Question:

For the following bond cleavages, use curved arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion.

Updated On: Nov 17, 2023
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Solution and Explanation

(a) The bond cleavage using curved arrows to show the electron flow of the given reaction can be represented as
curved-arrows
It is an example of homolytic cleavage as one of the shared pair in a covalent bond goes with the bonded atom. The reaction intermediate formed is a free radical.


(b) The bond cleavage using curved arrows to show the electron flow of the given reaction can be represented as
bond cleavage
It is an example of heterolytic cleavage as the bond breaks in such a manner that the shared pair of electrons remains with the carbon of propanone. The reaction intermediate formed is carbanion.


(c) The bond cleavage using curved arrows to show the electron flow of the given reaction can be represented as
heterolytic cleavage
It is an example of heterolytic cleavage as the bond breaks in such a manner that the shared pair of electrons remains with the bromine ion. The reaction intermediate formed is a carbocation.


(d) The bond cleavage using curved arrows to show the electron flow of the given reaction can be represented as
curved-arrows to show the electron flow
It is a heterolytic cleavage as the bond breaks in such a manner that the shared pair of electrons remains with one of the fragments. The intermediate formed is a carbocation.

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Concepts Used:

Organic Chemistry – Some Basic Principles and Techniques - Reaction Mechanism

SN1 Reaction Mechanism:

SN1 reaction mechanism takes place by following three steps –

  • Formation of carbocation 
  • Attack of nucleophile 
  • Deprotonation 

SN2 Reaction Mechanism:

The SN2 reaction mechanism involves the nucleophilic substitution reaction of the leaving group (which generally consists of halide groups or other electron-withdrawing groups) with a nucleophile in a given organic compound.

Electrophilic Aromatic Substitution Reaction Mechanism:

The mechanism of an electrophilic aromatic substitution reaction contains three main components which are:

  1. A new sigma bond from C=C is formed during the reaction in the arene nucleophile.
  2. Due to the breaking of the C-H sigma bond, a proton is removed.
  3. The C=C bond is reformed and it restores the aromaticity of the compound.

Electrophilic Substitution Reaction Mechanism:

The electrophilic substitution reaction mechanism is composed of three steps, which will be discussed more below.

  • Electrophile Generation
  • Carbocation Formation
  • Proton Removal