CHEMISTRY - Organic Compound

The simplest organic compounds containing only carbon and hydrogen are called hydrocarbons. They are considered to be parent organic compounds while all the organic compounds are thought to have been derived from them by replacement of one or more of their hydrogen atoms by other atoms or group's of atoms. As the study of ore chemistry advanced, the number of organic compounds became very large. As a result, it became rather inconvenient to study the chemical behavior of these compounds individually. Therefore, in order to simplify the systematize the study of organic chemistry, all the known organic compounds have been broadly divided into two categories depending upon the nature of their carbon skeleton. These are :-

1. Acyclic or open chain compounds.
2. Cyclic or closed chain compounds.

1. Acyclic or Open chain compounds :- These compounds contain open chains of carbon atoms in there molecules. The carbon chains may be either straight chains or branched chains.
Open chain compounds are also called alphabetic compounds since the earlier compounds of this class were obtain either from animal or vegetable fats.

2. Cyclic or closed chain or ring compounds :- These compounds contain one or more closed chain or rings of atoms in their molecules. Depending upon the constitution of the ring, these are further divided into the following two categories :-

* Homocyclic or Carbocyclic compounds :- These compounds contain rings which are made up of only one kind of atoms, I.e carbon atoms. These are further divided into the following two sub-classes.

(a) Acyclic compounds :- Carbocyclic compounds which are resemble alphabetic compounds in most of their properties are called alicyclic compounds.

(b) Aromatic compounds :- These are special type of cyclic unsaturated compounds. The name aromatic for this class of cyclic unsaturated compounds has been derived from the Greek word aroma meaning fragrant smell simple since most of the compounds discovered earlier had pleasant smell.

* Heterocyclic Compounds :- Cyclic compounds containing one or more heteroatoms in their ring are called heterocyclic compounds.
The heteroatoms commonly found in these compounds are oxygen , nitrogen and sulphur but occasionally phosphorus, boron, silicon and some metal atoms like tin, selenium etc. may also be present. Depending upon the chemical behavior , they are further classified into the following two categories :-

(a) Alicyclic Heterocyclic Compounds :-  Aliphatic cyclic compounds containing one or more heteroatoms in their ring are called alicyclic heterocyclic compounds.

(b) Aromatic heterocyclic compounds :- Aromatic cyclic compounds containing one or more heteroatoms in their molecule are called aromatic heterocyclic compounds.