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91.
92.
The equilibrium structure of CH3F has been determined using new sets of accurate rotational constants that have been determined by taking into account all the interactions between the excited vibrational states. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with the cc-pV(5, Q)Z basis set (including corrections for the core correlation and for the effect of diffuse functions on fluorine). Finally, the experimental and ab initio structures have been combined by a least-squares analysis. The results are
, and L
e(HCH) = 110.2 (1)°, where the uncertainties shown in parentheses correspond to three standard deviations. 相似文献
93.
The solid-state reactions of crystalline ferrocenyl- and ruthenocenylaldehydes with optically active primary β-hydroxyamines
were studied at ∼20 °C. The yield of the products increases substantially in the presence of K2CO3. The tautomeric equilibrium between imines and diastereomeric oxazolidines with the predominant formation of one of them
is established in solutions of the products in CDCl3.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2240–2243, December, 1997. 相似文献
94.
仲胺型双冠醚与四苯硼酸碱金属盐在丙酮溶液中。25℃下的电导说明它们与Na~+可能形成1∶1络合物(冠醚单元∶金属离子),而与K~+、Rb~+、Cs~+离子则形成2∶1络合物。用Schlff碱型和仲胺型双-(苯并15-冠-5)在水-氯仿体系中进行萃取,测量了分配比D和萃取平衡常数K,发现后者的K值均大于前者。双冠醚F_2对K~+的萃取能力最强,选择性最佳。 相似文献
95.
Computer modelling of the conformational equilibrium of 2-and 2,5,5-substituted 1,3,2-dioxaborinanes
V. V. Kuznetsov O. Yu. Valiakhmetova S. A. Bochkor 《Chemistry of Heterocyclic Compounds》2007,43(12):1577-1581
Empirical, semiempirical, and nonempirical quantum-chemical methods were used to study the conformational equilibrium of 2,5,5-substituted
1,3,2-dioxaborinanes. The sofa invertomers were found to correspond to the local and global minima on the potential energy
surface. The position of the equilibrium between these forms is a function of the substituents at C(5) of the heterocycle.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1860–1865, December, 2007. 相似文献
96.
The equilibrium in the systems containing a polymer based on dibenzo-18-crown-6 and binary or multicomponent aqueous solutions of NaNO3, KNO3, RbNO3, and AgNO3 was studied. The constants of the sorption of the individual electrolytes from solution into the polymer were determined. Preliminary calculations of the phase composition on sorption of 11 mixtures of electrolytes with a common anion from the data on the equilibria in the systems with one electrolyte are possible.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 464–466, March, 1993. 相似文献
97.
Romero S. Bustamante P. Escalera B. Cirri M. Mura P. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):541-554
Differential scanning calorimetry (DSC), supported by hot stage microscopy, IR spectroscopy and X-ray powder diffractometry,
was used to investigate the characteristics of the solid phases of mefenamic, niflumic, and flufenamic acids and of paracetamol,
before and after equilibration with saturated solutions in different solvents. Mixtures of Lewis base (dioxane and ethyl acetate)
and amphiprotic solvents (ethanol and water) were prepared for evaluating the influence of both nature and polarity of the
solvents. Solid-state analysis performed on the original samples (commercial products) made it possible to establish that
paracetamol, mefenamic acid and flufenamic acid were in their respective Form I. No polymorphic modifications are known for
niflumic acid. Paracetamol, niflumic and mefenamic acids did not show any change after equilibration with the various solvents
or solvent mixtures, regardless of their different chemical nature. In contrast, DSC, IR and X-ray analyses revealed the partial
recrystallization of flufenamic acid into its polymorphic Form III in solid phases at equilibrium with ethanol, ethyl acetate
and their blends, as well as in dioxane-water mixtures containing 30 to 100% dioxane and in ethanol-water mixtures with a
water content less than 50%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
Alexander V Lebedev Marina V Ivanova Alexander A Timoshin Enno K Ruuge 《Chemphyschem》2007,8(12):1863-1869
The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation. 相似文献
99.
The stoichiometric solubility constant of eitelite (NaMg
0.5
CO
3
+2H+ ⇄ Na++0.5Mg
2+
+CO
2
(g)+H
2
O, log*K
pso
I
=14.67±0.03 was determined at I=3 m (mol kg−1) (NaClO
4
) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account.
Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters
from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation
for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and
brucite (−835.90±0.80 kJ-mol
−1
). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking
a magnesium dicarbonato complex (Mg2++2CO
3
2−
⇄ Mg(CO3)
2
2−
, log βz = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic
acid in 1 to 3.5 m NaClO
4
media
which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously
studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO
4
. The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H+], [Mg
2+
]
tot
) measured in perchlorate medium within experimental uncertainty.
Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria. 相似文献
100.