Delocalized Pi Bond/Resonance

[Karina Rodriguez 2H]

Would a delocalized pi bond only exist in a substance with resonance structures?

[dana hu 1B]

Yes, you're correct. Because when there are only single bonds (and, therefore, only sigma bonds), there can't be resonance since all bonds are the same. Thus, resonance can only exist when a molecule has at least one double bond (for example, ), and, as we learned, a double bond consists of 1 sigma and 1 pi bonds. Therefore, any molecule that has resonance has at least 1 pi bond.

[Leyla Anwar 3B]

This would be true with any bond that is more than just a single bond because a double bond and triple bond mean that a pi bond is present. You can't have a pi bond with single bonds (because those are sigma). Any structure with resonance, means there is at least one bond greater than a single bond because otherwise the structure would not have any variation.