JEE Chemistry 2023 Question with Solution

Given: Molecular formula is $C_9H_{10}O$. The compounds do not dissolve in NaOH, do not dissolve in HCl, do not give orange precipitate with $2,4\text{-DNP}$, and on hydrogenation give an identical compound with molecular formula $C_9H_{12}O$.

Find: The number of isomeric compounds satisfying all these conditions.

The given conditions indicate that the compound must be neutral, so it should not react with either acid or base. Also, absence of orange precipitate with $2,4\text{-DNP}$ shows that it is not an aldehyde or ketone. Hence, the suitable functional group is an ether.

For molecular formula $C_9H_{10}O$, the aromatic ether isomers satisfying these conditions are:

1. p-Methoxy toluene
2. o-Methoxy toluene

These compounds are ethers, do not react with NaOH, HCl, or $2,4\text{-DNP}$, and remain the same functional type upon hydrogenation.

Therefore, the number of isomeric compounds is 2.

Given: The compound has molecular formula $C_9H_{10}O$ and must satisfy all four conditions.

Find: How many isomeric compounds are possible.

1. Not dissolving in NaOH means the compound is not acidic like phenol or carboxylic acid.
2. Not dissolving in HCl means the compound is not basic like an amine.
3. Not giving orange precipitate with $2,4\text{-DNP}$ means it does not contain a carbonyl group of aldehyde or ketone type.
4. On hydrogenation, it gives a compound of formula $C_9H_{12}O$, so only unsaturation is reduced while oxygen-containing functional group remains unchanged.

Thus, aromatic ethers fit the data.

From the extracted solution, the valid structures listed are o-methoxy toluene and p-methoxy toluene.

The source solution concludes that the total number of isomeric compounds is 2. Note that the answer key showing $0$ disagrees with the worked solution, and the worked solution is taken as authoritative here.