[Nescafe]

So in clayden Organic textbook they refer to sigma as the bonding orbital, sigma* as the antibonding orbital. When Sigma and Sigma* are both full they say these electrons cancel eachother out and they call these electrons nonbonding pairs of electrons that do not contribute to the bonding. Eghhhh. This confuses me, also later on they show energy diagrams such as this:


 _______    Pi*



_11_   _11_           Nonbonding lonepairs (please assume each #1 represents an electron and they they are opposite spin). Which orbitals do these lonepairs occupy? They dont give the orbital a label (like pi or sigma) they just call these nonbonding lone pairs


___11____ Pi

This was the molecular orbital diagram of Acetone. Those nonbonding lone pairs are those of the oxygen in the carbonyl. I just don't get which orbitals (pi, pi* or sigma, sigma*) do these nonbonding electrons occupy.

Please help me untangle this in my head, its bugging me and I have been looking online but I get more confused!

Nescafe.

[Nescafe]

For acetone I would arrange the MO as follows: (correct me if I am wrong please)


__ C-O Sigma*

__ __ C-H sigma *

__ C-O Pi *

_11_ _11_ Nonbonding electrons (Name of such an orbital?)

_11_  C-O pi

_11_ _11_  C-H sigma

_11_ C-O sigma