The Wolff rearrangement of six-membered ring o-diazo ketones, 1-oxo-2-diazo-1, 2- dihydronaphthaIene (DNQ) and its four 4-and 5-sulfonate analogues, l-oxo-2-diazo-1, 2- dihydrobenzene (DBQ), and diazoMeldrum (DM), are studied in solution at room temperature by laser flash photolysis. A presursor to a ketene is observed in most cases. It is assigned to be an oxirene on the basis of reactivity, kinetic results, and thermodynamic ...