Ranking Resonance Contributors

Not all resonance forms contribute equally. Use these rules (roughly in priority order) to decide which form is more significant:

1. Complete Octets

Forms where every atom (especially C, N, O) has a full octet are more significant.
An incomplete octet on carbon is a major penalty.

2. Fewer Formal Charges

Forms with fewer formal charges are generally more significant.
A neutral form usually beats a charge-separated form.

3. Negative Charge Placement

Negative charge is more stable on a more electronegative atom.
Electronegativity order: F > O > N > C.

4. Positive Charge Placement

Positive charge is more stable on a less electronegative atom or a more substituted carbon.

5. Aromaticity

Forms that preserve an aromatic ring are strongly favored.
Breaking aromaticity is a large energetic cost.

Equivalent Contributors

Some forms are equivalent by symmetry (e.g., the two C=O forms of a carboxylate).
Equivalent forms contribute equally.

Compare Resonance Contributors

Which resonance form is more significant?

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