Question

A trisubstituted compound ‘A’, \(\text{C}_{10}\text{H}_{12}\text{O}_2\), gives neutral FeCl\(_3\) test positive. Treatment of compound ‘A’ with NaOH and CH\(_3\)Br gives \(\text{C}_{11}\text{H}_{14}\text{O}_2\), with hydroiodic acid gives methyl iodide, and with hot conc. NaOH gives a compound ‘B’, \(\text{C}_{10}\text{H}_{10}\text{O}_2\). Compound ‘A’ also decolourises alkaline KMnO\(_4\). The number of \(\pi\)-bond/s present in the compound ‘A’ is ______.

Hint:

For determining the number of π bonds in a compound, carefully analyze the structure, including aromatic and aliphatic double bonds. Utilize chemical reactions (e.g., FeCl₃ test, KMnO₄ decolourisation  to identify functional groups and confirm bond types.)

Answer 1

Correct Answer: 4

To determine the number of \(\pi\)-bonds in compound 'A', \(\text{C}_{10}\text{H}_{12}\text{O}_2\), we need to analyze its reactivity and structural components based on the given reactions:

1. Compound 'A' gives a positive neutral FeCl\(_3\) test, indicating the presence of a phenolic (-OH) group.

2. Treatment with NaOH and CH\(_3\)Br leading to \(\text{C}_{11}\text{H}_{14}\text{O}_2\) suggests a Williamson ether synthesis, implying that 'A' contains a phenolic hydrogen replaced by a methyl group.

3. Reaction with hydroiodic acid yielding methyl iodide confirms the presence of a methoxy group (-OCH\(_3\)) in 'A'. Combined with step 2, 'A' likely contains a structure with both -OH and -OCH\(_3\).

4. Treatment with hot conc. NaOH forming 'B', \(\text{C}_{10}\text{H}_{10}\text{O}_2\), suggests the removal of \(\text{H}_2\) and formation of another double bond, indicating 'A' underwent dehydrogenation.

5. The compound decolourises alkaline KMnO\(_4\), supporting the presence of an alkene or a reactive site that gets oxidized.

Upon analyzing the given formula, \(\text{C}_{10}\text{H}_{12}\text{O}_2\), the presence of a benzene ring (6 carbon atoms) is plausible, contributing 3 \(\pi\)-bonds. Considering steps 1 to 5, formula symmetry, and typical structural possibilities:

• The structure can be a methyl-substituted alkene phenol, i.e., a benzene ring (3 \(\pi\)-bonds), one alkene side chain (1 \(\pi\)-bond).

Therefore, compound ‘A’ contains a total of 4 \(\pi\)-bonds. The number 4 matches the provided range (4,4), confirming our solution.