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Classifications of Organic Compounds

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Organic compounds are broadly divided into two categories

  1. Acyclic compounds (open chained)
  2. Cyclic compounds (closed chained)

Acyclic compounds

Acyclic compounds contain open chains of carbon atoms in their molecules. The carbon chains may be either straight chains or branched chains.

Examples of Straight chain compounds

CH3-CH2-CH2-CH3 → n-butane

CH3-CH=CH-CH3 → But-2-ene


Examples of Branched chain compounds

Branched chain alkane example: isobutane Branched chain alkane example: neopentane

Prefix iso

Prefix iso is used for those alkanes in which a methyl group is attached to the penultimate carbon atom of the main chain. For example : isobutane.

Prefix neo

Prefix neo is used for those alkanes in which two methyl groups are attached to the penultimate carbon atom of the main chain. For example : neopentane.

Open chain compounds are also called aliphatic compounds.

Cyclic Compounds

Cyclic compounds contain one or more closed chains or rings of atoms in their molecules.

Based on the constitution of the rings, cyclic compounds are further divided into

  1. Homocyclic or carbocyclic compounds.
  2. Heterocyclic compounds.

Homocyclic Compounds

Homocyclic compounds contain rings which are made up of only carbon atoms. Homocyclic compounds are also known as carbocyclic compounds. Homocyclic compounds are further divided into following categories.

  1. Alicyclic homocyclic compounds.
  2. Aromatic homocyclic compounds

Alicyclic Homocyclic Compounds

Homocyclic compounds which resemble acyclic compounds in most of their properties are called alicyclic homocyclic compounds.

Example : Cyclohexane

Homocyclic compounds example : cyclohexane Homocyclic compounds example : triplebond Homocyclic compounds example : cyclohexane

Aromatic Homocyclic Compounds

Organic compounds containing one or more benzene rings and their functionalized derivatives are called aromatic compounds.

Aromatic compounds exhibit resonance property .

Aromatic compounds are usually called benzenoid compounds since they resemble benzene in almost all of their properties.

Note: There are ,however, examples of aromatic compounds which do not contain a benzene ring but instead contain other highly unsaturated ring and are known as non-benzenoids.

Based on the number of benzene rings present in molecule, they are further classified as monocyclic (one benzene ring), bicyclic (two rings), tricyclic (three rings) aromatic compounds etc.

An example of monocyclic aromatic compounds, Toluene

monocyclic compounds example : Toluene

An example of bicyclic aromatic compounds, Naphthalene

bicyclic compounds example : Naphthalene

An example of tricyclic aromatic compounds, Anthracene

tricyclic compounds example : Anthracene

Heterocyclic Compounds

Cyclic compounds containing one or more heteroatoms in their rings are called heterocyclic compounds.

Atoms other than C and H are known as Heteroatoms.

Heterocyclic compounds are also divided into two categories

1. Alicyclic heterocyclic compounds.

2. Aromatic heterocyclic compounds.

Alicyclic Heterocyclic Compounds

Alicyclic compounds, containing one or more heteroatoms in their rings are called alicyclic heterocyclic compounds.

Examples of Alicyclic heterocyclic compounds

Alicyclic heterocyclic compounds example: Tetrahydrofuran Alicyclic heterocyclic compounds example: Tetrahydrothiopene

Aromatic Heterocyclic Compounds

Aromatic cyclic compounds containing one or more heteroatoms in their molecules are called aromatic heterocyclic compounds.

Examples of Aromatic heterocyclic compounds.

Aromatic heterocyclic compounds example: Furan Aromatic heterocyclic compounds example: Thiopene
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