# Orbital Electronegativity Considerations in Resonance Structures

After consulting three organic chemistry texts (Wade, Klein, and Brown), only one actually clearly delineates a few guidelines for picking the most significant resonance structure. The others mention the same factors (maybe less one or two). So in sum, the important factors to consider are:

1) A filled valance shell is preferable to a partially filled valance shell.

2) The more covalent bonds the better.

3) Least separation of oppositely signed charges. I'm thinking this is a Coulombic effect. Some books imply formal charge through the term "charge" but what about partial charges (which are much more reflective of true charges than formal charges. Which one should I really be looking at? Least separation of opposite formal charges or opposite partial charges?

4) Negative charges should generally be assigned to the more electronegative elements; the opposite is true for electropositive elements. Again, formal charge misleads - consider the ammonium ion (positive formal charge on nitrogen; negative partial charge on nitrogen). Again, one book implies formal charge but really, isn't looking at partial charges a bit more informative?

5) Unmentioned factor in any of the three textbooks: What about hybridization? If we have a molecule with two nitrogens, one $\ce{sp}$ hybridized and one $\ce{sp^2}$ hybridized but otherwise identical, shouldn't we also take into account "orbital electronegativity" - i.e. the ability of hybrid orbitals with higher s-character to better stabilize negative charge (and conversely higher p-character better stabilizes positive charge)?

6) Unmentioned factor in any of the three textbooks: Induction? Shouldn't induction also play a role in resonance stabilization? Resonance delocalizes electron(s); can't induction further stabilize electrons? debunked.

• Inductive effects can weaken resonance structures by localizing the electrons (observe the effect of various substituents on aromatic rings). You can't have resonance on $sp^3$ hybridized molecules – Dannnno May 18 '14 at 23:19
• Good points. I'll edit the text to reflect your catch! I should probably have written sp2 hybridization or something! And I should have caught that part about inductive effects localizing reaction; I just had a question answered earlier today about enols. I learned that the hydroxyl group of enols concentrates electron density in the C=C double bond adjacent to the alcohol group. – Dissenter May 18 '14 at 23:23
• Both ammonia and ammonium ion have nitrogen with a formal negative charge (to balance the positive hydrogens). – LDC3 May 19 '14 at 0:35
• Thank you for the comment! Another good term to research! – Dissenter May 19 '14 at 4:08
• What is the question here? – Lighthart May 19 '14 at 20:34