Tunneling Control of Chemical Reactions: The Third Reactivity Paradigm.

This Perspective describes the emergence of tunneling control as a new reactivity paradigm in chemistry. The term denotes a tunneling reaction that passes through a high but narrow potential energy barrier, leading to formation of a product that would be disfavored if the reaction proceeded by passage over kinetic barriers rather than through them. This reactivity paradigm should be considered along with thermodynamic and kinetic control as a factor that can determine which of two or more possible products is likely to be the one obtained. Tunneling control is a concept that can provide a deep and detailed understanding of a variety of reactions that undergo facile (and possibly unrecognized) tunneling.