This paper is dedicated to the memory of the late Professor Rajendra Rathore, Marquette University and the late Professor Jay K. Kochi, Houston University.
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 Introduction
2 Role of Entropy in Supramolecular Interactions
3 Selected Examples of Entropy-Driven Thermal Reactions
4 Classical Examples of Entropy Control in Photoreactions
5 Entropy-Driven Asymmetric Photoreactions
6 Advances in Entropy Control
7 Perspective
Key words
entropy-controlled asymmetric photoreactions - enantio- and diastereodifferentiating photoreactions - temperature dependence - Eyring analysis - enthalpy and entropy compensation