Inductive Effect (Polar Nature Of Covalent Bonds)

IUPAC & GOC of Class 12

Inductive Effect 

The displacement of an electron (shared) pair along the carbon chain due to the presence of an electron withdrawing or electron releasing groups in the carbon chain is known as inductive effect (I – effect).

  • It is a permanent effect which is transmitted along the chain.  

C……> ……C…>….C……>G (G – Functional group)

  • This permanent polarity is due to electron displacement due to difference in electronegativities.
  • This effect weakens steadily with increasing distance from the substitution
    (electron – withdrawing or electron – donating group) and actually diminishes down after three carbon atoms.

There are two types of inductive effect i.e. – I effect and +I effect.

Negative Inductive effect (⎯ I Effect)

If the substituent attached to the end of the carbon chain is electron withdrawing (X). The effect is called – I effect.

Inductive Effect (Polar Nature Of Covalent Bonds)

⎯I effect decreases as one goes away from groups (electron attacking)

Inductive Effect (Polar Nature Of Covalent Bonds)

C1(δ+) > C2(δδ+) > C3 (δδδ+) and other third carbon charge is negligible.

⎯I effect is in order.

NO2 > F > COOH > Cl > Br > I > OH > C6H5

Due to ⎯I effect (electron – with drawing nature) electron density decreases, hence basic nature is decreased and acidic nature is increased.

Chloroacetic acid is stronger than acetic acid since Cl shows (-I) effect, electron – density is decreased and O – H bond is weakens causing ionisation of (-COOH) to a greater extent than CH3COOH,

Inductive Effect (Polar Nature Of Covalent Bonds)

Inductive Effect (Polar Nature Of Covalent Bonds) is a base due to lone pair on nitrogen. Phenyl group is electron – withdrawing. What happens to electron – density of nitrogen in aniline, Naturally electron – density is decreased. Hence aniline is weaker base thanInductive Effect (Polar Nature Of Covalent Bonds) .

Inductive Effect (Polar Nature Of Covalent Bonds)

Similarly acidic nature of phenol is greater than  H2O due to electron – withdrawing nature of phenyl group.

Inductive Effect (Polar Nature Of Covalent Bonds)

Positive inductive effect (+I effect):

If the substituent attached to the end of the carbon chain is electron – donating, the effect is called +I effect.

This is due to electron – releasing (Y). It develops a negative charge on the chain.

Inductive Effect (Polar Nature Of Covalent Bonds)

+I effect also decreases as we go away from group Y (electron – releasing)

Inductive Effect (Polar Nature Of Covalent Bonds)

Inductive Effect (Polar Nature Of Covalent Bonds)

So +I effect is in the order of

Inductive Effect (Polar Nature Of Covalent Bonds)

Due to electron – releasing group electron density is increased, hence basic nature is also increased and naturally acidic nature is decreased, thus

 

-I effect

+I effect

Acidic Nature

Basic Nature

Note:

Inductive effect is a permanent effect operating in the ground state of the organic molecules and hence is responsible for high melting point, boiling point and dipole moment of polar compounds.

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