The Effect of Pressure on Organic Reactions in Fluids—a New Theoretical Perspective

Abstract

This Review brings a new perspective to the study of chemical reactions in compressed fluid media. We begin by reviewing the substantial insight gained from more than 50 years of experimental studies on organic reactions in solution under pressure. These led to a proper estimation of the critical roles of volume of activation (Δ≠V) and reaction volume (ΔV) in understanding pressure effect on rates and equilibria of organic reactions. A recently developed computational method, the XP‐PCM (extreme pressure polarizable continuum model) method, capable of carrying out quantum mechanical calculations of reaction pathways of molecules under pressure, is introduced. A case study of the Diels–Alder cycloaddition of cyclopentadiene with ethylene serves, in pedagogical detail, to describe the methodology. We then apply the XP‐PCM method to a selection of other pericyclic reactions, including the parent Diels–Alder cycloaddition of butadiene with ethylene, electrocyclic ring‐opening of cyclobutene, electrocyclic ring‐closing of Z‐hexatriene, the [1,5]‐H shift in Z‐pentadiene, and the Cope rearrangement. These serve as examples of some of the most common combinations of Δ≠V and ΔV. Interesting phenomena such as a shift in a transition state along a reaction coordinate, a switch of rate‐determining step, and the possible turning of a transition state into a stable minimum are revealed by the calculations. A reaction volume profile, the change in the volume of the reacting molecules as the reaction proceeds, emerges as being useful.

Non‐Bonded Radii of the Atoms Under Compression

“…One advantage of the XP‐PCM method is that it, in principle, allows the use of any level of theory in computing compression of single atoms and molecules [1,75,107–109] . In this work, we rely on all‐electron relativistic density functional theory (DFT) calculations using the Perdew‐Burke‐Ernzerhof hybrid‐exchange correlation functional PBE0 [110] .…”

Mechanochemistry in [6]Cycloparaphenylene: A Combined Raman Spectroscopy and Density Functional Theory Study

“…Recently significant progress has been achieved in the computational modeling of organic materials under high pressures yielding important new theoretical insights. [1,2,3] Mechanochemistry, as this general area of chemistry is referred to, deals with chemical effects of external pressures and forces on molecules and aggregates. This often yields unexpected changes of solid-state and molecular properties and leads to surprising reactivities .…”

Benchmarking of DFT methods using experimental free energies and volumes of activation for the cycloaddition of alkynes to cuboidal Mo3S4 clusters

“…Interestingly, a specific computational method has been developed recently to study the effect of extreme pressure on reactions taking place in solution (XP‐PCM), [ 63,64 ] ultimately allowing one to compute Δ V reac and Δ V ‡ values. [ 65 ] Unfortunately, the range of pressures required to obtain Δ V ‡ values via XP‐PCM calculations goes from 0 to 8 to 10 GPa (1 GPa = 104 bar), that is, two orders of magnitude larger than the highest pressures typically used in the experiments (0‐103 bar). Here, we have instead computed Δ V ‡ values based on the differences between the vdW volumes of transition state structures and reactants, a methodology successfully used, for instance, to study water exchange processes at transition metal complexes.…”