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Unformatted text preview: Chem 8A, Spring 09: Details about delocalized electrons and resonance structures Guidelines for predicting how much a structure contributes to a resonance hybrid: [as if you are comparing the relative energies (stability) between the structures] (in order of importance) 1) All Atoms with Filled Octets: Second row elements (C, N, O , F) want an octet (filled valence shell of electrons). Because C is the least electronegative, structures in which C has 6 electrons, 3 bonds and a positive charge are possible (not possible with N, O, F). 2) Minimum # of Formal Charges & Maximum # of Bonds 3) Negative Charges on Most Electronegative Atoms: O > N > C 4) Minimize Charge Separation: Try to keep the formal charges close together. 1) Only electrons move! Nuclei and the sigma- (single bond-) framework are unchanged. This means that you can not break a single bond!! 2) Every resonance structure must be a valid Lewis structure ....
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