Oxides of Carbon - Linear Carbon Monoxides

Linear Carbon Monoxides

Another family of oxocarbons are the linear carbon monoxides C_nO. The first member, ordinary carbon monoxide CO, seems to be the only one that is stable in the pure state at room temperature. Photolysis of the linear carbon dioxides in a cryogenic matrix leads to loss of CO, resulting in detectable amounts of even-numbered monoxides such as C₂O, C₄O, and C₆O. The members up to n=9 have also been obtained by electrical discharge on gaseous C₃O₂ diluted in argon. The first three members have been detected in interstellar space.

When n is even, the molecules are believed to be in the triplet (cumulene-like) state, with the atoms connected by double bonds and an unfilled orbital in the first carbon — as in :C=C=O, :C=C=C=C=O, and, in general, :(C=)_n=O. When n is odd, the triplet structure is believed to resonate with a singlet (acetylene-type) polar state with a negative charge on the carbon end and a positive one on the oxygen end, as in −C≡C-C≡O+, −C≡C-C≡C-C≡O+, and, in general, −(C≡C-)_n/2C≡O+. Carbon monoxide itself follows this pattern: its predominant form is believed to be −C≡O+.