CBSE Class 11 Chemistry Notes For Classification Of Organic Compounds On The Basis of Functional Group

Classification Of Organic Compounds On The Basis of Functional Group

Hydrocarbon

Hydrocarbons are the binary compounds of C and H. Based on their structural formulae, they are given types

1. Saturated hydrocarbons or alkanes or paraffins:

The open chain hydrocarbons in which the carbon atoms (except methane, CH4, in which the single carbon is bonded to four H -atoms) of each molecule are linked mutually by single covalent σ -bonds, and rest of the valencies of C atoms are satisfied by single covalent σ -bonds with H atoms, are known as saturated hydrocarbons or alkanes.

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Since these saturated hydrocarbons are quite less reactive due to absence of any functional group, they are also called paraffins (Latin: parum =little and affins = affinity or reactivity). The compounds of this class are representedby the general formula: C_n2n+ 2.

Classification of carbon and hydrogen atoms present in saturated hydrocarbons or alkanes:

The C-atoms present in an alkane molecule may be classified into four types primary (1°), secondary (2°), tertiary (3°), and quaternary (4°), C-atom as follows:

• A C-atom attached to only one (or no other) C-atom is called primary C-atom It is designated as 1° carbon.
• A C-atom attached to two other C-atoms is called a secondary C-atom.It is designated as 2°.
• A C-atom attached to three other C-atoms is called a tertiary C-atom.It is designated as 3° carbon.
• A C-atom attached to four other C-atoms is called a quaternary C-atom. It is designated as 4° carbon.

The hydrogen atoms may similarly be classified.

The hydrogen atoms attached to 1°, 2°, and 3° carbon atoms are called primary (1°), secondary (2°) and tertiary (3°) hydrogen atoms respectively. It is to be noted that unlike quaternary carbon atoms quaternary H atom has no existence because a quaternary carbon does not carry any hydrogen atom. The former example clearly illustrates the various types of carbon and hydrogen atoms.

2. Unsaturated hydrocarbons:

The open-chain hydrocarbons which contain at least one carbon-carbon double bond > C=C<or carbon-carbon triple (—C= C— ) bond in their molecules are called unsaturated hydrocarbons. These unsaturated hydrocarbons are further classified into two types: alkenes and alkynes.

The unsaturated hydrocarbons containing carbon-carbon double bonds are called alkenes, for example, ethylene (CH₂=CH₂), propylene (CH₃CH=CH₂) etc. A double bond is made up of one cr -bond and one n -bond. These hydrocarbons are also called olefins (Greek: olefiant = oil forming) because the lower members of this class react with chlorine to form products. The general formula of alkenes is C_nH_2n where n = 1, 2, 3— etc.

The unsaturated hydrocarbons containing carbon-carbon triple bonds are called alkynes, for example, acetylene (HC = CH), methyl acetylene (CH3C= CH) etc. A triple bond is made up of one σ-bond and two π-bonds. The general formula of alkynes is C_nH_2n-2 where n= 1, 2,3 – etc

Classification of hydrocarbon derivatives based on the functional group: