Are cumulenones kinked? A systematic high-level ab initio study of H2CCCO, H2CCCCO and H2CCCCCO

Abstract The cumulenones, propadienone (H 2 C C C O), butatrienone (H 2 C C C C O) and pentatetraenone (H 2 C C C C C O) have been systematically investigated with high-quality ab initio methods. At our highest levels of theory, the equilibrium structures of all three cumulenones show significant bending in the heavy-atom chain. Although the barrier to linearity of the carbon chain is significant for propadienone (approximately 5 kJ mol −1 ), the calculated barriers for butatrienone and pentatetraenone are very small (less than 0.5 kJ mol −1 ). Calculated spectroscopic properties of the cumulenones are in good agreement with available experimental data.