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Unit IV — Fundamentals of Organic Chemistry · Electronic Effects

Inductive Effect & Its Applications

CompleteFundamentals of Chemistry

The permanent polarization of a σ bond due to differing electronegativity — transmitted through the chain.

Full notes

Definition: The inductive effect is the permanent displacement of σ electrons along a chain of atoms due to the electronegativity difference between atoms. It weakens with distance.

1. −I groups (electron-withdrawing)

Groups that pull electron density away: –NO₂, –CN, –COOH, –F, –Cl, –OH, –OCH₃ in decreasing order. Order: NO₂ > CN > F > Cl > Br > I > OH > OCH₃.

2. +I groups (electron-releasing)

Alkyl groups push electron density: (CH₃)₃C– > (CH₃)₂CH– > CH₃CH₂– > CH₃–. More branching → stronger +I.

3. Consequences

  • Acid strength: H–COOH > H–CH₂COOH > (CH₃)₂CHCOOH > (CH₃)₃CCOOH (−I groups on α-carbon stabilize the conjugate base).
  • Electronegative substituent increases acidity: Cl₃CCOOH strongest among chloroacetic acids.
  • Basicity of amines: alkyl amines (more +I) are more basic than ammonia.
  • Stability of carbocations: 3° > 2° > 1° due to +I of alkyl groups.
Note: Exam point: write the acidity order of acetic acid with substituents and explain via conjugate-base stabilization by −I effect.

Exam notes

Permanent σ polarization. −I groups (NO₂, CN, halogen) increase acidity; +I (alkyl) decrease it. Weakens along the chain.

Important points

  • Inductive effect is permanent and distance-dependent; it operates through σ bonds.

Common mistakes

  • Confusing inductive (σ, permanent) with electromeric/resonance (π, temporary/delocalized) effects.
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