Q60E - Organic Chemistry (Mcmurry)

Question

The azide functional group, which occurs in azido benzene, contains three adjacent nitrogen atoms. One resonance structure for azido benzene is shown. Draw three additional resonance structures, and assign appropriate formal charges to the atoms in all four.

Step-by-Step Solution

Answer

The diagram is drawn below.

Step 1: Definition of Resonance structure and Formal Charge

The structures are formed by the electronic displacement of the 𝛑 bond present in the molecule. These are known as resonance structures

Resonance structures can only be formed by the electronic displacement of sigma bonds.

The formal charge (F.C) can be defined as the different valence electrons and the number of electrons present in the Lewis structure.

  $\mathrm{F}.\mathrm{C}=\left[\mathrm{V}\left(\mathrm{electrons}\right)-\mathrm{L}\left(\mathrm{electrons}\right)\right]$

V = valence shell

L = electrons present according to Lewis structures

Step 2: Assign formal charge to the respective atomic species

$\text{F.C = }\left[\text{V}\left(\text{electrons}\right)\text{ - L}\left(\text{electrons}\right)\right]$

$\text{F.C on Carbon = 4-- 3 = - 1}$

$\text{F.C on Nitrogen = 5 - 4 = 1}$

Step 3: Draw the resonance structure

By the electronic displacement of the 𝛑 bond in azobenzene, we can draw the resonance structures of a given compound.

All possible resonance structures of a given compound are shown below:

But as you can observe, (I) and (V) structures are the same.

And we have an additional three resonance structures related to Benzene.

The (VI) resonance structure is related to the Azo-group present in the compound.