# Nomenclature and General Principles: Steric Hinderance and Substitution Reaction (For CBSE, ICSE, IAS, NET, NRA 2022)

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## Steric Hinderance

The effect is caused by the large bulky groups present in the vicinity of the reaction centre.

When a compound of the type (where, , , , etc. and is treated with the reagents such as , , , etc. the reaction is hindered or retarded by the substituents at ‘R’ .

## Substitution Reaction

• A substitution reaction involves the displacement of one atom or group in a molecule by another atom or group.
• Aliphatic compounds undergo nucleophilic substitution reaction.
• For example, a haloalkane can be converted to a wide variety of compounds by replacing halogen atom (X) with different nucleophiles.

• In addition, reaction, the other reagent are added to unsaturated hydrocarbons such as alkenes and alkynes.
• For example, the colour of bromine solution disappears when added to the unsaturated hydrocarbons.

## Elimination Reaction

• An elimination reaction is characterized by the removal of a small molecule from adjacent carbon atoms and the formation of a double bond.
• For example , when alcohols are heated with a strong acid as the catalyst, a molecule of water is removed, and a double bond is formed.

## Molecular Rearrangements

• During this reaction, an atom or group migrates from one position to another.
• For instance, 1-chlorobutane in the presence of a Lewis acid rearranges to 2-chlorobutane.

## Isomerism

• Different substances which have the same molecular formula but differ in their structures, physical or chemical properties are called isomers and this phenomenon is known as isomerism.
• The isomerism can be of various types as shown:

### Structural Isomerism

Compounds which have the same molecular formula but differ in their structure are called structural isomers and the phenomenon is called Structural Isomerism.

This is subdivided into four types:

#### Chain Isomerism

These isomers differ in the chain of the carbon atoms, for instance, n-butane and isobutane are two isomers of .

#### Functional Isomerism

• These isomers differ in the type of functional group.
• For example, ethanol and ether the two isomers having molecular formula , belong to two different classes of organic compounds.

(Molecular Formula: )

and

#### Positional Isomerism

These isomers differ in the attachment of the functional group to the chain at different positions.

For examples

#### Metamerism

• It is exhibited by those compounds in which functional group comes in between the carbon chain and breaks the continuity of the chain.
• This breaking occurs at different positions and different isomers are formed which are called Metamers.
• For example, 1-methoxypropane a ethoxyethane are two metamers differing in chain length on the two sides of oxygen atom as shown below.

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