Substituent

Substituent is a term used in organic chemistry to describe an atom or group of atoms which replace hydrogen atoms on a parent hydrocarbon molecule. This process is known as substitution. Substituents can be classified into various types based on their chemical properties and the effects they have on the parent molecule.

Types of Substituents

There are several types of substituents, including:

• Electron-donating groups (EDGs): These are substituents that donate electron density to the parent molecule. They can stabilize a positive charge on the parent molecule and are generally ortho/para directors in electrophilic aromatic substitution reactions.

• Electron-withdrawing groups (EWGs): These are substituents that withdraw electron density from the parent molecule. They can stabilize a negative charge on the parent molecule and are generally meta directors in electrophilic aromatic substitution reactions.

• Sterically hindered substituents: These are large substituents that can affect the reactivity of the parent molecule due to their size.

Effects of Substituents

Substituents can have a significant impact on the properties of the parent molecule, including its reactivity, polarity, and physical properties such as boiling point and melting point. For example, the presence of an electron-donating group can increase the reactivity of the parent molecule towards electrophiles, while an electron-withdrawing group can decrease its reactivity.

File:Substituent effect.png

Illustration of the effect of substituents on the reactivity of a parent molecule.

See Also

• Functional group
• Addition reaction
• Elimination reaction