Matrix trapping, oxirenes

There is no doubt that matrix isolation experiments have provided many examples of great interest in this and other areas where reactive intermediates are produced, a-Diazoketones were discussed in an earlier section since the singlet state reaction undergoes the well-known photo-Wolff process. Other studies on these compounds in matrices at 77 K have shown that the diazoketones 571 and 572 undergo equilibration via an oxirene intermediate. Again this is an example of intramolecular trapping . Others have also observed the formation of oxirenes and the existence of a keto-carbene/oxirene equilibrium in a variety of systems, such as the diazoquinone 573. ... 

Despite these seemingly reliable reports of oxirenes, doubts have recently been raised that any oxirene has been observed under matrix isolation conditions. Most significantly, the computed IR spectrum of bis(trifluoromethyl)oxirene (52 R = R = CF,) differed significantly from the experimental spectrum previously assigned to this species. Extraordinarily accurate agreements between experimental matrix IR spectra and those computed by modern theoretical methods are now routinely achieved. In view of this, a significant discrepancy has to be taken seriously. Therefore, the existence of oxirenes as reaction intermediates, which can be trapped in matrices, is stiU open to question. 

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