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Aldehydes Ketones and Carboxylic Acids question

2025 · 4 Apr · Shift 1 · Q15
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Aldehydes Ketones and Carboxylic Acids question

2025 · 4 Apr · Shift 1 · Q15

JEE MainChemistryAldehydes Ketones and Carboxylic AcidsMCQ+4 / −1
An organic compound (X)(\mathrm{X})(X) with molecular formula C3H6O\mathrm{C}_3 \mathrm{H}_6 \mathrm{O}C3​H6​O is not readily oxidised. On reduction it gives C3H8O(Y)\mathrm{C}_3 \mathrm{H}_8 \mathrm{O}(\mathrm{Y})C3​H8​O(Y) which reacts with HBr to give a bromide (Z)(\mathrm{Z})(Z) which is converted to Grignard reagent. This Grignard reagent on reaction with (X)(\mathrm{X})(X) followed by hydrolysis give 2,3-dimethylbutan-2-ol. Compounds (X),(Y)(\mathrm{X}),(\mathrm{Y})(X),(Y) and (Z)(\mathrm{Z})(Z) respectively are:
  1. A
    CH3CH2CHO,CH3CH2CH2OH,CH3CH2CH2Br\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CHO}, \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}, \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Br}CH3​CH2​CHO,CH3​CH2​CH2​OH,CH3​CH2​CH2​Br
  2. B
    CH3COCH3,CH3CH(OH)CH3,CH3CH(Br)CH3\mathrm{CH}_3 \mathrm{COCH}_3, \mathrm{CH}_3 \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_3, \mathrm{CH}_3 \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3CH3​COCH3​,CH3​CH(OH)CH3​,CH3​CH(Br)CH3​
  3. C
    CH3COCH3,CH3CH2CH2OH,CH3CH(Br)CH3\mathrm{CH}_3 \mathrm{COCH}_3, \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}, \mathrm{CH}_3 \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3CH3​COCH3​,CH3​CH2​CH2​OH,CH3​CH(Br)CH3​
  4. D
    CH3CH2CHO,CH3CH=CH2,CH3CH(Br)CH3\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CHO}, \mathrm{CH}_3 \mathrm{CH}=\mathrm{CH}_2, \mathrm{CH}_3 \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_3CH3​CH2​CHO,CH3​CH=CH2​,CH3​CH(Br)CH3​
View written solutionFree

Correct answer: B

  1. Identify compound (X)(X)(X) from molecular formula and oxidation behavior

Given (X)(X)(X) has molecular formula C3H6O\mathrm{C_3H_6O}C3​H6​O and is not readily oxidised.

Possible carbonyl compounds with formula C3H6O\mathrm{C_3H_6O}C3​H6​O are:

  • Propanal: CH3CH2CHO\mathrm{CH_3CH_2CHO}CH3​CH2​CHO
  • Propanone: CH3COCH3\mathrm{CH_3COCH_3}CH3​COCH3​

Aldehydes are readily oxidised, whereas ketones are not readily oxidised.

Therefore, X=CH3COCH3(propanone/acetone)X = \mathrm{CH_3COCH_3} \quad \text{(propanone/acetone)}X=CH3​COCH3​(propanone/acetone)

  1. Reduction of (X)(X)(X) to (Y)(Y)(Y)

Reduction of propanone gives the corresponding secondary alcohol: CH3COCH3→[H]CH3CH(OH)CH3\mathrm{CH_3COCH_3} \xrightarrow{[H]} \mathrm{CH_3CH(OH)CH_3}CH3​COCH3​[H]​CH3​CH(OH)CH3​

So, Y=CH3CH(OH)CH3(propan-2-ol / isopropyl alcohol)Y = \mathrm{CH_3CH(OH)CH_3} \quad \text{(propan-2-ol / isopropyl alcohol)}Y=CH3​CH(OH)CH3​(propan-2-ol / isopropyl alcohol)

  1. Reaction of (Y)(Y)(Y) with HBr to form (Z)(Z)(Z)

Alcohol reacts with HBr to give alkyl bromide: CH3CH(OH)CH3+HBr→CH3CH(Br)CH3+H2O\mathrm{CH_3CH(OH)CH_3 + HBr \rightarrow CH_3CH(Br)CH_3 + H_2O}CH3​CH(OH)CH3​+HBr→CH3​CH(Br)CH3​+H2​O

Hence, Z=CH3CH(Br)CH3(2-bromopropane)Z = \mathrm{CH_3CH(Br)CH_3} \quad \text{(2-bromopropane)}Z=CH3​CH(Br)CH3​(2-bromopropane)

  1. Formation of Grignard reagent from (Z)(Z)(Z)

CH3CH(Br)CH3+Mg→dry etherCH3CH(MgBr)CH3\mathrm{CH_3CH(Br)CH_3 + Mg \xrightarrow{dry\ ether} CH_3CH(MgBr)CH_3}CH3​CH(Br)CH3​+Mgdry ether​CH3​CH(MgBr)CH3​

This is isopropyl magnesium bromide.

  1. Reaction of Grignard reagent with (X)(X)(X)

Now react isopropyl magnesium bromide with acetone (X)(X)(X):

CH3COCH3+CH3CH(MgBr)CH3\mathrm{CH_3COCH_3 + CH_3CH(MgBr)CH_3}CH3​COCH3​+CH3​CH(MgBr)CH3​

Grignard adds the isopropyl group to the carbonyl carbon. After hydrolysis, the product is a tertiary alcohol:

(CH3)2C(OH)CH(CH3)2\mathrm{(CH_3)_2C(OH)CH(CH_3)_2}(CH3​)2​C(OH)CH(CH3​)2​

Let us name it properly. The longest chain is butane, and the structure is:

  • OH at carbon 2
  • methyl groups at carbon 2 and 3

So the product is: 2,3−dimethylbutan−2−ol\mathrm{2,3-dimethylbutan-2-ol}2,3−dimethylbutan−2−ol

This matches the compound given in the question.

  1. Check options
  • A: XXX is propanal, an aldehyde, which is readily oxidised. Incorrect.
  • B: X=CH3COCH3,  Y=CH3CH(OH)CH3,  Z=CH3CH(Br)CH3X=\mathrm{CH_3COCH_3},\; Y=\mathrm{CH_3CH(OH)CH_3},\; Z=\mathrm{CH_3CH(Br)CH_3}X=CH3​COCH3​,Y=CH3​CH(OH)CH3​,Z=CH3​CH(Br)CH3​ — all consistent. Correct.
  • C: Reduction product of acetone is not CH3CH2CH2OH\mathrm{CH_3CH_2CH_2OH}CH3​CH2​CH2​OH. Incorrect.
  • D: YYY is alkene, not reduction product of aldehyde/ketone. Incorrect.

Therefore, the correct option is: B\boxed{\text{B}}B​

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