Organic Compounds with Functional Groups formulas for JEE Main & Advanced

12 formula entries for Organic Compounds with Functional Groups, in the order the chapter builds them. Each shows the formula, when to use it and the first trap to avoid.

Oxidation of Alcohols

\begin{array}{r} R C H_{2} O H \overset{[O]}{\to} R C H O \overset{[O]}{\to} R C O O H \\ R_{2} C H O H \overset{[O]}{\to} R_{2} C = O \\ R_{3} C O H \overset{[O]}{\to} No reaction \end{array}

When to use. Use when predicting products of alcohol oxidation reactions in JEE.

Trap. Using strong oxidants like KMnO4/H+ on primary alcohols directly gives carboxylic acids, not aldehydes.

Lucas Test for Alcohols

R O H + H C l \overset{Z n C l_{2}}{\to} R C l + H_{2} O

When to use. Use to distinguish between primary, secondary, and tertiary alcohols in lab-based JEE problems.

Trap. The test works only for alcohols soluble in the reagent (typically up to 6 carbons).

Acidity of Phenols

C_{6} H_{5} O H ⇌ C_{6} H_{5} O^{-} + H^{+} p K_{a} \approx 10

When to use. Use to predict the relative acidity of different phenols in JEE questions.

Trap. Do not compare pKa values directly without considering substituent effects; ortho-substituents also have steric effects.

Ethers (R-O-R')

R - O - R^{'} + H I \to R O H + R I (or R^{'} I + R O H)

When to use. Use when predicting cleavage products of ethers or comparing physical properties.

Trap. With HI, the smaller/primary alkyl group usually gives the alkyl iodide (SN2); if one group is tertiary the tertiary iodide forms (SN1); in aryl alkyl ethers the aryl C–O bond is never cleaved, so the products are phenol and the alkyl iodide.

Nucleophilic Addition to Carbonyl

R_{2} C = O + N u^{-} \to R_{2} C (N u) O^{-} \overset{H^{+}}{\to} R_{2} C (N u) O H

When to use. Use to predict products of addition reactions to aldehydes/ketones.

Trap. Grignard reagents (RMgX) add to carbonyls but are destroyed by protic solvents; use dry ether.

Tollens' Test for Aldehydes

R C H O + 2 [A g (N H_{3})_{2}]^{+} + 3 O H^{-} \to R C O O^{-} + 2 A g ↓ + 4 N H_{3} + 2 H_{2} O

When to use. Use to distinguish between aldehydes and ketones in JEE practical problems.

Trap. The reagent must be freshly prepared; stored/old reagent can deposit explosive silver nitride (fulminating silver, $A g_{3} N$ ), so discard it after use.

Esterification Reaction

R C O O H + R^{'} O H ⇌ R C O O R^{'} + H_{2} O

When to use. Use to predict the product of esterification or to design a synthesis of an ester.

Trap. The alcohol oxygen is retained in the ester; use 18O labeling to confirm.

Hinsberg Test for Amines

\begin{array}{r} R N H_{2} + C_{6} H_{5} S O_{2} C l \to C_{6} H_{5} S O_{2} N H R \overset{N a O H}{\to} soluble \\ R_{2} N H + C_{6} H_{5} S O_{2} C l \to C_{6} H_{5} S O_{2} N R_{2} (insoluble) \end{array}

When to use. Use to distinguish between primary, secondary, and tertiary amines in JEE practical problems.

Trap. The test works only for aliphatic and aromatic amines; some sterically hindered amines may give anomalous results.

Reduction of Nitro Compounds

R N O_{2} + 6 [H] \to R N H_{2} + 2 H_{2} O

When to use. Use to predict the product of reduction of nitro compounds.

Trap. In acidic medium, the amine is protonated; neutralize to get free amine.

SN1 vs SN2 Reactions

\begin{array}{r} S N 2 : N u^{-} + R - X \to R - N u + X^{-} (inversion) \\ S N 1 : R - X \to R^{+} + X^{-}; R^{+} + N u^{-} \to R - N u (racemization) \end{array}

When to use. Use to predict the product and stereochemistry of nucleophilic substitution reactions.

Trap. Polar aprotic solvents (e.g., DMSO) favor SN2; protic solvents favor SN1.

Reaction of Grignard with Carbonyl

\begin{array}{r} R M g X + H C H O \to R C H_{2} O H (primary) \\ R M g X + R^{'} C H O \to R^{'} C H (O H) R (secondary) \\ R M g X + R_{2}^{'} C = O \to R_{2}^{'} C (O H) R (tertiary) \end{array}

When to use. Use to predict the alcohol formed from a Grignard reaction.

Trap. With CO2, the product is a carboxylic acid after hydrolysis: RMgX + CO2 → RCOOH.

Sandmeyer Reaction

\begin{array}{r} A r N_{2}^{+} C l^{-} \overset{C u C l}{\to} A r C l + N_{2} \\ A r N_{2}^{+} B r^{-} \overset{C u B r}{\to} A r B r + N_{2} \\ A r N_{2}^{+} C l^{-} \overset{C u C N}{\to} A r C N + N_{2} \end{array}

When to use. Use to predict the product when a diazonium salt is treated with copper(I) halide.

Trap. For iodine, use KI directly (no copper needed) because I- is a good nucleophile.

Values to remember

$p K_{a} of phenol \approx 10$ Acidity of Phenols
$p K_{a} of ethanol \approx 16$ Acidity of Phenols
$p K_{a} of acetic acid \approx 4.76$ Carboxylic Acids (RCOOH)
$p K_{a} of formic acid \approx 3.75$ Carboxylic Acids (RCOOH)

Read the full chapter: Organic Compounds with Functional Groups for JEE, with what JEE asks and the common traps.