Organic Chemistry – Some Basic Principles and Techniques - Classification of Organic Compounds

Organic compounds are primarily classified based on their carbon skeleton into two main categories: Acyclic (Open chain) and Cyclic (Closed chain) compounds.

Acyclic or Aliphatic compounds consist of straight or branched chains of carbon atoms, such as ethane ($CH_3-CH_3$) or isobutane ($(CH_3)_3CH$).

Alicyclic compounds are cyclic compounds that exhibit properties similar to aliphatic compounds, for example, Cyclopropane ($C_3H_6$) or Cyclohexane ($C_6H_{12}$).

Aromatic compounds are special cyclic compounds which can be Benzenoid (containing a benzene ring like $C_6H_6$ or Naphthalene $C_{10}H_8$) or Non-benzenoid (like Tropolone $C_7H_6O_2$).

Heterocyclic compounds are cyclic structures containing one or more heteroatoms (atoms other than carbon) such as $N, O, S$ in the ring. Examples include Furan ($C_4H_4O$), Thiophene ($C_4H_4S$), and Pyridine ($C_5H_5N$).

A Functional Group is an atom or a group of atoms joined in a specific manner which determines the chemical properties of the organic compound, such as the carboxyl group ($-COOH$) or the aldehyde group ($-CHO$).

A Homologous Series is a group of organic compounds containing the same functional group where successive members differ by a $-CH_2-$ unit and possess a mass difference of $14u$.