The hydrides of carbon (hydrocarbons) and their derivatives are called organic compounds. The branch of chemistry which deals with these compounds is called organic chemistry.
Berzelius (1808) defined organic chemistry as the chemistry of substances found in living matter and gave the vital force theory. Synthesis of urea, the first organic compound synthesised in laboratory, by Wohler. gave death blow to the vital force theory.
Acetic acid is the first organic compound synthesised from its elements.
Reasons for Large Number of Organic Compounds:
It is the tendency of self combination and is maximum in carbon. A carbon atom can combine with other carbon atoms by single, double or triple bonds. Thus, it forms more compounds than the others.
(b) Tetravalency and small size
Carbon being tetravalent, is capable of bonding with four other C atoms or some other monovalent atoms. Carbon can form compound with oxygen, hydrogen, chlorine, sulphur, nitrogen and phosphorus. These compounds have specific properties depending upon the nature of the element or group attached with the carbon.
Furthermore, these compounds are exceptionally stable because of the small size of carbon.
General Characteristics of Organic Compounds:
1. These are the compounds of carbon with H, O, N, S, P, F, CI, Br and I.
2. These are generally found in living organisms. e.g., carbohydrates, proteins etc.
3. These may be gases, liquids or solids.
4. Being covalent in nature, these have low boiling point and melting point and soluble in organic solvents.
5. These are generally volatile and inflammable.
6. They do not conduct electricity because of the absence of free ions.
7. They possess distinct colour and odour.
Classification of Organic Compounds
Fig: Classification Of Organic Compounds
Classification of Carbon Atoms:
1. On the Basis of Number of C Attached
(i) Primary carbon atom When carbon atom is attached with one other carbon atom only, it is called primary or 1° carbon atom.
(ii) Secondary carbon atom When carbon atom is attached with two other carbon atoms, it is called secondary or 2°carbon atom.
(iii) Tertiary carbon atom When carbon atom is attached with three other carbon atoms, it is called tertiary or 3° carbon atom.
(iv) Quaternary carbon atom When carbon atom is attached with four other carbon atoms, it is called quaternary or 4º carbon atom.
Reactivity order of carbon atoms is as follows 3° > 2° > 1°.
On the Basis of Position of Functional Group:
(i) α – carbon Carbon which is directly attached to the functional group.
(ii) β- carbon Carbon which is directly attached to the n-carbon.
Classification of Hydrogen Atoms:
Classification of Organic Compound
The existing large number of organic compounds and their ever -increasing numbers has made it necessary to classify them on the basis of their structures. Organic compounds are broadly classified as follows:
I. Acyclic or open chain compounds
These compounds are also called as aliphatic compounds and consist of straight or branched chain compounds, for example:
II Alicyclic or closed chain or ring compounds
Alicyclic (aliphatic cyclic) compounds contain carbon atoms joined in the form of a ring (homocyclic). Sometimes atoms other than carbon are also present in the ring (heterocylic). Some examples of this type of compounds are:
These exhibit some of the properties similar to those of aliphatic compounds.
Aromatic compounds are special types of compounds. You will learn about these compounds in detail in Unit 13. These include benzene and other related ring compounds (benzenoid). Like alicyclic compounds, aromatic comounds may also have hetero atom in the ring. Such compounds are called hetrocyclic aromatic compounds. Some of the examples of various types of aromatic compounds are:
Benzenoid aromatic compounds
Heterocyclic aromatic compounds
Organic compounds can also be classified on the basis of functional groups, into families or homologous series.