Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids?
(a) Cl3CCOOH > Cl2CHCOOH > ClCH2COOH
(b) CH3CH2COOH > (CH3)2CHCOOH > (CH3)3C.COOH
Inductive effect
The permanent displacement of sigma electrons along a saturated chain, whenever an electron withdrawing or donating group is present, is called inductive effect.
Inductive effect could be +I effect or –I effect. When an atom or group electrons towards itself more strongly than hydrogen, it is said to possess –I effect. For example.
When an atom or group attracts electrons towards itself less strongly than hydrogen, it is said to possess +I effect. For example.
Electrometric effect
It involves the complete transfer of the shared pair of ∏ electrons to the two atoms linked by multiple bonds in the presence of an attacking agent. For example
Electronic effect could be +E effect or –E effect.
+E effect: When the electrons are transferred towards the attacking reagent.
-E effect: When the electrons are transferred away from the attacking reagent.
(a) Cl3CCOOH > Cl2CHCOOH > ClCH2COOH
The order of acidity can be explained on the basis of inductive effect(-I) effect. As the number of chlorine atoms increases, the –I effect increases. With the increase in-I effect, the acid strength also increases accordingly.
(b) CH3CH2COOH > (CH3)2CHCOOH > (CH3)3C.COOH
The order of acidity can be explained on the basis of inductive effect(+I) effect. As the number of alkyl group increases, the +I effect increases. With the increase in +I effect, the acid strength also increases accordingly.