<h2>Introduction</h2> <p>Aldehydes (–CHO) and ketones (C=O flanked by two carbon groups) are carbonyl compounds. This chapter is very important for NEET — typically 2–3 questions on named reactions and tests.</p> <h2>Preparation</h2> <ul> <li><strong>Aldehydes:</strong> Oxidation of primary alcohols; Rosenmund reduction (acid chloride + H₂/Pd-BaSO₄)</li> <li><strong>Ketones:</strong> Oxidation of secondary alcohols; Dry distillation of calcium salts of fatty acids</li> <li><strong>Both:</strong> Ozonolysis of alkenes</li> </ul> <h2>Nucleophilic Addition Reactions</h2> <p>The carbonyl carbon is electrophilic. Nu⁻ attacks → addition product.</p> <ul> <li>Addition of HCN → cyanohydrin</li> <li>Addition of NaHSO₃ → bisulphite addition (only methyl ketones and aldehydes)</li> <li>Addition of NH₂OH → oxime (–C=N–OH)</li> <li>Addition of NH₂–NH₂ → hydrazone</li> <li>Addition of Grignard reagent (RMgX) → secondary/tertiary alcohol</li> </ul> <h2>Tests to Distinguish Aldehyde from Ketone</h2> <table> <tr><th>Test</th><th>Aldehydes</th><th>Ketones</th></tr> <tr><td>Tollens' (silver mirror test)</td><td>+ve (silver mirror)</td><td>−ve</td></tr> <tr><td>Fehling's test</td><td>+ve (brick red ppt)</td><td>−ve (except HCHO)</td></tr> <tr><td>Schiff's reagent</td><td>Pink/red colour</td><td>−ve</td></tr> </table> <h2>Named Reactions</h2> <ul> <li><strong>Aldol Condensation:</strong> Aldehydes/ketones with α-H undergo self-condensation in dilute base → β-hydroxy carbonyl compound</li> <li><strong>Cannizzaro Reaction:</strong> Aldehydes without α-H (HCHO, C₆H₅CHO) undergo self-disproportionation in conc. NaOH → one oxidised (carboxylate) + one reduced (alcohol)</li> <li><strong>Clemmensen Reduction:</strong> C=O → CH₂ using Zn/Hg + conc. HCl (acidic medium)</li> <li><strong>Wolff–Kishner Reduction:</strong> C=O → CH₂ using NH₂–NH₂ then KOH/Δ (basic medium)</li> <li><strong>Cross Aldol:</strong> Between two different aldehydes</li> </ul> <h2>Iodoform Test</h2> <p>Positive for methyl ketones (CH₃COR), acetaldehyde (CH₃CHO), and secondary alcohols with –CH(OH)CH₃ group. Yellow precipitate of CHI₃ formed.</p>