Cue Column | Notes Column

What is a carboxylic acid? | RCOOH — contains the carboxyl group (–C(=O)OH). Most acidic common organic functional group. General SMILES pattern: OC(=O)R

Why so acidic? | RCOO– is resonance-stabilized: negative charge delocalized equally over two C–O bonds (bond order 1.5). Carboxylic acid pKa ≈ 4–5 vs. alcohol pKa 16–18.

Acidity Ladder | RCOOH (4–5) > ArOH (~10) > H2O (15.7) > ROH (16–18) > RC≡CH (~25)

Substituent Effect | –I groups (Cl, F, NO2): increase acidity by stabilizing COO–. +I groups (alkyl): decrease acidity by destabilizing COO–. Effect decreases with distance.

Preparation Routes | (1) Oxidation: RCH2OH or RCHO --[KMnO4 or K2Cr2O7/H+]--> RCOOH. (2) Grignard: RMgX + CO2 --[dry ether]--> RCOOH. (3) Nitrile hydrolysis: RCN + H3O+ --> RCOOH. (4) Saponification: RCOOR' + NaOH --> RCOONa.

Key Reactions | HVZ, Decarboxylation, Fischer esterification, SOCl2/PCl5, LiAlH4 reduction, Kolbe electrolysis.

NEET Traps | NaBH4 does NOT reduce RCOOH. HCOOH and ArCOOH cannot do HVZ. Soda lime decarboxylation of formate → H2 (not alkane).

Summary

Carboxylic acids owe their acidity to resonance-stabilized carboxylate ions. Substituent effects (–I vs. +I), all preparation routes, and the six key reactions (especially HVZ limitations and reduction agent differences) are the three pillars of NEET questions on this topic.

Apparatus Reference

Standard reflux apparatus used for nitrile hydrolysis and saponification reactions.