Question 12.17 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
Class XI Organic Chemistry : Some Basic Principles and Techniques Page 363
Answers
+δ -δ
A -----B
A---->--A---->>----A----->>>---B⁻δ,
or, C--->--C---->>----C--->>>----X⁻δ
Thus, polarisation of a σ-bond due to polarisation of neighbouring σ-bond is called inductive effect.inductive effect decreases with increases in the distance from the electronegative atom.
The effect is said to be -I If a group pulls the electrons from the carbon chain. such a group is called electron withdrawing group . or -I.
decreasing order of -I group is
R₃N⁺-->---NO₂⁻ >---CN > ---COOH > ---F > --Cl >--Br > --I >--OCH₃ > --OH > --C₂H₅
the effect is said to be +I If a group pushes the electrons from the carbon chain.such a group is called is called electron releasing group or +I.
decreasing order of +I is
--O⁻ > --COO⁻ > (CH₃)₃C >---(CH₃)₂N >CH₃CH₂CH₂-- > CH₃---
inductive effect is parmanent effect , it explains greater reactivity of alkyl halides as compared to alkane, realtive acidic strength of carboxylic acid, basic strength of amines etc.
Electromeric effect :- it is a temporary displacement of π-electrons in a multiple bond towards one of the bonded atom at the call of attacking species.
(a) -I effect As the number of halogen atoms decreases, the overall -I effect decreases and the acidic strength of carboxylic acids decreases accordingly.
Cl₃CCOOH > Cl₂CHCOOH > ClCH₂COOH
(b) +I effect As the number of alkyl group decreases, the overall +I effect increase and hence, acidic strength of carboxylic acids decreases accordingly.
CH₃CH₂COOH > (CH₃)₂CHCOOH > (CH₃)₃C.COOH
Inductive effect :- when A is less electronegative element than B ,shared pair of electrons is displaced near B, induced negative charge in B and induced positive charge in A.
+δ -δ
A -----B
A---->--A---->>----A----->>>---B⁻δ,
or, C--->--C---->>----C--->>>----X⁻δ
Thus, polarisation of a σ-bond due to polarisation of neighbouring σ-bond is called inductive effect.inductive effect decreases with increases in the distance from the electronegative atom.
The effect is said to be -I If a group pulls the electrons from the carbon chain. such a group is called electron withdrawing group . or -I.
decreasing order of -I group is
R₃N⁺-->---NO₂⁻ >---CN > ---COOH > ---F > --Cl >--Br > --I >--OCH₃ > --OH > --C₂H₅
the effect is said to be +I If a group pushes the electrons from the carbon chain.such a group is called is called electron releasing group or +I.
decreasing order of +I is
--O⁻ > --COO⁻ > (CH₃)₃C >---(CH₃)₂N >CH₃CH₂CH₂-- > CH₃---
inductive effect is parmanent effect , it explains greater reactivity of alkyl halides as compared to alkane, realtive acidic strength of carboxylic acid, basic strength of amines etc.
Electromeric effect :- it is a temporary displacement of π-electrons in a multiple bond towards one of the bonded atom at the call of attacking species.
(a) -I effect As the number of halogen atoms decreases, the overall -I effect decreases and the acidic strength of carboxylic acids decreases accordingly.
Cl₃CCOOH > Cl₂CHCOOH > ClCH₂COOH
(b) +I effect As the number of alkyl group decreases, the overall +I effect increase and hence, acidic strength of carboxylic acids decreases accordingly.
CH₃CH₂COOH > (CH₃)₂CHCOOH >(CH3)3C.COOH