What is the bond order of CO

To construct the MO scheme of CO

The MO scheme of a molecule made up of atoms of different electronegativity cannot simply be drawn free-hand. However, if the orbital energies and the contributions of the individual atomic orbitals to the molecular orbitals are determined by quantum chemical calculations, the scheme can be interpreted plausibly. The following results for carbon monoxide: The valence shell of carbon provides four atomic orbitals, namely the 2s and three 2p orbitals; in the case of oxygen there are also the 2s and three 2p orbitals, but here these are in line with the higher electronegativity of oxygen at lower orbital energy. If the z-axis is chosen as the C-O bond direction, there are two px- and py-Orbitals opposite each other in such a way that two degenerate bonding and two degenerate antibonding π-orbitals arise (dashed lines in the figure). The s and p remain on each atomz-Orbital left that can be combined to form bonding and antibonding interactions of the σ-type. How these four atomic orbitals come together to form four molecular orbitals can be read from the shape of these MOs shown in the main text:

Atomic orbitals of C and O as well as MOs of the CO molecule (for the O-Ato, α and β spin orbital energies were averaged). Note that the orbital energies of unoccupied orbitals are largely meaningless.

1σ and 3σ are orbitals without a nodal plane between the nuclei, they are binding, 2σ and (the not shown) 4σ, on the other hand, have a nodal plane between the nuclei and are therefore essentially antibonding (at 1π and 2π [= π and π *] is each a Orbital shown, the second is created by a 90 ° rotation around the z-axis). If the total of 10 valence electrons from carbon and oxygen are filled into the MOs, then 3σ results as the highest occupied orbital. One speaks of the "HOMO" from English. Highest Occupied M.olecular Orbital. The unoccupied orbital of lowest energy, the "LUMO" - from English. L.east Unoccupied M.olecular Orbital -, is the 2π orbital. HOMO and LUMO together form the "frontier orbitals" (engl. frontier orbitals) of the carbon monoxide molecule. The frontier orbitals of a molecule determine its chemical behavior to a particular degree. Note that the frontier orbitals of CO are more strongly localized on carbon, i.e. on the atom that also establishes the bond to a metal.