Inductive Effect (Polar Nature Of Covalent Bonds)

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.

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

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,

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 than.

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

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.

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

So +I effect is in the order of

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

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.