An organic compound (X) with molecular formula C_3H_6O$C_3H_6O$ is not readily oxidised. On reduction it gives C_3H_8O$C_3H_8O$ (Y) which reacts with HBr$HBr$ to give a bromide (Z) which is converted to Grignard reagent. This Grignard reagent on reaction with (X) followed by hydrolysis gives 2, 3-dimethylbutan-2-ol. Compounds (X), (Y) and (Z) respectively are:
### Core Logic
Let's deduce the identities stepwise:
1. Compound (X) has the formula C_3H_6O$C_3H_6O$ and is resistant to mild oxidation, which identifies it as a ketone: **Acetone** (CH_3COCH_3$CH_3COCH_3$).
2. Reduction of Acetone yields a secondary alcohol, Propan-2-ol (CH_3CH(OH)CH_3$CH_3CH(OH)CH_3$, Compound Y).
3. Treatment of Propan-2-ol with HBr$HBr$ substitutes the hydroxyl group to form 2-Bromopropane (CH_3CH(Br)CH_3$CH_3CH(Br)CH_3$, Compound Z).
4. Reacting 2-Bromopropane with Magnesium in ether creates the branched Grignard reagent, Isopropylmagnesium bromide ((CH_3)_2CHMgBr$(CH_3)_2CHMgBr$).
5. Finally, nucleophilic addition of this Grignard reagent to Acetone followed by aqueous workup yields the highly branched tertiary alcohol: **2,3-dimethylbutan-2-ol**.
### Pattern Recognition
Resistance to mild oxidation immediately distinguishes ketones from isomeric aldehydes. Nucleophilic addition of an isopropyl Grignard to acetone cleanly yields the 2,3-dimethylbutan-2-ol framework.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Class 12 Chemistry: Alcohols, Phenols and Ethers
Grignard reaction pathways structural connectivity diagram for Q41
More Aldehydes, Ketones and Carboxylic Acids Previous-Year Questions — Page 5
Q502025Chemical Reactions of Carbonyl Compounds
Based on the reaction sequence:
A structural flow charts the transformation of a cyclic dialcohol into final product S.
0.1 mole of compound 'S' will weigh ________ g.
(Given molar mass in mathrmg \, mol^-1$\mathrm{g \, mol^{-1}}$ C:12, H:1, O:16)
Numerical Answer.Answer: 13 to 13
Solution
### Related Formula
textMass = textMoles cdot textMolar Mass$\text{Mass} = \text{Moles} \cdot \text{Molar Mass}$
### Core Logic
Let us trace the reaction scheme row-by-row:
1. Reactant: 2-(hydroxymethyl)cyclopentan-1-ol.
2. Step 1: Excess mathrmCrO_3$\mathrm{CrO}_3$ (Jones oxidation) oxidizes the secondary alcohol to a ketone and the primary alcohol to a carboxylic acid
ightarrow$
ightarrow$ Product P.
3. Step 2: Reaction with 1 mole of glycol protects the ketone selectively as a cyclic ketal
ightarrow$
ightarrow$ Product Q.
4. Step 3: Treatment with mathrmCH_3mathrmMgI$\mathrm{CH}_3\mathrm{MgI}$ targets the free carboxylic acid (or ester equivalent) to form a methyl ketone after workup
ightarrow$
ightarrow$ Product R.
5. Step 4: mathrmNaBH_4$\mathrm{NaBH}_4$ reduces the methyl ketone to a secondary alcohol, and acid workup deprotects the ketal back to the original ketone
ightarrow$
ightarrow$ Compound S .
Chemical structural formula of S: 2-(1-hydroxyethyl)cyclopentan-1-one (mathrmC_7mathrmH_12mathrmO_2$\mathrm{C}_7\mathrm{H}_{12}\mathrm{O}_2$) .
Molar mass of S (mathrmC_7mathrmH_12mathrmO_2$\mathrm{C}_7\mathrm{H}_{12}\mathrm{O}_2$) :
M = (7 cdot 12) + (12 cdot 1) + (2 cdot 16) = 84 + 12 + 32 = 130 \, mathrmg/mol$M = (7 \cdot 12) + (12 \cdot 1) + (2 \cdot 16) = 84 + 12 + 32 = 130 \, \mathrm{g/mol}$textMass of 0.1 mole = 0.1 cdot 130 = 13 \, mathrmg$\text{Mass of 0.1 mole} = 0.1 \cdot 130 = 13 \, \mathrm{g}$
### Pattern Recognition
Ketal groups serve as stable protective masks that shield ketones, allowing selective organometallic reactions to take place elsewhere on the molecule.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
More Aldehydes, Ketones and Carboxylic Acids Questions — jee_main_2025_04_april_morning
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