[ethylenediamine]

1) Construct two MO diagrams for C2: one with sp mixing and one without.
the following for each MO diagram:
a. What is the bond order?
b. Is the molecule paramagnetic or diamagnetic?
c. Would you expect to observe sp mixing? Please explain.

How should I start this??? Any help will be appreciated.

[Dan]

How far have you got? Do you have the MO diagram?

[DevaDevil]

First of all you start with taking a single carbon atom.

Make the MO first without sp-hybridisation: (1s) 2s orbital, 3 2p
Fill in with electrons; 6 of them
Then you put 2 of them next to each other and make the C₂ diagram, with bond coupling.
Fill in with the total of 2 x 6 (12) electrons, from the bottom.
Look at the filled orbitals: (Bonding - Antibonding) gives the bond order.
Are all the electrons coupled? Yes: Diamagnetic, No: Paramagnetic

Then with sp-hybridisation:
Make the single MO again: (1s) 3 sp² and 1p_z
Put 2 of them next to each other again, and fill in the electrons.
Bond order is again (Bonding-Antibonding), and magnetism is the same definition as well.

Which one has the highest bond order? So which one will you expect to see?



Spoiler for the non-sp-hybridised Carbon (1s orbital not displayed):
Here