Q.2-2-9P - Organic Chemistry (Mcmurry)

Question

Question: Which of the following pairs of structures represent resonance forms, and which do not? Explain.

(a)

(b)

Step-by-Step Solution

Answer

Answer:

 

1. These two structures represent resonance forms.
2. These two structures represent different compounds, not resonance structures.

Step 1: Resonance

Resonance is a method of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis structure. A molecule or ion with such delocalized electron is represented by several contributing structures called resonance structure.

 

Step 2: Resonance in pair of structure (a)

Try to locate three atom groupings that are present in resonance forms.

                                                    Resonance in a

(a) These two structures represent resonance forms. The three atom grouping (C-C) double bond and an adjacent vacant p-orbital is pictured on the right. 

Step 3: Resonance in pair of structure (b)

(b)

                                                Resonance in pair b

 

(b) The above two structures represents different compounds, which violate the rule of resonance. So these two pairs are not resonance structures.