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Dynamic Effects in Ordinary Organic Reaction

 

Dynamic effects are kinetic phenomena associated with the motions and momenta of atoms that cannot be explained using transition state theory.  Dynamic effects cannot be explained using transition state theory, so they violate the paradigm we use to understand reactivity and selectivity in organic chemistry.  It has usually been assumed that reactions impacted by dynamic effects are rare.

We have uncovered a way in which dynamic effects can be important in ordinary organic reactions in solution.  The key is that the reaction must involve two successive transition states without an intervening intermediate.  That may sound impossible; in fact, it is likely quite common.  Our goal is to experimentally test for dynamic effects in diverse organic reactions, pinning down the breadth of chemistry for which our most fundamental concepts and assumptions fail.

The known examples for dynamic effects all fall into a specialized category involving high-energy diradical intermediates in gas phase reactions. Our first example was with singlet oxygen ene reactions, published in J. Am. Chem. Soc. in 2002.  The regiochemistry of these reactions is determined after the rate-limiting transition state and the selectivity is not associated with barriers.  Rather, the product mixture is determined by the detailed momenta of the atoms.

 

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