Oxirene photolysis experiments

Bachmann, C., N Guessan, T. Y., Debu, F., Monnier, M., Pourcin, J., Aycard, J. P., Bodot, H. Oxirenes and ketocarbenes from a-diazoketone photolysis experiments in rare gas matrices. Relative stabilities and isomerization barriers from MNDOC-BWEN calculations. 

Neither ground-state ethynol (hydroxyacetylene) (80) nor carbenaoxirane (81) appears to be a viable point of ingress to the oxirene-methanoylcarbene system, as both can isomerize to ketene by lower-energy pathways. The limited experimental information available on carbenaoxirane (Section 5.05.6.3.4(f/)) indicates that it is indeed largely isolated from the oxirene-methanoylcarbene manifold (but note the photolysis of ketene in Section 5.5.6.3.4(ff)) appropriate labelling experiments with (the unknown) ethynol have not been performed. 

An extensive series of low-temperature matrix isolation experiments has failed to provide any evidence of oxirene formation, either by diazo ketone photolysis (82CB2192) or by attempted photo-retro-cycloaddition (82CB2202). 

Flash photolysis allowed even better detection of transient intermediates but the assignment of structures to any metastable intermediate observed in such an experiment is an additional problem This fact is demonstrated very well in an investigation of several naphthoquinonediazides by Tanigaki and Ebbesen (1987, 1989). They assigned oxirene and ketene structures to two successively formed transient species. In other studies (Delaire et al., 1987 Shibata et al., 1988), however, the first transient species was assigned as a ketene and the second the structure 8.99, i. e., the water addition product of the ketene. ... 

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