Hello Guys, Today we are going to discuss a very important topic for jee Mains, advanced, NEET & AIIMS.
First of all, we are providing some important points about inductive effect.
(1) When an electron withdrawing (X) or electron-releasing (Y) group is attached to a carbon chain, polarity is induced on the carbon atom and on the substituent attached to it. This permanent polarity is due to displacement of shared electron of a covalent bond towards a more electronegative atom. This is called inductive effect or simply as I – effect.
(2) Carbon-hydrogen bond is taken as a standard of inductive effect. Zero effect is assumed for this bond. Atoms or groups which have a greater electron withdrawing capacity than hydrogen are said to have–I effect whereas atoms or groups which have a greater electron releasing power are said to have +I effect.
Applications of Inductive Effect
1. Effect on Bond lengths: Since the inductive effect leads to ionic character in the bond, the increase in –I effect usually decreases the bond length.
2. Dipole moment : Since, inductive effect leads to a dipolar character in the molecule, it develops some dipole moment in the molecule, which increases with the increase in the inductive effect.
CH3 – I, CH3 — Br, CH3 — Cl
Increasing dipole moment
3. Reactivity of alkyl halides: Alkyl halides are more reactive than the corresponding alkanes due to presence of C––X bond which is polar due to I effect, furthermore reactivity increases with increase of branching.
4. The acidity of carboxylic acid is due to inductive effect and resonance stabilisation of the carboxylate anion. Thus any group or atom, which is highly electronegative help in removing the hydrogen atom as proton and the group or atom which is less electronegative than C makes the removal of proton difficult.
Hence (–I) effect group increases acidic strength and (+I) effect groups decreases the acidic strength of carboxylic acid.
5. Basic strength of Amines : The basic character of amines is due to presence of unshared electron pair on nitrogen atom which accepts proton; the readiness with which the lone pair of electrons available for protonotion determines the relative strength of amines.
Due to +I effect of alkyl group, the nitrogen atom becomes rich in electrons with the result the lone pair of electron on nitrogen atom in amines is more easily available than in ammonia and hence generally, amines are stronger bases than ammonia. On the other (–I) groups or electron groups attached to nitrogen atom makes it difficult for protonation.
Note: Relative basic strength of amines is not in total accordance with the inductive effect, other factors like steric effect and stabilisation of cation by hydration also play important role to determine the basic strength of amines.
Due to electron – releasing group electron density is increased, hence basic nature is also increased and naturally acidic nature is decreased.
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