Question
Thu March 27, 2014 By: Sanskrati Gawande

explain the following giving suitable examples

functional group

isomers

homologous series

Expert Reply
Thu March 27, 2014

Functional Group

It is an atom or a group of atoms that defines the structure (or the properties of a particular family) of organic compounds.

Characteristics of functional group

(i)Compounds of the same functional groups are identified using the same type of tests.

(ii)The physical and chemical properties of the compounds of different functional groups are different.

(iii)There exists a homologous series of compounds containing a particular type of functional groups.

For example :

Halides : F, Cl, Br

Aldehydes : CHO

Isomers

Compounds having same molecular formula but different structural formula are known as isomers and the phenomenon as isomerism.

E.g. Butane and isobutane are two different compounds  with same molecular formula C4H10.

                 

             

                                              Butane                                          Isobutane

Homologous Series

 It is a group of organic compounds having a similar structure and similar chemical properties in which the successive compounds differ by a CH2 group.

Characteristics of a Homologous series 

(i)Each member of the series differs from the preceding one by the addition of CH2 group and by 14 a.m.u.

(ii)All members of a homologous series share the general formula.

For example, general formula for alkane is CnH2n+2, alkene is CnH2n.

(iii)The physical properties of the members show gradation in properties as molecular mass increases.

(iv)The chemical properties also show gradient similarity.

For example: Methane and ethane reacts with chlorine to form methyl chloride and ethyl chloride respectively.

               CH4 + Cl2 → CH3Cl

              C2H6 + Cl2 → C2H5Cl

(v) All members of a homologous series can be prepared by same general method of preparation.

 For example: Alcohols can be prepared by from alkyl halides.

               ?

Examples of Homologous series

1. Alkane

General formula CnH2n+2                           

Molecular formula

Methane

CH4

Ethane

C2H6

Propane

C3H8

Butane

C4H10

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