- No.11.What is general properties of organic compounds?
Answer. Organic compounds have the following general characteristics:
(i) Origin: Naturally occurring substances are obtained from plants and animals. On the other hand, inorganic compounds are obtained from minerals and rocks.
(ii) Composition: Carbon is an essential constituent of all organic compounds. They are made up of few elements such as carbon, hydrogen, nitrogen, oxygen, halogen, sulphur etc. On the other hand inorganic compounds are made up of almost all the elements of the Periodic Table known so far.
(iii) Covalent linkage: Organic compounds contain covalent bonds that may be polar or non-polar, while the inorganic compounds mostly contain ionic bonds.
(iv) Solubility: Organic compounds haying non-polar linkages are generally soluble in organic solvents like alcohol, ether, benzene, carbon disulphide etc. On the other hand, the inorganic compounds with ionic bonds are soluble in polar solvents like water.
(v) Electrical conductivity: Due to the presence of covalent bonds, organic compounds are poor conductor of electricity, whereas inorganic compounds being ionic in nature are good conductors of electricity.
(vi). Melting and boiling points: Generally organic compounds have low melting and boiling points and are volatile in nature. Inorganic compounds, on the other hand, have comparatively high melting and boiling points.
(vii) Stability: Since organic compounds have low melting and boiling points they are less stable than inorganic compounds.
(viii) Combustibility: Organic compounds with high percentage of carbon are generally combustible. On the other hand, inorganic compounds are mostly non-combustible.
- No.12. Write a detailed note on classification of organic compounds.
Answer. All known organic compounds have been broadly divided into two categories depending upon their carbon skeleton. These are:
- Open chain or acyclic compounds.
- Closed chain or cyclic compounds.
(i) Open chain or acyclic compounds.
Acyclic compounds contain open chains of carbon atoms in their molecules. These chains may be either straight or branched. For example,
(a) Straight chain compounds are those in which carbon atom links with other carbon atoms or other atoms through a single, double or triple bonds forming a straight chain, such as
I I I I I I
I I I I I I H3C-CH2-CH2-CH3
Straight chain Straight chain (n-Butane)
(b) Branched chain compounds are those in which there is a branch along a straight chain, suc
Branched chain Branched chain (isobutane)
Open chain compounds are also called aliphatic compounds.
(ii) Closed chain or Cyclic compounds
Closed chain or cyclic compounds contain one or more closed chains, i.e., the carbon atoms at the end of the chain are not free. They are further divided into two classes:
(a) Homocyclic or carbocyclic compounds.
(b) Heterocyclic compounds.
(a) Homocyclic or Carbocyclic compounds.
Homocyclic or carbocyclic compounds contain rings which are made up of only one kind of atoms, i.e., carbon atoms. These are further divided into two classes:
- Aromatic compounds
- Alicyclic compounds
Aromatic compounds: These organic compounds contain at least one benzene ring in their molecule. A benzene ring is made up of six carbon atoms with three alternating double bonds. They are called aromatic because of aroma. Aroma means smell. Examples,
They are also called benzenoid compounds.
Alicyclic or non-benzenoid compounds: Carbocyclic compounds which do not have benzene ring in their molecules are called alicyclic or non-benzenoid compounds. For example
Cyclic compounds that contain one or more atoms other than that of carbon atoms in their rings are called heterocyclic compounds.
The above classification may be summarized as follows: