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MO Diagrams for Heteronuclear Diatomic Molecules

by ThomasMagnus
Tags: diagrams, diatomic, heteronuclear, molecules
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ThomasMagnus
#1
Mar31-14, 07:06 PM
ThomasMagnus's Avatar
P: 138
I'm trying to understand how to draw MO diagram for molecules such as CO, HF, and NO. I am finding so much conflicting information on how to order the σ and pi boxes in the diagram. Now, I know that the more electronegative atom's orbitals are going to be lower in energy than the less electronegative atom.

I have learned so far that there are two ways to set up MO diagrams for homo-nuclear diatomic molecules: one was with the pi 2p bonding MO below the σ2p bonding orbital and the reverse for atoms with an atomic number ≥8. How can this be applied to heteronuclear molecules? I keep finding different sources using both ways:

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Are both correct then?

Thanks!
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DrDu
#2
Apr1-14, 03:33 AM
Sci Advisor
P: 3,596
The correct order of the orbitals depends on the s-p energy gap in both atoms, the relative energetic distance of the s and p orbitals on both atoms, respectively, the orbital overlapp etc. So to obtain the correct ordering will require a calculation.
You may try this yourself using e.g. some Extended Hueckel Calculators:
http://www.chembio.uoguelph.ca/educm...5/software.htm
or
http://yaehmop.sourceforge.net/

On the other hand, the correct ordering is often not important, e.g. when both orbitals whose relative energy is unclear are both occupied.


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