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1.
Summary Two different methods were used to determine the separation factor at different temperatures and the Gibbs-Helmholtz parameters ((H), (S)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of ln versus 1/T. We first studied each factor (fraction of water in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes in (H) and (S) in relation to a volume fraction of water in an ACN/water mixture were examined. In the ACN/water system, (H) was fairly constant in the acetonitrile region of 0.52 and appears to be a roughly linear function of for 0.52. In this system (S) is approximately a parabolic function of with an optimum at 0.52. The retention mechanism of ten benzodiazepines was found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44°C gave the most efficient separation conditions in the ACN/water mixture.  相似文献   

2.
Summary Gas chromatographic retention of cyclohexane and benzene on microcolumns packed with silica-based materials for liquid chromatography has been investigated to elucidate the relationship with the surface properties of the packing materials. Differences in capacity factors (k) for these two hydrocarbons were related to the surface area of the packing materials. For untreated silica gels, the k value increased with increasing total surface area of the column employed and measurement of k for chemically-bonded stationary phases allowed estimation of accessible residual silanol groups.  相似文献   

3.
Enthalpies of protonation of polyacrylates and polymethacrylates with different molecular weights in aqueous NaCl solutions, 0 I 2 mol-L–1 were determined by titration calorimetry at 25°C. H values are dependent on both the neutralization degree, , and the molecular weight of polyacids. T S of protonation was obtained using pK values already reported and the present H results. Empirical equations for the dependence on I, , and molecular weight are reported for both H and T S.  相似文献   

4.
Second order rate constants and activation parameters H, S, and V have been measured for the oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82– and by IO4– in highly aqueous H2O – t-BuOH mixtures. The changes in solvation on going from the initial to the transition state are discussed on the basis of the transfer functions Gto, Hto and Sto. Whereas Gt changes smoothly as the proportion of t-BuOH increases, the plots of Ht and TSt exhibit mirror behaviour and pass through extrema located around x2(t- BuOH)=0.038. Information on the role of solvation is complemented by the determination of activation volumes. These are discussed in terms of intrinsic and solvational contributions. It is proposed that changes in hydrophobic hydration are of principal importance in determining the response of H, S, and V to changes in solvent composition in H2O – t-BuOH mixtures.  相似文献   

5.
Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke.  相似文献   

6.
The frequency shifts of the O-H stretching modes and the resonance components R of these shifts in the IR spectra of H-complexes of phenol with thiophene derivatives having organic and organosilicon substituents have been analyzed. Relationship of and R parameters to values calculated by nonempirical methods that characterize the electronic effect of organic substituents on the effective charges of the thiophene ring atoms has been established. It has been shown that in the complexation of phenol (hard acid) with thiophene derivatives charge control prevails over frontier orbital control. The changes in the effective charges of the thiophene ring atoms due to the effect of organosilicon substituents have been calculated.For the previous publication of this series see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2163–2168, December, 1994.This work was supported by the Russian Foundation for Basic Research, Project No. 93-03-18725.  相似文献   

7.
The oxime of 5-pregnen-3-ol-20-one reacts with acetylene in the KOH-DMSO system to form a mixture of products containing 3-vinyloxy-17-(1-vinyl-2-pyrrolyl)-5-androstene as the major product (63% yield) and also the O-vinyloxime of 3-vinyloxy-5-pregnen-20-one (10%), 3-vinyloxy-17- and 3-vinyloxy-17-5-pregnen-20-one (25%, 1:4 ratio).  相似文献   

8.
The isomerization of eugenol to isoeugenol was investigated by employing catalysis by KOH in amyl alcohol or glycerol, or by RhCl3. A number of factors which affect the reaction (solvent, temperature, molar ratios, presence of water) were examined.
(KOH ) (RhCl3). , (, , , ).
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9.
It is shown that the CH acidity of di- and trisubstituted methanes can be studied using the ap- proaches consisting in singling out the contributions of physically significant factors from the overall acidification mechanisms in the gas phase and in solution. This procedure implies formal decomposition of the calculated gas-phase deprotonation energy Edeprot into the following terms: electrostatic energy of proton detachment from the acid CH bond, with the state of the remainder of the molecule absolutely unperturbed (E 1); electronic relaxation energy of the resulting molecular residue and formation of a virtual carbanion therefrom (E 2); the Edeprot component due to displacement of the atomic nuclei on changing from the virtual to real carbanion E 3. Relationships between the energy components E 1, E 2, E 3, and the commonly used characteristics of the molecular structure were investigated. The parameter E 1 is selectively sensitive to the inductive effect of the substituent. Imperfect correlation between E 1 and the sum of the I constants can be due to the fact that the contributions to the I constants from the effective charge on the hydrogen atom of the CH bond being deprotonated and from the polarizabilities of the substituents are not taken into account. In contrast to monosubstituted methanes, in di- and trisubstituted methanes there is no correlation between the E 2 component and the 1 J(13CH) constants. The linear dependence linking the sums of the components E 1 + E 2 and the pyramidal angle in the carbanions is responsible for the relaxation nature of the effects associated with the E 2 + E 3 sum. Comparison of the data obtained with the calculated patterns of redistribution of the effective charges on atoms accompanying conversion of CH acids to carbanions enabled elucidation of the relative contribution of each of the components, E 2 and E 3, to the deprotonation energy of selected groups of substituted methanes. The previously developed technique of separating the energy of protolytic equilibrium in the gas from that of solvation processes in solution enabled assessment of the contributions from electrostatic solvation to pK a in DMSO. The same technique of singling out the solvation component due to intermolecular hydrogen bonds from pK a(H2O) was used in studying the acid-base equilibria for substituted methanes in aqueous solution. It was shown that the solvation effects manifested in the liquid-phase CH acidity can be modeled by the effects revealed for analogous hydrogen bonds of ion-molecule complexes in the gas phase. The relationships between the strength of hydrogen bonds and the CH-acidic properties of compounds in the gas phase and liquid water are similar.  相似文献   

10.
Summary Using a rapid chemometric methodology to determine the separation factor, , at different temperatures, Gibbs Helmholtz parameters ( (H), (S), (G)) of two adjacent benodiazepines on a chromatogram were obtained from ln versus T–1 plots. A temperature dependent reversal of the elution order was studied and the mobile phase composition and column temperature were optimized to obtain the best separation. A flow rate of 0.80 ml min–1 with 52.6% methanol in the methanol-water mixture and a column temperature of 48°C gave the most efficient separation of ten benzodiazepines.  相似文献   

11.
The aqueous reactions, Mg2++Cl=MgCl+, Ca2++Cl=CaCl+, and H+ +Cl=HCl(aq), were studied as a function of ionic strength at 250, 275, 300, and 325°C using a flow calorimetric technique. The logK, H, S and Cp values were determined from the fits of the calculated and experimental heast. The data were reduced assuming a known functionality of the activity coefficient. Hence, the logK, H, S and Cp values determined in this study are dependent on the activity coefficient model used. These thermodynamic values were compared with literature results. The logK values for the formation of MgCl+ agree reasonably well with those reported in the literature. The logK values for CaCl+ formation agree reasonably well with those reported in the literature at 300 and 325°C. At lower temperatures, the agreement is poorer. The logK values for the formation of HCl(aq) are generally lower than those reported in the literature. The logK, H, S and Cp values for all three ion association reactions are positive and increase with temperature over the temperature range studied. These values are the first determined calorimetrically for the formation of MgCl+ and CaCl+ in the temperature range 275–325°C.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.  相似文献   

12.
The linear compensation plot of H versus S for associative substitution reactions of Ru5C(CO)14 {P(OPh3)} with seven P-donor nucleophiles suggests that an isokinetic temperature, Tiso, of 253±10K exists. A detailed statistical analysis by the Linert-Exner method shows that the data are consistent with there being a genuine isokinetic temperature at 245K at which reactions with six out of the seven nucleophiles proceed at the same rate. This can be shown more easily, graphically more vividly, and with quantitatively the same or better results, by a simplified version of an earlier method due to Krug, Greiger et al. in which H values are found to depend linearly on corresponding values of G calculated at a suitably chosen temperature. This isokinetic behaviour is closely related to that shown by the linear free energy analysis of the rates in terms of the electronic and steric properties of the nucleophiles. The temperature dependence of the sensitivity of the rates to these electronic and steric properties suggests that the major factors involved are entropic rather than enthalpic, reactions with larger nucleophiles actually being favoured by enthalpic factors. Steric profiles obtained at different temperatures all pass through a common point with an isokinetic cone angle of 153°. A few examples of other reactions of organometallic or coordination compounds that show linear compensation plots of H versus S are also analysed by the Linert- Exner and Krug-Greiger methods. Some do show unambiguous isokinetic behaviour but others do not, even though the compensation plots appear to be linear.  相似文献   

13.
Zusammenfassung Für eine numerische Auswertung von Enzymanalysen erscheint es zunächst naheliegend, in die Meßpunkte eine Ausgleichsgerade einzupassen und deren Steigung als Schätzwert für die gesuchte Anfangsgeschwindigkeit E/t 0 zu nehmen. Die Steigung der Ausgleichsgeraden liefert aber die mittlere Reaktionsgeschwindigkeit über die gesamte Meßzeit und unterschätzt E/t 0 immer dann, wenn die Reaktion gegen Ende der Meßzeit etwas langsamer läuft. Bei automatischen Geräten muß das Auswerteverfahren auch in solchen Fällen E/t 0 richtig schätzen. In der vorliegenden Arbeit wird eine einfache Möglichkeit, die zu diesem Ziel führt, diskutiert, nämlich die Schätzung von E/t 0 mit einer Ausgleichsparabel, die dem Reaktionsverlauf folgen kann.
Numerical evaluation of enzyme analyses
To calculate enzyme concentrations numerically, it seems obvious to fit a straight line into the data points and take the slope as an estimate for the starting velocity E/t 0. This slope, however, is proportional to the average reaction rate over the total measurement interval and always underestimates E/t 0 when the reaction is slowing down towards the end. Automatic analyzers must correctly estimate E/t 0 even in such cases. As discussed in this article, this can be achieved by fitting a second order parabola, that can follow the reaction, into the data points.
  相似文献   

14.
The enthalpy changes at zero ionic strength (H°) for the ionization of water (H2O=H++OH) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C p ° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C p ° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.  相似文献   

15.
Summary The reaction of the 3-acetate of the 20-ketal of 16,17-oxido-5-pregnenol-3-one-20 with methylmagnesium iodide and subsequent hydrolysis of the reaction product yielded 16-methyl-5-pregnenediol-3 –17-one –20. 18-Nor-17-methyl-17-iso-5.11-pregnadienediol-3,16-one-20 was formed as a by-product.  相似文献   

16.
Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C p ° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C p ° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C p ° values which approach those associated with charge reduction reactions. As the temperature increases, C p ° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.  相似文献   

17.
It is shown that the oxidative condensation of ethane on CoMo/-Al2O3 catalysts is in principle possible. The conceivable paths of this reaction are analyzed.
- .
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18.
The AM1 quantum-chemical semi-empirical method was used to calculate the values of the enthalpy of activation (H#), the heats of reaction (H), and the tautomeric equilibrium constants (KT) for several -substituted pyridines. It was found that the keto-enol tautomeric conversion in -pyridone occurs more readily than the amino-imino conversion in 2-aminopyridine but in 2-methylpyridine the tautomeric equilibrium does not exist at all.  相似文献   

19.
Glucose hydrogenation has been studied in weakly alkaline water-ethanol media over 5% Ru/Al2O3. The solvent is shown to affect the activity and selectivity.
- 5% Ru/Al2O3. .
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20.
Summary The thermodynamic characteristics (F, H, and S) of the formation of ferrocinium and ruthenocinium triand pentaiodides were measured.  相似文献   

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