3 Marks Question

Question 13 Marks

Arrange the following in increasing order of their basic strength.
(ii) $\left.C _6 H _5 NH _2, C _6 H _5 N_{\left( CH _3\right.}\right)_2,\left( C _2 H _5\right)_2 NH$

(ii) Aniline, p -nitro aniline, p -toluidine
(iii) $C _6 H _5 NH _2, \quad C _6 H _5 NHCH _3, \quad C _6 H _5 CH _2 NH _2$

Answer

(i) $C _6 H _5 NH _2< C _6 H _5 N\left( CH _3\right)_2<\left( C _2 H _5\right)_2 NH$
(ii) Aniline < p-nitro < p-toluidine
(iii) $C _6 H _5 NH _2< C _6 H _5 NHCH _3< C _6 H _5 CH _2 NH _2$

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Question 23 Marks

Give conversion in three steps: Nitrobenzene into chlorobenzene.

Answer

→Nitrobenzene into chlorobenzene

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Question 33 Marks

Explain the displacement of diazonium group of benzene diazonium salt by halide or cyanide ion with equation. ###Short note on Sandmeyer reaction and Gattermann reaction.

Answer

→Replacement by halide or cyanide ion:→The CI^- Br^- and CN^-nucleophiles can easily be introduced in benzene ring in the presence of Cu(I) ion.
→This reaction is called Sandmeyer reaction.

→Alternatively, chlorine or bromine can also be introduced in the benzene ring by treating the diazonium salt solution with corresponding halogen acid in the presence of copper powder. This is referred as Gattermann reaction.

→The yield in sandmeyer reaction is found to be better than Gattermann reaction.

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Question 43 Marks

Explain nitration of aniline. Explain what is done by this process to obtain the para nitro derivative as the major product.

Answer

→ Direct nitration of aniline yields tarry oxidation products in addition to the nitro derivatives. Moreover in the strongly acidic medium, aniline is protonated to form the anilinium ion which is meta directing. That is why besides the ortho and para derivatives, significant amount of meta derivative is also formed.

→ However by protecting the - NH₂group by acetylation reaction with acetic anhydride, the nitration reaction can be controlled and the Pderivative can be obtained as the major product.

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Question 53 Marks

Explain the bromination of Aniline. State what is done if Mono substituted derivative of aniline is to be formed by this process.

Answer

→Aniline reacts with bromine water at room temperature to give a white precipitate of 2, 4, 6-tribromoaniline.

→Aromatic amine compounds are very reactive towards electrophilic substitution reactions.
→If we have to prepare monosubstituted aniline derivative than we have to control the activating effect of -NH₂ group.
→This can be done by protecting the -NH₂ group by acetylation with acetic anhydride, then carrying out the desired substitution followed by hydrolysis of the substituted amide to the substituted amine.

→The lone pair of electrons on nitrogen of acetanilide interacts with oxygen atom due to resonance as shown below:

→Hence, the lone pair of electrons on nitrogen is less available for donation to benzene ring by resonance. Therefore activating effect of -NHCOCH₃group is less than that of amino group.

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Question 63 Marks

Explain the displacement equation of the diazonium group of benzene diazonium salt by the hydroxyl group as well as by the nitro group.

Answer

→Replacement by hydroxyl group :
→If the temperature of the diazonium salt solution is allowed to rise upto 283 K, the salt gets hydrolyzed to phenol.
$Ar \stackrel{+}{N}_2 C \overline{1}+ H _2 O \rightarrow ArOH + N _2+ HCl$
→Replacement by nitrogroup: When diazonium fluroborate is heated with aqueous sodium nitrite solution in the presence of copper, the diazonium group is replaced by -NO₂ group.

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Question 73 Marks

Discuss the formation of amine compounds by reduction of nitrile and amide compounds.

Answer

→ Nitriles on reduction with lithium aluminium hydride (LiAlH₄) or catalytic hydrogenation produce primary amines. This reaction is used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine.

→ The amides on reduction with lithium aluminium hydride yield amines.

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Chemistry 3 Marks Question

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