Photochemistry of α-oxo-oximes. Part 1. Photoisomerization of biacetyl mono-oxime ethyl ether

Abstract

Upon irradiation at 366 nm (E)-3-ethoxyiminobutan-2-one undergoes EZ-isomerization. By spectroscopic analysis [i.r., u.v., and n.m.r. (a.s.i.s.)] it was established that the E- isomer exists in the s-trans-and the Z-isomer in the s-cis-conformation. The photostationary state (PSS) ratio obtained by direct irradiation of both the (E)- and the (Z)-oxime ether was found to be 6.0 (±0.3) :1. The isomerization could also be induced by triplet sensitization. The plot of the PSS ratio against the triplet energy of the sensitizer shows three distinct regions, indicating different routes of energy transfer. It is suggested that the reactive states in the direct photoisomerization and the tripletsensitized isomerization are the same.