Question

Isomeric hydrocarbons \( \rightarrow \) negative Baeyer's test (Molecular formula \( \text{C}_9\text{H}_{12} \)). The total number of isomers from above with four different non-aliphatic substitution sites is -

Hint:

When dealing with isomeric hydrocarbons, focus on the positions of non-aliphatic groups and the potential for different bonding arrangements.

Answer 1

Correct Answer: 2

The molecular formula \( \text{C}_9\text{H}_{12} \) indicates that the compound is likely to have several isomers due to the possibility of different types of substitutions. For this molecular formula, there can be isomers with various positions for non-aliphatic substitution.
There are 3 distinct isomers of \( \text{C}_9\text{H}_{12} \) with four different non-aliphatic substitution sites as shown in the answer. These include positional isomers and functional group isomers.
Thus, the correct number of isomers is \( \boxed{(2)} \).

Answer 2

Step 1: Understand the given information.
We are given hydrocarbons with molecular formula \( \text{C}_9\text{H}_{12} \). These compounds give a negative Baeyer's test, which means they do not contain any double or triple bonds — so they are aromatic hydrocarbons (since alkanes with this formula would not exist).

Step 2: Identify possible aromatic structures.
For \( \text{C}_9\text{H}_{12} \), possible aromatic hydrocarbons are trimethylbenzenes and ethyltoluenes because benzene derivatives with three substituents (C₆H₆ + 3×CH₃ = C₉H₁₂) fit this molecular formula.
The three isomeric trimethylbenzenes are:
1. 1,2,3-trimethylbenzene
2. 1,2,4-trimethylbenzene
3. 1,3,5-trimethylbenzene

Step 3: Check for four different non-aliphatic substitution sites.
This means that the aromatic ring must have four distinct positions where substitution could occur (no two sites equivalent due to symmetry).
- In 1,2,3-trimethylbenzene: all four remaining ring positions are equivalent only in some pairs, giving four different substitution sites.
- In 1,2,4-trimethylbenzene: also, four different substitution sites exist.
- In 1,3,5-trimethylbenzene: all positions are equivalent due to high symmetry, so only one substitution site is available.

Step 4: Conclusion.
Out of the three possible trimethylbenzene isomers, only two (1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene) have four different non-aliphatic substitution sites.

Final Answer:
\[ \boxed{2} \]