Question

Given below are two statements for the following reaction sequence:

• A. Both Statement I and Statement II are true
• B. Statement I is false but Statement II is true
• C. Statement I is true but Statement II is false
• D. Both Statement I and Statement II are false

Hint:

Terminal alkynes give methyl ketones on hydration and undergo cyclotrimerisation to aromatic compounds at high temperatures.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This sequence involves dehydrohalogenation to form an alkyne, followed by hydration (Kucherov reaction) and cyclic trimerization.
Step 2: Detailed Explanation:
1. X to Y: \(C_3H_6Cl_2\) (X) reacts with excess \(NaNH_2\) to give propyne (\(CH_3-C \equiv CH\)) (Y) via double dehydrohalogenation.
2. Y to Z: Hydration of propyne (\(CH_3-C \equiv CH\)) using \(Hg^{2+}/H^+\) follows Markovnikov addition to give acetone (\(CH_3COCH_3\)) (Z).
Acetone contains a methyl keto group (\(CH_3CO-\)), so it undergoes the iodoform test with \(NaOI\) to give a yellow precipitate of \(CHI_3\). Statement I is true.
3. Y to Q: Cyclic trimerization of propyne over a red hot iron tube yields Mesitylene (\(1,3,5\)-trimethylbenzene) (Q, \(C_9H_{12}\)).
Mesitylene structure: A benzene ring with methyl groups at positions 1, 3, and 5.
- Aromatic H atoms: 3 (at positions 2, 4, and 6).
- Aliphatic H atoms: 9 (from three \(-CH_3\) groups).
Ratio of aromatic H to aliphatic H = \(3:9 = 1:3\). Statement II is true.
Step 3: Final Answer:
Both Statement I and Statement II are true.