JEE Challenger
More from Organic Chemistry - Basic Principles
ChemHardAdv 2010 • Paper 2

Match Organic Reactions in Column I with Column II Features

Match the reactions in Column I with appropriate options in Column II.

Column I
A) Reaction of benzene diazonium chloride with phenol in basic medium
B) Acid-catalyzed rearrangement of pinacol
C) Reduction of ketone using LiAlH4\text{LiAlH}_4 followed by hydrolysis
D) Intramolecular reaction of halo-thiol in basic medium

Column II
p) Racemic mixture
q) Addition reaction
r) Substitution reaction
s) Coupling reaction
t) Carbocation intermediate

Options

A

(A)→(R),  (B)→(T),  (C)→(P,Q),  (D)→(R)(\text{A}) \rightarrow (\text{R}),\; (\text{B}) \rightarrow (\text{T}),\; (\text{C}) \rightarrow (\text{P}, \text{Q}),\; (\text{D}) \rightarrow (\text{R})

B

(A)→(R,S),  (B)→(S,T),  (C)→(P),  (D)→(R)(\text{A}) \rightarrow (\text{R}, \text{S}),\; (\text{B}) \rightarrow (\text{S}, \text{T}),\; (\text{C}) \rightarrow (\text{P}),\; (\text{D}) \rightarrow (\text{R})

C

(A)→(R,S),  (B)→(T),  (C)→(P,Q),  (D)→(R)(\text{A}) \rightarrow (\text{R}, \text{S}),\; (\text{B}) \rightarrow (\text{T}),\; (\text{C}) \rightarrow (\text{P}, \text{Q}),\; (\text{D}) \rightarrow (\text{R})

Correct
D

(A)→(S),  (B)→(T),  (C)→(P,Q),  (D)→(P,R)(\text{A}) \rightarrow (\text{S}),\; (\text{B}) \rightarrow (\text{T}),\; (\text{C}) \rightarrow (\text{P}, \text{Q}),\; (\text{D}) \rightarrow (\text{P}, \text{R})

Topics & Concepts

Organic Chemistry - Basic PrinciplesNucleophilic SubstitutionElectrophilic AdditionAminesAlcohols and Ethers

Step-by-Step Solution

To solve the matching type problem, let us analyze each organic reaction in Column I step-by-step and determine its corresponding features in Column II:

A) Reaction of Benzene Diazonium Chloride with Phenol in Basic Medium

  • Reaction:
    C6H5N2+Cl−+C6H5OH→0∘CNaOH/H2Op-HO−C6H4−N=N−C6H5+HCl\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- + \text{C}_6\text{H}_5\text{OH} \xrightarrow[\text{0}^\circ\text{C}]{\text{NaOH/H}_2\text{O}} \text{p-HO}-\text{C}_6\text{H}_4-\text{N}=\text{N}-\text{C}_6\text{H}_5 + \text{HCl}
  • Mechanism & Characteristics:
    1. In a basic medium (pH≈9−10\text{pH} \approx 9-10), phenol is converted to the strongly activating phenoxide ion (C6H5O−\text{C}_6\text{H}_5\text{O}^-).
    2. The electrophilic diazonium cation (Ar-N2+\text{Ar-N}_2^+) attacks the para-position of the phenoxide ion, substituting a hydrogen atom. Thus, it is an Electrophilic Aromatic Substitution Reaction (r\mathbf{r}).
    3. The coupling of two aromatic rings via an azo bridge (−N=N−-\text{N}=\text{N}-) to form an azo dye is classified as a Coupling Reaction (s\mathbf{s}).

Matching: A→r,s\text{A} \rightarrow \mathbf{r, s}

B) Acid-Catalyzed Rearrangement of Pinacol

  • Reaction:
    (CH3)2C(OH)−C(OH)(CH3)2→H2SO4CH3−CO−C(CH3)3+H2O\text{(CH}_3)_2\text{C(OH)}-\text{C(OH)(CH}_3)_2 \xrightarrow{\text{H}_2\text{SO}_4} \text{CH}_3-\text{CO}-\text{C(CH}_3)_3 + \text{H}_2\text{O}
  • Mechanism & Characteristics:
    1. Protonation of one of the hydroxyl groups (-OH\text{-OH}) yields an oxonium ion (−OH2+-\text{OH}_2^+).
    2. Loss of a water molecule produces a tertiary carbocation intermediate (t\mathbf{t}):
      (CH3)2C(OH)−C+(CH3)2\text{(CH}_3)_2\text{C(OH)}-\overset{+}{\text{C}}\text{(CH}_3)_2
    3. A 1,2-methyl shift subsequently occurs to generate a resonance-stabilized oxonium ion, which deprotonates to yield pinacolone.

Matching: B→t\text{B} \rightarrow \mathbf{t}

C) Reduction of Ketone using LiAlH4\text{LiAlH}_4 Followed by Hydrolysis

  • Reaction:
    C6H5−CO−CH3→2.  H3O+1.  LiAlH4C6H5−CH(OH)−CH3\text{C}_6\text{H}_5-\text{CO}-\text{CH}_3 \xrightarrow[2.\; \text{H}_3\text{O}^+]{1.\; \text{LiAlH}_4} \text{C}_6\text{H}_5-\text{CH(OH)}-\text{CH}_3
  • Mechanism & Characteristics:
    1. LiAlH4\text{LiAlH}_4 delivers a nucleophilic hydride ion (H−\text{H}^-) to the electrophilic carbonyl carbon, breaking the C=O\text{C}=\text{O} π\pi-bond. Since components (H−\text{H}^- and H+\text{H}^+) are added across the double bond without loss of any group, it is an Addition Reaction (q\mathbf{q}).
    2. The starting ketone has a planar sp2sp^2-hybridized carbonyl carbon. The nucleophilic attack of hydride occurs with equal probability from both the re-face and si-face (top and bottom attacks).
    3. As a result, an equal amount (50:50 ratio) of (R)(R)- and (S)(S)-enantiomers of 1-phenylethanol is produced, resulting in an optically inactive Racemic Mixture (p\mathbf{p}).

Matching: C→p,q\text{C} \rightarrow \mathbf{p, q}

D) Intramolecular Reaction of Halo-Thiol in Basic Medium

  • Reaction:
    HS−C6H10−Cl→BaseCyclic Sulfide Derivative+Cl−\text{HS}-\text{C}_6\text{H}_{10}-\text{Cl} \xrightarrow{\text{Base}} \text{Cyclic Sulfide Derivative} + \text{Cl}^-
  • Mechanism & Characteristics:
    1. The base abstracts the proton from the thiol group (−SH-\text{SH}) to form a strong thiolate nucleophile (−S−-\text{S}^-).
    2. The thiolate anion undergoes an intramolecular nucleophilic substitution (SN2\text{S}_\text{N}2) attack on the carbon bearing the chlorine atom, displacing the chloride ion (Cl−\text{Cl}^-) as a leaving group.
    3. Therefore, this process is an intramolecular Substitution Reaction (r\mathbf{r}).

Matching: D→r\text{D} \rightarrow \mathbf{r}

Final Correct Matching:

  • A: r,s\mathbf{r, s}
  • B: t\mathbf{t}
  • C: p,q\mathbf{p, q}
  • D: r\mathbf{r}
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