Question

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

Short answer

Here four resonating structures are possible.

Step-by-step solution

 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.

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.

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.

Structures of resonance forms

Resonating structures