Abstract
AbstractThe photoisomerization of a series of (highly) crowded α‐oxo oxime ethers (3–8) has been studied under conditions of direct irradiation (λ 300 and 350 nm) and of triplet photosensitization. The decay ratios k5/k6 for the two conditions are the same for a given compound, illustrating that the isomerization of the α‐oxo oxime ethers, upon direct irradiation, also proceeds from the (lowest) excited triplet state. The excited singlet and triplet state energies are reported, as well as ΔG0(E)‐ΔG0(Z) for 4 (‐ 8.2 ± 0.5) and 6 (7.7 ± 0.5 kJ·mol−1), determined by thermal equilibration with I2 at 353 K. The decay ratio k5/k6 is significantly smaller for 4 and 5 than for 3 and 6‐8 due to steric hindrance upon relaxation of the perpendicular ground state to the (E)‐isomer of 4 and 5.
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