Heterocyclic Compound

Have you ever wondered how we encounter many heterocyclic compounds in our daily lives?

• Nucleic Acid that is present in the body responsible for storing and expressing genetic information, is an example of a Heterocyclic compound.
• Essential micronutrient vitamins are also an example of a heterocyclic compound.
• The majority of drugs, pesticides, dyes, and plastics are examples of heterocyclic compounds.

Table of Content

• What is a Heterocyclic Compound?
• Classification of Heterocyclic Compounds
• Aliphatic Heterocyclic Compound
• Aromatic Heterocyclic Compound
• Three-Membered Heterocyclic Compounds
• Four-Membered Heterocyclic Compounds
• Five-Membered Heterocyclic Compounds
• Six-Membered Heterocyclic Compounds
• Condensed or Fused Heterocyclic Compounds
• Applications of Heterocyclic Compounds
• Frequently Asked Questions – FAQs

What is a Heterocyclic Compound?

A heterocyclic compound has at least two different elements as a member of its ring.

• The most common hetero atoms found on a cyclic ring are Oxygen (O), Nitrogen (N) and Sulphur (S).

Example:

• Nucleic Acid that is present in the body responsible for storing and expressing genetic information, is an example of a Heterocyclic compound.
• Essential micronutrient, Vitamins is also an example of a heterocyclic compound.
• The majority of drugs, pesticides, dyes, and plastics are examples of heterocyclic compounds.

Classification of Heterocyclic Compounds

Based on the electronic arrangement, we can classify Heterocyclic compounds into two types:

• Aliphatic Heterocyclic Compounds
• Aromatic Heterocyclic Compounds

Aliphatic Heterocyclic Compounds

• Aliphatic heterocyclic compounds are those cyclic heterocycles that do not contain any double bond.
• The properties of aliphatic heterocyclic compounds are mainly affected due to ring strain.
• Examples of aliphatic heterocyclic compounds are Aziridine, Ethylene Oxide, Thiirane, Oxetane, Azetidine, Thietane, Tetrahydrofuran (THF), Dioxane, Pyrrolidine, Piperidine, etc.

Aromatic Heterocyclic Compound

• Aromatic heterocyclic compounds, as the name suggests, are cyclic aromatic compounds.
• Aromatic Heterocyclic compounds obey Huckels Rule, i.e.
• It should be cyclic.
• It should be planar.
• It should not contain any sp3 hybridised atoms.
• It must have (4n+2) 𝛑 electrons.
• Aromatic Heterocyclic compounds are analogous to Benzene.
• Examples: Furan, Pyrrole, Thiophene, Indole, Benzofuran, Carbazole, Quinoline, Isoquinoline, Imidazole, Oxazole, Pyrazole, Pyridazine, Pyrimidine, Purine, etc.

Based on structure, we can classify Heterocyclic compounds into five types:

1. Three-Membered Heterocyclic Compounds
2. Four-Membered Heterocyclic Compounds
3. Five-Membered Heterocyclic Compounds
4. Six-Membered Heterocyclic Compounds
5. Condensed or Fused Heterocyclic Compounds

Three-Membered Heterocyclic Compounds

These heterocyclic compounds contain three atoms which may be saturated or unsaturated.

Based on the number of heteroatoms present, we can further classify them into two categories:

Heterocyclic compounds with one heteroatom.

• As the name suggests, it has one heteroatom present in its ring.
• Examples: Aziridine, Oxirane, Thiirane, Azirine, Oxirene and Thiirene.

Heterocyclic compounds with more than one heteroatom.

• As the name suggests, it has more than one heteroatom present in its ring.
• The heteroatom atom in the ring can be the same or different.
• Examples: Diaziridine and Oxiaziridine.

Four-Membered Heterocyclic Compounds

These heterocyclic compounds contain four atoms which may be saturated or unsaturated.

Based on the number of heteroatoms present, we can further classify them into two categories:

Heterocyclic compounds with one heteroatom.

• As the name suggests, it has one heteroatom present in its ring.
• Examples: Azetidine, Oxetane, Thietane, Azete, Oxete, Thiete, etc

Heterocyclic compounds with more than one heteroatom.

• As the name suggests, it has more than one heteroatom present in its ring.
• The heteroatom atom in the ring can be the same or different.
• Examples: Diazetidine and Dioxetane.

Five-Membered Heterocyclic Compounds

These heterocyclic compounds are derived from Benzene by replacing a C=C bond with a hetero atom having a lone pair of electrons.

Based on the number of heteroatoms present, we can further classify them into two categories:

Heterocyclic compounds with one heteroatom.

• As the name suggests, it has one heteroatom present in its ring.
• Examples: furan, pyrrole and thiophene.

Heterocyclic compounds with more than one heteroatom.

• As the name suggests, it has more than one heteroatom present in its ring.
• The heteroatom atom in the ring can be the same or different.
• Examples: Pyrazole, Imidazole, Oxazole, Thiazole, Triazole and Tetrazole, etc.

Six-Membered Heterocyclic Compounds

These heterocyclic compounds are derived from Benzene by replacing one of the Carbon with a hetero atom having a lone pair of electrons.

Based on the number of heteroatoms present, we can further classify them into two categories:

Heterocyclic compounds with one heteroatom.

• As the name suggests, it has one heteroatom present in its ring.
• Examples: Pyridine, Pyran, Thiopyran, etc.

Heterocyclic compounds with more than one heteroatom.

• As the name suggests, it has more than one heteroatom present in its ring.
• The heteroatom atom in the ring can be the same or different.
• Examples: Pyridazine, Pyrimidine, Pyrazine, etc.

Condensed or Fused Heterocyclic Compound

• Condensed or Fused Heterocyclic Compound contains two or more fused rings.
• Condensed or Fused Heterocyclic Compounds can be partly carbocyclic or partly heterocyclic.
• Examples: Indole, Quinoine, Isoquionoline, Cabazole, etc.
• Condensed or Fused Heterocyclic Compounds can also be completely heterocyclic.
• Examples: Purine, Pteridine, etc.

Applications of Heterocyclic Compound

• Heterocyclic compounds are used in agrochemicals and pharmaceuticals industries.
• Heterocyclic compounds are used as starting materials in the synthesis of organic compounds.
• Heterocyclic compounds are used in corrosion inhibitors, sanitisers, anti-ordinates, and developers.
• Heterocyclic compounds are used in pesticides, dyes and plastics.