Pressure dependence of activation and reaction volumes

Abstract

A simple theoretical model of high-pressure kinetic effects is proposed based on the assumption that characteristic (initial, transition or product) states of a reacting system should be identified with stationary points of an enthalpy surface rather than those of a regular potential-energy surface (p.e.s.). An explicit treatment of the deformation of a p.e.s. promoted by pressure enables one to improve the simple cylinder Stearn-Eyring model of activation volumes so as to describe the pressure dependence of activation and reaction volumes. The dependence thus obtained agrees well with experimental data in the wide pressure range from 0 to 45 kbar. The pressure behaviour of activation enthalpies and entropies is also discussed.

A new extension of the polarizable continuum model: Toward a quantum chemical description of chemical reactions at extreme high pressure

“…[34,35] Second, as a Diels-Alder reaction, the dimerization of cyclopentadiene shows a large pressure effect for which there are experimental data to compare. [11,15,36] In the gas phase, the PES for the dimerization of cyclopentadiene presents three different reaction mechanisms the endo pericyclic reaction, the exo pericyclic reaction, and the stepwise (diradical). The reaction passes through a well-defined transition state to reach the product, without other stationary points along the reaction coordinate.…”

“…We close with a historical remark. The development of modeling the pressure effect on chemical reactions began with a seminal paper by Stearn and Eyring [48] in the 1940s, and it has been followed by decisive contributions by Nakahara (1983), [49] Basilevsky (1985Basilevsky ( -1995, [11,12,19] Kl€ arner (1994), [50] Weinberg (2012-2014), [14,15] and Hoffmann (2011). [51] It is a pleasure to recognize that our PCM-XP model has been deeply inspired by all these contributions.…”

“…In this article, we present an extension of the PCM-XP method to study the potential energy surfaces (PES) of chemical reactions at extreme high pressure. With respect to other methods with a similar aim, [11][12][13][14][15] our approach is characterized by a detailed, accurate, and general Quantum Chemical description of the chemical events at extreme pressure. † The article is organized as follows.…”

Supercritical Fluid‐Facilitated Exfoliation and Processing of 2D Materials

“…We are used to thinking in terms of thermal activation, and we have become skilled at analyzing Arrhenius behaviors to estimate activation energies. Activation volumes may also be significant and can be derived from supercritical high‐pressure measurements . It has been suggested that SCFs jam themselves into interlayer spaces to initiate exfoliation.…”

Effect of high pressure on the topography of potential energy surfaces

“…5,6 Although GES are more appropriate for discussion of high pressure effects on condensed phase reaction kinetics and mechanisms, high pressure PES (or, more precisely, enthalpy surfaces) offer a significantly cheaper alternative at sufficiently high levels of compression, when entropy effects are no longer essential. 7 It has previously been demonstrated for the Diels-Alder dimerization of cyclopentadiene 8 and hydrogen transfer between halogen atoms 5 that under the extreme pressure conditions their energy landscapes undergo significant changes resulting in considerable reduction and, sometimes, complete elimination of reaction barriers. In the present work, we discuss general trends in pressure-induced changes to PES of compressed species, and report our findings for hydrogen transfer in hydrocarbon systems and methyl transfer in S N 2 processes in comparison with the results for simple triatomic X-H-Y systems (X,Y= F,Cl,Br).…”