Question

Question: (a) Draw a second resonance structure for A. (b) Why can’t a second resonance

structure be drawn for B?

Short answer

Answer

(a)

(b) The electrons’ delocalization is not possible.

Step-by-step solution

Step-by-Step Solution Step 1: Guidelines for drawing resonance structures

The resonance structures are drawn by following the guidelines given below:

• The atoms of resonance structures will be the same as the original structure.
• The resonance structure must be the correct representation of Lewis structures.
• The molecular formula of the original structure and resonance structures must be the same.

Delocalization of electrons

The electrons that have no association with one atom or bond are named delocalized electrons. The term delocalization refers to the free movement of electrons in a molecule.

Determination of second resonance structure

(a) The lone pairs on nitrogen atoms facilitate resonance as the movement of the electrons occurs. A double bond is formed between carbon and nitrogen, whereas the existing carbon-carbon double bond converts into a single bond.

Representation of second resonance structure

(b) The second resonance structure of B cannot be formed because the delocalization of electrons in that structure is not possible.

All the atoms are bonded to the central carbons. The nitrogen atom is hybridized to which hydrogen atoms are attached. Thus, no resonance is possible for structure B.