Indole Reaction Mechanism

The reaction between indole, sodium amide ($NaNH$_2$), and benzenesulfonyl chloride ($PhSO$_2$Cl$) proceeds via nucleophilic substitution.

• Step 1: Deprotonation
  Sodium amide ($NaNH$_2$) is a strong base that abstracts the acidic proton from the indole nitrogen. This generates the indolate anion, a potent nucleophile.
  Reaction: Indole-NH + NaNH$_2$ $\rightarrow$ [Indole-N]$^-$ Na$^+$ + NH$_3$
• Step 2: Nucleophilic Attack
  The indolate anion attacks the electrophilic sulfur atom of benzenesulfonyl chloride ($PhSO$_2$Cl$).
• Step 3: Substitution
  The chloride ion (Cl$^-$) is eliminated as a leaving group, forming the N-sulfonylated indole derivative.
  Product: Indole-N-SO$_2$Ph (N-(phenylsulfonyl)indole)

Product Identification

The strong base $NaNH$_2$ directs the reaction to the nitrogen atom of indole. The electrophile $PhSO$_2$Cl$ then reacts at this nitrogen. Therefore, the phenylsulfonyl group ($PhSO$_2$-$) attaches to the N1 position of the indole ring.

Option 4 correctly depicts this N-substitution product, N-(phenylsulfonyl)indole.

Option	Structure	Analysis
1		Incorrect (C3 substitution)
2		Incorrect (C2 substitution)
3		Incorrect (Benzene ring substitution)
4		Correct (N1 substitution)