Linear free energy relationships in electrostatic catalysis

TL;DR

This paper introduces a linear free energy relationship in electrostatic catalysis that links changes in activation energy to reaction energy, verified through first-principles calculations, revealing new insights into reaction mechanisms under electric fields.

Contribution

It develops a microscopic linear free energy relationship for electrostatic catalysis, connecting kinetic and thermodynamic effects, and demonstrates its validity with computational examples.

Findings

Linear free energy relationships are observed in electrostatic catalysis.

The relationship can predict shifts to early or late transition states.

A counterintuitive case shows product stabilization can increase activation energy.

Abstract

The use of electric fields to modify chemical reactions is a promising, emerging technique in catalysis. However, there exist few guiding principles, and rational design requires assumptions about the transition state or explicit atomistic calculations. Here, we present a linear free energy relationship, familiar in other areas of physical organic chemistry, that microscopically relates field-induced changes in the activation energy to those in the reaction energy, connecting kinetic and thermodynamic behaviors. We verify our theory using first-principles electronic structure calculations of a symmetric S$_\mathrm{N}$2 reaction and the dehalogenation of an aryl halide on gold surfaces and observe hallmarks of linear free energy relationships, such as the shifting to early and late transition states. We also report and explain a counterintuitive case, where the constant of proportionality relating the activation and reaction energies is negative, such that stabilizing the product increases the activation energy, i.e., opposite of the Bell-Evans-Polanyi principle.