Types of Reactions In Organic Chemistry

Organic reactions are basically chemical reactions involving organic compounds. 

One of the first organic reactions was combustion reactions of fuels and saponification. 

In 1912 Nobel Prize was awarded for the invention of the Grignard reaction. 

There are different types of organic reactions:

• Addition reactions

• Elimination reactions

• Substitution reactions

• Pericyclic events

• Rearrangement reactions

• Photochemical reactions

• Redox reactions

• Condensation reactions

• Isomerization reactions

• Polymerization reactions

Though there are so many different types, let’s discuss some of them:

• Substitution reactions 

• Addition reactions 

• Elimination reactions 

• Rearrangement reactions 

Substitution Reaction

The direct replacement (displacement or substitution) of an associate degree atom or cluster of atoms in an associate degree organic molecule by another atom or cluster of atoms with no alteration within the remaining part of the molecule is thought of as a substitution reaction. By product obtained as a result of the substitution is termed the substitution product, and also the new atom or cluster of atoms that enter the molecule is termed substituent.

Substitution reactions are also subdivided into different types i.e.

• Nucleophilic Substitution Reactions

Substitution reactions when the attacking reagent is a nucleophile (Nu– or Z–),  such reactions are called nucleophilic substitution reactions. These reactions are typical of alkyl halides.

For example, hydrolysis of an alkyl halide with an aqueous base.

• Electrophilic Substitution Reactions

In these reactions, the assaultive chemical agent is an associate degree electrophile. These reactions square measure typical of arenes and alternative aromatic compounds.

For example, halogenation, nitration, sulphonation, and Friedel-Crafts reactions.

• Free Radical Substitution Reaction

The invading reagent in response to a free radical substitution is a free radical. This reaction occurs at high temperatures or in the presence of UV rays.

For example, methane immersion to make chloromethane. 

The invading reagent is a free radical (Cl) 

The reaction taking place through a free radical mechanism involves the following steps:

a. Initiation: In this step, free radicals are formed.

b. Propagation: The distribution phase describes the ‘chain’ part of the chain reaction.

c. Termination: In this process, two types of free radicals combine to form a stable, non-radical 

So, all these steps take place simultaneously, as you can see in the figure given below.

Addition Reaction

An addition reaction is defined as the reaction when two active molecules combine to form a single product molecule. A combination of multiple bonds (two or three) is at risk of such a reaction.

 For example, 

Additional reactions are divided into three categories based on the type of invasive species. They are free electrophiles, nucleophiles, or free radicals. 

• Electrophilic Addition Reaction

Electrophilic addition reactions are addition reactions caused by electrophiles. These are typical alkene and alkyne reactions.

For example, the addition of halogen acids to alkenes proceeds by an electrophilic mechanism.

• Nucleophilic Addition Reaction

Nucleophilic addition reactions are those that are caused by nucleophiles. These are typical aldehyde and ketone reactions.

For example, consider the base-catalyzed addition of HCN to aldehydes or ketones.

• Free Radical Addition Reaction

Free radical addition reactions are addition reactions caused by free radicals.

For example, consider the addition of HBr to alkenes in the presence of peroxides:

• Free radical addition reaction occurs by the following mechanism:

a. Initiation: In this step, free radicals are formed.

b. Propagation: The propagation phase describes the ‘chain’ component of chain reactions.

c. Termination: In this process, two free radical species react with each other to form a stable, non-radical adduct.

Elimination Reactions 

The reaction in which two atoms or groups, either from the adjacent positions or from the same position, get eliminated or removed, leading to the formation of multiple bonds (i. e., double or triple bond), is known as an elimination reaction.

These reactions are of two types. They are;

a. β– Elimination reactions: In these reactions, the loss of two atoms or groups takes place from the adjacent carbon atoms in the molecule.

b. α– Elimination reactions: In these reactions, there is a loss or elimination of two atoms or groups from the same carbon atom in the molecule.

Rearrangement Reaction

Reactions involving the migration of an atom or a group from one atom to another within the same molecule are called rearrangement reactions.

For example,

But-1-ene is the expected dehydration product in this reaction. However, but-2-ene is formed as a result of a rearrangement reaction. As a result of rearrangement, the less stable primary carbocation has been converted to the more stable secondary carbocation.

Conclusion

Organic reactions are basically chemical reactions involving organic compounds. 

One of the first organic reactions was combustion reactions of fuels and saponification. Now we know the different types of organic reactions and their significance, with the examples discussed in the article. This concept can be easily understood.