Match the LIST-I Reagent with LIST-II Functional Group detected: Sodium bicarbonate solution, Neutral ferric chloride, Ceric ammonium nitrate, Alkaline KMnO4

Sodium bicarbonate (NaHCO₃) is a mild base that reacts exclusively with carboxylic acids among common organic functional groups. The reaction produces carbon dioxide gas as brisk effervescence, which is a highly visible and reliable positive test. The underlying principle is acid strength: carboxylic acids (pKa ~4–5) are stronger than carbonic acid (pKa ~6.4), so they displace CO₂ from bicarbonate. Phenols, with pKa ~10, are much weaker acids than carbonic acid and therefore cannot react with NaHCO₃. This makes the sodium bicarbonate test a powerful tool for distinguishing carboxylic acids from phenols — both react with NaOH but only carboxylic acids react with NaHCO₃. In JEE, this distinction is frequently tested in both theoretical and match-the-list format questions.

Neutral ferric chloride (FeCl₃) solution gives characteristic colours with phenolic compounds due to the formation of coloured iron-phenolate complexes of the type [Fe(OAr)ₙ]^(3-n)+. Simple phenol gives a violet or purple colour. Different phenols give different colours: catechol (1,2-dihydroxybenzene) gives green, resorcinol (1,3-dihydroxybenzene) gives violet, and hydroquinone (1,4-dihydroxybenzene) gives transient greenish colour. It is important to use neutral FeCl₃ — acidic FeCl₃ gives different results. Enols (tautomers with C=C–OH) also give positive FeCl₃ test. Aliphatic alcohols and saturated carboxylic acids do not give a colour change. This makes neutral FeCl₃ a highly specific reagent for identifying phenolic –OH groups.

Ceric ammonium nitrate [(NH₄)₂Ce(NO₃)₆], commonly called CAN, is a Ce⁴⁺ based oxidising reagent used to detect the presence of alcoholic –OH groups. In the CAN test, an alcohol forms a coordination complex with the Ce⁴⁺ ion, producing a characteristic red or orange-red colour. The reagent itself is yellow-orange in solution, so the development of a red colour indicates a positive result. The test is effective for primary, secondary, and tertiary alcohols. It is particularly useful because it distinguishes alcohols from ethers (which do not react). Some phenols may also give a colour change with CAN but the product colour differs. CAN is also widely used in organic synthesis as a mild selective oxidant and as a stain in thin layer chromatography (TLC) for visualising alcohol-containing compounds.

Baeyer’s test uses cold, dilute, alkaline potassium permanganate (KMnO₄) to detect the presence of carbon–carbon double bonds (C=C) or triple bonds (C≡C). The test is simple and visually striking: the deep purple KMnO₄ solution is decolourised when an unsaturated compound is added, and a brown precipitate of MnO₂ forms. The permanganate ion (MnO₄⁻, purple) is reduced to MnO₂ (brown) while the alkene is oxidised to a diol (syn dihydroxylation). Saturated compounds do not decolourise KMnO₄ under mild conditions. It is important to note that the test must be performed with cold, dilute, alkaline KMnO₄ — hot concentrated KMnO₄ can cleave C=C bonds and give oxidative cleavage products, which is used synthetically but is not the Baeyer’s test. The test also turns positive with other easily oxidised groups like aldehydes, so the context must be noted carefully in JEE questions.