What are minor resonance structures?
1 Answer
Minor resonance structures are all the resonance contributors that are higher in energy than the lowest-energy contributor.
For example, we can draw three possible contributors for formamide, HCONH₂.
We have to decide which of these is the lowest-energy form. That one will be the major contributor. All the others will be minor contributors.
In order of importance, some rules that enable you to decide are:
- Satisfy the octet rule.
- Minimize charge separation.
- Put negative charge on the more electronegative atom.
Structures III and IV both obey the octet rule, but III has no charge separation. Structure V does not give the C atom an octet.
III is the major contributor. So IV and V are minor contributors.
IV is a more important contributor than V, because it obeys the octet rule.
We could say that IV is a minor contributor and V is a very minor contributor.
