CBSE Class 12 Chemistry Organic Chemistry Amines Worksheet

Question. What is the correct IUPAC name of H₂N-(CH₂)₅-NH₂?
a. Pentan-1,5-diamine
b. 1,5-Diaminopentane
c. Pentamethylenediamine
d. Pentane-1,5-diamine
Answer. D

Question. Which of the following does not react with Hinsberg reagent?
a. C₂H₅NH₂
b. (CH₃)₂NH
c. (CH₃)₃N
d. CH₃ CH(NH₂)CH₃
Answer. C

Question. Which of the following amines are insoluble in water?
a. Methanamine
b. Ethanamine
c. Propanamine
d. Benzenamine
Answer. D

Question. In this reaction acetamide is converted to methanamine
a. Gabriel phthalimide synthesis
b. Carbylamine reaction
c. Stephen’s reaction
d. Hoffmann bromamide reaction
Answer. A

Question. Which of the following is not a final product of the reaction between propylamine and nitrous acid?
a. CH₃CH₂CH₂N₂Cl
b. CH₃CH₂CH₂OH
c. N₂ gas
d. HCI
Answer. A

Question. Hinsberg’s reagent is
a. Benzenesulphonic acid
b. Benzenesulphonyl chloride
c. p-toluenesulphonyl chloride
d. Chlorosulphuric acid
Answer. B

Question. Starting from propanoic acid, the following reactions were carried out, what is the compound Z?
a. CH₃-CH₂−Br
b. CH₃-CH₂−NH₂
c. CH₃-CH₂-COBr
d. CH₃−CH₂−CH₂−NH₂
Answer. A

Question. Aniline in a set of reactions yielded a product D. The structure of D would be
a. C₆H₅CH₂OH
b. C₆H₅CH₂NH₂
c. C₆H₅NHOH
d. C₆H₅NHCH₂CH₃.
Answer. A

Question. The hybridisation state of N of R2NH
a. sp³
b. sp²
c. sp
d. dsp²
Answer. A

ASSERTION -REASON TYPE QUESTIONS

Choose the correct answer from the following choices
a Both assertion and reason are correct statements and reason is correct explanation of assertion
b Both assertion and reason are correct statements but reason is not correct explanation of assertion
c Assertion is correct statement but reason is wrong statement
d Assertion is wrong statement but reason is correct statement

Question. Assertion: Alkylation of amines gives polysubstituted product where as acylation of amines gives a monosubstituted product
Reason: Steric hindrance of an acyl group prevents the approach of further acyl groups.
Answer. C

Question. Assertion: Anilinium chloride is more acidic than ammonium chloride
Reason: Anilinium ion is resonance stabilized.
Answer. C

Question. Assertion: Gabriel phthalimide reaction can be used to prepare aryl and alkyl amines
Reason: Aryl halides have same reactivity as alkyl halides towards nucleophilic substitution reactions.
Answer. D

Question. Assertion: Aniline does not undergo Friedel -Crafts reaction
Reason: Friedel-Crafts reaction is electrophilic substitution reaction
Answer. B

Question. Assertion: CuCl₂ gives a deep blue colored solution with ethyl amine
Reason: Ethylamine molecules coordinate with cupric ions forming a blue coloured complex.
Answer. A

Question. Assertion: The order of boiling points of isomeric amines is Primary>Secondary>Tertiary
Reason: Intermolecular association is more in primary ,then in secondary and least in tertiary amines.
Answer. A

Question. Assertion: Aliphatic amines are weaker base than ammonia
Reason:+I effect of alkyl group results in high electron density on nitrogen atom.
Answer. D

Question. Assertion: Pkb value of aniline is low,
Reason: The unshared pair on nitrogen atom to be in conjugation with the benzene ring making it less available
Answer. D

CASE BASED QUESTIONS

1 The basicity of amines of different classes do not follow a simple pattern because the number of groups bonded to nitrogen affects the electron density at the nitrogen atom. And, the stability of the conjugate acid in the solvent has a major effect on basicity. Thus, the basicity of amines can be explained only for amines with similar structures at the nitrogen atoms.
The basicity of an amine is increased by electron-donating groups and decreased by electron- withdrawing groups. Aryl amines are less basic than alkyl-substituted amines because some electron density provided by the nitrogen atom is distributed throughout the aromatic ring. Basicity is expressed using Kb values measured from the reaction of the amine with water. An alternate indicator of basicity is pKb, which is −log Kb. A strong base has a large Kb and a small pKb. The basicity of amines is also expressed by the acidity of their conjugate acids. A strong base has a weak conjugate acid, as given by a small value of Ka and a large pKa. 

Question. pKb values for NH₃ , CH₃NH₂,(CH₃)₂NH and (CH₃)3N has 4.75,3.38,3.27 and 4.22 respectively.
Write them in the decreasing order of basic strength. Usually the order of basicity of amines will be different from the expected order.
Answer. (CH₃)₂NH> CH₃NH₂>(CH₃)₃N>NH₃

Question. Which are the three main factors affecting basicity of amines?
Answer. +I effect ,extent of hydrogen bonding with water molecules and steric effects of the alkyl group

Question.Write the decreasing order of basicity for CH₃CH₂NH₂,(CH₃CH₂)₂NH and (CH₃CH₂)₃N
Answer. (CH₃CH₂)₂NH>(CH₃CH₂)₃N> CH₃CH₂NH₂>NH₃

Question. Compare the basicity of m-toluidine and Aniline.
Answer. m-Toluidine is more basic than aniline due to +I effect from meta position

SHORT ANSWER TYPE QUESTIONS:

Question. Write the chemical equations involved when C₂H₅NH₂ is treated with
(1) CH₃COCl/Pyridine (2) CHCl₃+KOH.
Answer. (1) C₂H₅NH₂+ CH₃COCl/Pyridine → CH₃CONHC₂H₅
(2) C₂H₅NH₂+ CHCl₃+3KOH(Alcoholic) →C₂H₅NC+3KCl+3H₂O

Question. How will you convert (1)Aniline to Bromobenzene(2)Aniline to Benzene?
NaNO₂/HCl/50C CuBr/HBr
Answer. (1) C₆H₅NH₂ → C₆H₅N2Cl → C₆H₅Br
(2) NaNO₂/HCl/50C H₃PO₂/H₂O
(1) C₆H₅NH₂ → C₆H₅N₂Cl → C₆H₆

Question. pKb of aniline is more than that of methylamine. Why?
Answer. Aniline is a weaker base than methylamine since lone pair on N is not available for donation since it is involved in conjugation with pi electrons of benzene ring.

Question. Ethylamine is soluble in water whereas aniline is not. Why?
Answer. Ethylamine can form hydrogen bonding with water while aniline can not due bulky phenyl group.

Question. Give one chemical test to distinguish between the following pairs of compounds
(1) Methylamine and Dimethylamine
(2)Aniline and benzylamine
Answer. (1) Methylamine on reaction with chloroform and alcoholic KOH gives foul smelling methyl isocynide while dimethylamine does not.
(2) Aniline on treatment with nitrous acid forms Benzene diazonium chloride which on coupling with phenol forms orange dye while benzylamine does not.

Question. Give a simple chemical test to distinguish between the following pair of compounds:
(CH₃)₂NH and (CH₃)₃N 
Answer. When treated with benzenesulphonyl chloride (Hinsberg’s reagent), (CH₃)₂NH forms insoluble N, N-dialkylbenzene sulphonamide which is insoluble in KOH whereas tertiary amine does not react at all.

Question. Why do amines act as nucleophiles?
Answer. Because the electron pair of nitrogen can coordinate with the electron deficient electrophiles

Question. Give reasons for the following:
(i) Aniline does not undergo Friedel-Crafts reaction.
(ii) (CH₃)₂NH is more basic than (CH₃)₃N in an aqueous solution.
Answer. (i) In Friedel - Crafts reaction, AlCl₃ is added as a catalyst which is a Lewis acid. It forms a salt with aniline due to which the nitrogen of aniline acquires positive charge. This positively charged nitrogen acts as a strong deactivating group, hence aniline does not undergo Friedel - Crafts reaction.
(ii) In aqueous solution 2° amine is more basic than 3° amine due to the combination of inductive effect, solvation effect and steric reasons.