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1.
Gas-chromatographic experiments were carried out in various phases of the solvents 4-acetoxy-N-[4-methoxy-benzylidene]-aniline, dibutoxyazoxybenzene, lithium stearate, dihexoxyazoxybenzene, and diheptoxyazoxybenzene. The solutes were linear, branched and cyclic alkanes, and substituted benzenes. Excess enthalpies, entropies, and free entropies were calculated from net retention volumes. In the nematic liquid crystalline phases the effect of order disturbance was significant in
and
but it was, by enthalpy-entropy compensation, not demonstrable in
. Differences in flexibility and degree of expansion of the solutes did not result in significantly different values of the excess quantities. 相似文献
2.
Group contributions to
in seven solvents and to
in three solvents have been tabulated. The variation of
group parameters is discussed in terms of the solvent compressibility coefficient, T. The scaled particle theory (SPT) is used to calculate cavity contributions to
and C
p2
o
. Interaction contributions are obtained from the cavity terms and
and
values estimated through the additivity schemes.
values are more sensitive to solute-solvent interactions than
in water and less sensitive in methanol. The SPT results for heat capacities support the concept of structural promotion by hydrophobic solutes in water. 相似文献
3.
J. Op De Beeck 《Journal of Radioanalytical and Nuclear Chemistry》1985,89(1):169-190
The epithermal reactor neutron spectrum shape-factor, and the associated effective resonance energy
for a given nuclide, are examined theoretically in great detail. First the necessity, meaning and importance of the choice of a reference neutron energy in a non-ideal spectrum (0) are explained. Next, the definition and practical calculation of
are discussed, showing that the relation between the reasonance integrals in ideal and non-ideal spectra cannot be described adequately by two independent parameters
and . The exact meaning of the logarithmic expression defining an
independent of is clarified, its limits of validity are established as a function of and, as a result, it follows that relatively large systematic errors on
can be introduced by its use. It is shown that
is dominated by the first lowest resonance energies for a given nuclide, making its vulnerability to literature updates of resonance parameters almost equal to those of individual resonances. The effect, on the epithermal and total activation of specific nuclides, of large systematic and statistical errors on
and, is calculated for a series of nuclides (different I0/0 and
) and irradiation facilities (different and the), and represented graphically.Finally, the effect of important errors on and
is calculated for final NAA results in terms of concentrations, botained by a comparator technique based on the197Au reference nuclide. Conclusions are drawn concerning the impact of the foregoing on the usefulness of comparator type reactor NAA as an alternative to classical NAA using multi-element standards. 相似文献
4.
Harry P. Hopkins Jr. Wayne C. Duer Frank J. Millero 《Journal of solution chemistry》1976,5(4):263-268
The apparent molal heat capacities
have been determined at 25°C for phenol,meta-nitrophenol,para-nitrophenol,meta-cyanophenol, andpara-cyanophenol and the corresponding sodium salts in water at several concentrations. These values have been extrapolated to infinite dilution to provide the
values from which the heat capacity changes for the ionization of the aqueous phenols have been calculated. The observed
values are virtually identical within experimental error for the phenols studied. The volume data needed to calculate the
values from the experimental data are also reported.To whom correspondence should be addressed. 相似文献
5.
Zusammenfassung Bei niedrigen Umsätzen und einer Polymerisationstemperatur von 50°C erhaltene Polyvinylacetate sind unverzweigt; das gleiche gilt für Polyvinylchoracetate. Bei diesen wurde die bei höheren Umsätzen auftretende Verzweigung durch Verseifung und Acetylierung der Polymeren sowie durch Messung von []-,
und
Werten an den Polymeren bestimmt. Eine Selbstverzweigung der wachsenden Kette konnte nicht gefunden werden. *** DIRECT SUPPORT *** A3615144 00012
Chain branching in vinyl chloroacetate and vinyl acetate polymerization
Polymerization of vinyl acetate and vinyl chloroacetate to low conversions at 50°C gave unbranced polymers. The branching of polyvinyl chloroacetates at higher conversions was determined by hydrolysis and acetylation of the polymers and by measuring [], and . No self-branching of the growing chains could be found.相似文献
6.
Previously developed additivity schemes for nonelectrolytes have been used to estimate
and
for tetraalkyl and tetraphenyl methanes in methanol and water. Corrections have been applied to the thermodynamic values of these model compounds to account for a variation in size of the central atom, and these were used to ascertain the effect of charge on
and
of alkyl and phenyl quaternary ions having N, P and B as central atoms. Investigations of R4NBr, (R=methyl to heptyl) salts show that the charge effect on
and
of R4N+ ions is large and relatively independent of ion size suggesting that the solvent molecules penetrate the ions. The ability to estimate
and
of the quaternary ions in the bromide salt solutions has made it possible to make ionic assignments with some confidence;
(Br–) has been evaluated as 19.7±2 and 30.2±7 cm3-mol–1 and
(Br–) as –83±7 and –68±30 J-K–1-mol–1 in methanol and water, respectively. The use of organic ions for making ionic assignments of
and
is critically examined and comparisons with other assignments are made. The scaled particle theory is employed to divide the heat capacities of electrolytes into cavity and interaction contributions. 相似文献
7.
Cellulosic fabric was carboxymethylated by single-bath method for different durations.
arrived at a maximum when plotted against the time of reaction. This might be interpreted by the dissolution of the highly substituted fractions. The fibrous character of the carboxymethylated samples
remained unchanged, but the accessibility of the cellulose characterized by iodine sorption, porosity, and wettability changed significantly. The carboxymethylation had a complex effect on the investigated parameters: the values of accessibility were increasing initially, caused by opening the fibrillar structure, but decreasing later as the swollen structure was collapsing during air-drying. The studied properties were depending not only on the changes in
but also on the reaction parameters. 相似文献
8.
The difference between the partial molal entropies of ferrocene and ferricinium
has been determined in nine solvents from the temperature dependence of the formal potential of the ferricinium-ferrocene redox couple using a nonisothermal electrochemical cell arrangement in order to probe possible structural reasons for the limitations of the ferrocene assumption for estimating the transfer thermodynamics of single ions between different solvents. In contrast to the uniformly small positive values of
predicted by the Born model, the experimental quantities varied widely from small or even negative values in hydrogen-bonded solvents (–5 to 3 e.u.) to substantially larger values (11–14 e.u.) in dipolar aprotic media. These variations appear to arise chiefly from additional solvent ordering in the vicinity of the ferricinium cation compared to the ferrocene molecule which is enhanced in the aprotic solvents. The variations in
between water and a number of nonaqueous solvents provide a predominate contribution to the differences between the free energies of single ion transfer calculated using the ferrocene and alternative extrathermodynamic assumptions. 相似文献
9.
It has been found that in the transconfiguration, the Hückel hyperpolarizability of -shells (
) vanishes at a bond angle of 125. The cis configuration is characterized by alternation of the sign of
, depending on whether N/2 is odd or even (N is the number of carbon atoms). Approximate relationships have been established:
for the trans form, and
for the cis form.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 25–28, January–February, 1992.The authors wish to express their sincere appreciation to A. V. Luzanov for steady interest in the work and for detailed discussion of the entire set of problems that are involved. 相似文献
10.
Debashis Banerjee Ashis Kumar Laha Prasanta Chatterjee Sanjib Bagchi 《Journal of solution chemistry》1995,24(3):301-310
The extent of local excess or deficiency of a component solvent near the solute
in a mixed binary solvent has been calculated using the Hall formalism for the Kirkwood-Buff equation. The possibility of calculation of the two solute-solvent Kirkwood-Buff parameters
using the
values is discussed. A model calculation using literature data for preferential solvation in mixed binary solvents is presented. The solute-solvent and solvent-solvent interactions and the relative size of the solvents are also shown to be relevant factors in determining the
values. 相似文献
11.
Shigeharu Harada Toshio Nakajima Tsuyoshi Komatsu Tsurutaro Nakagawa 《Journal of solution chemistry》1978,7(6):463-474
Density and ultrasonic velocity measurements were made on a series of dilute equeous solutions of H(OCH
2
CH
2
)nOH, CH
3
(OCH
2
CH
2
)nOCH
3
, H(CH
2
)nOCH
2
CH
2
OH (n=1–4), and poly(ethylene glycol) at 5, 25, and 45°C. The additivity of the limiting partial molal volumes (
) and adiabatic compressibilities (
) for CH
2
and CH
2
CH
2
O groups was tested by using the observed
and
values of the solutes. The
and
values of the CH
3
, CH
2
, CH
2
CH
2
O, and CH
2
OH groups were estimated and discussed in relation to hydration effects. The
and
values of alkoxyethanols calculated on the basis of the additivity of the group partial molal quantities were in good agreement with the observed values. The behavior of the limiting partial molal isothermal compressibility of alkoxyethanols was similar to that of the adiabatic compressibility. 相似文献
12.
The apparent molal volumes (v) and compressibilities (K) of CaSO4 solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of v and K from the limiting law and various additivity estimates for the free ions (Ca2+, SO
4
2–
) have been used to estimate the partial molal volume (
) and compressibility (
) for the formation of the CaSO
4
0
ion pair. Values of
= 25 ± 3 cm3-mole–1 and
= (54±21)×10–4 cm3-mole–1-bar–1 were found. Since these values are larger than the value for the formation of MgSO
4
0
, the results indicate that more inner-sphere ion pairs are formed when SO
4
2–
complexes with Ca2+ than with Mg2+. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO4 solutions is estimated to be 36 to 37%. 相似文献
13.
Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs
and
, related by a chemical transformation
, the reaction graph
is determined using a maximal common subgraph defined for vertex mapping
. A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph
into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at
and ending at
corresponds to a breakdown of the transformation
into a sequence of intermediates. 相似文献
14.
Isothermal compressibilities T and isobaric thermal expansion coefficients p have been determined for mixtures of ethylbenzene+n-nonane, +n-decane, and +n-dodecane at 25 and 45°C in the whole range of composition. The excess functions
and
have been obtained at each measured mole fraction. The first one
is zero for ethylbenzene +n-nonane, positive for ethylbenzene +n-decane, and +n-dodecane and increases with chain length n of the n-alkane. The
function is positive for the three studied systems and nearly constant with n. Both mixing functions increase slightly with temperature. From this measurement and supplementary literature data of molar heat capacities at constant pressure C
P
, the isentropic compressibilities S, the molar heat capacities at constant volume C
V
and the corresponding mixing functions have been calculated at 25°C. Furthermore, the pressure dependence of excess enthalpy H
B
,
at zero pressure and at 25°C has been obtained from our experimental results of
and experimental literature values for excess volume V
E
. 相似文献
15.
Relative densities,
, and heat capacity ratios,
of aqueous L-histidine, L-phenylalanine, L-tyrosine, L-tryptophan, and L-2,3-dihydroxyphenylalanine (L-dopa) have been measured at 15, 25, 40, and 55°C and 0.1 MPa. Apparent molar volumes, V
2,, apparent molar heat capacities, CP2,, partial molar volumes at infinite dilution,
, and partial molar heat capacities at infinite dilution,
, have been calculated from these measurements and compared to available literature values. The partial molar properties at infinite dilution for these systems have been added to those previously obtained for amino acids and peptides in water and the combined set used as input to a novel additivity analysis. The model we develop is based upon the equations of state of Helgeson, Kirkham, and Flowers (HKF) and has been constructed with additive parameters. The model may be used to predict thermodynamic properties of many aqueous biochemicals over an extended temperature range. Group contributions to the parameters in our model and effective Born coefficients are reported for 24 aqueous amino acid and peptide systems. Our results are compared to data previously published in the literature. 相似文献
16.
Partial molar heat capacities
and volumes
of some nucleic acid bases, nucleosides and nucleotides have been measured in 1m aqueous NaCl and CaCl2 solutions using Picker flow microcalorimeter and a vibrating tube digital densimeter. The partial molar heat capacities of transfer and volumes of transfer from water to the electrolyte solutions were calculated using earlier data for these compounds in water. The values of these transfer parameters are positive. The higher values for transfer to aqueous CaCl2 solutions reflect the stronger interactions of the constituents of the nucleic acids with Ca+2 ions than with the Na+ ions. 相似文献
17.
K. I. Rezchikova N. V. Grigor'eva I. I. Bannova O. P. Shitov V. A. Shlyapochnikov 《Russian Chemical Bulletin》1991,40(11):2167-2173
Vibrational spectroscopy and x-ray structure analysis have been used to investigate three new types of sulfonium nitroimides: N-nitrosulfylimides, N-nitrosulfoximides, and N,N-dinitrosulfodiimides. Structural parameters have been determined for the molecules
,
, and
.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2489–2496, November, 1991. 相似文献
18.
G. I. Golodets 《Theoretical and Experimental Chemistry》1967,1(6):506-510
A correlation has been found between the ease of reduction of oxides,
(where
is the reciprocal of the absolute temperature at which reduction by hydrogen commences), and their catalytic activity in relation to the oxidation of hydrogen, propylene, methane and the dehydrogenation of isopropyl alcohol. In the oxidation of hydrogen, propylene, and methane, the catalytic activity in the series of oxides investigated increases with increase in
; in the cases of the oxidation of ammonia and naphthalene, the dependence of the catalytic activity on
is represented by an inverted-V curve. 相似文献
19.
The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes (
) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes (
) for the ionization of water, H2OH++OH–, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H2O. The partial molal compressibilities (
for HCl, NaOH, NaCl, and H2O have been estimated from data in the literature and used to determine the partial molal compressibility changes (
) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation
from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.Contribution Number 1548 from the University of Miami. 相似文献
20.
The densities of aqueous solutions of the phosphonium halides, Bu
4-n
Ph
n
PX(n=0–4), some of which were synthesized from the phosphines, were measured at 15, 25 and 35°C. Partial molal volumes at infinite dilution,
, and B
v
coefficients for the apparent molal volumes were determined at each temperature. For the first four cations
varies little with n. For all salts B
v
are negative but become less negative with increasing n. The temperature dependence of B
v
is positive for butyl-rich salts (n<2) but negative for phenyl-rich salts (n>1). Also it appears that
is relatively large for phenyl-rich cations in comparison with that for butyl-rich cations. 相似文献