排序方式: 共有14条查询结果,搜索用时 31 毫秒
1.
A. A. Hasanein G. M. El-Subruiti G. O. Younes M. H. Srour 《Journal of solution chemistry》2004,33(12):1481-1499
The electronic absorption spectra of 2-aminopyrimidine (compound I), 2-amino-4-methylpyrimidine (compound II), 2-amino-4,6-dimethylpyrimidine (compound III), 2-amino-4,6-dimethoxypyrimidine (compound IV), 4-amino-2,6-dimethylpyrimidine (compound V), and 4,5-diamopyrimidine (compound VI) have been measured in water and in a series of different organic solvents. The solvent effects on the spectra are discussed and the solvent induced spectral shifts are analyzed in terms of different solute–solvent interaction mechanisms, using the multiple linear regression technique. 相似文献
2.
Gehan M. El-Subruiti Kamal H. Halawani Cecil F. Wells Ibrahim M. Sidahmed 《Transition Metal Chemistry》1993,18(3):323-328
Summary The kinetics of the solvolysis of complex ions trans-[Co(Rpy)4Cl2]+, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of [Co(Rpy)4Cl2]+ in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the Co3+ cation in the transition state is more stable than the Co3+ cation in the initial state in the water + urea mixtures. 相似文献
3.
Solvent effects on the initial and transition states for the solvolysis of the trans-dichlorobis-(N-methylethylenediamine)cobalt(III), (meen), complex have been investigated in the 25–55 °C range in aqueous DMSO mixtures, of varying solvent composition up to 60% by vol. The log of the first order rate constant, k, varies non-linearly with the reciprocal of the dielectric constant at the same temperature, due to differential solvation of the initial and transition states. The changes in the enthalpy, H
, and entropy, S
, of activation with the mole fraction of the co-solvent show extrema at the composition range where the change in solvent structure occurs. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the effect of solvent structure on the complex ion in the transition state dominates the initial state and that this effect increases as the mole fraction of co-solvent increases. 相似文献
4.
Gehan M. El-Subruiti Ghassan O. Younes Farah S. Zeitouni Mohamed F. Amira 《国际化学动力学杂志》2008,40(7):416-422
Kinetic studies of solvent structure effects and solute–solvent interactions on the solvolysis of [Co(NH3)5Cl]2+ complex ion have been investigated spectrophotometrically in binary aqueous mixtures. Three cosolvents were used (acetonitrile, dimethylsulfoxide, and urea) over a wide range of temperatures. Nonlinear plots were found for log(rate constant) against the reciprocal of the relative permitivity of the medium. The enthalpy and entropy of activation (ΔH# and ΔS#) exhibited extrema in the same composition region where the physical properties indicate sharp changes in the structure of the solvent, confirming that the solvent structure is an important factor in determining the solvolytic reactivity. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 416–422, 2008 相似文献
5.
6.
Gehan M. A. El-Subruiti Cecil F. Wells Ibrahim M. Sidahmed 《Journal of solution chemistry》1991,20(4):403-415
The solubility of salts [Co(3Rpy)4Cl2]2]ReCl6] has been determined in water + methanol mixtures. By comparing these with the solubilities of the salt Cs2ReCl6 and using calculated activity coefficients for the ions in the water+methanol mixtures, values for {G
t
o
(Co(3Rpy)4Cl
2
+
)–G
t
o
(Cs+)} can be determined where G
t
o
is the standard Gibbs free energy of transfer from water to an aqueous mixture. G
t
o
(Cs+) from the solvent sorting scale and from the TPTB scale are then used to calculate G
t
o
(Co(3Rpy)4Cl
2
+
). These two sets of values for G
t
o
(Co(3Rpy)4Cl
2
+
) on the differing scales are then inserted into a free energy cycle applied to the bond extension Co(3Rpy)4Cl
2
+
(initial state)Co(3Rpy)4Cl2++Cl– (transition state) for the solvolysis in water and in water + methanol mixtures to produce values for G
t
o
(Co(3Rpy)4Cl2+) using both scales. Data for the solubilites of [Copy4Cl2]2[ReCl6] and [Co(4Rpy)4Cl2]2[ReCl6] have been re-calculated to compare free energies of transfer for these complex cations with those specified above. 相似文献
7.
Gehan M. El-Subruiti Salah S. Massoud Aziza K. Chehata 《Transition Metal Chemistry》1996,21(5):437-441
Summary The trans-[Co(meen)2Cl2]Cl complex was prepared and characterized by elemental analysis, and u.v.-vis. and i.r. spectroscopies. The kinetics of the
primary aquation of trans-[Co(meen)2Cl2]+ in H2O and H2O-MeOH have been investigated over a wide range of solvent compositions and temperatures (45–60 °C). Plots of rate constants
(log k) versus the reciprocal of the dielectric constant of the medium (D
infs
sup−1
) and Grunwald-Winstein values of the solvent (Y) were non-linear. The variation of enthalpies (ΔH
*) and entropies (ΔS
*) of activation with solvent composition have been determined. Plots of ΔH
* or ΔS
*
versus the mole fraction of the solvent exhibit a maximum at x
2 ca. 0.1 and a minimum of x
2 ca. 0.3; a linear plot of ΔH
*
versus ΔS
* is obtained. Furthermore, the cycle relating the free energy of activation in H2O to that in H2O-MeOH shows that changes in the solvent structure in H2O-MeOH mixtures generally stabilize the five-coordinate cation in the transition state, more than the cation in the initial
state as the mole fraction of MeOH increases. The results are discussed and compared with other related systems. 相似文献
8.
Gehan M. A. El-Subruiti Cecil F. Wells Ibrahim M. Sidahmed 《Journal of solution chemistry》1992,21(1):93-103
Rates of solvolysis of [Co(CN)
5
Cl]
3–
have been determined in a range of water-rich water + 2-propanol mixtures over a range of temperatures and they show no simple correlation with dielectric constant. The variation of the enthalpy and entropy of activation with solvent composition show broad extrema and these are discussed in relation to the physical properties of the media. The application of a free energy cycle to the dissociative loss of the chloride ion in the transition state shows that the effect of changes in solvent structure as the alcohol content increases is to stabilize the emergent pentacyanocobaltate(III) ion Co(CN)
5
2–
relative to the chloropentacyanocobaltate(III) anion in the initial state. 相似文献
9.
Gehan M. El-Subruiti Cecil F. Wells Ibrahim M. Sidahmed 《Journal of solution chemistry》1993,22(10):883-894
The solubilities of the hexachlororhenate(IV) salts of the complex cations trans-[Co(3Mepy)4Cl2]+ and trans-[Co(3Etpy)4Cl2]+ have been determined in water+t-butyl alcohol mixtures. By reference to the solubilities of Cs2ReCl6 and the Gibbs energies of transfer of Cs+ from water into water+t-butyl alcohol mixtures, G
t
o
(Cs+), G
t
o
[Co(3Mepy)4Cl
2
+
] and G
t
o
[Co(3Etpy)4Cl
2
+
] are calculated. These latter values, when introduced into the equation for a free energy cycle applied to the process of the initial state going to the transition state for the solvolyses of these two cations, produces values for G
t
o
[Co(3Mepy)4Cl2+*] and G
t
o
[Co(3Etpy)4Cl2+*] for the Co3+ cations in the transition state. These values are compared with (G
t
o
(i) for i=[Co(Rpy)4Cl2]+, [Co(Rpy)4Cl]2+*, [Coen2XCl]+ and [Coen2X]2+* to investigate the influence of the hydrophobicity of the surface of the complex on its stability in the mixtures. G
t
o
(i) (solvent sorting) are compared with G
t
o
(i) (TATB). 相似文献
10.
Gehan Moustafa El-Subruiti 《Journal of solution chemistry》2002,31(5):415-423
Rate constants and derived thermodynamic activation parameters are reported for solvolysis of trans-[Co(3Mepy)4Cl2]+ and [Co(CN)5Cl]3– ions in water-rich mixtures of water with ethanol at various temperatures and are analyzed by initial- and transition-state contributions. The variation of enthalpies and entropies of activation with solvent composition show extrema in composition ranges where the physical properties of the mixtures, influenced by changes in solvent structures, also show extrema. From the application of a free-energy cycle to the process of the initial state going to the transition state, it is concluded for the solvolysis of both complexes that the Co(III) species in the transition state is more stable in water + ethanol mixtures than in the initial state. 相似文献