CUET UG Chemistry Booster Test - 1 Properties and Reactions of Amines
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QUESTION 1 OF 20
Even though lower amines and corresponding alcohols both form hydrogen bonds, lower amines remain gases at room temperature while corresponding alcohols are liquids. This implies that:
QUESTION 2 OF 20
Regarding the phase state of aliphatic amines:
(I) An increase in the size of the hydrophobic alkyl part increases Van der Waals forces, pushing the phase from gas to liquid to solid.
(II) All aromatic amines are inherently highly volatile gases at room temperature.
QUESTION 3 OF 20
Methanamine is recognized by a characteristic fishy odour. What is its exact molar mass?
QUESTION 4 OF 20
Aniline is observed to change from colourless to a coloured state upon prolonged storage. This transformation, an atmospheric oxidation, is facilitated because the amino group is a powerful:
QUESTION 5 OF 20
Why does the solubility of aliphatic amines in water decrease sharply as the molar mass increases?
(I) The hydrophobic alkyl part increases in size, which resists solvation.
(II) Higher molar mass amines undergo rapid hydrolysis.
QUESTION 6 OF 20
List 1 (Physical Property / Solubility Characteristic) | List 2 (Amine Class)
| List 1 | List 2 |
|---|---|
| 1. Highly soluble in water, fishy odour | a. Lower aliphatic amines |
| 2. Insoluble in water, highly soluble in benzene | b. Higher aliphatic amines |
| 3. No intermolecular hydrogen bonding in pure liquid | c. Tertiary amines |
QUESTION 7 OF 20
The presence of an unshared pair of electrons and covalent bonds dictates the geometry around the nitrogen atom in amines. What is the geometry of trimethylamine?
QUESTION 8 OF 20
Arrange the following substituted ammonium ions in decreasing order of their stabilization via hydrogen bonding with water (solvation effect):
QUESTION 9 OF 20
Evaluate the reasoning for boiling point differences:
(I) n-Butan-1-amine (350.8 K) has a higher boiling point than N,N-Dimethylethanamine (310.5 K) strictly because primary amines form extensive intermolecular hydrogen bonds, while tertiary amines cannot.
(II) The boiling points of isomeric amines follow the order: Tertiary > Secondary > Primary.
QUESTION 10 OF 20
A specific amine of formula C₃H₉N exists as a liquid with the lowest boiling point among its isomers. What is its IUPAC name?
QUESTION 11 OF 20
The base dissociation constant, Kb, and pKb determine basic strength. The pKb of ammonia is 4.75. If a new amine has a pKb of 3.00, it is:
QUESTION 12 OF 20
When aniline reacts with highly concentrated sulphuric acid, it initially forms anilinium hydrogensulphate. This indicates aniline is acting as a base. In electrophilic substitution, the resulting anilinium ion acts as a:
QUESTION 13 OF 20
Arrange the following amines in decreasing order of their basic strength in the aqueous phase:
(C₂H₅)₂NH, C₂H₅NH₂, C₆H₅NH₂
QUESTION 14 OF 20
In substituted anilines, electron-releasing groups increase basic strength, while electron-withdrawing groups decrease it. Arrange p-nitroaniline, aniline, and p-toluidine in increasing order of basic strength:
QUESTION 15 OF 20
QUESTION 16 OF 20
List 1 (Factor Affecting Basicity) | List 2 (Specific Role in Aqueous Solution)
| List 1 | List 2 |
|---|---|
| 1. Inductive (+I) Effect | a. Pushes electron density toward nitrogen |
| 2. Solvation with Water | b. Stabilises substituted ammonium ion through H-bonding |
| 3. Steric Hindrance | c. Restricts effective solvation of larger alkyl-substituted ions |
| 4. Resonance in Aniline | d. Delocalises lone pair, decreasing basicity |
QUESTION 17 OF 20
Amines undergo a specific reaction with alkyl halides to form a carbon-nitrogen bond. What is this reaction known as?
QUESTION 18 OF 20
When a primary amine continuously reacts with alkyl halides, it forms secondary and tertiary amines, and finally yields which class of compounds?
QUESTION 19 OF 20
Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides, and esters. What is the name of the product class formed by this acylation reaction?
QUESTION 20 OF 20
The specific reaction of amines with benzoyl chloride (C₆H₅COCl) is known as:
Test Complete!
Answer Review
1 Even though lower amines and corresponding alcohols both form hydrogen bonds, lower amines remain gases at room temperature while corresponding alcohols are liquids. This implies that:
�� Both alcohols and amines exhibit hydrogen bonding. �� Oxygen is more electronegative than nitrogen. �� Alcohols therefore form stronger intermolecular hydrogen bonds.
- Lower amines can form intermolecular hydrogen bonds because they contain N–H bonds and a lone pair on nitrogen. → However, oxygen is more electronegative than nitrogen, making O–H bonds more polar than N–H bonds. → Consequently, alcohols exhibit stronger intermolecular hydrogen bonding than corresponding amines. → Stronger intermolecular forces result in higher boiling points, causing lower alcohols to be liquids while lower amines remain gases.
- �� Option A → Amines generally have comparable or lower molar masses.
- �� Option B → Oxygen is more electronegative than nitrogen.
- �� Option D → Amines do form hydrogen bonds.
Used
- Conceptual Elimination
Application:
- �� Compare intermolecular forces in alcohols and amines.
Final Logic:
- �� Stronger hydrogen bonding in alcohols causes higher boiling points.
- Oxygen Bonds Stronger than Nitrogen
2 Regarding the phase state of aliphatic amines:
(I) An increase in the size of the hydrophobic alkyl part increases Van der Waals forces, pushing the phase from gas to liquid to solid.
(II) All aromatic amines are inherently highly volatile gases at room temperature.
�� Larger alkyl groups increase intermolecular attraction. �� Physical state changes from gas → liquid → solid. �� Aromatic amines are generally not gases.
- As carbon chain length increases, molecular size and Van der Waals forces increase. → Lower aliphatic amines are gases, medium-chain amines are liquids, and higher amines are solids. → Aromatic amines such as aniline are liquids or solids and are not highly volatile gases.
- �� Option B → Statement II is incorrect.
- �� Option C → Statement II is false.
- �� Option D → Statement I is true.
Used
- Elimination
Application:
- �� Check each statement independently.
Final Logic:
- �� Only Statement I is correct.
- Bigger Chain → Stronger Forces
3 Methanamine is recognized by a characteristic fishy odour. What is its exact molar mass?
�� Formula of methanamine = CH₃NH₂. �� Calculate atomic masses. �� Total equals 31 g mol⁻¹.
- Methanamine formula: CH₃NH₂ Molar mass: C = 12 H₅ = 5 N = 14 Total = 12 + 5 + 14 = 31 g mol⁻¹
- �� Option A → Underestimated value.
- �� Option C → Does not match formula.
- �� Option D → Too large for methanamine.
Used
- Dimensional/Unit Analysis
Application:
- �� Calculate molecular mass directly.
Final Logic:
- �� CH₃NH₂ = 31 g mol⁻¹.
- 12 + 5 + 14 = 31
4 Aniline is observed to change from colourless to a coloured state upon prolonged storage. This transformation, an atmospheric oxidation, is facilitated because the amino group is a powerful:
�� –NH₂ donates electron density to benzene ring. �� Ring becomes highly reactive. �� Oxidation occurs on exposure to air.
- The amino group exhibits a strong +M effect. → It increases electron density in the aromatic ring, especially at ortho and para positions. → The electron-rich ring becomes more susceptible to atmospheric oxidation, causing aniline to develop colour during storage.
- �� Option A → –NH₂ is activating, not deactivating.
- �� Option C → Steric effects are not responsible.
- �� Option D → Aniline behaves as a base, not a Lewis acid.
Used
- Contextual/Tonal Matching
Application:
- �� Connect oxidation tendency with electron density.
Final Logic:
- �� Electron-rich aromatic rings oxidize more easily.
- NH₂ Activates Ring
5 Why does the solubility of aliphatic amines in water decrease sharply as the molar mass increases?
(I) The hydrophobic alkyl part increases in size, which resists solvation.
(II) Higher molar mass amines undergo rapid hydrolysis.
�� Hydrogen bonding favors solubility. �� Larger alkyl chains are hydrophobic. �� Solubility decreases as chain length increases.
- Lower amines dissolve in water through hydrogen bonding. → As alkyl chain size increases, the nonpolar hydrophobic portion becomes dominant. → This reduces interaction with water molecules and lowers solubility. → Hydrolysis is unrelated to the solubility trend.
- �� Option B → Hydrolysis is not the reason.
- �� Option C → Statement II is incorrect.
- �� Option D → Statement I is correct.
Used
- Elimination
Application:
- �� Identify the factor affecting water solubility.
Final Logic:
- �� Hydrophobic alkyl chains reduce solubility.
- Long Chain = Less Solubility
6 List 1 (Physical Property / Solubility Characteristic) | List 2 (Amine Class)
| List 1 | List 2 |
|---|---|
| 1. Highly soluble in water, fishy odour | a. Lower aliphatic amines |
| 2. Insoluble in water, highly soluble in benzene | b. Higher aliphatic amines |
| 3. No intermolecular hydrogen bonding in pure liquid | c. Tertiary amines |
�� Lower amines are water soluble. �� Higher amines dissolve in organic solvents. �� Tertiary amines lack N–H bonds.
- Lower aliphatic amines are water soluble and possess fishy odour. → Higher amines become insoluble in water and dissolve readily in organic solvents. → Tertiary amines lack N–H bonds and therefore cannot form intermolecular hydrogen bonds among themselves. Thus: 1 → a 2 → b 3 → c
- �� Options B, C, D incorrectly assign amine classes.
Used
- Option Grouping
Application:
- �� Match physical properties with amine types.
Final Logic:
- �� Solubility and H-bonding determine the classification.
- Lower = Water, Higher = Benzene, Tertiary = No N–H
7 The presence of an unshared pair of electrons and covalent bonds dictates the geometry around the nitrogen atom in amines. What is the geometry of trimethylamine?
�� Nitrogen is sp³ hybridized. �� One lone pair is present. �� Shape becomes pyramidal.
- Nitrogen in amines possesses three bond pairs and one lone pair. → The electron pair geometry is tetrahedral. → Due to the lone pair, the molecular geometry becomes trigonal pyramidal.
- �� Option A → Electron pair geometry, not molecular geometry.
- �� Option C → Requires sp² hybridization.
- �� Option D → Requires sp hybridization.
Used
- Conceptual Elimination
Application:
- �� Recall geometry of amines.
Final Logic:
- �� Lone pair converts tetrahedral arrangement into pyramidal shape.
- 3 Bonds + 1 Lone Pair = Pyramid
8 Arrange the following substituted ammonium ions in decreasing order of their stabilization via hydrogen bonding with water (solvation effect):
�� Smaller ions are better solvated. �� More N–H bonds allow stronger hydration. �� Solvation decreases with increasing alkyl substitution.
- Solvation depends on hydrogen bonding with water. → Primary ammonium ions possess the greatest capacity for hydrogen bonding. → Increasing alkyl substitution introduces steric hindrance. Therefore: RNH₃⁺ > R₂NH₂⁺ > R₃NH⁺
- �� Options B, C, D contradict solvation trends.
Used
- Ordering
Application:
- �� Compare extent of hydrogen bonding.
Final Logic:
- �� Greater hydrogen bonding gives greater stabilization.
- 1° > 2° > 3° (Solvation)
9 Evaluate the reasoning for boiling point differences:
(I) n-Butan-1-amine (350.8 K) has a higher boiling point than N,N-Dimethylethanamine (310.5 K) strictly because primary amines form extensive intermolecular hydrogen bonds, while tertiary amines cannot.
(II) The boiling points of isomeric amines follow the order: Tertiary > Secondary > Primary.
�� Primary amines form strong H-bonds. �� Tertiary amines cannot self-associate through N–H bonds. �� Boiling point order is Primary > Secondary > Tertiary.
- Primary amines possess N–H bonds that participate extensively in intermolecular hydrogen bonding. → Tertiary amines lack N–H bonds and cannot form intermolecular hydrogen bonds among themselves. → Hence primary amines have higher boiling points. → Statement II reverses the actual order.
- �� Option B → Statement I is correct.
- �� Option C → Statement II is false.
- �� Option D → Statement I is true.
Used
- Elimination
Application:
- �� Compare hydrogen-bonding capability.
Final Logic:
- �� Greater H-bonding results in higher boiling point.
- 1° > 2° > 3° Boiling Point
10 A specific amine of formula C₃H₉N exists as a liquid with the lowest boiling point among its isomers. What is its IUPAC name?
�� Tertiary amines show the lowest boiling points. �� They cannot form intermolecular hydrogen bonds. �� N,N-Dimethylmethanamine is a tertiary amine.
- Among C₃H₉N isomers: • Propan-1-amine → Primary • Propan-2-amine → Primary • N-Methylethanamine → Secondary • N,N-Dimethylmethanamine → Tertiary → Tertiary amines lack N–H bonds and therefore have the weakest intermolecular association. → Hence they possess the lowest boiling point.
- �� Options A and D → Primary amines.
- �� Option B → Secondary amine.
Used
- Odd One Out
Application:
- �� Identify the tertiary amine among isomers.
Final Logic:
- �� Tertiary amines have the lowest boiling points.
- Tertiary = Lowest BP
11 The base dissociation constant, Kb, and pKb determine basic strength. The pKb of ammonia is 4.75. If a new amine has a pKb of 3.00, it is:
�� Lower pKb means stronger base. �� 3.00 is less than 4.75. �� Therefore, the new amine is stronger than ammonia.
- Basic strength is inversely related to pKb value. → Smaller pKb indicates greater basic strength. Given: New amine pKb = 3.00 Ammonia pKb = 4.75 Since 3.00 < 4.75, the new amine is a stronger base than ammonia.
- �� Option A → Higher pKb would indicate weaker base, but the new amine has lower pKb.
- �� Option C → pKb relates to basicity, not acidity.
- �� Option D → Solubility cannot be concluded from pKb alone.
Used
- Dimensional/Unit Analysis
Application:
- �� Compare numerical pKb values.
Final Logic:
- �� Smaller pKb = stronger base.
- Low pKb = Strong Base
12 When aniline reacts with highly concentrated sulphuric acid, it initially forms anilinium hydrogensulphate. This indicates aniline is acting as a base. In electrophilic substitution, the resulting anilinium ion acts as a:
�� Aniline gets protonated in strong acid. �� Anilinium ion is electron-withdrawing. �� It directs electrophilic substitution to meta position.
- In highly concentrated sulphuric acid, aniline accepts a proton and forms the anilinium ion. → The –NH₃⁺ group withdraws electron density from the benzene ring. → Because of this deactivating effect, the anilinium ion behaves as a meta-directing group in electrophilic substitution reactions.
- �� Option A → Anilinium ion is deactivating, not strongly activating.
- �� Option C → Neutral –NH₂ is ortho/para-directing, but –NH₃⁺ is meta-directing.
- �� Option D → The anilinium ion does not act as a nucleophile in electrophilic substitution.
Used
- Elimination
Application:
- �� Distinguish neutral aniline from protonated anilinium ion.
Final Logic:
- �� Protonated –NH₃⁺ group is meta-directing.
- NH₂ = o,p; NH₃⁺ = meta
13 Arrange the following amines in decreasing order of their basic strength in the aqueous phase:
(C₂H₅)₂NH, C₂H₅NH₂, C₆H₅NH₂
�� Aliphatic amines are stronger bases than arylamines. �� Secondary ethylamine is stronger than primary ethylamine in water. �� Aniline is weakest due to resonance.
- In aqueous solution, ethyl-substituted aliphatic amines are stronger bases than aniline because alkyl groups increase electron density on nitrogen through the +I effect. → Diethylamine is stronger than ethylamine because it has greater electron donation and sufficient solvation. → Aniline is weakest because the lone pair of nitrogen is delocalized into the benzene ring, making it less available for protonation. Therefore: (C₂H₅)₂NH > C₂H₅NH₂ > C₆H₅NH₂
- �� Option A → Incorrectly places aniline as strongest.
- �� Option C → Incorrectly places ethylamine above diethylamine.
- �� Option D → Incorrectly places aniline above ethylamine.
Used
- Ordering
Application:
- �� Compare +I effect, solvation, and resonance.
Final Logic:
- �� Aliphatic secondary > aliphatic primary > aromatic amine.
- Diethyl > Ethyl > Aniline
14 In substituted anilines, electron-releasing groups increase basic strength, while electron-withdrawing groups decrease it. Arrange p-nitroaniline, aniline, and p-toluidine in increasing order of basic strength:
�� –NO₂ decreases basicity. �� –CH₃ increases basicity. �� Therefore, p-toluidine is strongest.
- p-Nitroaniline contains the –NO₂ group, which is strongly electron-withdrawing. It reduces electron density on nitrogen and decreases basic strength. → Aniline has no extra electron-donating or withdrawing substituent. → p-Toluidine contains the –CH₃ group, which is electron-releasing and increases electron density on nitrogen. Increasing basic strength: p-nitroaniline < aniline < p-toluidine
- �� Option B → Gives reverse logic.
- �� Option C → Places aniline below p-nitroaniline incorrectly.
- �� Option D → Places p-toluidine below aniline incorrectly.
Used
- Ordering
Application:
- �� Rank substituents by electron-withdrawing/electron-releasing effects.
Final Logic:
- �� EWG lowers basicity; ERG raises basicity.
- NO₂ Down, CH₃ Up
15
�� Gas phase has no solvation effect. �� Basicity depends mainly on +I effect. �� More alkyl groups increase electron density on nitrogen.
- In the gas phase, there is no solvation of ammonium ions and steric hindrance to hydration does not apply. → Therefore, the basic strength depends mainly on the electron-releasing +I effect of alkyl groups. → Tertiary amines have three alkyl groups, secondary amines have two, primary amines have one, and ammonia has none. Thus: Tertiary > Secondary > Primary > Ammonia
- �� Option A → Gives opposite order of +I effect.
- �� Option C → Places ammonia incorrectly as strongest.
- �� Option D → Places secondary above tertiary without solvation logic.
Used
- Ordering
Application:
- �� Count the number of electron-releasing alkyl groups.
Final Logic:
- �� More alkyl groups = stronger +I effect = stronger base.
- 3R > 2R > 1R > NH₃
16 List 1 (Factor Affecting Basicity) | List 2 (Specific Role in Aqueous Solution)
| List 1 | List 2 |
|---|---|
| 1. Inductive (+I) Effect | a. Pushes electron density toward nitrogen |
| 2. Solvation with Water | b. Stabilises substituted ammonium ion through H-bonding |
| 3. Steric Hindrance | c. Restricts effective solvation of larger alkyl-substituted ions |
| 4. Resonance in Aniline | d. Delocalises lone pair, decreasing basicity |
�� +I effect increases electron density on nitrogen. �� Solvation stabilizes ammonium ions. �� Steric hindrance reduces hydration. �� Resonance decreases availability of lone pair.
- Alkyl groups exhibit a +I effect and push electron density toward nitrogen, increasing basicity. → Solvation stabilizes the conjugate acid (ammonium ion) through hydrogen bonding with water molecules. → Larger alkyl groups hinder effective hydrogen bonding and decrease solvation. → In aniline, the lone pair is delocalized into the benzene ring by resonance, reducing basic strength. Thus: 1 → a 2 → b 3 → c 4 → d
- �� Option B → Incorrectly swaps inductive effect and solvation roles.
- �� Option C → Steric hindrance does not stabilize ammonium ions.
- �� Option D → Resonance does not increase electron density on nitrogen.
Used
- Option Grouping
Application:
- �� Match each factor with its direct effect on basicity.
Final Logic:
- �� Correct understanding of +I effect, solvation, steric effect, and resonance gives the required matching.
- I–S–S–R = Increase, Solvate, Stop, Resonance
17 Amines undergo a specific reaction with alkyl halides to form a carbon-nitrogen bond. What is this reaction known as?
�� Alkyl halides transfer alkyl groups to amines. �� A new C–N bond is formed. �� This process is called alkylation.
- Amines possess a lone pair on nitrogen and behave as nucleophiles. → They attack alkyl halides and replace the halogen atom. → As a result, an alkyl group becomes attached to nitrogen. → The reaction is therefore known as alkylation.
- �� Option A → Acylation introduces an acyl group (RCO–), not an alkyl group.
- �� Option C → Diazotisation involves aromatic primary amines and nitrous acid.
- �� Option D → Bromination introduces bromine into a molecule.
Used
- Odd One Out
Application:
- �� Identify the reaction specifically involving alkyl group transfer.
Final Logic:
- �� Alkyl halide + amine = Alkylation.
- Alkyl Halide → Alkylation
18 When a primary amine continuously reacts with alkyl halides, it forms secondary and tertiary amines, and finally yields which class of compounds?
�� Amines continue reacting with alkyl halides. �� Successive alkylation occurs. �� Final product is a quaternary ammonium salt.
- A primary amine formed initially still contains a lone pair and remains nucleophilic. → It reacts further with alkyl halides to form secondary and tertiary amines. → Continued alkylation finally produces a positively charged nitrogen species having four alkyl groups. → Such compounds are called quaternary ammonium salts.
- �� Option A → Amides are formed by acylation.
- �� Option C → Diazonium salts arise from diazotisation.
- �� Option D → Sulphonamides result from reaction with sulphonyl chlorides.
Used
- Conceptual Elimination
Application:
- �� Follow the sequence of repeated alkylation.
Final Logic:
- �� Exhaustive alkylation ends at quaternary ammonium salts.
- 1° → 2° → 3° → Quaternary
19 Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides, and esters. What is the name of the product class formed by this acylation reaction?
�� Acylation introduces an acyl group. �� Amines react with acid derivatives. �� Products formed are amides.
- Primary and secondary amines react with acid chlorides, acid anhydrides, and esters. → The acyl group (RCO–) becomes attached to nitrogen. → The resulting compounds contain the –CONH– linkage characteristic of amides.
- �� Option A → Nitriles contain –C≡N groups.
- �� Option C → Imines contain C=N bonds.
- �� Option D → Isocyanides contain –NC groups.
Used
- Elimination
Application:
- �� Identify the product of acyl group transfer.
Final Logic:
- �� Acylation of amines gives amides.
- Acylation → Amide
20 The specific reaction of amines with benzoyl chloride (C₆H₅COCl) is known as:
�� Benzoyl chloride provides a benzoyl group. �� Amines undergo acylation with benzoyl chloride. �� This special acylation is called benzoylation.
- Benzoyl chloride (C₆H₅COCl) reacts with primary and secondary amines. → The benzoyl group (C₆H₅CO–) becomes attached to nitrogen. → This reaction is specifically known as benzoylation and is commonly used in the Hinsberg test.
- �� Option A → Acetylation involves acetyl chloride or acetic anhydride.
- �� Option C → Sandmeyer reaction involves diazonium salts.
- �� Option D → Carbylamine reaction produces isocyanides.
Used
- Contextual/Tonal Matching
Application:
- �� Match reagent name with reaction name.
Final Logic:
- �� Benzoyl chloride gives benzoylation.
- Benzoyl Chloride → Benzoylation
