Push-pull substitution evidently does not stabilize the oxirene system: an AM1 and ab initio study

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AM1 and ab initio calculations were performed on 1-amino-2-methanoyloxirene (1-amino-2-formyloxirene), the two corresponding oxo carbenes (“ketocarbenes”) resulting from alternative CO cleavage, and the transition states linking these species. The purpose was to see if delocalization of electron density from the double bond by the push-pull effect of the substituents would stabilize the oxirene system by diminishing its antiaromaticity. This stabilization was not seen: although at the AM1 level the oxirene is a relative minimum, it is merely an inflection point at the HF/3-21G level, and at the HF/6-31G ∗ and MP2(FC)/6-31G ∗ levels the oxirene is merely a transition state.