Dibenzoylketene 5 undergoes degenerate 1,3-shifts of the phenylgroup between acyl and ketene carbon atoms, thus interconverting it with 6 and 7. This 1,3-shift takes place in the gas phase under flash vacuum thermolysis (FVT) conditions, but not in solution at 110-145 degrees C. Imidoyl(benzoyl)ketene 13 undergoes degenerate 1,3-shift of the phenylgroup on FVT, thus interconverting it with 14, but the ketenimine