Class 12 Chemistry Aldehydes Ketones Acids Chemical properties of Carboxylic Acid

Chemical properties of carboxylic acid

 Main four  types of reactions shown by them:

  1. Reaction due to Hydrogen atom of carboxylic acid: This property actually shows acidic character of carboxylic acid acids that is :

        Class_12_Chemistry_Carboxylic_Acid_Reaction_Of_Carboxylic_Acids_WithHydrogen

 If we talk about Strength of acidic character of CH3 COOH,then we have : 

   CH3 COOH + H2O --> CH3 COO- + H3O+

According to Arhenius acid and Bronstedconcept: Carboxylic acid is regarded as an acid.We can write its expression for dissociation constant as written below.

 Class_12_Chemistry_Carboxylic_Acid_Reaction_Of_Carboxylic_Acids_ArcheniusAcid

It is seen that :

  • Higher the value of ka, stronger is the acid.
  • Pka = -log ka
  • Higher the value of Pka, weaker is the acid.

 

Effect of substituents on strength of acid

We can have subsituents of two types :

  • Electron withdrawing
  • Electron Releasing groups

 Electron withdrawing subsituents: They will neutralize the intensity of  -ve charge and hence, RCOO- ion gets stablized. Therefore , the acid srength increases. Eg:Halogens

Electron releasing subsituents : They will increase the intensity of negative charge  and hence ,RCOO- ion gets less stablized. Therefore, acidic strength due to this decreases.

The acidic strength also depends upon other factors such as :

  1. Type of halogen attached :

        F>Cl>Br

Fluroine is much more electronegative

Acidic Strength CH3COOF more stronger acid > CH3COCl

BrCH3COOH > CH3COOI

  1. Acidic strength depending upon number of halogen atoms attached :

  Class_12_Chemistry_Carboxylic_Acid_Acidic_Strength

  1.  Depending upon the position, where X is attached

                Class_12_Chemistry_Carboxylic_Acid_Acidic_Strength_1  

  1. Depending upon hybridisation:

           Class_12_Chemistry_Carboxylic_Acid_Acidic_Strength_2

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