Summary & Master Memory Capsule

Master Memory Capsule — Aldehydes, Ketones & Carboxylic Acids

A one-glance revision sheet for the morning of your Board, JEE or NEET paper.

The carbonyl group: sp$^2$, planar, δ+ carbon / δ− oxygen — electrophilic carbon attacked by nucleophiles. Naming: aldehyde = -al (C-1), ketone = -one (lowest locant), acid = -oic acid (C-1).

Preparation — The Routes to Remember

Aldehydes: 1° alcohol + PCC; acyl chloride + H$_2$/Pd-BaSO$_4$ (Rosenmund); nitrile + SnCl$_2$/HCl (Stephen); toluene + CrO$_2$Cl$_2$ (Etard); benzene + CO/HCl/AlCl$_3$ (Gattermann-Koch).

Ketones: 2° alcohol oxidation; Friedel-Crafts acylation (arene + R-COCl/AlCl$_3$); nitrile + Grignard.

Carboxylic acids: oxidation of 1° alcohols/aldehydes (KMnO$_4$); side-chain oxidation of any alkylbenzene → benzoic acid; nitrile hydrolysis and Grignard + CO$_2$ (both add one carbon); hydrolysis of acyl halides/anhydrides/esters.

Key Reactions & Named Reactions

Nucleophilic addition (aldehyde > ketone; HCHO most reactive): HCN → cyanohydrin; NaHSO$_3$ → bisulphite adduct; alcohol → acetal; H$_2$N-Z → oxime/hydrazone/2,4-DNP/Schiff's base.

alpha-Hydrogen reactions: aldol (with alpha-H, dilute NaOH → beta-hydroxy carbonyl → alpha,beta-unsaturated on heating); Cannizzaro (no alpha-H, conc. alkali → alcohol + carboxylate).

Redox: aldehydes oxidise easily (Tollens, Fehling), ketones resist; reduce C=O to alcohol (NaBH$_4$/LiAlH$_4$) or to CH$_2$ (Clemmensen Zn-Hg/HCl; Wolff-Kishner NH$_2$NH$_2$/KOH).

Carboxylic acids: salt + CO$_2$ (NaHCO$_3$), esterification, acyl chloride (SOCl$_2$)/anhydride/amide, LiAlH$_4$ → 1° alcohol, decarboxylation (soda lime), HVZ alpha-halogenation, meta-directing on the ring.

Tests, Acidity & Last-Minute Triggers

Distinguishing tests: 2,4-DNP = any carbonyl; Tollens (silver mirror) / Fehling (red Cu$_2$O) = aldehydes (Fehling only aliphatic); iodoform (yellow CHI$_3$) = CH$_3$CO-/CH$_3$CH(OH)-; NaHCO$_3$ effervescence = carboxylic acid; neutral FeCl$_3$ violet = phenol.

Acidity: carboxylic acid > phenol > water > alcohol. EWG (Cl, NO$_2$) raise acidity (CCl$_3$COOH strongest); EDG (alkyl) lower it (HCOOH > CH$_3$COOH).

Important compounds: formalin (preservative), acetone (solvent, cumene process), acetic acid (vinegar), sodium benzoate (food preservative), fatty-acid salts (soaps).

One-line recall: δ+ carbonyl carbon → nucleophilic addition (aldehyde > ketone); alpha-H → aldol, no alpha-H → Cannizzaro; Tollens/Fehling spot aldehydes, iodoform spots methyl ketones; acid > phenol > water > alcohol with EWG up / EDG down; remember Rosenmund, Stephen, Etard, Gattermann-Koch, Clemmensen, Wolff-Kishner, HVZ, decarboxylation.