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1.
Kalyan K. Banerji 《Journal of Chemical Sciences》1988,100(5):397-403
The kinetics of the oxidation of twelve ortho-substituted benzaldehydes by N-bromobenzamide (NBB) to the corresponding benzoic
acids have been studied. The reaction is first order with respect to NBB, the aldehyde and hydrogen ions. The addition of
benzamide has no effect on the reaction rate. (PhCONH2Br)+ has been postulated as the reactive oxidising species. The correlation of rates with the single substituent-parameter equations
is poor. The correlation with Charton’s equation of inductive, resonance and steric parameters is satisfactory. However, excellent
correlations were obtained, when Charton’s steric parameter was used along with Taft’s σ1; andσ
R
+
substituent constants. The polar reaction constants have negative values. The reaction is subject to steric hindrance by
the ortho-substituents. 相似文献
2.
The kinetics and mechanism of the reactions of diarylthallium, trifluoroacetates with molecular iodine in dioxane solutions
have been studied. The reaction has the overall second order with the first order with respect to each reagent. The effect
of substituents in the aromatic ring on the rate constant of iodination is described by the equation logk
2ρσ+(ρ=-1.60, r=0.97). The reaction is catalyzed by the iodide ion. The activation enthalpies and entropies of iodination of diarylthallium
trifluoroacetates in dioxane and di(p-anisyl)thallium trifluoroacetate in various solvents have been calculated. The effect of solvents on the rate constant of
iodination of di(p-anisyl)thallium trifluoroacetate has been studied. The reaction mechanism is considered as an electrophilicS
EC process.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–455, March, 1999. 相似文献
3.
Sancheeta Kolay Kallol K. Ghosh Amy MacDonald Jonathan Moulins Rama M. Palepu 《Journal of solution chemistry》2008,37(1):59-72
The thermodynamics of micellization and other micellar properties of alkyl- (C10-, C12-, C14- and C16-) triphenylphosphonium bromides in water + ethylene glycol (EG) (0 to 30% v/v) mixtures over a temperature range of 298 to
318 K and cetyltriphenylphosphonium bromide in water + diethylene glycol (DEG) mixtures (0 to 30% v/v) at 298 K have been
studied conductometrically. In all cases, an increase in the percentage of co-solvent results in an increase in the cmc values.
On the basis of these results, the thermodynamic parameters, the Gibbs energy (ΔG
mo), enthalpy (ΔH
mo) and entropy (ΔS
mo) of micellization have been evaluated. In addition to the conductivity measurements, kinetic experiments have also been done
to determine the dependence of observed rate constant for the nucleophilic substitution reaction of p-nitrophenyl acetate and benzohydroxamate ions in the presence of the surfactant cetyltriphenylphosphonium bromide with a
varying concentration of EG and DEG ranging from 0 to 50% v/v at pH=7.9 and 300 K. All of the reactions followed pseudo-first-order
kinetics. An increase in the surfactant concentration results in an increase in the reaction rate and for a given surfactant
concentration, the rate constant decreases as the concentration of co-solvent in the mixture increases. The kinetic micellar
effects have been explained by using the pseudophase model. The thermodynamic and structural changes originating from the
presence of solvents control the micellar kinetic effects. 相似文献
4.
The kinetics of oxidation of ethyl S-phenylmercapto acetate and several para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B have been studied in 50% (V/V) aqueous ethanol medium containing phosphate buffer. This oxidation is of first order with respect to substrate and zero order with respect to oxidant. A catalytic effect of mercury is observed and the order with respect to mercury is fractional (0.74). The increase in pH decreases the rate of oxidation and the order with respect to H+ is 0.05. In general electron-releasing substituents accelerate the rate while electron-attracting groups retard the rate. A good correlation is found to exist between log k 1 and Hammett constants. Susceptibility of the reaction to the steric effect of ortho-substituents has been analyzed in the light of application of Taft's steric energy parameters. © John Wiley & Sons, Inc. 相似文献
5.
The basicities of several 2′-, 3′-, and 4′-substituted 4-acetylbiphenyls and biphenyl-4-carboxylic acids have been determined
spectrophotometrically in sulphuric acid media at 30°C. The pKBH
+ of 3′- and 4′-substituted compounds are correlated by the Hammett equation. The 4′-methoxy group deviates considerably in
the Hammett plot. This is attributed to its conjugative interaction with the carbonyl or carboxyl group aided by protonation.
Good correlation exists between pKBH
+ and σ+. The basicities of 2′-substituted 4-acetylbiphenyls and biphenyl-4-carboxylic acids reaffirm the existence of π-electron
steric effect of 2′substituents. 相似文献
6.
Effect of the substituents on radical copolymerization of dialkyl fumarates with some vinyl monomers
Takayuki Otsu Akikazu Matsumoto Kohei Shiraishi Naoyuki Amaya Yasumi Koinuma 《Journal of polymer science. Part A, Polymer chemistry》1992,30(8):1559-1565
Radical copolymerization of dialkyl fumarates (DRF) with various vinyl monomers was carried out in benzene at 60°C. The monomer reactivity ratios, r1 and r2, were determined from the comonomer-copolymer composition curves. The relative reactivity of DRFs with various ester substituents toward a polystyryl radical was revealed to depend on both steric and polar effects of the ester groups. It has also been clarified that α-substituents of the polymer radical have a significant role in addition of DRF, from the comparison of the monomer reactivity ratios determined in copolymerizations with monosubstituted and 1,1-disubstituted ethylenes. The absolute cross-propagation rate constants were also evaluated and discussed. © 1992 John Wiley & Sons, Inc. 相似文献
7.
Magda F. Fathalla 《Journal of solution chemistry》2011,40(7):1258-1270
The kinetics of alkaline hydrolysis of 2-chloroquinoxaline (QCl) with hydroxide ion was investigated spectrophotometrically
at different percentages of aqueous–organic solvent mixtures with acetonitrile (10–60% v/v) and with dimethylesulphoxide (10–80%)
over the temperature range from 25 to 45 °C. The reaction was performed under pseudo first order conditions with respect to
2-chloroquinoxaline (QCl). An increase in the percentage of organic solvent (v/v) has different effects on the reaction rate
constants, presumably due to hydrogen bond donor and acceptor differences of the media and other solvatochromic parameters.
The data were discussed in terms of the Kamelt-Taft parameter and E
T(30). A nonlinear relation between the logarithm of the rate constant and reciprocal of the dielectric constant suggests the
presence of selective solvation by the polar water molecules. Activation parameters ΔH
#, ΔS
# and ΔG
# were determined and discussed. 相似文献
8.
Ahmed A. Taha 《国际化学动力学杂志》2012,44(8):514-523
The objective of this study is to test the suitability of the extended Hammett–Brown equation, log (kXX/kHH) = ρ+Σσ+, in depicting satisfactorily additive effects of electronegative atom‐bearing substituents, which are known to possess diverse and multicomponent influences on the side chain reactions of polysubstituted benzenes. The equation has been used to correlate, for the first time, the additive effect of substituents in the specific rates of solvolysis of 2‐chloro‐2‐phenylpropanes ( 3b–3f ) having 3‐F,4‐Me, 3‐Br,4‐Me, 3‐I,4‐Me, 3‐Me,4‐Me, or 3‐MeO,4‐Me substituents. The rates were determined titrimetrically at 288, 298, and 308 K using 90% aqueous acetone as solvent. Measured additive effects of these substituents on the solvolysis rate and activation parameters of the parent cumyl chloride (2‐chloro‐2‐phenylpropane) are found to be well correlated using the equation given above. Plots of log (kXX/kHH) of 3b–3f together with mainly di‐, but also tri‐ and mono‐substituted cumyl chlorides from previous studies against Σσ+ give a linear correlation coefficient of 0.990 as a measure of the validity of the equation to depict such systems. The halogen substituents' extent of conformity with additivity reflected in their relative (kobsd/kcalcd) rate ratios is found to correlate with the steric size of substituents. Plots of rate ratios against Taft's steric factor of each halogen give a linear correlation coefficient of 0.994 for the 3‐halo substituents. The 3,4‐dimethyl substituents' relative rate ratio of 1.03 shows excellent additivity, whereas the 3‐methoxy‐4‐methyl ratio of 1.43 shows the methoxy group to be far less deactivating than predicted. Similar trends were found for the free energy of activation (ΔG? – ΔG0?) differences, which correlated linearly with a coefficient of 0.983 with Taft's steric factor of halogen atoms. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 514–523, 2012 相似文献
9.
Samuel González-Mancebo Javier Lacadena Yolanda García-Alonso Jesús Hernández-Benito Emilio Calle Julio Casado 《Monatshefte für Chemie / Chemical Monthly》2002,133(2):157-166
Summary. Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of
the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction
was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2
+ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron
donating substituents, and a good Hammett correlation was observed with ρ = −6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH ≈ 3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly
by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.
Received July 13, 2001. Accepted (revised) September 18, 2001 相似文献
10.
V. I. Tararov C. Orizu N. S. Ikonnikov V. S. Larichev M. A. Moscalenko L. V. Yashkina M. North Yu. N. Belokon 《Russian Chemical Bulletin》1999,48(6):1128-1130
The enantiomeric purity (ee) of the addition product of Me3SiCN to PhCHO at ∼20 °C catalyzed by chiral TiIV complexes, which were preparedin situ from Ti(OPri)4 and the Schiff bases (condensation products of substituted salicylaldehydes with (1R, 2R)-1,2-diaminocyclohexane), was, on the average, 20–30% lower than that achieved at −80 °C. The substituents at position 5
of 3-tert-butylsalicylaldehyde exert only the steric effect. It was shown that the stereochemical result of the reaction is controlled
by the stage which involves the formation of the C−C bond rather than the transfer of the Me3Si group.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1139–1141, June, 1999. 相似文献
11.
Protonation constants of a number of di-substituted anilines were determined potentiometrically in 0, 20, 30, 40, 50, and
60% (v/v) dioxane–water mixtures at (25.00 ± 0.02) ∘C with an ionic strength of 0.10 mol-dm−3 sodium perchlorate. The data are discussed in terms of the electronic character of the substituents. Two different methods
were used to study the effects of the solvents on the protonation constants; one involved a single polarity parameter, the
Dimroth–Reichardt parameter ET(30); the other involved the Kamlet–Taft multi-parametric method. The protonation constants of di-substituted anilines correlate
with the molecular parameters for the dipolarity/polarizability of the solvent, π∗, and its hydrogen-bond acceptor ability, β. 相似文献
12.
Samuel González-Mancebo Javier Lacadena Yolanda García-Alonso Jesús Hernández-Benito Emilio Calle Julio Casado 《Monatshefte für Chemie / Chemical Monthly》2002,17(5):157-166
Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2 + followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron donating substituents, and a good Hammett correlation was observed with ρ = −6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH ≈ 3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant. 相似文献
13.
V. M. Vlasov 《Russian Journal of Organic Chemistry》2010,46(1):73-81
The reaction constants δΔH
≠ and δΔS
≠ derived from the dependences of the ΔH
≠ and ΔS
≠ activation parameters on substituent constants σ in SNAr reactions of substituted benzenes with anionic and neutral nucleophiles in various solvents were found to be linearly related
upon variation of substituents in the substrate and nucleophile. The δΔH
≠—δΔS≠ dependences make it possible to estimate the contribution of the internal enthalpy δΔH≠
t into the enthalpy reaction constant δΔH
≠. The δΔH
≠
int values are linearly related to the Hammett p values. Deviations from the linear dependence δΔH≠
int—n were interpreted in terms of change of the reaction mechanism. Substituent effect on the development of charge in the transition
state is determined by the δΔH
≠
int value. 相似文献
14.
Rate constants for the reaction of ethyl bromoacetate with three series of substituted naphthoate ions have been measured
in an acetone-water mixture (90% v/v). Using σ
p
values rate constants at 30o correlate well with the Hammett equation yielding ρ=−0.54, −0.19 and −0.25 for (4,1−), (6,1−) and (6,2−) series, respectively.
Comparison of these ρ values with those of the reaction of phenacyl bromide reveals the failure of the reactivity-selectivity
principle RSP in these reactions. Failure of RSP has been explained in terms of isoselective temperature. 相似文献
15.
Robert Faure Jeanine Llinares Emile-Jean Vincent Jos Elguero 《Magnetic resonance in chemistry : MRC》1979,12(10):579-582
The 13C chemical shifts of 1-phenyl-2-pyrazoline and 25 N-nitrophenyl-2-pyrazolines, with different substituents on the heterocyclic ring, have been assigned. These values are discussed as a function of the steric and electronic nature of the various substituents. The steric effects produced conformational modifications, both in the nitrophenyl and 2-pyrazoline moieties, which explain some of the chemical shifts. 相似文献
16.
Mehmet Tümer Nihal Deligönül Ayşegül Gölcü Eyüp Akgün Mustafa Dolaz Havva Demirelli Metin Dığrak 《Transition Metal Chemistry》2006,31(1):1-12
Schiff base ligands HL1–HL6 have been prepared from the reaction of 2,6-diformyl-4-t-butylphenol and 2,6-di-formyl-4-methylphenol with various aromatic amines in ethanolic solution. The Schiff base ligands
2,2′-dipyridine (dp) mixed-ligand CuII complexes have been obtained. Mixed-ligand CuII complexes containing the dp ligand have ionic nature and they conduct the electricity in solution media. The complexes have
been obtained in two different forms: one of them is [Cu2(Ln)Cl3] (n: 1, 2, 3, 4, 5 and 6) and other complexes have the general formula [Cu2(Ln)(dp)2]3Cl. Ligands and their complexes have been characterized by elemental analyses, FT-IR, electronic spectra, molar conductance,
1H(13C)-n.m.r. and mass spectral data. Their stoichiometric protonation constants have been determined potentiometrically in dioxan
using a combined pH electrode at 25 °C, under a nitrogen atmosphere. For the calculation of the protonation constants, PKAS
computer programme has been used. The effects of the substituents on the protonation constants and the additivities of these
effects are discussed. The antimicrobial activity studies of the ligands and their complexes have been studied against the
Bacillus megaterium, Micrococcus luteus, Corynebavterium xenosis, Enterococcuc faecalis, bacteria and Saccoramyces cerevisia, yeast. The catalytic properties of the complexes have been studied on the ascorbic acid, catechol and 2,6-di-t-butylphenol substrates. Thermal behaviour of the complexes has been studied by thermal techniques. 相似文献
17.
Ibrahim M. EI-Mehasseb Abd El-Motaleb M. Ramadan Raafat M. Issa 《Transition Metal Chemistry》2006,31(6):730-739
The oxidation of catechol by molecular oxygen in the presence of a catalytic amount of copper(II) complex with 2-methyl-3-amino-(3H)quinazoline-4-one (MAQ) and various anions (Cl−, Br−, ClO
4
−
, SCN−, NO
3
−
and SO
4
–
) was studied. The catecholase biomimetic catalytic activity of the copper(II) complexes has been determined spectrophotometrically
by monitoring the oxidative transformation of catechol to the corresponding light absorbing o-quinone (Q). The rate of the catalytic oxidation reaction was investigated and correlated with the catalyst structure, time,
concentration of catalyst and substrate and finally solvent effects. Addition of pyridine or Et3N showed a dramatic effect on the rate of oxidation reaction. Kinetic investigations demonstrate that the rate of oxidation
reaction has a first order dependence with respect to the catalyst and catechol concentration and obeying Michaelis–Menten
Kinetics. It was shown that the catalytic activity depends on the coordination environment of the catalyst created by the
nature of counter anions bound to copper(II) ion in the complex molecule and follows the order: Cl− > NO
3
−
> Br− > SO
4
–
> SCN− > ClO
4
−
. To further elucidate the catalytic activity of the complexes, their electrochemical properties were investigated and the
catecholase mimetic activity has been correlated with the redox potential of the Cu2+/Cu+ couple in the complexes. 相似文献
18.
H. Mager 《Tetrahedron》1981,37(3):509-521
In order to attain a better insight into the composition of Taft Eso, constants the rate data of hydrion catalysed esterification of both m,p-substituted and o-substiluted benzoic acids by cyclohexanol and methanol were submitted to a statistical analysis using inductive mesomeric and steric substituent constants and various dummy variables differently structured. Furthermore a principal component analysis with subsequent identification of the first principal component via multiple regression analysis was applied. It has been demonstrated that in the reactions of m,p substituted compounds some substituents capable of exerting strong mesomeric effects show peculiar characteristics deviating from the general trend. Since the same result was obtained in the correlations of ortho substituted benzoic acids this effect was taken into account using an appropriate dummy variable which in all cases improved the multiple coefficient of determination. It is concluded that the esterification rates of the ortho substituted compounds depend essentially upon inductive and steric effects (taken away OMe OEt and NO2) as proposed by Taft. While generally the Eso values may be regarded as some measure of a steric effect, this is not true for the methoxy and ethoxy groups. 相似文献
19.
The kinetics of addition of a number of ortho‐, meta‐, and para‐substituted benzylamines to benzylidenemalononitrile (BMN) in acetonitrile have been studied. The reaction is first‐order with respect to BMN. The order with respect to the amine is more than one. It has been shown that the reaction followed two mechanistic pathways, uncatalyzed and catalyzed by the amine. The enthalpy of activation for the catalyzed path is negative indicating the presence of a preequilibrium (k1, k−1) leading to the formation of a zwitterion. The values of rate constant, k1, for the nucleophilic attack have been determined for twenty‐eight benzylamines. The rate constant, k1 was subjected to correlation analyses using various single‐ and multi‐parametric equations. The best correlation is obtained in terms of Charton's LDR and LDRS equations. The polar regression coefficients are negative indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho‐substituents. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 245–252, 1999 相似文献
20.
Solutions of 1-adamantanol in sulfuric acid at T < 100 °C interact with alkanes (RH, [H2SO4] > 85%) and arenes (ArH, [H2SO4] > 59%). The data on the kinetics, kinetic isotope effect (KIE), effects of the structure of RH and ArH and acidity of the
medium, and the observation of 1,4-cis-dimethylcyclohexane isomerization indicate that adamanyl cations (Ad+) serve as reactive species. In the reactions with alkanes, the Ad+ cation abstracts the hydride ion from RH in the rate-determining step. Compensation dependences appear between the activaion
parameters for the KIE and “effect 5/6” (ratio of the rate constants for the C–H bond cleavage in cyclopentane and cyclohexane)
in the reactions of cycloalkanes with Ad+ and other electrophilic reagents, such as “anthracene” (An2)H+ and hydroxymethyl (CH2OH)+ cations and HgII ions, including the points of the lower selectivity limit (k
H/k
D) = 1.4, (“5/6”) = 1. In the reactions with the Ad+ cation, the bond selectivity 30: 20 of alkanes is higher, while 20: 20 is lower compared to other reagents. In the first case, the selectivity is probably determined predominantly by the energies
of the cleaved C–H bonds, whereas in the second case it is determined by steric hindrances. Judging by the kinetic and selectivity
data in the series benzene—toluene—o-xylene—m-xylene and the absence of the reaction with p-xylene, mesitylene, and pseudocumene, it can be concluded that the main contribution to the Ad+ + ArH interaction is made by adamantylation to the para- and meta-positions of the benzene ring, whereas the ortho-positions are inaccessible to the attack because of steric hindrances.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1581–1596, August, 2008. 相似文献