Learning Objective: To study the three broad types of displacement reactions that nucleophiles undergo.
Prerequisites:
Chapter: Fundamentals of Organic Reactions
Sub-topic: Nucleophiles
Author's Note: Reactions involving the nucleophiles form the core of all organic chemistry. Since organic chemistry mainly concerns the barter of electrons with covalent bonds, such a symbiotic relationship works due to the nucleophiles. Therefore, before beginning the study of organic reactions, it becomes essential to look at the types of reactions a nucleophile would undergo, the molecular change, and the reaction path. Such a study would negate all the need to memorize a reaction outcome. I have covered the types of displacement reactions a nucleophile is expected to undergo, the commonly seen nucleophiles in such reactions, and their outcomes.
Nucleophile Reactions - Displacement Type
The nucleophile's donation of the electrons occurs via two main reaction types- addition or displacement reactions.
In the addition reaction, the molecules combine to form a larger molecule, whereas, in displacement reactions, one incoming group displaces another group in a molecule.
Nucleophilic Displacement Reactions
The nucleophile displaces another group of atoms initially attached to the parent during the reaction. The expelled group of atoms is called the leaving group. While detaching itself from the substrate, the leaving group departs with the bond electron pair.
For example, in a displacement reaction between methyl bromide and nucleophile hydroxide, the hydroxide attacks the substrate methyl bromide to form methyl alcohol. Here the bromide ion is the leaving group.
The Nucleophilic Displacement Reactions are of three types:
a) Aliphatic Nucleophilic Displacement – SN1 and SN2
b) Nucleophilic Addition and Displacement at Acyl group- Formation of various functional groups of Carbonyl and alcohol
c) Aromatic Displacement Reactions – Electrophilic and Nucleophilic
Aliphatic Nucleophilic Displacement
In aliphatic compounds, interconversion of functional groups takes place by SN1, SN2, and displacement reactions at the Acyl group (R-C=O). But the type of reaction a molecule will undergo depends on the nature of the substrate molecule.....
SN1...
SN2...
Nucleophilic Displacement at the Acyl group
An R-C=O group is called an acyl group and is made of an R group (an alkyl or an aryl) and a carbonyl carbon (C=O)....
The order of faster nucleophilic displacement reactions is shown...
Aromatic Displacement Reactions
Benzene is the most common compound used to study the chemical reactions of the aromatic ring. Both benzene and alkenes have pie bonds, but benzene shows resonance, a form of pie bond delocalization, unlike alkenes....
