Liquid-Crystalline Solvents as Mechanistic Probes. 26. Norrish II Photolyses and Deuterium Magnetic Resonance Studies on the Solubilization Sites and Mobilities of 2- and sym-Alkanones in Interdigitated and Bilayer Phases of Aqueous Surfactants

Article abstract of DOI:10.1021/ja00215a028

The Norrish II photolyses of 2- and sym-alkanones have been conducted in the aqueous gel phases of potassium stearate (KS), potassium palmitate (KP), and a 1/1 molar ratio of potassium steaate/1-octadecanol (KSO).From the elimination/cyclization and trans/cis cyclobutanol product ratios and deuterium magnetic resonance studies, we have been able to identify the initial ketone solubilization sites and the influence exerted by the ordered solvents on the intermediate 1,4-biradicals.Both the polarity and order of the local environment of the biradicals within the gels determine the product ratios.When the solutes are less than about equal in length to the solvent amphiphile, they reside in extended conformations within a lipophilic layer; when the solutes are much longer than the amphiphile, they adopt a U-shape in order to remain within a single layer.Surprisingly, the long solutes remain U-shaped even in bulayers that could accommodate their extended conformations.In the gels, the product ratios are controlled by the lipophilic ordering imposed on the sym-alkanones and by the polarity of the layer interface experienced by the 2-alkanones.The trans/cis cyclobutanol ratios from the Norrish II reaction of the sym-alkanones, especially, display a very strong dependence upon the length matching between the ketones and the surfactants.The results suggest that small differences in solute order can lead to large differences in reaction selectivities.