JEE Challenger
More from Aldehydes, Ketones and Carboxylic Acids
ChemMedAdv 2017 • Paper 2

Identification of Organic Compounds P and R via Ozonolysis Reactions

Ozonolysis of compounds P\mathbf{P} and R\mathbf{R} yields products Q\mathbf{Q} and S\mathbf{S}, respectively. Both Q\mathbf{Q} and S\mathbf{S} share the molecular formula C8H8O\text{C}_8\text{H}_8\text{O}. Product Q\mathbf{Q} gives a positive Cannizzaro reaction but does not undergo haloform reaction, while product S\mathbf{S} undergoes haloform reaction but fails to undergo Cannizzaro reaction.

(i) P→ii) Zn/H2Oi) O3/CH2Cl2Q(C8H8O)\text{(i) } \mathbf{P} \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \mathbf{Q} \quad (\text{C}_8\text{H}_8\text{O})

(ii) R→ii) Zn/H2Oi) O3/CH2Cl2S(C8H8O)\text{(ii) } \mathbf{R} \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \mathbf{S} \quad (\text{C}_8\text{H}_8\text{O})

Identify the suitable combination(s) for P\mathbf{P} and R\mathbf{R}, respectively, from the options given below.

Question Diagram 1

Options

A
Option A
Correct
B
Option B
Correct
C
Option C
D
Option D

Topics & Concepts

Aldehydes, Ketones and Carboxylic AcidsAldehydes and KetonesOxidation and Reduction (Organic)

Step-by-Step Solution

To determine the suitable combination(s) for compounds P\mathbf{P} and R\mathbf{R}, let us analyze the chemical characteristics and requirements given for their ozonolysis products Q\mathbf{Q} and S\mathbf{S}.

1. Analysis of Product Q\mathbf{Q}

  • Molecular Formula: C8H8O\text{C}_8\text{H}_8\text{O}
  • Cannizzaro Reaction: Product Q\mathbf{Q} undergoes a positive Cannizzaro reaction, which implies that Q\mathbf{Q} must be an aldehyde that lacks α\alpha-hydrogens (α-H=0\alpha\text{-H} = 0).
  • Haloform Reaction: Product Q\mathbf{Q} does not undergo a haloform reaction, which means it lacks the methyl ketone group (−C(=O)CH3-\text{C}(=\text{O})\text{CH}_3) or the −CH(OH)CH3-\text{CH}(\text{OH})\text{CH}_3 unit.

Therefore, Q\mathbf{Q} must be a methyl-substituted benzaldehyde isomer (such as 22-methylbenzaldehyde, 33-methylbenzaldehyde, or 44-methylbenzaldehyde), all of which have the molecular formula C8H8O\text{C}_8\text{H}_8\text{O} and contain zero α\alpha-hydrogens.

2. Analysis of Product S\mathbf{S}

  • Molecular Formula: C8H8O\text{C}_8\text{H}_8\text{O}
  • Haloform Reaction: Product S\mathbf{S} undergoes a haloform reaction, indicating the presence of a methyl ketone group (−C(=O)CH3-\text{C}(=\text{O})\text{CH}_3).
  • Cannizzaro Reaction: Product S\mathbf{S} fails to undergo a Cannizzaro reaction.

Given the molecular formula C8H8O\text{C}_8\text{H}_8\text{O} and the presence of a methyl ketone group, product S\mathbf{S} is uniquely identified as acetophenone (C6H5COCH3\text{C}_6\text{H}_5\text{COCH}_3). Acetophenone contains 33 α\alpha-hydrogens on its methyl group, enabling the haloform reaction and preventing the Cannizzaro reaction.

3. Evaluation of Options

Option [A]:

  • Compound P\mathbf{P} (44-methylstyrene): H3C−C6H4−CH=CH2→ii) Zn/H2Oi) O3/CH2Cl2H3C−C6H4−CHO⏟Q (C8H8O)+HCHO\text{H}_3\text{C}-\text{C}_6\text{H}_4-\text{CH}=\text{CH}_2 \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \underbrace{\text{H}_3\text{C}-\text{C}_6\text{H}_4-\text{CHO}}_{\mathbf{Q} \ (\text{C}_8\text{H}_8\text{O})} + \text{HCHO}

    • Q=4\mathbf{Q} = 4-methylbenzaldehyde (C8H8O\text{C}_8\text{H}_8\text{O}). It has no α\alpha-hydrogens (gives Cannizzaro) and no −COCH3-\text{COCH}_3 group (fails haloform). ✓\checkmark

  • Compound R\mathbf{R} (22-phenylpropene): C6H5−C(CH3)=CH2→ii) Zn/H2Oi) O3/CH2Cl2C6H5−COCH3⏟S (C8H8O)+HCHO\text{C}_6\text{H}_5-\text{C}(\text{CH}_3)=\text{CH}_2 \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \underbrace{\text{C}_6\text{H}_5-\text{COCH}_3}_{\mathbf{S} \ (\text{C}_8\text{H}_8\text{O})} + \text{HCHO}

    • S=acetophenone\mathbf{S} = \text{acetophenone} (C8H8O\text{C}_8\text{H}_8\text{O}). It undergoes haloform reaction and fails Cannizzaro reaction. ✓\checkmark

Thus, Option [A] is correct.

Option [B]:

  • Compound P\mathbf{P} (11-methyl-33-(prop-11-en-11-yl)benzene): m-CH3−C6H4−CH=CH−CH3→ii) Zn/H2Oi) O3/CH2Cl2m-CH3−C6H4−CHO⏟Q (C8H8O)+CH3CHOm\text{-CH}_3-\text{C}_6\text{H}_4-\text{CH}=\text{CH}-\text{CH}_3 \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \underbrace{m\text{-CH}_3-\text{C}_6\text{H}_4-\text{CHO}}_{\mathbf{Q} \ (\text{C}_8\text{H}_8\text{O})} + \text{CH}_3\text{CHO}

    • Q=3\mathbf{Q} = 3-methylbenzaldehyde (C8H8O\text{C}_8\text{H}_8\text{O}). It gives Cannizzaro reaction and fails haloform reaction. ✓\checkmark

  • Compound R\mathbf{R} ((3(3-methylbut-22-en-22-yl)benzene): C6H5−C(CH3)=C(CH3)2→ii) Zn/H2Oi) O3/CH2Cl2C6H5−COCH3⏟S (C8H8O)+(CH3)2C=O\text{C}_6\text{H}_5-\text{C}(\text{CH}_3)=\text{C}(\text{CH}_3)_2 \xrightarrow[\text{ii) } \text{Zn/H}_2\text{O}]{\text{i) } \text{O}_3/\text{CH}_2\text{Cl}_2} \underbrace{\text{C}_6\text{H}_5-\text{COCH}_3}_{\mathbf{S} \ (\text{C}_8\text{H}_8\text{O})} + (\text{CH}_3)_2\text{C}=\text{O}

    • S=acetophenone\mathbf{S} = \text{acetophenone} (C8H8O\text{C}_8\text{H}_8\text{O}). It undergoes haloform reaction and fails Cannizzaro reaction. ✓\checkmark

Thus, Option [B] is correct.

Option [C]:

  • Ozonolysis of compound R\mathbf{R} (11-methyl-22-(3-methylbut-22-en-22-yl)benzene) yields: S=o-CH3−C6H4−COCH3(Molecular Formula: C9H10O)\mathbf{S} = o\text{-CH}_3-\text{C}_6\text{H}_4-\text{COCH}_3 \quad (\text{Molecular Formula: } \text{C}_9\text{H}_{10}\text{O})
  • Since the molecular formula of S\mathbf{S} is C9H10O\text{C}_9\text{H}_{10}\text{O} instead of C8H8O\text{C}_8\text{H}_8\text{O}, Option [C] is incorrect.

Option [D]:

  • Ozonolysis of compound R\mathbf{R} (11-methyl-44-(prop-11-en-22-yl)benzene) yields: S=p-CH3−C6H4−COCH3(Molecular Formula: C9H10O)\mathbf{S} = p\text{-CH}_3-\text{C}_6\text{H}_4-\text{COCH}_3 \quad (\text{Molecular Formula: } \text{C}_9\text{H}_{10}\text{O})
  • Since the molecular formula of S\mathbf{S} is C9H10O\text{C}_9\text{H}_{10}\text{O} instead of C8H8O\text{C}_8\text{H}_8\text{O}, Option [D] is incorrect.

Conclusion

The suitable combinations for P\mathbf{P} and R\mathbf{R} are given by options A and B.

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