Cornell Note — Substituent Effects on Acidity — Notes

Cue Column | Notes Column

–I Effect on Acidity | Electron-withdrawing groups stabilize RCOO– → increase acidity → lower pKa.

+I Effect on Acidity | Electron-donating alkyl groups destabilize RCOO– → decrease acidity → raise pKa.

Chlorine Substitution Series | Cl3CCOOH (0.65) > Cl2CHCOOH (1.26) > ClCH2COOH (2.87) > CH3COOH (4.76). Each Cl adds ~0.6–1.6 pKa units of acidity.

Alkyl Group Series | HCOOH (3.75) > CH3COOH (4.76) > C2H5COOH (4.87) > (CH3)3CCOOH (5.05). More/larger alkyl = stronger +I = weaker acid.

Distance Effect | 2-Chlorobutanoic acid > 3-Chlorobutanoic acid > 4-Chlorobutanoic acid. –I effect attenuates with distance through sigma bonds.

Formic vs. Acetic | HCOOH stronger because H has zero inductive effect; CH3 has +I that destabilizes CH3COO–.

Aromatic Carboxylic Acids | Para-substituents follow: –NO2 (EWG) > –H (benzoic) > –CH3 (EDG). EWG para-substituents increase acidity; EDG decrease acidity.

Summary

Every acidity comparison in NEET reduces to: count the number and type of inductive substituents, determine whether they are –I (increase acidity) or +I (decrease acidity), and note their distance from –COOH.