Question: Which of the following pairs of structures represent resonance forms?

Resonance is a way to represent delocalized electrons within certain molecules or polyatomic ions when the bonding cannot be concluded by a single Lewis structure.

Resonance occurs when two double bonds are present consecutively, or a double bond is followed by a single bond which is followed by another double bond, triple bond, positive charge, negative charge or a free radical.

Rule 1

Individual resonance forms are imaginary, which means they are not real. The real structure is a composite or resonance hybrid of all the different forms together.

Rule 2

Resonance forms differ only in the placement of their or nonbonding electrons. So, the position or the hybridization of an atom doesn’t change.

Rule 3

Different resonance forms of the molecule don’t have to be equivalent. It can be converted into its anion by reaction with a strong base. The resultant anion can have resonance forms.

Rule 4

Resonance forms obey normal rules of valency. Like any other structure, a resonance form has to follow the octet rule.

Rule 5

The resonance hybrid is more stable than any individual resonance form. So, resonance leads to stability. The more the number of resonance structures, the more stability will be.

Structural comparison

We will see if the rules are followed:

Here all rules are followed:

Rule 2: Resonance forms differ only in the placement of their or nonbonding electrons. So, the position or the hybridization of an atom doesn’t change.

Here, the position of only ornonbonding electron is changed.

Rule 4: Resonance forms obey normal rules of valency. Like any other structure, a resonance form must follow the octet rule.

Here, each atom follows the octet rule.

So, it can be concluded these are resonating forms.