Quantum Mechanical Tunneling Is Essential to Understanding Chemical Reactivity

Quantum mechanical tunneling is a consequence of the wave nature of particles that implies that a particle can penetrate a potential energy barrier even though there is insufficient energy to overcome it. This has serious consequences for chemical reactions, a fact that has, however, not been appreciated fully. Only in the last few years has it become clear how important tunneling is for understanding the rates and selectivities of chemical reactions. This review emphasizes the role that tunneling plays in reactions of exemplary small molecules, where the effects are most readily discerned. Once fully understood, the control and application of tunneling in chemical synthesis, ideally stimulated externally through catalysis or energy transfer, will open fascinating new ways of conducting chemical reactions.