Consider the nucleophilic addition of ammonia to benzoyl chloride shown below. Which of the following statements is true?

Question

BlackTom AI · Accepted Answer

In nucleophilic acyl substitution, chloride is a good leaving group because Cl– is a relatively stable, weak base (conjugate base of the very strong acid HCl) and is well solvated in solution.

1) Relevant knowledge points and concepts
- Acyl chlorides (like benzoyl chloride) undergo nucleophilic attack at the carbonyl carbon (electrophilic center) to give a tetrahedral intermediate, then expel a leaving group (= nucleophilic acyl substitution).
- Good leaving groups are stable as anions in solution (weak bases, well solvated); leaving-group ability correlates inversely with the pKa of the conjugate acid (HCl has a very low pKa, so Cl– is a good leaving group).
- Ammonia (NH3) is a nucleophile because it has a lone pair on nitrogen that can attack electrophilic centers.

2) Step-by-step reasoning and mechanism
- Step 1: The lone pair on NH3 attacks the electrophilic carbonyl carbon of benzoyl chloride, forming a tetrahedral (alkoxide-like) intermediate: Ph–C(OH)(Cl)(NH3).
- Step 2: Proton transfers within the intermediate (or between molecules/solvent) convert the intermediate to a form that can expel chloride (one N–H proton is removed, oxygen re-forms C=O).
- Step 3: The tetrahedral intermediate collapses; the C–Cl bond breaks and Cl– leaves. This gives benzamide (Ph–C(=O)NH2) and free chloride.
- Step 4: Chloride picks up a proton (from ammonium or solvent) to give HCl (observed product).

3) Intermediate/chemical-logic details
- The key thermodynamic/kinetic driving force: Cl– is a poor base (stable anion) and easily departs; acyl chlorides are highly reactive toward nucleophiles, so the substitution proceeds readily.

4) Why the correct answer is correct
- Option (d) correctly states that chloride anions are good leaving groups because they are stable in solution; this stability (weak basicity, good solvation) allows Cl– to depart during collapse of the tetrahedral intermediate.

5) Why other options are incorrect
- (a) is the opposite of the truth: Cl– is stable, not unstable, so it is a good leaving group.
- (b) ammonia is the nucleophile (electron-pair donor), not the electrophile.
- (c) benzoyl chloride is the electrophile (carbonyl carbon is electron-poor), not the nucleophile.
- (e) is false: the amide product forms readily from acyl chlorides; the reaction does occur and is commonly used to make amides.

Conclusion: The correct statement is (d). This matches the provided answer.

Consider the nucleophilic addition of ammonia to benzoyl chloride shown below. Which of the following statements is true?单项选择题

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