CLASSIFICATION OF ORGANIC COMPOUNDS

Organic compounds can be broadly classified into two – Acyclic or open chain compounds and cyclic or ring compounds.

1.  Acyclic or open chain or aliphatic compounds: In these compounds, the carbon atoms are joined together to form long chains which may be straight chain or branched chain.

 (i) They are further classified as saturated compounds and unsaturated compounds.

 (ii) Saturated compounds contain only carbon – carbon single bonds. But unsaturated  compounds contain atleast one carbon – carbon multiple bond (double or triple bond.

 (iii) Saturated hydrocarbons are called alkanes and unsaturated hydrocarbons are of two types – alkenes and alkynes.

2.  Cyclic or closed chain or ring compounds: In these compounds, the carbon atoms are joined together to form rings. These rings may be homocyclic or heterocyclic.

    • If the ring contains only carbon atoms, it is called homocyclic compound and if it contains atoms other than carbon (like O, N, S etc), it is called heterocyclic compound.
    • Homocyclic compounds are further classified into two – Alicyclic compounds and Aromatic compounds.
    • Alicyclic compounds contain atleast one carbo-cyclic ring. Alicyclic hydrocarbons are of three types – cycloalkanes, cycloalkenes and cycloalkynes.
    • Aromatic compounds are some special type of compounds.
    • These are of two types. Aromatic compounds containing benzene ring are called benzenoid compounds and those which do not contain benzene ring are called non-benzenoid compounds.
    • E.g. for a non-benzenoid aromatic compound is tropolone. Heterocyclic compounds may be alicyclic heterocyclic compounds or aromatic heterocyclic compounds.

The classification of organic compounds can be diagrammatically represented as follows:

Functional groups: Atoms or group of atoms (except hydrogen) which are bonded to carbon atoms are called functional groups. These groups are responsible for the characteristic chemical properties of the organic compounds. Some important functional groups, their names and name of the compounds are listed below

Homologous series: A series or group of organic compounds in which adjacent members are differed by a –CH2 group is called a homologous series. The members of a homologous series are called homologues. They contain same functional groups, have similar chemical properties and show gradation in physical properties. They can be prepared by some general methods of preparation. E.g. for homologous series are alkanes, alkenes, alkynes, alcohols, ethers, carboxylic acids, aldehydes, ketones, amines, halo compounds etc.