[plu]

Hello,

Would the presence of electron-donating groups on a benzene ring (such as on phenol or aniline) lower or raise the energy of the ring's bonding molecular orbitals?  I believe these groups would stabilize the bonding molecular orbitals and thus lower their energies but I am not certain.  Thanks for any *delete me*

[fishyuyue]

for benzene, it always undergoes electrophilic subsititution reaction.  The electron-donating group cann increace the charge density in benzene and  activate the benzen. It is more active and it molecular obital energy is increased. That is my view

[plu]

Thank you for your reply, fishyuyue.  I've been thinking more about the problem and I've tried relating it to the differences in the energies of the atomic orbitals of different elements.  For example, the 2s and 2p atomic orbitals of oxygen are lower in energy than those of carbon (this can clearly be seen when one looks at a molecular orbital diagram of carbon monoxide).  Is this because of the increase in electron density on oxygen?  If so, can this concept be applied to benzene derivatives (electron-donating groups decrease molecular orbital energies) ?

[nearly.alex]

from my view you are right, the reason for the oxygen in carbon monoxide having lower energy 2p and 2s orbitals is because the great effective nuclear charge which the electrons experience in oxygen. thus they are closer to the nucleus and at a lower energy level. in the carbon monoxide energy level diagram the (largely) oxygen lone pair cancels out with the lowest carbon oxygen sigma bond. but they dont cancel out perfectly so add to the bond energy a little bit. from my knowledge this can be applied to any other energy level diagram.

[fishyuyue]

from my view you are right, the reason for the oxygen in carbon monoxide having lower energy 2p and 2s orbitals is because the great effective nuclear charge which the electrons experience in oxygen. thus they are closer to the nucleus and at a lower energy level. in the carbon monoxide energy level diagram the (largely) oxygen lone pair cancels out with the lowest carbon oxygen sigma bond. but they dont cancel out perfectly so add to the bond energy a little bit. from my knowledge this can be applied to any other energy level diagram.

I don't agree with you.No hybridization for C in CO. But sp2 hybridization for C in Benzene. The chemical surrouding is differnt.
The Molecular Obital Theory  is based on experiemental result. The electron-donating group really increases the reactivity of benzene. There is basic principle in nature:More energy , more reactive. So MO in bezene is increased
This is my view!