The Impact of Electric Fields on Chemical Structure and Reactivity

Abstract

This chapter describes the use of external-electric fields (EEFs) as effectors of chemical change, with the aim of providing a guiding conceptual framework. As such, the following text intends to serve as a teaching material for readers, on how to conceptualize and design electric-field effects on bonds, structures, and reactions. Many of these effects can be comprehended in terms of valence bond (VB) concepts as the field-induced stabilization of ionic structures. Thus, orienting the field along the “bond axis” will facilitate bond breaking. Similarly, orienting the field along the “reaction axis”, the direction in which electron pairs transform from reactant-to product-like, will lower the reaction barrier. Flipping the field's orientation along the reaction axis will cause inhibition. Orienting the field off-reaction-axis will generally control stereo-selectivity and enantioselectivity, and the removal of forbidden-orbital mixing. Three-directional fields will orient the reactants in space and control their reactivity and selectivity patterns. Increasing the field strength for concerted reactions, e.g., in Diels–Alder and oxidative addition reactions, will cause mechanistic-switchover to stepwise mechanisms with ionic intermediates. Examples of bond breaking and control of reactivity/selectivity and mechanistic crossovers are presented and analysed from the “ionic perspective”. Textboxes and rules summarize the various effects of electric fields.

Electron Density Geometry and the Quantum Theory of Atoms in Molecules

“…These observations, drawn from an inspection of the contours in just two planes, are suggestive of more spherical C and O atoms resulting from a field-induced reduction to the CO bond π character. This agrees with our present understanding that an electric field oriented along the carbonyl bond axis will weaken the bond by stabilizing the more ionic field-induced bond structure, 29,30 with a corresponding density decrease at the CO bond CP. 28 Inspecting Global and Local Curvature Distribution.…”

Fast and Simple Evaluation of the Catalysis and Selectivity Induced by External Electric Fields

“…It is important to remark that the truncation at the linear term of eq 4 has been used in the literature to estimate the changes in the energy barriers induced by EEFs and lightemitting diodes (LEDs). 1c,5e, 25 The total electric polarizabilities and hyperpolarizabilities can be divided into the electronic contribution (P el ), the nuclear relaxation (nr) contribution (P nr ), and the curvature contribution (P curv ). 26 = + + P P P P el nr curv…”

Gradient bundle analysis of ketosteroid isomerase

“…Only recently have accurate assessments of electrostatic preorganization become computationally feasible, with researchers now exploring available methods for such assessments. Meanwhile, the effects of applied electric fields on chemical reactivity have been experimentally and computationally observed for a variety of chemical reactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], many of which are also catalyzed enzymatically. Hence the specific problem of electrostatic preorganization, and the general problem of electric field catalysis, are of interest to enzymologists.…”