Amines are a high-yield topic because they connect structure with basicity, reactivity, and stereochemical outcomes. Board and competitive exams commonly test trends in basic strength (gas vs aqueous), resonance/inductive effects of substituents on aniline, and classic transformations such as diazotization and Gabriel/Hofmann reactions—so mastering these concepts directly improves scoring.
25
Minutes
20
Questions
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Marking
Q1. A 0.10 M aqueous solution of aniline () has . At pH , what percentage of aniline molecules are present as the protonated form ? (Use and assume activity ≈ concentration.)
2.3%
92.5%
97.7%
50.0%
Q2. Arrange the following amines in decreasing order of basicity in aqueous solution: (i) , (ii) (benzylamine), (iii) (aniline), (iv) . Which order is correct?
Q3. Consider these substituted anilines in aqueous solution: (A) -anisidine (-methoxyaniline, -), (B) aniline (), (C) -nitroaniline, (D) -nitroaniline. Which of the following gives the correct order of decreasing basicity?
-anisidine -nitroaniline > p$-nitroaniline
aniline -anisidine -nitroaniline -nitroaniline
-nitroaniline -nitroaniline aniline -anisidine
-anisidine > m> p$-nitroaniline
Q4. For the series of amines , , , , which one of the following pairs correctly gives the order of basicity in (i) gas phase and (ii) aqueous solution?
(i) ; (ii)
(i) ; (ii)
(i) ; (ii)
(i) ; (ii)
Q5. The primary amine has structure (2‑methylbutan‑1‑amine). Exhaustive methylation of followed by Ag_2O/heat (Hofmann elimination) affords a major alkene. Which alkene is expected as the major product?
‑methyl‑2‑butene
‑butene
‑methyl‑1‑butene
‑methyl‑1‑butene
Q6. The of the conjugate acid of methylamine () is at . Using , the of methylamine () is approximately:
Q7. A aqueous solution contains each of aniline () and methylamine (). Given and , at which amine has the higher concentration of the unprotonated base and by approximately what factor (ratio )?
Q8. Optically active (R)-1-phenylethylamine () is treated with at and then warmed; the isolated product is 1-phenylethanol which is racemic (no optical activity). Which explanation best accounts for this observation?
Reaction proceeds with retention of configuration via a concerted displacement by nitrite.
Reaction proceeds by an displacement at the stereocentre giving inversion of configuration.
Nitrosation produces a stable aliphatic diazonium that undergoes internal return preserving configuration.
The aliphatic diazonium decomposes with loss of to a planar carbocation; water attacks from either face giving racemization.
Q9. A diethyl ether solution contains equal amounts of three amines: methylamine (, ), aniline (, ) and -nitroaniline (-NO–CH–NH, ). Which sequence of aqueous extractions (with indicated pH) will selectively separate them so that methylamine is removed first, then aniline, leaving -nitroaniline in the organic layer?
Extract with HCl () to remove methylamine; then basify and extract again to separate aniline.
Wash the ether layer with water at to extract methylamine as its ammonium salt; then acidify the remaining organic layer to to extract aniline as its ammonium salt (leaving -nitroaniline in ether); finally basify the aqueous extracts to recover the amines.
First extract with aqueous solution at to remove -nitroaniline, then extract the remaining organic layer with NaOH to remove aniline.
Wash with brine, then extract with NaOH to selectively protonate aniline and methylamine.
Q10. Assertion (A): In the gas phase the basicity of amines increases with alkyl substitution (i.e. tertiary secondary primary ammonia), but in aqueous solution secondary amines are generally more basic than tertiary amines. Reason (R): In the gas phase intrinsic electronic effects (electron-donating alkyl groups) dominate; in aqueous solution solvation stabilizes protonated primary and secondary ammonium ions by hydrogen bonding, while tertiary ammonium ions are sterically hindered and less well solvated.
Both (A) and (R) are true, but (R) does not correctly explain (A).
(A) is true but (R) is false.
Both (A) and (R) are true, and (R) correctly explains (A).
(A) is false but (R) is true.
Q11. Given methylamine with at , what percentage of methylamine exists as its conjugate acid in a solution of pH ? (Assume .)
Q12. Which sequence of steps will give predominantly p-nitroaniline from aniline () while minimizing oxidation and ortho/para mixture?
Direct nitration of aniline with (no protection), then isolate product
Acetylation of aniline with (→ acetanilide) Nitration with (gives mainly p-nitroacetanilide) Hydrolysis of the acetamide to yield p-nitroaniline
Diazotization of aniline () followed by a Sandmeyer-type procedure to introduce
First form aniline hydrochloride (treat with HCl) then carry out nitration and finally basify
Q13. Four amines A–D have values at as follows: A: , B: , C: , D: . In a solution at pH , which of these amines will exist more than as their protonated forms ()? (Assume .)
Only A and C
Only A
A, C and D
All four (A, B, C and D)
Q14. A solution contains aniline and methylamine. At pH , calculate the ratio . Given and at (assume ).
Q15. Assertion (A): Primary aromatic amines form isolable diazonium salts on treatment with at , whereas primary aliphatic amines do not give isolable diazonium salts under these conditions.
Reason (R): Aryldiazonium ions are resonance-stabilized by the aromatic ring, but alkyldiazonium ions lack such resonance stabilization and readily decompose (e.g. ), the resulting carbocations being trapped by nucleophiles (such as water) to give alcohols.
A is true but R is false
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 false but R is true
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