Effects of Electric Fields on Structure and Reactivity: New Horizons in Chemistry
CHAPTER 2: The Impact of Electric Fields on Chemical Structure and Reactivity
Published:05 Mar 2021
S. Shaik, D. Danovich, K. D. Dubey, and T. Stuyver, in Effects of Electric Fields on Structure and Reactivity: New Horizons in Chemistry, ed. S. Shaik and T. Stuyver, The Royal Society of Chemistry, 2021, pp. 12-70.
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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.