Dibenzoylketene 5 undergoes degenerate 1, 3-shifts of the phenyl group 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° C. Imidoyl (benzoyl) ketene 13 undergoes degenerate 1, 3-shift of the phenyl group on FVT, thus interconverting it with 14, but the ketenimine isomer 15 is not formed, and none of ...