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