Abstract
Quantum mechanical tunneling offers an alternative pathway to the classical (thermal) overcoming of energetic barriers, by penetrating these barriers instead. Recent years have shed light on its impact on organic synthesis in terms of kinetics, reaction outcomes and lifetimes (and thus feasibility) of reactive intermediates or supposedly stable products. This concept article summarizes recent computational and experimental studies and illuminates how the insights from these studies, e.g. regarding the concepts of tunneling control and instability, should inform synthesis design and optimization.