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Introduction to Organic Chemistry

Organic chemistry is the study of the synthesis, structure, reactivity and properties of the diverse group of chemical compounds primarily constructed of carbon. Simply, it can be defined as organic chemistry is the study of hydrocarbons and its derivatives. In earlier days, the branch of chemistry, devoted to the study of carbon compounds, whose source was related to the living system, was termed as organic chemistry (organic means life).



Essentially, all the chemical reactions that take place in the living system are organic reactions. This is because the molecules of life such as proteins, vitamins, lipids, carbohydrates, chlorophyll, haemoglobin, nucleic acids, and so on contain carbon. In fact, our dependency on nature for food, clothing (cotton, wool, and silk) and energy (natural gas and petroleum) is, basically, the dependency on organic compounds.

Friedrich Wohler carried the very first synthesis of an organic compound, called urea, way back in 1828, by heating ammonium cyanate (a compound from non-living source).

ammonium cyanate and urea

The synthesis of urea marked the beginning of a new era in organic chemistry, thereby, starting off the process of identification of natural products and their synthesis. Further, with the advancement in chemistry, a variety of new organic compounds, catering the needs of mankind, were synthesized. This endless list of compounds includes plastic, rubber, fiber, medicines, dyes, agrochemicals, and so on. The synthesis of natural and synthetic organic compounds has become a continuous process and each day new compounds are added to the literature of organic chemistry.

This development needed a new definition of organic chemistry, which is not restricted only to the carbon compounds of living system but also includes the synthetic organic compounds under its umbrella. Thus, the simplest definition of organic chemistry is the study of compounds that contain carbon, that is it is chiefly, the study of compounds where carbon is covalently bonded to carbon, hydrogen, halogens, oxygen, nitrogen and sulfur.

Classification of Organic Compounds

The chemistry of organic compounds is most systematic and depends on the class of the compound. So, classification of the organic compounds is the first step towards their study.

Carbon forms the basic skeleton of every organic compound. On this basis, the compounds are broadly divided into two groups:

Aliphatic or open-chain compounds

In aliphatic compounds, carbon may form either straight or branched chains. The word ‘Aliphatic’ is derived from the Greek word ‘Aliphos’ meaning fat. Some of the compounds of this class were initially obtained from fat and so they were called aliphatic.

Aliphatic or open-chain compounds

Cyclic or closed-chain compounds

In such compounds, carbon forms a ring. This class is further divided into two groups:

  1. Homocyclic or Carbocyclic
  2. Heterocyclic
(a) Carbocyclic or homocyclic

The compounds of this class contain only carbon atoms in the ring. Carbocyclic compounds are further divided into two groups:

  1. Alicyclic compounds
  2. Aromatic compounds

1. Alicyclic compounds

Compounds of this class have properties similar to the aliphatic compounds.

Alicyclic compounds

ii) Aromatic compounds

The word ‘Aromatic’ is derived from the Greek word ‘Aroma’ meaning ‘Fragrant Smell’. Compounds of this class possess specific odour and so they are called aromatic. The name is still in use. Aromatic compounds contain alternate single and double bonds in their structure. It imparts special stability to such compounds that is termed as ‘Aromaticity’.

Aromatic compounds

(b) Heterocyclic

The word ‘Hetero’ means different. Therefore, organic cyclic compounds containing other polyvalent atoms (N, O, S, etc.) in the ring are called ‘Heterocyclic’ compounds.


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