CBSE 2025, Set 1

Question

Give plausible explanation for each of the following:

(i) Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.

(ii) Amides are less basic than amines.

Edvaya · Accepted Answer

The correct answer is Subjective. **(i) Gabriel Phthalimide cannot give aromatic primary amines:** The Gabriel Phthalimide synthesis requires the potassium phthalimide anion to react with an **alkyl halide** via the S$_N$2 mechanism. **Aryl halides** (Ar–X) cannot undergo S$_N$2 reactions because the C–X bond has partial double bond character due to conjugation between the lone pair on halogen and the $\pi$ system of the ring, making the carbon less electrophilic and backside attack impossible. **(ii) Amides are less basic than amines:** ![Amide resonance — lone pair delocalisation into carbonyl](https://www.edvaya.com/images/chemistry/cbse/2025/set1/q27b-amide-resonance.webp) In amides (RCONH$_2$), the lone pair on nitrogen is **delocalised into the carbonyl group** by resonance (+R effect): $$	ext{–NH–C=O} \longleftrightarrow 	ext{–N}^+=	ext{C–O}^-$$ This reduces the electron density on N, making the lone pair **far less available for protonation** compared to amines where the lone pair is fully localised on N.

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Chemistry > Organic Chemistry > Amines

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