Q56E - Organic Chemistry (Mcmurry)

Question

Which of the following pairs represent resonance structures?

Step-by-Step Solution

Answer

1. Given structures are resonance structures

2. Given structures are not resonance structures

3. Given structures are not resonance structures

4. Given structures are resonance structures

Step 1: Definition of resonance structure

When there is an electronic displacement of π-bonds in the molecule, then the structures generated are known as resonance structures.

Displacement of sigma bonds are NOT resonance structures.

Step 2: Try to displace the π-bonds present in the molecule and try to form the given structure (a)

From the displacement of π-bond between carbon, nitrogen and Oxygen provide us different resonance structure

Step 3: Try to identify how these structures are forming (b)

We can form these two structures then you can observe that we can only form these two structures by breaking of sigma bonds C-H and O-H only.

From the structures you can see that these are structures are not resonance structures 

Step 4: Try to identify how these structures are forming (c)

If you draw the structures of these two compounds then you observe that these two structures cannot be formed by displacement of $\pi$ bonds but breaking and formation of sigma bonds C-H and N-H in NH₂ group.

Hence the given structure are not the resonance structures

Step 5: Try to draw above given structures (d)

Try to draw the above structures by the displacement of $\pi$ bonds only no sigma bond should not be displaced.

Given structure can be formed by displacement of $\pi$ bonds, hence this structure can be considered as resonance structures.