Question

a)With appropriate examples taken from at least two different homologous series, explain the relationship between physical properties and structure of organic compounds

Answer 1

A homologous series in organic chemistry is the series having the general formula and generally increasing the size with -CH2- group. For example straight chain alkanes having the general formula CnH2n+2 and increase the size with -CH2- group , Methane ( CH4) , Ethane( CH3 - CH3) etc.

Homologous series having the similar gradation I.e gradual increase and decrease in their physical properties due to gradual increase in mass.

Example 1: Boiling point of alkanes:

The boiling points of this homologous series increases as the size of the molecule increases dipole moment increases and as a result London Dispersion forces between molecules increases, thus due to gradual increase in intermolecular forces gradual increase in boiling points occurring.

Example 2 :Boiling point of straight chain alcohol:

As the size of the alcohol increases boiling point is increasing in this series due to as the length of hydro carbon increases vander Waals dispersion force between molecules increasing and this increase in gradual as the size gradually increasing with one -CH2 - group. Examples of boiling Points: Methonol:68°C,Ethenol:78°C ,1-Propanol:97°C and 1-Propanol : 117°C etc.