Exam Master Review Sheet - Functional Group Tests

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EXAM MASTER REVIEW SHEET

Practical Organic Chemistry (POC)

Functional Group Identification & Elemental Analysis for JEE/NEET

1 Detection of Elements (Lassaigne's Test)

Organic compound is fused with Sodium metal to convert covalent elements into ionic sodium salts ($NaCN, Na_2S, NaX$).

Nitrogen ($N$)

Add freshly prepared $FeSO_4$, boil, cool, and add few drops of conc. $H_2SO_4$ or $FeCl_3$.

Prussian Blue / Green Color

Complex: $Fe_4[Fe(CN)_6]_3$

Sulphur ($S$)

1. Lead Acetate: Add acetic acid and lead acetate. $\rightarrow$ Black ppt ($PbS$).

2. Sodium Nitroprusside: Add to extract.

Deep Violet Color

Complex: $Na_4[Fe(CN)_5NOS]$

Halogens ($X$)

Boil with conc. $HNO_3$ (to expel $HCN/H_2S$), then add $AgNO_3$ solution.

• White ppt (sol in $NH_4OH$): $Cl$
• Pale Yellow ppt (sparingly sol): $Br$
• Yellow ppt (insoluble): $I$

Trap: If N and S are both present, $NaSCN$ is formed. Adding $Fe^{3+}$ gives a Blood Red color ($[Fe(SCN)]^{2+}$).

2 Tests for Unsaturation

Bromine Water Test

Reagent: $Br_2$ dissolved in $CCl_4$ or water (Reddish-Orange color).

Alkenes / Alkynes + $Br_2$ $\rightarrow$ Dibromo/Tetrabromo addition product.

Observation: Decolorization of orange color.

Baeyer's Test

Reagent: Cold, dilute, aqueous alkaline $KMnO_4$ solution (Pink/Purple color).

Alkenes + $KMnO_4$ $\rightarrow$ Vicinal Diols (Glycols) + $MnO_2 \downarrow$

Observation: Purple color disappears; Brown ppt ($MnO_2$) forms.

3 Hydroxyl Groups: Alcohols & Phenols

Alcohols ($R-OH$)

• Ceric Ammonium Nitrate (CAN) Test

  General test for all alcohols. Reagent: $(NH_4)_2[Ce(NO_3)_6]$.

  Result: Red or Pink Coloration.

• Lucas Test (Distinction)

  Reagent: Anhydrous $ZnCl_2$ + conc. $HCl$. Tests for $S_N1$ reactivity.

  • $3^\circ$ Alcohol: Immediate Turbidity (cloudiness).

  • $2^\circ$ Alcohol: Turbidity after 5-10 minutes.

  • $1^\circ$ Alcohol: No Turbidity at room temp (only on heating).

Phenols ($Ar-OH$)

• Neutral $FeCl_3$ Test

  Detects enolic/phenolic $-OH$ groups.

  Result: Violet / Blue / Green Coloration.

• Liebermann's Nitroso Test

  Phenol + $NaNO_2$ + conc. $H_2SO_4$ $\rightarrow$ Deep Blue/Green. Dilute with water $\rightarrow$ turns Red. Add excess $NaOH$ $\rightarrow$ Original Deep Blue is restored.

• Bromine Water Test

  Phenol is highly activated.

  Result: White Precipitate (2,4,6-tribromophenol).

4 Carbonyls, Acids & Amines

Functional Group	Test Name & Reagent	Observation & Inference
Carbonyls (Ald/Ket)	2,4-DNP Test (Brady's Reagent)	Yellow, Orange, or Red Precipitate.
Aldehydes Only	Tollens' Test (Ammoniacal $AgNO_3$)	Bright Silver Mirror on test tube walls.
Aliphatic Aldehydes	Fehling's Test (Aq. $CuSO_4$ + Rochelle salt)	Reddish-Brown Precipitate of $Cu_2O$.
Methyl Ketones	Iodoform Test ($NaOH + I_2$)	Yellow Crystalline Precipitate of $CHI_3$.
Carboxylic Acids	Bicarbonate Test (Aq. $NaHCO_3$)	Brisk effervescence of $CO_2$ gas. (Distinguishes from Phenols).
Carboxylic Acids	Esterification (Alcohol + conc. $H_2SO_4$)	Pleasant / Fruity Smell of ester.
$1^\circ$ Amines	Carbylamine Test ($CHCl_3$ + alc. $KOH$)	Extremely foul / offensive smell (Isocyanide).
Aromatic $1^\circ$ Amines	Azo Dye Test ($NaNO_2/HCl$ then $\beta$-naphthol)	Brilliant Orange-Red Dye.
Amines ($1^\circ, 2^\circ, 3^\circ$)	Hinsberg Test (Benzene sulphonyl chloride)	$1^\circ$: Ppt soluble in alkali. $2^\circ$: Ppt insoluble in alkali. $3^\circ$: No reaction.

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