[jamestemple]

I am at a community college and we are currently studying aromatic compounds.  After listening to a lecture about heterocyclic compounds it occured to me that furan should have a higher resonance energy than thiophene.  This is obvoiusly not the case since furan has an energy of 16 kcal/mol and thiophene has an energy of 29 kcal/mol.  I asked my teacher this and she drew a blank.  

[movies]

How did you come to the conclusion that furan should have a higher resonance energy?  And what precisely do you mean by "resonance energy"?  The aromatic stabilization energy?

I think that the best explanation is that the aromaticity decrease as the electronegativity of the heteroatom increases (O is more electronegative than S).  A more electronegative atom is less "willing" to donate its electrons to the aromatic system.  In effect, the electrons are more localized on a very electronegative atom than in the rest of the aromatic ring.  Benzene is the most stable simple aromatic because all of it's bonds and atoms are the same.