Relevance of the Entropy Factor in Stereoselectivity Control of Asymmetric Photoreactions

Abstract

Entropy as well as enthalpy factors play substantial roles in various chemical phenomena such as equilibrium and reactions. However, the entropy factors are frequently underestimated in most instances, particularly in synthetic chemistry. In reality, the entropy factor can be in competition with the enthalpy factor or can even be decisive in determining the overall free or activation energy change upon molecular interaction and chemical transformation, particularly where weak interactions in ground and/or excited states are significant. In this account, we overview the importance of the entropy factor in various chemical phenomena in both thermodynamics and kinetics and in the ground and excited states. It is immediately apparent that many diastereo- and enantioselective photoreactions are entropy-controlled. Recent advances on the entropy-control concept in asymmetric photoreactions are further discussed. Understanding the entropy-control concept will pave the way to improve, fine-tune, and even invert the chemo- and stereoselectivity of relevant chemical phenomena.1 Introduction2 Role of Entropy in Supramolecular Interactions3 Selected Examples of Entropy-Driven Thermal Reactions4 Classical Examples of Entropy Control in Photoreactions5 Entropy-Driven Asymmetric Photoreactions6 Advances in Entropy Control7 Perspective