Inductive Effect

The permanent displacement of sigma ($\sigma$) electrons along a carbon chain.

By chemca Team • Updated Jan 2026

The Inductive Effect (I-Effect) is a permanent electronic effect that involves the shifting of sigma ($\sigma$) bond electrons due to the electronegativity difference between atoms. It creates a permanent dipole in the molecule.

1. Key Characteristics

Permanent Effect: It is always present in the molecule.
Sigma ($\sigma$) Bonds Only: It operates through sigma bonds, not pi bonds.
Distance Dependent: Its magnitude decreases rapidly with distance and becomes negligible after 3 to 4 carbon atoms.
Direction: Electrons shift towards the more electronegative atom.

$$ C^{\delta\delta\delta+} - C^{\delta\delta+} - C^{\delta+} - X^{\delta-} $$

Where X is an electron-withdrawing group.

2. Types of Inductive Effect

Groups are classified based on their electron-donating or withdrawing power relative to Hydrogen (whose I-effect is taken as zero).

-I Effect (Electron Withdrawing)

Groups that withdraw electron density from the carbon chain (More electronegative than H).

Order of Strength:

$NO_2 > CN > COOH > F > Cl > Br > I > OH > OR > NH_2 > C_6H_5$

+I Effect (Electron Donating)

Groups that push/release electron density towards the carbon chain.

Order of Strength:

$O^- > COO^- > (CH_3)_3C- > (CH_3)_2CH- > CH_3CH_2- > CH_3- > D > H$

3. Applications

A. Stability of Reaction Intermediates

Carbocations ($C^+$): Electron deficient. Stabilized by +I groups (electron donors) which disperse the positive charge.
$3^\circ (R_3C^+) > 2^\circ (R_2CH^+) > 1^\circ (RCH_2^+) > \text{Methyl} (CH_3^+)$
Carbanions ($C^-$): Electron rich. Stabilized by -I groups (electron withdrawers) which disperse the negative charge. Destabilized by +I groups.
$\text{Methyl} (CH_3^-) > 1^\circ > 2^\circ > 3^\circ$

B. Acidic Strength of Carboxylic Acids

Acidic strength depends on the stability of the conjugate base (Carboxylate ion, $RCOO^-$).

-I Effect: Withdraws electrons, stabilizes the negative charge on $COO^-$, thus Increasing Acidity.
+I Effect: Donates electrons, destabilizes the negative charge, thus Decreasing Acidity.

Example: $F-CH_2-COOH > Cl-CH_2-COOH > CH_3-COOH$
(Fluoroacetic acid is stronger than Chloroacetic, which is stronger than Acetic acid).

C. Basic Strength of Amines

Basicity depends on the availability of the lone pair on Nitrogen for protonation.

+I Effect: Increases electron density on Nitrogen, making the lone pair more available. Increases Basicity.
-I Effect: Withdraws electron density, making the lone pair less available. Decreases Basicity.

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