Mechanistic Aspects of Ketene Formation Deduced from Femtosecond Photolysis of Diazocyclohexadienone, o-Phenylene Thioxocarbonate, and 2-Chlorophenol
2013
Burdzinski, Gotard | Kubicki, Jacek | Sliwa, Michel | Réhault, Julien | Zhang, Yunlong | Vyas, Shubham | Luk, Hoi Ling | Hadad, Christopher M. | Platz, Matthew
The photochemistry of diazocyclohexadienone (1), o-phenylene thioxocarbonate (2), and 2-chlorophenol (3) in solution was studied using time-resolved UV–vis and IR transient absorption spectroscopies. In these three cases, the same product cyclopentadienyl ketene (5) is formed, and two different mechanistic pathways leading to this product are discussed: (a) rearrangement in the excited state (RIES) and (b) a stepwise route involving the intermediacy of vibrationally excited or relaxed carbene. Femtosecond UV–vis detection allows observation of an absorption band assigned to singlet 2-oxocyclohexa-3,5-dienylidene (4), and this absorption feature decays with an ∼30 ps time constant in hexane and acetonitrile. The excess vibrational energy present in nascent carbenes results in the ultrafast Wolff rearrangement of the hot species. IR detection shows that photoexcited o-phenylene thioxocarbonate (2) and 2-chlorophenol (3) efficiently form the carbene species while diazocyclohexadienone (1) photochemistry proceeds mainly by a concerted process.
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