Amines

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans: (C) 

S_N¹ reaction: A nucleophilic reaction that occurs in two steps, first is the bond-breaking step and the second is the production of the carbocation. The stability of carbocation formed in the second step determines the rate of reactivity of reactant toward S_N¹ reaction.  Here, C₆H₅CH₂Br,  

In the process of ionization, removal of bromine, a stable Benzyl carbocation is produced. Therefore, it is best suited for reaction through the S_N¹ mechanism. 

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans:  (A) 

The NH₂ group is directly attached to the benzene ring in aniline and other aryl amines. As a result, the unshared electron pair on the nitrogen atom is conjugated with the benzene ring, making it less available for protonation.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans:  (C)

Because of the electron-releasing nature of the alkyl group, it (R) pushes electrons towards nitrogen, making the unshared electron pair more available for sharing with the acid's proton. Furthermore, the +I effect of the alkyl group stabilizes the substituted ammonium ion formed from the amine by dispersing the positive charge.

As a result, alkylamines are more powerful bases than ammonia.

As a result, the basic nature of aliphatic amines should increase as the number of alkyl groups increases.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans: Correct answer: (D) 

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans: (B) Triethylamine 

The structure of the given amines are shown below.

(i) Aromatic amines react with nitrous acid (prepared in situ fromNaNO₂ and a mineral acid such as HCl) at 273 - 278 K to form stable aromatic diazonium salts i.e., NaCl and water. This reaction is widely used for preparation of variety of compounds.

(ii) Aliphatic primary amines react with nitrous acid (prepared in situ from NaNO₂ and a mineral acid such as HCl) to form unstable aliphatic diazonium salts, which is very reactive, which further produce alcohol and HCl with the evolution of nitrogen gas.

Gabriel phthalimide synthesis is used for the preparation of aliphatic primary amines. It involves nucleophilic substitution (S_N2) of alkyl halides by the anion formed by the phthalimide.But aryl halides do not undergo nucleophilic substitution with the anion formed by the phthalimide.

Therefore aromatic primary amines cannot be formed by gabriel phthalimide process.

It is given that compound 'C' having the molecular formula, C₆H₇N is formed by heating compound 'B' with Br₂and KOH. This is a Hoffmann bromamide degradation reaction (in which isocyanide compound is formed). Therefore, compound 'B' is an amide and compound 'C' is an amine. The only amine having the molecular formula, C₆H₇N is aniline. Therefore, compound 'B' (from which 'C' is formed) must be benzamide.

Further, benzamide is formed by heating compound 'A' with aqueous ammonia. Therefore, compound 'A' must be benzoic acid. The given reactions can be explained with the help of the following equations: