these substances (from 30 microg/kg for danofloxacin in milk to 1900 microg/kg for difloxacin in poultry liver). The limit of performance of the method in terms of CCalpha and CCbeta, the critical concentrations stated in the Decision No. 2002/657/EC and the ISO Standard No. 11843, has been calculated for the authorized (MRL) substances but only estimated in the case of the nonauthorized (non-MRL) substances.     

Reductive cleavage of axially disymmetric tertiary amines and quaternary ammonium salts by lithium aluminium hydride. Synthesis of new 1,1′-binaphthyl substituted amines

Axially disymmetric tertiary amines or quaternary ammonium salts $\text{A}$ are synthesized by double alkylation of primary or secondary amines with racemic or optically pure 2,2′-bis (bromomethyl)-1,1′-binaphthyl. Their reductive cleavage by lithium aluminium hydride in refluxing THF leads to chiral secondary or tertiary amines $\text{B}$, substituted by a binaphthyl unit, with high yields and absence of racemization.     

Mass-spectrometric behavior of some cyano-substituted 4-(β-chloroethylmercapto)-sym-triazines

Intense [M-Cl]⁺ and [M-CT₂=CCNCl]⁺ ion peaks are characteristic for the mass spectra of 4-(-chloro--cyanoethylmercapto)-sym-triazines. The introduction of monoalkylamino groups into the 2 and 6 positions of the heteroring does not lead to the development of [M-HCl]⁺ ion peaks in the mass spectra or to a change in the characteristic fragmentation pathways.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1270, September, 1982.     

Prediction of chromatographic parameters for some anilines by molecular connectivity

Summary The possible relation existing between R_F values obtained by thin-layer chromatography for a group of anilines with connectivity indices proposed by Kier and Hall has been studied. Using multivariable regression the corresponding connectivity functions, selected for their respective correlation coefficients, standard deviations, Snedecor's F and Student's t were obtained. Regression analysis of the connectivity functions gives a correct prediction of the experimental elution sequence for this group of substances on silica gel stationary phases and various mobile phases of different polarity. The corresponding random and stability studies of the different prediction models selected were carried out, showing good stability and null randomness in all cases.     

Thermochemical properties of benzoic acid derivatives VIII. Enthalpies of combustion and formation of o-, m-, and p- t-butylbenzoic acids

The enthalpies of formation in the crystalline state at 298.15 K of o-, m-, and p-t-butyl-benzoic acids have been determined by static-bomb calorimetry. Vapour-pressure determinations were made by the Knudsen-effusion technique and the sublimation enthalpies at the mean temperatures of the measurement ranges have been derived for the three acids. The values obtained are:

     

[首页] « 上一页 [11] [12] [13] [14] [15] 16 [17] [18] [19] [20] [21] 下一页 » 末  页»

	$\text{ΔH}{}_{\mathrm{f}}{}^{\mathrm{o}}\text{(c, 298.15 K)/kJ mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{s}}\text{/kJ mol}{}^{\mathrm{?1}}$
o-t-butylbenzoic acid	476.2 ± 1.9	99.8 ± 0.4	(at 314.6 K)
m-t-butylbenzoic acid	504.3 ± 1.6	103.0 ± 0.5	(at 326.5 K)
p-t-butylbenzoic acid	502.9 ± 1.7	103.8 ± 0.4	(at 334.1 K)