Cyclobutanes, anisotropy

In studies where cholesteric phase order appears to influence the course of bimolecular reactions, solute diffusion and collisional orientations appear to be affected by solvent anisotropy. An example is the stereoselective photodimerization of 1,3-dlmethylthymine(24). While all four possible cis-fused cyclobutane photodimers are produced in isotropic solutions and disordered glasses, the cis-syn dimer is formed almost exclusively in liquid-crystalline media. Furthermore, selectivity of reaction products in the mesophases is greatly decreased upon addition of an isotropic diluent which disturbs local solvent order (e.g., dioxane or DMSO). Since all of the... 

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