Q37E_a - Organic Chemistry (Mcmurry)

Question

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

Step-by-Step Solution

Answer

Answer

 

These are not resonance forms.

Step 1: Resonance

Resonance is a representation of delocalized electrons within specific molecules or polyatomic ions when a single Lewis structure cannot conclude the bonding.

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

Step 2: Rules for structures of resonance form

Rule 1

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

 

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 standard 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 particular resonance form. So, resonance leads to stability. The more the number of resonance structures, the more stability will be.

Step 3: Structure comparison for resonance forms

                                                                     Structural comparison

We will see if the 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.

But here, the position of atoms is changed.

Hence these are not resonating forms.