Molecular Orbitals

[Andrew Polyak]

Hey All,

 

I have quite a few questions about drawing molecular orbitals. How does one know what endergy differences to draw? Are they given? I'm in organic chemistry 1, and I'm having a really bad time.

 

Any insight would be appreciated!

[spirochete27]

As a general rule, the relative energy of orbitals in organic molecules goes sigma<pi<n<pi star<sigma star. Thus in alkenes the homo will be a pi orbital and the lumo will be a pi star orbital.

 

This ordering is generally true because antibonding orbital is always destabilized slightly more than a bonding orbital is stabilized. So antibonding orbitals are roughly a mirror image of their corresponding bonding orbitals.

 

The exact relative energies are found through very complex calculations using powerful computers, and even then the numbers are often wrong. You would not be expected to know that.

Edited September 12, 2013 by spirochete27