Ab initio molecular orbital
theory with minimal (STO-3G) and split- valence (4-31G) basis sets has been
used to obtain fully optimized structures for propadienone, allene, butatriene,
carbon dioxide, ketene and vinylidene. Propadienone is predicted to be a planar
molecule with C2V symmetry. The systematic deficiencies of the
STO-3G and 4-31G basis sets have been taken into account in deriving a complete
ro structure for propadienone. A striking feature of this structure
is the HCH angle (117.°) which is about 5° smaller than the corresponding
angle (122.3°) in ketene. An estimate (125 kJ mol-1) of the heat of
formation of propadienone is reported. The alternating dipole moment magnitudes
in the series H2CO, H2CCO and H2CCCO are
explained in terms of orbital interactions. Propadienone is predicted to be considerably
(about 135 kJ mol-1) more stable than vinylidene+carbon
monoxide but slightly (about 10-20 kJ mol-1) less stable than acetylene+carbon monoxide.
