The inductive effect is a permanent polarization transmitted through sigma bonds. It arises from electronegativity differences and decreases rapidly with distance (practically zero beyond 4 bonds).

-I order (electron-withdrawing): NH3+ > NO2 > CN > F > Cl > Br > I > OH > OR > C6H5 > H +I order (electron-donating): (CH3)3C > (CH3)2CH > C2H5 > CH3 > H

Key applications:

1. Acidity of carboxylic acids: CHF2COOH > CH2FCOOH > CH3COOH (more -I = more acidic)
2. Basicity of amines: (CH3)3N > (CH3)2NH > CH3NH2 > NH3 (in gas phase; aqueous phase differs due to solvation)
3. Stability of carbocations: More +I groups = more stable