Chemistry · Amines · chapter 9 of 10

Class 12 Chemistry Chapter 9: Amines MCQs with answers

10 multiple-choice questions on Amines, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter.

Question 1
Which of the following is a tertiary amine?
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Answer: (a) CH₃CH₂–N(CH₃)–CH₂CH₂CH₃

A tertiary amine has all three hydrogens of NH₃ replaced: in CH₃CH₂–N(CH₃)–CH₂CH₂CH₃ the nitrogen carries three alkyl groups. (c) is primary although its carbon skeleton is branched; (b) and (d) carry one N–H and are secondary.

Question 2
The IUPAC name of CH₃CH₂CH₂–NH–CH₂CH₃ is
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Answer: (d) N-ethylpropan-1-amine

The longer chain on nitrogen, propyl, gives the parent propan-1-amine; the ethyl group on nitrogen takes the locant N. Ethylpropylamine is the common name, not the IUPAC name; (a) takes the shorter chain as parent; (b) puts the nitrogen on C-2.

Question 3
An aromatic amine C₇H₉N has –NH₂ and –CH₃ on the benzene ring, para to each other. Its IUPAC name is
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Answer: (d) 4-methylaniline

Both groups are on the ring, so the parent is aniline, with –CH₃ at C-4. 2-Methylaniline is the ortho isomer; N-methylaniline has CH₃ on nitrogen; phenylmethanamine, C₆H₅CH₂NH₂, has –NH₂ off the ring.

Question 4
In trimethylamine, (CH₃)₃N, the nitrogen atom is
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Answer: (b) sp³ hybridised, pyramidal, C–N–C angle 108°

Three sp³ orbitals bond to the CH₃ groups and the fourth holds the unshared pair; the pair pushes the bonds closer, so the shape is pyramidal and the angle is 108°, less than 109.5°.

Question 5
1-Bromobutane is heated in a sealed tube at 373 K with a large excess of ethanolic ammonia, and the salt is then treated with NaOH. The amine obtained as the major product is
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Answer: (d) butan-1-amine

Ammonolysis can run on to 2°, 3° amines and the quaternary salt, because each amine formed is itself a nucleophile; a large excess of ammonia makes it far more likely that the halide meets NH₃, so the primary amine is the major product.

Question 6
Which of these amines can be prepared by the Gabriel phthalimide synthesis?
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Answer: (a) 2-phenylethanamine

Gabriel synthesis gives only primary amines, from alkyl halides: (2-bromoethyl)benzene, C₆H₅CH₂CH₂Br, gives C₆H₅CH₂CH₂NH₂. 4-Methylaniline would need an aryl halide, which does not substitute with the phthalimide anion; (b) and (d) are secondary and tertiary.

Question 7
Pentanamide, CH₃(CH₂)₃CONH₂, is warmed with bromine and aqueous sodium hydroxide. The organic product is
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Answer: (a) butan-1-amine

In Hoffmann bromamide degradation the alkyl group migrates from the carbonyl carbon to nitrogen and the carbonyl carbon leaves as Na₂CO₃: the amine, CH₃(CH₂)₃NH₂, has one carbon less than the amide.

Question 8
Nitrobenzene is reduced to aniline with iron scrap and hydrochloric acid in preference to other metal–acid pairs because
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Answer: (d) the FeCl₂ formed is hydrolysed and releases HCl, so only a small amount of acid is needed to start the reaction

Iron is consumed, forming FeCl₂; its hydrolysis regenerates hydrochloric acid during the reaction, so a little acid is enough to start it.

Question 9
Which of the following isomers of C₅H₁₃N has the highest boiling point?
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Answer: (c) pentan-1-amine

Primary amines have two N–H hydrogens for hydrogen bonding and associate most; secondary amines have one; tertiary amines, (a) and (d), have none. So the boiling point order of isomers is 1° > 2° > 3°.

Question 10
A colourless sample of aniline turns brown after some weeks in a half-filled bottle. The change is due to
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Answer: (c) oxidation by the air in the bottle

Arylamines are usually colourless but become coloured on storage through atmospheric oxidation.

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