Resonance and bond length

[206189669]

I understand that when a molecule has resonance, you're meant to take the average of the bond lengths if there are a single/double bond in the same place. But, if one structure is clearly more favorable, does that have an affect on the bond length that you report?

[905994971]

The bond length will always be the average of the bonds of the resonance structures. Unless the question is asking about a certain resonance structure, the bond length reported should be the average of the resonance structures. For the most part, resonance structures are shared between bonds of the same atoms, so whether or not one is favored wouldn't make a significant difference to the bond angle anyway.