Carbonyl Group Detection (Aldehydes & Ketones)

Formula / Core Reaction:

$$\text{R}_2\text{C=O} + \text{H}_2\text{N-NH-C}_6\text{H}_3(\text{NO}_2)_2 \xrightarrow{\text{H}^+} \text{R}_2\text{C=N-NH-C}_6\text{H}_3(\text{NO}_2)_2 \downarrow + \text{H}_2\text{O}$$

Concept: Nucleophilic addition-elimination reaction between a carbonyl compound (aldehyde or ketone) and 2,4-Dinitrophenylhydrazine (Brady's Reagent) yields an insoluble hydrazone precipitate.

Notation / Key Observation:

• 2,4-DNP: 2,4-Dinitrophenylhydrazine;
• Orange/Red crystalline precipitate: Positive indication of a carbonyl group ($$>\text{C=O}$$).