Cavity Quantum Electrodynamics Enables para- and ortho-Selective Electrophilic Bromination of Nitrobenzene

Abstract

Coupling molecules to a quantized radiation field inside an optical cavity has shown great promise to modify chemical reactivity. In this work, we show that the ground-state selectivity of the electrophilic bromination of nitrobenzene can be fundamentally changed by strongly coupling the reaction to the cavity, generating ortho-or para-substituted products instead of the meta product. Importantly, these are products that are not obtained from the same reaction outside the cavity. A recently developed ab initio approach was used to theoretically compute the relative energies of the cationic Wheland intermediates, which indicate the kinetically preferred bromination site for all products. Performing an analysis of the ground-state electron density for the Wheland intermediates inside and outside the cavity, we demonstrate how strong coupling induces reorganization of the molecular charge distribution, which in turn leads to different bromination sites directly dependent on the cavity conditions. Overall, the results presented here can be used to understand cavity induced changes to ground-state chemical reactivity from a mechanistic perspective as well as to directly connect frontier theoretical simulations to state-of-the-art, but realistic, experimental cavity conditions.

Comparing parameterized and self-consistent approaches to ab initio cavity quantum electrodynamics for electronic strong coupling

“…In the limit of molecular electronic strong or ultra-strong coupling to one or a few molecules, it is desirable to treat the molecular electronic degrees of freedom using the tools of ab initio quantum chemistry, yielding an approach referred to as ab initio cavity quantum electrodynamics (ai-QED), where the photon degrees of freedom are treated at the level of cavity quantum electrodynamics. Two complementary approaches have emerged for ai-QED: (1) parameterized CQED 20,[23][24][25][26][27] (pQED), a twostep approach where the matter degrees of freedom are computed using existing electronic structure theories, enabling one to build rigorous ai-QED Hamiltonians in a basis of many-electron eigenstates, and (2) self-consistent CQED 19,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] (scQED), a one-step approach where electronic structure methods are generalized to include coupling between electrons and photon degrees of freedom.…”

Do Molecular Geometries Change Under Vibrational Strong Coupling?

“…In almost every example, both a fixed orientation relative to the polarization axes of the cavity mode and fixed molecular geometries are assumed, despite the fact that the coupling strengths used are quite large. Recently, first studies − have highlighted the importance of orientation with respect to the cavity polarization mode.…”