Oxirene problem

Another system that has yielded results which are dependent on the level of theory used, but which unlike the oxirene problem provides a textbook example of a smooth gradation in the nature of the answers obtained, is the ethyl cation (Fig. 5.17). At the Hartree-Fock STO-3G and 3-21G( ) levels the classical... 

Let s start with what looks like a simple problem what can computational chemistry tell us about oxirene (oxacyclopropene, Fig. 9.1 the oxirene literature till 1983 has been reviewed [2]). Labelling one of the carbons of a diazo ketone (R-C(N2)-CO-R) can lead to a ketene with scrambled labelling. After excluding the possibility of scrambling in the diazo compound, this indicates that an oxirene... 

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. ... 

Evidence for the involvement of oxirenes in the photolysis and thermolysis of a-carbonyldiazo compounds (54, 56) was obtained from the fate of isotopic labels, as indicated in Scheme 9. Nevertheless, the goal of detecting an oxirene directly proved elusive. The problem was dealt with in a study of the matrix photolysis of diazoketones, from which it was concluded that oxirenes were, at best, intermediates lying in very shallow energy wells. ... 

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