Reaction Kinetics of Meisenheimer σ-Complex Formation between 2,4,6-Trinitrophenyl Chloride and Hydroxide Ion in Cationic Micellar Solution

Kinetic study was carried out by using stopped-flow method for the Meisenheimer σ-complex formation reaction between 2,4,6-trinitrophenyl chloride (picryl chloride: Pic-Cl) and hydroxide in aqueous cationic micellar solutions of dodecyltrimethylammonium bromide (DTAB), myristyltrimethylammonium bromide (MyTAB) and cetyltrimethyl-ammonium bromide (CTAB) dissolved in aqueous solution, for the purpose of elucidating the influence of the microscopic heterogeneity of reaction field on activation parameters. The reaction rate analysis based on a pseudo-phase ion exchange model led us to a conclusion that on the activation process the enthalpy-entropy compensation relationships worked over the wide range of surfactant concentration, and that, for the reaction occurring at the micellar surface, a reactant molecule effective to the reaction had to move into some restricted direction

Effect of Cationic Micellar Reaction Field on Reaction Kinetics of Meisenheimer σ-Complex Formation between 1,3,5-Trinitrobenzene and Hydroxide Ion

Kinetic studies were done by using stopped-flow method for the Meisenheimer σ-complex formation reaction between 1,3,5-trinitrobenzene (TNB) and hydroxide ion in cationic micellar solutions of dodecyl-trimethylammonium bromide (DTAB), myristyltrimethylammonium bromide (MyTAB) and cetyltrimethylammonium bromide (CTAB) dissolved in aqueous solution, for the purpose of elucidating the influence of the microscopic heterogeneity of reaction field. The reaction rate analysis based on a pseudo-phase ion exchange model led us to a conclusion that the partition of reactant molecules between the micelle and water phase, and ion exchange between hydroxide ion and bromide ion existing as counter ions of cationic micellar surface were important. On the activation process, the enthalpy-entropy compensation relationships worked over the wide range of surfactant concentration. The derived isokinetic temperature, T_ revealed that in CTAB the reaction might be of enthalpy-control, and that in MyTAB be of entropy-control

RNA/DNA hybrid duplexes with identical nearest-neighbor base-pairs have identical stability

AbstractEnergetic behaviors of eight pairs of RNA/DNA hybrid duplexes with identical nearest neighbors have been investigated by UV melting analysis. In the pairs with identical nearest-neighbor pairs, the melting curve traces at the same strand concentration were very similar. The average difference in stabilization energy of these pairs was 4%, which was about expected within experimental error. These results indicate that the nearest-neighbor model is valid for predicting the stability of RNA/DNA hybrid duplexes as well as RNA/RNA and DNA/DNA duplexes

Kinetic studies on fast reactions in solution VI : the kinetic studies on the reaction between tetrahalogeno-p-benzoquinones and alkali iodides

The reactions to produce the semiquinone ion radicals by the electron transfer between tetrahalogeno-p-benzoquinones (fluoranil, chloranil, bromanil and iodanil) and alkali iodides (NaI and KI) were investigated photometrically in acetone solution in the temperature range, 20°～35℃, from the view point of kinetics. The rate of semiquinone ion radical formation is of first order for p-benzoquinones and of second order for alkali iodides. Activation energies and entropies are as follows: for chloranil-NaI, ΔE≠6.8 kcal/mole, ΔS≠=-19.4 e.u.; for chloranil-KI, ΔE≠=7.6 kcal/mole, ΔS≠=-18.6 e.u.; for bromanil-NaI, ΔE≠=9.7 kcal/mole, ΔS≠=-16.6 e.u.; for bromanil-KI, ΔE≠=9.8 kcal/mole, ΔS≠=-16 .3 e.u. Moreover, it was considered that 1) the electron donor is not a dissociated ion but the ion pair of alkali iodide. 2) a kind of charge transfer complex is formed as an intermediate in the electron transfer process and that 3) the rate of reaction is in the following order for the substituted halogen, F>Cl>Br>I. But the reaction rate can not be successfully explained in terms of electron affinity of the electron acceptor

Kinetic studies on fast reactions in solution VII : the kinetic studies on the reactions of p-benzoquinone and its derivatives with alkoxy ions

The fast reactions to produce semiquinone ion radicals by electron transfer from alkoxy ions (RO^-) to p-benzoquinone (BQ), 2-methyl-p-benzoquinone (MeBQ), 2-chloro-p-benzoquinone (CIBQ) and 2-bromo-p-benzoquinone (BrBQ) were kinetically studied using the stopped flow apparatus in alcoholic solutions corresponding to the alkoxy ions, by means of the spectrophotometric and ESR methods. In the reactions of BQ and MeBQ with MeO^-. EtO^-, n-PrO^- and with n-BuO^-, the corresponding semiquinone ion radicals were first produced. And then it was found that the substitution reactions of alkoxy ion follows consecutively or concurrently, in the reaction of BQ and CIBQ with MeO^- and EtO^-. But is the case of BrBQ, the formation is presumed to be too fast to be detected. The rates of the semiquinone formation is of first order for benzoquinones and also of first order for RO^- in the cases of BQ and CIBQ, but of non-integral order for RO^- is the case of MeBQ. From these results, the reaction scheme was considered assuming a kind of the charge-transfer complex. The activation parameters were obtained, and the reaction rate was discussed in terms of electron affinities of benzoquinones and the influence of Z-value of the solvent

Kinetic study of the intermediate in the reaction between picryl chloride and sodium sulphite in aqueous solution

The reaction between picryl chloride and sulphite ion in aqueous solution takes place rapidly to give an intense color which is attributed to a 1, 3-σ-complex formed by the reversible attack of a sulphite ion on the C_3-position of picryl chloride. The color slowly fades because picryl chloride present at equilibrium is attacked by sulphite ion to give 1, 1-σ-complex which rapidly loses chloride ion to form picryl sulphonate ion finally. The 1, 3-σ-complex dissociates to maintain equilibrium. The rates of appearance and disappearance of the transient colored species were measured in the range of 15-35℃ by the stopped-flow method. The rate constants at 25℃, activation enthalpies and activation entropies an each process are shown in Table 2 in the text. The 1, 3-σ-complex was verified by NMR spectrum in DMSO-H_2O solution. The formation of the 1, 1-σ-complex was inferred from the nature of the final products. It may be concluded that the sulphite attacks on C_1-position and C_3-position take place concurrently and the former may be accompanied with higher energy barrier

Kinetic and equilibrium studies on σ-complexes of 2,4,6-trinitroanisole and picrylsulphonate with sulphite ion in aqueous solution

The reactions of 2, 4 , 6-trinitroanisole (TNA) and picrylsulphonate with sulphite ion in aqueous solution take place to give intensely colored σ-complexes. Kinetic studies on the formations of these complexes have been carried out by the stopped-flow method in the temperature range, 15.0～30.0℃. The respective rate constants for the formation and the decomposition (reverse reaction) of σ-complexes were well consistent with the results of the separate equilibrium study. The effect of ionic strength on the anion-anion reaction was well explained by taking into account of the Debye-Huckel equation. Kinetic and thermodynamic parameters were determined and compared with the previous data on the interaction of 1, 3, 5-trinitrobenzene with sulphite ion, and with the results of methoxide attack to TNB and TNA

Kinetic studies on free radical reactions : II. The photochemical reaction between DPPH and methylmethacrylate

The reaction between α, α'-diphenyl-β-picrylhydrazyl (DPPH) and methylmethacrylate (MMA) in benzene solution induced by UV irradiation was investigated. The change of DPPH concentration was photometrically pursued, and electron spin resonance spectra of the solutions in the course of reaction were observed, where the significant influence of dissolved oxygen was found. In the case of the absence of dissolved oxygen the apparent rate of disappearance of DPPH is of the first order, only corresponding hydrazine being produced. On the other hand, in the presence of dissolved oxygen it is of the zero order and hydrazine, diphenylnitroxide (DPNO) which was identified by ESR spectrum, and a diamagnetic substance which will be produced from the reaction of one DPPH and one peroxy radical, are produced concurrently. In both cases it was interred from the view-point of kinetics that DPPH not only acts as a radical scavenger but also its photo-ecxited molecule participates in the step of radical production from MMA molecule

Kinetic studies on fast reactions in solution : II. The reaction between 1,3,5-trinitrobenzene and diethyl amine in acetone

The reaction between 1, 3, 5-trinitrobenzene (TNB) and diethylamine (DEA) in acetone was investigated at room temperature by the stopped flow method. By measuring the optical densities at 472 and 516 mμ in the course of the reaction, it was found that the reaction proceeded in two consecutive steps ; one is moderately fast and the other is slow. The stoichiometry of the intermediate having a maximum peak at 470 mμ may be one TNB molecule and one DEA molecule. This reaction is reversible and of first order both in TNB and in DEA. The influence of "aging" of DEA in acetone is conspicuous on the rate of increase in the optical density at 516 mμ. It was indicated from an elementary analysis and an infrared spectrum of the product that the product-complex having the maximum peak at 520 mμ may possess the stoichiometry, 1 : 2 : 1 for TNB, DEA and acetone. The overall reaction was discussd from the view point of kinetics