Part I: Photochemical reactions in supercritical carbon dioxide Part II: Conformational analysis of the photocycloadduct of N-acylindoles with cyclopentene.

摘要

Part I. The photochemical decomposition of 2'-p-methylphenyl-2-2'-azopropane and the photoinduced homolysis of (4-methylphenyl)phenylmethyl chloride were used as probes for the investigation of solute-solvent clustering in supercritical carbon dioxide. These photolyses proceed via solvent-caged singlet radical pairs that results in products formed from either in-cage recombination or cage-escape recombination. In supercritical carbon dioxide, the photochemical decompositions of 2'- p-methylphenyl- 2-2'-azopropane demonstrated the relative yield of the cage escape products decreases considerably as the pressure or density of carbon dioxide is reduced in the near critical region. This observation has been attributed to solute-solvent clustering phenomenon reported in supercritical carbon dioxide. The photoinduced homolysis of (4-methylphenyl)phenylmethyl chloride did not show any evidence of solute-solvent clustering. The photolysis study followed a typical viscosity trend for a cage reaction where the formation of cage escape products increases as the pressure or density of carbon dioxide decreases.;Part II. The conformations of three N-acylindole photocycloadduct with cyclopentene were found to exist as two slowly interconverting conformers: the syn conformer and the anti conformer. The interconversion arises from the restricted rotation around a single bond within the amide moiety such that the conformational interconversion becomes slow on the nmr time scale. The isolation of the syn and anti conformers of allowed for the kinetic study of the interconversion of the two conformers by 1H-nmr spectroscopy. The results were compared to those predicted by molecular mechanics calculations.