To simplify and systematize the study of organic compounds classified on the basis of their structure as, open chain (or) acyclic compounds and closed chain (or) cyclic (or) ring compounds. Open chain compounds are also known as aliphatic compounds. Open chain (or) acyclic compounds are compounds in which carbon atoms are linked by straight (or) branched chains.
Ex: For straight chain compounds: Butene, Butyne, Pentyl alcohol, Acetone...etc
For branched chain compounds: Isobutane, Isobutylene. In a cyclic (or) ring (or) closed chain compound, the carbon atom and any other atom (if any) are joined together to form a closed chain.
Ex: In cyclohexane the six carbon atoms join together and form a closed Chain.
Cyclic compounds can be further classified as- Homocyclic compounds and heterocyclic compounds.
Homocyclic compounds are those in which the ring consists of only carbon atoms.
Ex: In cyclohexane the ring consist of only carbon atoms.
Heterocyclic compounds are those in which the ring consists of carbon atoms, as well the other atoms like sulphur, oxygen or nitrogen...etc
Homocyclic compounds can be further classified as alicyclic compounds and aromatic compounds on the basis of their characteristic properties.
Homocyclic compounds which resemble aliphatic compounds in their properties are called alicyclic compounds or aliphatic cyclic compounds.
An alicyclic compound consists of a ring which has only carbon atoms.
Ex: cyclopropane, cyclobutane and cyclohexane…etc
Aromatic compounds are benzene and compounds those resemble benzene in their behaviour. Aromatic compounds can be further classified as benzenoid compounds and non-benzenoid compounds on the basis of the presence or absence of benzene ring.
Aromatic compounds containing isolated (or) one or more fused benzene rings and their functional derivates are known as benzenoid aromatic compounds. Benzene is the parent compound in Benzenoid derivatives.
A non-benzenoid compound is one that does not contain a benzene ring.
The compounds which contain hetero atoms such as Nitrogen or Sulphur or Oxygen in addition to carbon atoms in the ring and resemble benzene in their properties are called Heterocyclic aromatic compounds.
Thiophene and Furan are heterocyclic compounds containing hetero atoms Sulphur and Oxygen. Another classification of organic compounds is based on Functional groups.
A functional group is an atom or a group of atoms present in a molecule, which determine its characteristic properties.
Ex: Hydroxyl group and Carboxylic acid group is the functional group of alcohols and carboxylic acids respectively.
Organic compounds can also be classified on the basis of Homologous series. The successive members or series of organic compounds with a characteristic functional group having the same general molecular formulae and differ by –CH2
unit are called homologous series. The successive members of a homologous series are called homologues
Ex: Homologous series of Alkanes are Methane, Ethane, Propane, Butane...etc