Hel photoelectron studies of unstable ketenes: mono- and di-phenylketenes, and their gas-phase conformations
Hel photoelectron spectra are reported for the semistable mono- and di-phenylketene molecules generated in high yield by in situ metal dehalogenation reactions of the appropriate chlorophenylsubstituted acid chlorides. The photoelectron results can be interpreted through a simple perturbation approach, and in conjunction with semiempirical MNDO and AM1 calculations provide gas-phase structural evidence for a planar π-conjugated monophenylketene molecule, and a non-planar diphenylketene species in which both phenyl groups are rotated, in a conrotatory fashion, some 30–40° out of the [graphic omitted]CCO π system. The limitations of the MNDO method and the greater reliability of AM1 for the assessment of the relative energies of rotational conformers is discussed. HAM/3 calculations are in excellent agreement with the experimental ionisation potentials.