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Aldehydes Ketones and Carboxylic Acids question

2017 · Shift 1 · Q14
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Aldehydes Ketones and Carboxylic Acids question

2017 · Shift 1 · Q14

JEE AdvancedChemistryAldehydes Ketones and Carboxylic AcidsMCQ+3 / −1
Columns 1, 2 and 3 contain starting materials, reaction conditions, and type of reactions, respectively.

Column 1 Column 2 Column 3
(I) Toluene (i) NaOHNaOHNaOH/Br2 (P) Condensation
(II) Acetophenone (ii) Br2/hv (Q) Carboxylation
(III) Benzaldehyde (iii) (CH3CO)2O/
CH3COOK		 (R) Substitution
(IV) Phenol (iv) NaOHNaOHNaOH/CO2 (S) Haloform
The only CORRECT combination in which the reaction proceeds through radical mechanism is :
  1. A
    (III) (ii) (P)
  2. B
    (IV) (i) (Q)
  3. C
    (II) (iii) (R)
  4. D
    (I) (ii) (R)
View written solutionFree

Correct answer: D

  1. We need the combination in which the reaction proceeds through a radical mechanism.

  2. Let us inspect each option.

Option A: (III) (ii) (P)(III)\ (ii)\ (P)(III) (ii) (P)

  • (III)(III)(III) = Benzaldehyde
  • (ii)(ii)(ii) = Br2/hνBr_2/h\nuBr2​/hν
  • (P)(P)(P) = Condensation

Under Br2/hνBr_2/h\nuBr2​/hν, the reaction condition suggests free radical bromination. However, benzaldehyde does not undergo a condensation reaction under these conditions.

So this combination is incorrect.

Option B: (IV) (i) (Q)(IV)\ (i)\ (Q)(IV) (i) (Q)

  • (IV)(IV)(IV) = Phenol
  • (i)(i)(i) = NaOH/Br2NaOH/Br_2NaOH/Br2​
  • (Q)(Q)(Q) = Carboxylation

Phenol with NaOH/Br2NaOH/Br_2NaOH/Br2​ does not correspond to carboxylation. Carboxylation of phenol occurs in the Kolbe reaction with NaOH/CO2NaOH/CO_2NaOH/CO2​, not with Br2/NaOHBr_2/NaOHBr2​/NaOH.

Also, this is not a radical mechanism.

So this option is incorrect.

Option C: (II) (iii) (R)(II)\ (iii)\ (R)(II) (iii) (R)

  • (II)(II)(II) = Acetophenone
  • (iii)(iii)(iii) = (CH3CO)2O/CH3COOK(CH_3CO)_2O/CH_3COOK(CH3​CO)2​O/CH3​COOK
  • (R)(R)(R) = Substitution

Acetophenone with acetic anhydride/sodium acetate does not represent a radical substitution. These conditions are associated with condensation-type reactions in aromatic aldehyde chemistry, not radical substitution here.

So this option is incorrect.

Option D: (I) (ii) (R)(I)\ (ii)\ (R)(I) (ii) (R)

  • (I)(I)(I) = Toluene
  • (ii)(ii)(ii) = Br2/hνBr_2/h\nuBr2​/hν
  • (R)(R)(R) = Substitution

Toluene reacts with Br2Br_2Br2​ in presence of light via free radical side-chain bromination:

C6H5CH3→Br2/hνC6H5CH2BrC_6H_5CH_3 \xrightarrow{Br_2/h\nu} C_6H_5CH_2BrC6​H5​CH3​Br2​/hν​C6​H5​CH2​Br

This is a substitution reaction proceeding through a radical chain mechanism.

So this option is correct.

  1. Therefore, the only correct combination is:

(I) (ii) (R)\boxed{(I)\ (ii)\ (R)}(I) (ii) (R)​

which corresponds to Option D.

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