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A ketene comes and goes: The first intermediate in the photoredox reaction of o-nitrobenzaldehyde (1) is identified as ketene 2. In a femtosecond IR experiment a resonance at 2100 cm−1 corresponding to the ketene stretching vibration appears less than one picosecond after photoexcitation. The 90-ps decay of this band is a manifestation of a nucleophilic addition to the CC double bond, which is supported by other spectroscopic experiments (IR and Raman).
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Laimgruber et al. (2005) studied this question.
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