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Abstract
This work explores the intriguing domain of Frustrated Radical Pairs (FRPs) and their potential to form non-covalent dimers, termed Entangled Radical Pairs (ERPs), which exhibit unique singlet ground states and potential concerted reactivity, differing from traditional stepwise reactions. A few recent publications showed that in certain cases when two radicals cannot form a covalent bond, they unexpectedly form a non-covalent dimer with a singlet ground state. This potentially opens a new elusive route of FRPs’ reactivity, in which both radicals react simultaneously as one molecule. Here, we review several published articles, in which such reactivity probably took place, but was overlooked. The idea presented in this proposal suggests a path towards many interesting reactions, such as low-temperature metal-free dehydrogenation of aliphatic hydrocarbons and others. Additionally, an alternative mechanism for the reactivity of Frustrated Lewis Pairs (FLPs) based on the ERP framework is proposed. Lastly, the implications of the ERP model on the general theory of chemical bond formation are contemplated, suggesting a revision of the traditional views on hybridization and electron entanglement. The manuscript calls for further experimental and theoretical investigations to substantiate the presented hypotheses, aiming to unlock new pathways in radical chemistry and beyond.
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Description
When two radicals collide to make a chemical bond, a new molecular orbital forms on which the two previously unpaired electrons become paired. Pauli's Exclusion Principle states that two electrons in the same orbital must have opposite spins. That means that upon the formation of the bond, the two electrons that before the collision were each in a superposition of both spins (positive and negative) become "entangled", i.e. still exist in a superposition but with spins of opposite signs. The bond formation and the entanglement are believed to happen simultaneously upon collision. But several recent publications suggest that at least in certain cases they might happen independently. I.e., if the collision is prevented and the radicals are stopped at a certain distance - the electrons interact to acquire the superposition of opposite spins without bond formation. This may have interesting implications for organic chemistry and beyond.
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