Today, there are about ten millions of organic compounds and thousands of new organic compounds are being prepared every year. Therefore, the old definition has been rejected. A detailed investigation of organic compounds revealed that all of them contain covalently bonded carbon and hydrogen as their essential constituent. Hence, organic compounds are hydrocarbons (compounds of carbon and hydrogen only) and their derivatives, in which covalently bonded carbon is an essential constituent. The branch of chemistry which deals with the study of hydrocarbons and their derivatives is known as organic chemistry.
Though, the oxides of carbon like carbon monoxide and carbon dioxide, carbonates, bicarbonates and carbides are also carbon compounds, they are not treated as organic compounds because their properties are quite different from those of organic compounds. Each organic compound has specific formula.
There are four types of formulae of organic compounds:
Molecular formula Structural formula Condensed formula Dot and cross formula
(i) Molecular Formula
The formula which represents the actual number of atoms in one molecule of the organic compound is called the molecular formula, e.g., molecular formula of butane is . It shows: a. Butane is made up of carbon and hydrogen atoms. b. Each molecule of butane consists of 4 carbon atoms and 10 hydrogen atoms.