CBSE Class 12 · 2018 · Compounds Containing NitrogenLong Answer

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(a) Write the reactions involved in the following:
(i) Hofmann bromamide degradation
(ii) diazotisation
(iii) Gabriel phthalimide synthesis
(b) Give reasons:
(i) (CH₃)₂NH is more basic than (CH₃)₃N in aqueous solution.
(ii) Aromatic diazonium salts are more stable than aliphatic diazonium salts.

Solution

(a)(i)

RCON H_{2} + B r_{2} + 4NaOH \to RN H_{2} + N a_{2} C O_{3} + 2NaBr + 2 H_{2} O

(ii)

C_{6} H_{5} N H_{2} + NaN O_{2} + 2HCl 273 - 278K C_{6} H_{5} N_{2}^{+} C l^{-} + NaCl + 2 H_{2} O

(iii) phthalimide →KOH→ K-salt →RX→ N-alkylphthalimide →NaOH(aq)→ RNH

_{2}

+ phthalate.
(b)(i) The dimethylammonium ion keeps two N–H's for hydration and avoids the crowding of three methyls — so (CH

_{3}

)

_{2}

NH > (CH

_{3}

)

_{3}

N in water.
(ii) In ArN

_{2}^{+}

the positive charge delocalises into the ring (several resonance structures); an alkyl diazonium has no such stabilisation and expels N

_{2}

at once.

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CBSE Class 12 · 2018 · Compounds Containing NitrogenLong Answer

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