Carbon and Its Compounds

HOMOLOGOUS SERIES

A group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH₂ group.

Two adjacent homologous groups differ by 1 carbon atom and 2 hydrogen atoms .

General formula of Alkanes ---  C_nH_2n+2

Characteristics of a Homologus Series

1.  All members represented by same general formula.
2. Two adjacent homologues differ by a CH₂
3. Difference between molecular masses of any 2 homologues is 14μ.
4. All compounds show similar chemical properties.
5. There is gradual change in their physical properties with increase in molecular masses. ( melting , boiling points and densities increase)

Alkenes ---- C_nH_2n

Alkynes ---- C_nH_2n-2

Functional Groups

An ‘atom’ or a ‘group of atoms’ which makes a carbon compound reactive and decides its properties.

1. Halo Group :   −X  (  X can be  Cl, Br or I)
   

   Chloro , Bromo and Iodo group ----
   When 1 H atom of an alkane is replaced by a halogen atom, we get Haloalkane.
   Eg. CH₄ → Replace one H by Cl → CH₃Cl

   General  formula  is  C_nC_2n+1–X   (  X  may be Cl ; Br  ;I  )

   Chloromethane – CH₃ Cl   ---- methyl chloride
   Bromomethane -  CH₃Br   ---- methyl  bromide
   Chloroethane    -  C₂H₅Cl  ----  ethyl  chloride
   Chloropropane  -  C₃H₇Cl  ----  propyl chloride

2. Alcohol Group :  −OH  ( alcoholic  /  hydroxyl group)
   

   Alcohol group is made up of  1 oxygen and 1 hydrogen atom joined together.
   1 H atom is replaced by an alkane  by a hydroxyl group ( OH  group)
   CH₄  → Replace  1 H by  OH → CH₃OH

   General formula  is  C_nH_2n+1OH
   Methanol  - CH₃OH  ---- methyl  alcohol
   Ethanol - C₂H₅OH ---- ethyl alcohol
   Propanol  - C₃H₅OH ----  propyl  alcohol

3. Aldehyde  Group :

   It consists of 1 carbon, 1 hydrogen and 1 oxygen atom joined together.

   General formula  ---  C_nH_2nO
   Methanal  -  HCHO ---  formaldehyde
   Ethanal -  CH₃CHO ---- acetaldehyde
   Propanal – CH₃CH₂CHO  ---  propionaldehyde
   Butanal  -  CH₃CH₂CH₂CHO

4. Ketone  Group :

   It consists of 1 carbon and 1 oxygen atom. A ketone group must contain at least 3 carbon atoms.
   General formula --  C_nH_2nO
   Propanone  -  CH₃COCH₃ ----  acetone  ( simplest ketone)
   Butanone - CH₃COCH₂CH₃
   Pentanone - CH₃COCH₂CH₂CH₃

5. 
6. Alkene  Group  :

   It is a Carbon – carbon double bond.
   Ethene   -  CH₂ = CH₂  
   Propene -  CH₃− CH = CH₂

7. Alkyne Group  : −C≡C−
   Ethyne  -  CH≡CH
   Propyne  - CH₃−C≡CH

Submitted By Mrs. Kritika Bhola
Email Id : kritikabhola@yahoo.co.in