✍ Scribed by Günther Maier; Axel Bothur
No coin nor oath required. For personal study only.
The thermally induced ring opening of 1 and 5 proceeds with found, a behaviour that corresponds with the known photochemistry of cyclobutenes. A surprising reaction was high stereospecifity in a conrotatory fashion in agreement with the Woodward-Hoffmann rules. Upon flash pyrolysis of found if 1 and 5 were irradiated in a xenon matrix with λ Ͼ 270 nm. The precursors, which were photostable in an argon 1 the matrix-isolated (Xe, 12 K) products 2a and 2b were found, whereas the corresponding reaction of 5 yielded 3a matrix, opened the ring in a conrotatory fashion, the expected pathway for a thermal reaction. In this case the and 3b. The s-cis conformers 2b and 3b were identified for the first time by comparison of the experimental and light is absorbed by the solid xenon in a cooperative process with the precursor molecules. A detailed discussion of the calculated (BLYP/6-311G*) IR absorptions. A nonstereospecific photochemical reaction could be observed if possible energy transfer mechanisms is given. Most probably, a hot ground-state reaction of vibrationally excited matrix-isolated (Ar or Xe, 12 K) 1 was excited directly with λ = 193 nm. Products of the allowed disrotatory pathway as 1 and 5 occurs, although the reaction of the radical cations cannot be excluded. well as those of the forbidden conrotatory reaction were
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