New simple functions to describe kinetic and thermodynamic effects of pressure. Application to Z-E isomerization of 4-(dimethylamino)-4'-nitroazobenzene and other reactions

Abstract

due to the differences in electronic configuration and thus differences in polarizabilities of these molecules. In this work, the polarizability differences are taken into account in the calculation of the adsorption potential as the mean polarizability and the polarizability ratio of the adsorbate molecule (ail/ais) assigned to each C force center of the molecule, derived from the corresponding molecular experimental data. The predicted s value for phenanthrene/anthracene adsorption on graphite is 1.44 when polarizability data are taken from Lefevre et al.39 and 1.55 from Schuyer et al.40 instead of 1.23 for the experimental value as measured by gas-adsorption chromatography. These calculations demonstrate how sensitive the model is to the value accepted for the mean polarizability of the carbon force center of the adsorbate molecule. ConclusionThese results show that the anisotropic adsorption potential model of Meyer and Dietz,14Js when applied to the molecular theory of adsorption, predicts with good agreement, at least as well as the empirical adsorption potential laws, the thermodynamic functions of adsorption of alkanes and aromatic hydrocarbons on graphite.The adsorption potential which takes into account the high anisotropic polarizability of graphite can be expressed with a good approximation by a Lennard-Jones (12-6) potential. The Kirkwood-Muller constant used for isotropic adsorption potential calculations on graphite is 4/3 larger than the attractive constant which assumes that the polarizability in the direction normal to the basal plane is zero. Therefore, adsorption potential laws which use the Kirkwood-Muller attractive constants to predict BAS and qst values for the adsorption on graphite give results which are too large.The relative retention of geometrical isomers are equal when calculated with the anisotropic or isotropic potential models if the same polarizability and diamagnetic susceptibility increments are assigned to the adsorbate force centers. Similarly the conclusions of Battezzati et al." which cencern the most stable equilibrium adsorbate conformations on graphite still hold with the anisotropic adsorption potential model.Finally, this work shows that correct knowledge of the polarizability of the adsorbate molecule and the structural properties of the adsorbed layers is of great importance in order to derive the constants of the adsorption potential laws.Two simple three-parameter equations are proposed as functions to describe kinetic and thermodynamic effects of pressure. The functions are found to reproduce experimental results more accurately than the most frequently used quadratic equation. The estimated activation volumes at zero pressure are almost independent of the experimental pressure range for most of the reactions examined and their standard deviations are reasonably small. The activation volumes at infinite pressure are, in many cases, in fairly good agreement with the intrinsic activation volumes calculated by an independent procedure. IntroductionActivation volume ...

Efficient coloration and decoloration reactions of fast photochromic 3H–naphthopyrans in PMMA-b-PBA block copolymer

“…Generally, the investigation of pressure effect on the rate of chemical reactions provides the important insights into the conformational changes during chemical reactions [14][15][16]. We previously demonstrated that the value of the activation free volume (ΔV ‡ ) for the thermal back reaction is an effective measure to evaluate the efficiency of the photochromic reaction in polymer matrix [17,18].…”

Modelling the effect of pressure on the rates of ionic and polar reactions

“…We have derived simple expressions for the pressure dependence of the reaction rate (eqn (12)] and the activation volume [eqn (15)] for ionic and polar reactions. We have assumed that the pressure dependence of the solvent volume and dielectric constant (reciprocal value), in the vicinity of the reactants, follows similar Tait equations, having the same B parameter.…”

“…In order to compare eqn (12) with experimental data we shall rewrite it in the following form : where Xl = P / B and X , = In (1 + P / B ) . A , is expected to be zero.…”

“…Shows the results of fitting eqn (12) to the high-pressure kinetic data of the reactions listed in table 1, using multilinear regression [eqn ( 1 This turns out to be the case in the studied reactions. The calculated values of Uo are found to be comparable with a typical strength of electrostatic interaction in the range of a few Angstroms.…”

Organic Reactions and High Pressure. Theoretical Models in High Pressure Reaction Kinetics: from Empirical Correlations to Molecular Dynamics.

“…Even though Marcus cross-relation (7), was originally derived for the electron transfer reactions, it proved to be applicable to a wider range of processes, such as, for example, hydrogen transfer or SN2 reactions [13] . Therefore, one may expect that cross-relation (8) will also apply to a wider class of exchange reactions. there is no single cross-section that can be consistently assigned, the cylindrical model becomes ambiguous.…”