The tests performed on compound X and their inferences are :
Test : Inference
(a) 2, 4- DNP test : C

Q: Why doesn't compound (a) give a positive iodoform test?

Compound (a) contains an aldehyde group ($-CHO$). The iodoform test requires a methyl group directly attached to the carbonyl carbon ($-COCH_3$), which is absent in compound (a).

Q: Can secondary amines give a positive azo-dye test?

No, only primary aromatic amines ($-NH_2$ attached to a benzene ring) can form the stable diazonium salts required to couple and form an azo dye. Secondary and tertiary amines react differently with nitrous acid.

Q: What exactly is the coloured precipitate in the 2,4-DNP test?

The precipitate is a 2,4-dinitrophenylhydrazone derivative. It forms when the hydrazine group of the reagent undergoes a condensation reaction with the carbonyl group of the aldehyde or ketone, eliminating a water molecule.

Q: Why did we eliminate compound (c) immediately?

Compound (c) is an alcohol and does not contain a carbonyl group ($>C=O$). Since the 2,4-DNP test was positive, the compound must have a carbonyl group, ruling out (c) right away.

Q: Is it possible for an aldehyde to give a positive iodoform test?

Yes, but there is only one specific aldehyde that does: acetaldehyde ($CH_3CHO$), because it has a methyl group directly attached to the carbonyl carbon. None of the options here are acetaldehyde.

Question

The tests performed on compound X and their inferences are : \begin{array}{ll} 	extbf{Test} & 	extbf{Inference} \ 	ext{(a) 2, 4- DNP test} & 	ext{Coloured precipitate} \ 	ext{(b) Iodoform test} & 	ext{Yellow precipitate} \ 	ext{(c) Azo-dye test} & 	ext{No dye formation} \end{array} Compound 'X' is

Sigma Percentile · Accepted Answer

### Decoding the Mystery Compound

Imagine you are a chemical detective, and you've just been handed a mystery compound, let's call it Compound X. Your job is to deduce its exact molecular structure using a series of classic chemical tests. Let's break down the evidence step by step.

### The 2,4-DNP Test: Hunting for Carbonyls

Our first piece of evidence is the **2,4-DNP test**, which yields a brightly coloured precipitate. What does this tell us? The 2,4-dinitrophenylhydrazine reagent is a classic chemical probe that specifically hunts for **carbonyl groups** ($>C=O$). When it finds an aldehyde or a ketone, it reacts to form a hydrazone, which crashes out of the solution as a yellow, orange, or red precipitate.

Looking at our suspects (the given options), compounds (a), (b), and (d) all possess carbonyl groups—either as aldehydes ($-CHO$) or ketones ($-COCH_3$). However, compound (c) is merely an alcohol and completely lacks a carbonyl carbon. Therefore, we can confidently eliminate option (c) from our investigation.

### The Iodoform Test: Spotting the Methyl Ketone

Next, we subject Compound X to the **iodoform test**, and it produces a distinct yellow precipitate of iodoform ($CHI_3$). This is a highly specific reaction! The iodoform test is only positive for compounds containing a **methyl ketone group** ($-COCH_3$) or a methyl carbinol group ($-CH(OH)CH_3$) that can be oxidized to a methyl ketone.

Let's re-examine our remaining suspects: (a), (b), and (d). Compounds (a) and (d) feature aldehyde groups ($-CHO$), which do not respond to the iodoform test. Only compound (b) contains the crucial $-COCH_3$ group. At this point, the evidence strongly points to (b), but let's verify with our final test to be absolutely sure.

### The Azo-Dye Test: Ruling out Primary Amines

Our final clue is the **azo-dye test**, which results in *no dye formation*. The azo-dye test involves treating the compound with nitrous acid ($NaNO_2 + HCl$) at cold temperatures to form a diazonium salt, followed by coupling with a phenol or naphthol to create a brilliantly coloured azo dye. This reaction is the hallmark of **primary aromatic amines** ($-NH_2$ attached directly to a benzene ring).

Since our test was negative, Compound X must *not* contain a primary aromatic amine. If we look at compound (b), the nitrogen atom is bonded to two methyl groups, making it a **tertiary amine** ($-N(CH_3)_2$). Tertiary amines cannot undergo diazotization and thus fail the azo-dye test. This perfectly aligns with our experimental observation!

### Final Calculation

By piecing together all the chemical evidence—the presence of a carbonyl group, the specific identification of a methyl ketone, and the absence of a primary aromatic amine—we can definitively conclude that Compound X is **3-(N,N-dimethylamino)acetophenone**.

**Correct Option: (b)**

Select Answer:

Visualized Solution

2,4-DNP Test for Carbonyls

Iodoform Test for Methyl Ketones

Azo-Dye Test for Primary Amines

Final Conclusion

The Sigma Insight: Carbonyl Compounds

Decoding the Mystery Compound

The 2,4-DNP Test

The Iodoform Test

The Azo-Dye Test

Final Calculation

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