Addition Reaction: Introduction, Types, Polar & Non-Polar Addition

In organic chemistry, an addition reaction is a chemical reaction wherein two or more reactants come together to form a larger single product.

Introduction of Addition Reaction

In addition, only chemical compounds containing multiple bond characters can undergo an additional reaction as a double or triple bond is usually broken to form the required single bonds. An addition reaction is essentially a reverse of a decomposition reaction whereas a decomposition reaction is a reaction where one compound decomposes into one or more elements or compounds.

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This Story also Contains

1. Introduction of Addition Reaction
2. Types Of Addition Reactions
3. Polar addition reactions it has two types, they are:
4. Types of Free Radical Reactions
5. Types Of Cycloaddition

Addition reactions are unsaturated organic compounds like alkenes. Alkenes contain a carbon-to-carbon double bond. On the other hand, alkynes have a carbon-to-carbon triple bond. Aldehydes and ketones have a carbon-to-oxygen double bond.

An additional reaction always has a visualized process by which the double or any triple bonds are fully or partially broken to accommodate additional atoms or groups of atoms in the molecule. Additional reactions to alkenes and alkynes are called saturation reactions because the reason behind is that the reaction causes the carbon atoms to become saturated with the maximum number of attached groups. An addition reaction may be illustrated by the hydrochlorination of propene (an alkene), for which the equation is

\mathrm{CH_3CH=CH_2+HCl\longrightarrow\:CH_3-\overset{+}{C}H-CH_3+Cl^{-}\longrightarrow\:CH_3CHClCH_3}

Types Of Addition Reactions

Polar addition reactions has two types, they are given below:

1. Electrophilic reactions

2. Nucleophilic reactions

For non-polar addition reactions also have two types, they are:

1. Free radical addition reactions

2. Cycloadditions reactions

Polar addition reactions it has two types, they are:

1. Electrophilic addition

An electrophilic addition reaction can be defined as an addition reaction in which a reactant which has multiple bonds as in a double or any triple bond undergoes its π( pie) bond which is broken and two new σ (sigma) bonds are formed.

2. Nucleophilic addition

A nucleophilic addition reaction is defined as an addition reaction where a chemical compound with an electron-deficient, electrophilic double, triple bond and a π(pie) bond reacts with a nucleophile which is electron-rich reactants with the disappearance of the double bond and creates two new single or σ(sigma) bonds.

For non-polar addition reactions also have two types, they are:

A. Free radical addition reactions

A free radical addition reaction is defined as a species that contains one or more unpaired electrons. Due to the presence of unpaired electron(s) free radicals are known as paramagnetic.

Types of Free Radical Reactions

Free radical reactions have two types, they are,

1. Propagation reactions

2. Termination reactions.

Involving these reactions, free radicals undergo most of the general types of reactions such as substitution reaction, addition reaction, rearrangement reaction, oxidation reaction and reduction reaction.

1. Propagation reactions

The Propagation reactions lead to other radicals, which themselves react further.

There are four main propagation reactions in free radical reactions and the first two are the most common.

• Abstraction of another atom or group such as a hydrogen atom
• Addition to multiple bonds
• Decomposition
• Rearrangement

2. Termination reactions

The termination reactions give stable products. The most common termination reactions are simple combinations of similar or different radicals and another termination process is disproportionation. Basically in a disproportionation reaction, an alkane and an alkene are produced from a pair of radicals and the hydrogen atom of one radical is abstracted by another radical.

B. Cycloaddition reaction

A concerted combination is defined as when the two (pie) π-electron systems form a ring of atoms having two new σ (sigma) bonds and two fewer π (pie) bonds known as a cycloaddition reaction.

Types Of Cycloaddition

1. Diels-Alder cycloaddition reactions

2. Huisgen cycloadditions reactions

3. Nitrone-olefin cycloaddition reactions

4. Cheletropic cycloaddition reactions

• Diels-Alder reactions

The Diels-Alder cycloaddition reaction is the most important and commonly taught in the cycloaddition reaction. It is a [4+2] cycloaddition reaction. It exists in a huge range of forms which include the inverse electron demand Diels-alder reaction, and Hexadehydro Diels-Alder reaction and this is related to alkyne trimerisation.

• Huisgen cycloadditions

In the Huisgen cycloaddition reaction, it has (2+3)cycloaddition.

• Nitrone-olefin cycloaddition

In Nitrone-olefin cycloaddition, it has (3+2)cycloaddition.

• Cheletropic reactions

The cheletropic reaction is a subclass of cycloadditions. The feature of cheletropic reactions is that one of the reagents, both new bonds which are made to the same atom.The example of cheletropic reaction is the reaction of sulfur dioxide with a diene.