Q10-36E - Organic Chemistry (Mcmurry)

Question

Draw resonance structures for the benzyl radical, the intermediate produced in the NBS bromination reaction of toluene (Problem 10-35).

Step-by-Step Solution

Answer

Here four resonating structures are possible.

Step 1: Free radical

These molecular species have at least one unpaired electron. Molecules normally consist of pairs of electrons. These are electron deficient species. Radicals are stabilized by resonance.

Step 2: Resonance

Resonance is a method to represent delocalized electrons within certain molecules or polyatomic ions when the bonding cannot be concluded by a single Lewis structure. 

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

Step 3: 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 the different forms together.

 

Rule 2

Resonance forms differ only in the placement of their  or nonbonding electrons. So,  the position or the hybridization of any atom doesn’t change.

 

Rule 3

Different resonance forms of 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 normal rules of valency. A resonance form like any other structure has to follow the octet rule.

 

Rule 5

 

The resonance hybrid is more stable than any individual resonance form. So, resonance leads to stability. More the number of resonance structures more will be stability.

Step 4: Structures of resonance forms

Resonating structures