Inductive Effect
The permanent polarisation of a sigma bond caused by the differing electronegativity of the attached atoms.
Formula / equation
−I and +I effects
Unit
Dimensionless
In depth
Electron-withdrawing groups exert a −I effect and electron-donating alkyl groups a +I effect. The influence is transmitted through the sigma framework but weakens rapidly with distance, becoming negligible beyond three or four bonds. It explains many trends in acidity and stability.
Examples in the real world
Chloroethanoic acid (pKa 2.87) being far stronger than ethanoic acid (4.76) because of chlorine's −I effect.