Abstract
Time-resolved electronic absorption spectroscopy has been successfully applied to clarify the mechanism of the “abnormal” photochemical cleavage of 4-nitrophenyl piperidinoalkyl ethers induced by controlled Coulombic disturbance of the “normal” electronic distribution of the radical anion intermediate. Thus, photolysis of 1-piperidino-2-(2-methoxy-4-nitrophenoxy)ethane (a system with an amine with limited freedom of motion) in acetonitrile leads to C−O bond photocleavage in a relatively slow process (k ≈ 4 × 105 s-1) from intermediate species that show radical-ion pair behavior. Systems with higher freedom of motion of the amine moiety, such as 1-piperidino-5-(2-methoxy-4-nitrophenoxy)pentane or 4-nitroveratrole + triethylamine, show the intermediate radical-ion pairs mainly evolving to reduction products, probably a result of intermediates with geometries not allowed for the system with limited freedom of motion of the amine.
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