Definition of Organic Chemistry

Old Concept: - The world Organic signifies life. Therefore, all substances which were obtained directly or indirectly from living organisms, plants and animals, were called organic compounds and the branch of chemistry which deals with these compounds was called organic chemistry. Although, a large number of organic compounds such as sugar, starch, alcohol, oils, indigo, resins, etc, had been known from earliest times, very little information was known regarding their chemistry until the beginning of eighteenth century.

In 1675, Lemery published his famous Cours de Chymie, in which he classified the natural substances into three classes according to their respective origin

i) Mineral Substances obtained from the mineral kingdom.

ii) Vegetable substances obtained from the vegetable kingdom.

iii) Animal substances obtained from the animal kingdom.

This classification was accepted quickly but it was Lavoisier (father of chemistry) who first showed, in 1785, that all compounds obtained from vegetables and animals sources always contained carbon and hydrogen, and frequently nitrogen and phosphorus. It was also realized that some organic compounds occurred both in plants and animals. This led to the re-classification of natural substances into two categories.

i) All those which could be obtained from vegetables or animals, i.e., the substance which were produced by living organisms. These substances were classified as organic compounds.

ii) All those which were not obtained from the living organisms. These substances were classified as inorganic compounds.

Quite a large number of organic compounds have been discovered and isolated from natural sources by the first quarter of nineteenth century but till then none of the organic compounds could be prepared in laboratory. This led to believe that organic compounds followed laws of formation different from inorganic compounds. Brezelius assumed that some vital forces was necessary to produce organic compounds and synthesis of these compounds in the laboratory was impossible ude to the absence of this vital force which only existed in living organisms.

The vital force theory suffered the first death blow, in 1828, when Wohler synthesized first organic compound, urea, in the laboratory by heating ammonium cyanate (an inorganic compound)