The chapter “Amines” is crucial for both board and competitive exams because it links organic functional group chemistry with key ideas such as basicity trends, preparation and reactions of amines, and diagnostic tests (e.g., Hinsberg test). Many numericals also rely on equilibrium concepts (acid–base, Henderson-type relations), making this chapter a frequent scoring area.
15
Minutes
10
Questions
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Marking
Q1. (At pH 7.4, what percentage of methylamine (given ) exists as its protonated form ? (Use and ).)
0.055%
50.0%
99.95%
99.45%
Q2. (Arrange the following amines in decreasing order of their initial rate of reaction with methyl iodide (nucleophilic methylation) under identical conditions: (methylamine), (dimethylamine), (trimethylamine).)
Q3. (Three amines X, Y and Z were treated with benzenesulfonyl chloride (, Hinsberg reagent) and then shaken with aqueous NaOH. Observations: X dissolves in NaOH and on acidification a white solid precipitates; Y gives a sulfonyl derivative that is insoluble in NaOH (no change on acidification); Z does not give a sulfonyl derivative but on addition of HCl the amine dissolves as a water‑soluble salt. Which assignment is correct?)
X = secondary, Y = primary, Z = tertiary
X = primary, Y = secondary, Z = tertiary
X = secondary, Y = tertiary, Z = primary
X = tertiary, Y = primary, Z = secondary
Q4. (Assertion (A): Tertiary amines readily form diazonium salts on treatment with and at –C.
Reason (R): Formation of diazonium salts requires an group (a primary amine); tertiary amines lack an N–H bond and hence cannot form diazonium ions.)
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true but R is false.
A is false but R is true.
Q5. (At 25°C in aqueous solution, is observed to be a stronger base than . Which of the following best explains this observation?)
has lower electron density on nitrogen because methyl groups withdraw electrons by inductive effect.
Steric hindrance around nitrogen in reduces solvation of its conjugate acid, so the conjugate acid of is less stabilized in water than that of .
cannot be protonated in water due to formation of a stable hydrate.
Hyperconjugation in delocalizes the lone pair to a much greater extent than in , drastically lowering basicity.
Q6. A solution contains equimolar amounts of the following amines. At pH 7.0 which species will be present predominantly in its protonated form? (Given conjugate-acid values: methylammonium , anilinium , ammonium , -nitroanilinium )
Aniline ()
p‑Nitroaniline (‑NO‑NH)
Methylamine ()
Ammonia ()
Q7. Arrange the following amines in decreasing order of basicity (most → least) in (i) the gas phase and (ii) aqueous solution: .
(i) ; (ii)
(i) ; (ii)
(i) ; (ii)
(i) ; (ii)
Q8. Which of the following reaction sequences will convert aniline () into ‑nitroaniline (‑NO‑NH) as the major product with minimal ortho substitution?
Direct nitration: treat with and then neutralize
Diazotization (C) to give diazonium salt, then treat with to introduce
Sulfonation (fuming ) of , then nitration () and finally desulfonation by heating with water
Protect the amino group by acetylation ( or → acetanilide), nitrate acetanilide with (gives ‑nitroacetanilide), then hydrolyse the acetamide to obtain ‑nitroaniline
Q9. Considering both electronic (+I/hyperconjugation) effects and steric/solvation effects, which of the following gives the correct order of basicity (most basic → least) in aqueous solution?
Aniline (), o‑methylaniline (2‑CH‑NH), p‑methylaniline (4‑CH‑NH)
Aniline p‑methylaniline o‑methylaniline
p‑Methylaniline Aniline o‑Methylaniline
o‑Methylaniline Aniline p‑Methylaniline
p‑Methylaniline o‑Methylaniline Aniline
Q10. A mixture containing aniline (), benzylamine () and benzoic acid () is dissolved in diethyl ether. The solution is first shaken with 5% aqueous NaHCO and the aqueous layer is set aside. The separated organic layer is then shaken with a buffered aqueous solution at pH 7.0. Which compounds will be found in (i) the first aqueous extract and (ii) the second aqueous extract, respectively?
(i) none; (ii) anilinium and benzylammonium salts
(i) benzoic acid (undissociated); (ii) anilinium salt
(i) benzoate (from benzoic acid); (ii) benzylammonium (from benzylamine)
(i) benzoate and anilinium; (ii) benzylammonium