Why is CO a Lewis base?
Because it can be a
It's also a
- If you examine the HOMO, which is the
#3a_1#, even though it is energetically owned by oxygen, the carbon lobe is bigger (the wave function coefficient is larger), lessening its Lewis basic behavior.
Even so, it donates electrons from its
#sigma#MO (on the carbon side) as a #sigma#donor in Ligand Field Theory.
- If you examine the LUMO, which is the
#2b_1#or #2b_2#, it is energetically owned by carbon, AND the lobes on carbon are bigger (the wave function coefficient is larger).
Thus, it accepts electrons into its
#pi^"*"#MOs (on the carbon side) as a #pi#acceptor in Ligand Field Theory.
As a result, CO is both a Lewis acid and a Lewis base, and it demonstrates that in Ligand Field Theory as a sigma donor and pi acceptor.
Well, what is a
It is an electron pair DONOR....i.e. carbon monoxide contains a lone pair of electrons that can BIND to transition metals for example.
The back donation is ANTIBONDING with respect to the