ABSTRACT
Chemists have long recognized the important role the reaction media (solvents with varying characteristics) play in controlling the rates, product distributions and stereochemistry of organic reactions. Recently, much effort has been directed toward the use of organized media to modify the photochemical reactivities achieved with isotropic liquids [1,2]. A principal goal of such studies is to utilize the order of the medium to increase the rate and selectivity of a chemical process in much the same way that enzymes modify the reactivity of the substrates to which they are bound. Notable among themanyordered or constrained systems aremicelles,microemulsions, liquid crystals, inclusion complexes, monolayers and solid phases such as porous solids (silica, alumina, clay, and zeolites) and crystals [3-77]. The differences in chemical reactivities occurring in orderedmedia as compared to isotropic solvent phases are largely due to the physical restraints imposed by the environment. These include preventing large amplitude conformational, configurational and translational changes along the reaction coordinate, and modifying diffusional characteristics of reactants and facilitating alternate reactionpathways. The intrinsic reactivity of amolecule in anorderedmedium is frequently of secondary importance in comparison to features such as site symmetry, nearest neighbor separation, and other geometric considerations.
