Organic Chemistry01
Aldol Condensation & Cannizzaro Reaction
Cross-aldol occurs between two different carbonyl compounds with α-hydrogen.
Examiner Tip: Cannizzaro reaction: 2 HCHO + conc. NaOH -> CH₃OH + HCOONa (disproportionation).
Aldehydes, Ketones & Carboxylic Acids Formulas
Nucleophilic addition, Aldol condensation, Cannizzaro reaction, Tollens/Fehling test, Hell-Volhard-Zelinsky (HVZ) reaction.
9 Formulas•395+ Questions in Bank
Core Formulas & Mathematical Identities
902
Haloform (Iodoform) Test
Positive test given by compounds containing CH₃-CO- group or CH₃-CH(OH)- group.
Examiner Tip: Ethanol gives positive iodoform test, but methanol does not.
03
Tollens' & Fehling's Distinction Tests
Aldehydes reduce Tollens' reagent to give silver mirror; ketones do not.
Examiner Tip: Fehling's solution oxidizes aliphatic aldehydes to give red cuprous oxide Cu₂O precipitate.
04
Hell-Volhard-Zelinsky (HVZ) Reaction
Halogenation specifically at the α-position of carboxylic acids containing α-hydrogen.
Examiner Tip: Formic acid (HCOOH) and benzoic acid cannot undergo HVZ reaction (no α-hydrogen).
05
Clemmensen & Wolff-Kishner Reductions to Hydrocarbons
Total reduction of carbonyl group to methylene (>C=O → >CH₂). Clemmensen for base-sensitive substrates; Wolff-Kishner for acid-sensitive substrates.
Examiner Tip: Clemmensen cannot be used if molecule contains -OH (undergoes substitution to -Cl) or C=C double bonds.
06
Rosenmund & DIBAL-H Selective Reductions to Aldehydes
Controlled partial reduction of acyl chlorides, esters, and nitriles avoiding over-reduction to primary alcohols.
Examiner Tip: DIBAL-H at -78°C selectively reduces esters and nitriles to aldehydes without affecting isolated C=C double bonds.
07
Decarboxylation of \beta-Keto Acids & Blanc's Rule for Di-acids
β-dicarboxylic and β-keto acids lose carbon dioxide easily upon gentle heating. Di-acids with 4-5 carbon chains form cyclic anhydrides; 6-7 carbon chains form cyclic ketones.
Examiner Tip: Oxalic and Malonic acids eliminate CO₂; Succinic and Glutaric acids eliminate H₂O to form cyclic anhydrides.
08
Perkin & Benzoin Condensation
Perkin condensation: aromatic aldehyde + acid anhydride → α,β-unsaturated carboxylic acid (base = sodium salt of the acid). Benzoin condensation: 2 PhCHO → PhCH(OH)COPh (α-hydroxy ketone) catalysed by KCN (CN⁻ acts as nucleophile).
Examiner Tip: Perkin product undergoes decarboxylation to give cinnamic acid analogs. Benzoin condensation is reversed by NaOH (benzoin oxidation → benzil) and reduced by Raney Ni to give diol.
09
Nucleophilic Addition Reactivity Order of Carbonyls
Carbonyl electrophilicity is governed by steric bulk (alkyl/aryl groups hinder nucleophile approach) and electronic effects (electron-donating groups reduce carbonyl δ⁺ character).
Examiner Tip: Aldehyde > Ketone always. Benzaldehyde is less reactive than acetaldehyde due to resonance delocalization of carbonyl π-electrons into benzene ring. Ketones can undergo nucleophilic addition only under acidic or basic catalysis.
Top Examiner Traps & Pitfalls
Frequently tested misconceptions in Aldehydes, Ketones & Carboxylic Acids
- •Aldol condensation requires α-hydrogens; Cannizzaro reaction occurs ONLY in aldehydes LACKING α-hydrogens (like HCHO, PhCHO).
- •Ketones do NOT reduce Tollens' reagent or Fehling's solution (except α-hydroxy ketones).
