Every Book Back multiple-choice question from Organic Nitrogen Compounds (12th Standard Chemistry, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which of the following nitro compounds can show tautomerism?
- A. NitroethaneCorrect
- B. 2-Methyl-2-nitropropane
- C. Nitrobenzene
- D. None of these
Explanation. Primary and secondary nitroalkanes having at least one alpha-hydrogen atom exhibit tautomerism to form nitro and aci-forms. Nitroethane is a primary nitroalkane with alpha-hydrogens, whereas 2-methyl-2-nitropropane and nitrobenzene do not have alpha-hydrogens on the nitro-bearing carbon.
Q2
Which of the following reactions does not yield aniline?
- A. degradation of benzamide with Br2 / NaOH
- B. potassium salt of phthalimide treated with chlorobenzene followed by hydrolysis with aqueous NaOH solutionCorrect
- C. reduction of nitrobenzene with Ni or Pt
- D. reduction of nitrobenzene by Sn / HCl
Explanation. Chlorobenzene does not undergo nucleophilic substitution with potassium phthalimide under ordinary conditions because the carbon-chlorine bond has partial double bond character due to resonance. Thus, Gabriel phthalimide synthesis cannot be used to prepare aniline.
Q3
Which one of the following will not undergo Hofmann bromamide reaction?
- A. CH3CONHCH3Correct
- B. CH3CH2CONH2
- C. CH3CONH2
- D. C6H5CONH2
Explanation. Only primary amides containing a -CONH2 group undergo the Hofmann bromamide reaction to form primary amines. N-methylacetamide (CH3CONHCH3) is a secondary amide and therefore does not undergo this reaction.
Q4
Assertion : Acetamide on reaction with KOH and bromine gives acetic acid
Reason : Bromine catalyses hydrolysis of acetamide.
- A. if both assertion and reason are true and reason is the correct explanation of assertion
- B. if both assertion and reason are true but reason is not the correct explanation of assertion
- C. assertion is true but reason is false
- D. both assertion and reason are falseCorrect
Explanation. Acetamide reacts with bromine and KOH in the Hofmann bromamide reaction to yield methylamine, not acetic acid, so the assertion is false. Bromine does not catalyze the hydrolysis of acetamide, so the reason is also false.
Q5
In the following sequence of reactions,
CH3CH2Br --aq. NaOH--> A --KMnO4/H+--> B --NH3/heat--> C --Br2/NaOH--> D
the product D is:
- A. bromomethane
- B. alpha-bromo sodium acetate
- C. methanamineCorrect
- D. acetamide
Explanation. Ethyl bromide undergoes nucleophilic substitution with aqueous NaOH to give ethanol (A), which is oxidized to ethanoic acid (B). Reaction of B with ammonia and heating gives acetamide (C). Hofmann bromamide degradation of C yields methanamine (D).
Q6
Which one of the following nitro compounds does not react with nitrous acid?
- A. CH3-CH2-CH2-NO2
- B. (CH3)2CH-CH2NO2
- C. (CH3)3CNO2Correct
- D. CH3-C(O)-CH(CH3)-NO2
Explanation. Primary and secondary nitroalkanes react with nitrous acid because they possess alpha-hydrogens. Tertiary nitroalkanes like 2-methyl-2-nitropropane ((CH3)3CNO2) do not possess any alpha-hydrogen and therefore do not react with nitrous acid.
Q7
Aniline reacts with benzoyl chloride in the presence of NaOH to give benzanilide. This reaction is known as:
- A. Friedel-Crafts reaction
- B. Hell-Volhard-Zelinsky reaction
- C. Schotten-Baumann reactionCorrect
- D. None of these
Explanation. The acylation of aromatic amines like aniline with acid chlorides such as benzoyl chloride in the presence of an aqueous base like NaOH is known as the Schotten-Baumann reaction.
Q8
The product formed by the reaction of an aldehyde with a primary amine is:
- A. carboxylic acid
- B. aromatic acid
- C. Schiff's baseCorrect
- D. ketone
Explanation. Aldehydes react with primary aliphatic or aromatic amines to undergo a condensation reaction with the elimination of water, forming imines containing a carbon-nitrogen double bond, which are commonly known as Schiff's bases.
Q9
Which of the following reactions is not correct?
- A. CH3CH2NH2 --HNO2--> CH3CH2OH + N2
- B. (CH3)2N-C6H5 --NaNO2/HCl--> (CH3)2N-N=NClCorrect
- C. CH3CONH2 --Br2/NaOH--> CH3NH2
- D. None of these
Explanation. N,N-dimethylaniline is a tertiary aromatic amine. Upon reaction with nitrous acid, it undergoes electrophilic substitution at the para-position of the benzene ring to yield p-nitroso-N,N-dimethylaniline, rather than forming a diazonium-like chloride derivative.
Q10
When aniline reacts with acetic anhydride, the product formed is:
- A. o-aminoacetophenone
- B. m-aminoacetophenone
- C. p-aminoacetophenone
- D. acetanilideCorrect
Explanation. Aniline reacts with acetic anhydride in the presence of a base like pyridine to undergo nucleophilic acyl substitution (acetylation), yielding acetanilide as the major product.
Q11
The correct order of basic strength for methyl-substituted amines in aqueous solution is:
- A. N(CH3)3 > N(CH3)2H > N(CH3)H2 > NH3
- B. N(CH3)H2 > N(CH3)2H > N(CH3)3 > NH3
- C. NH3 > N(CH3)H2 > N(CH3)2H > N(CH3)3
- D. N(CH3)2H > N(CH3)H2 > N(CH3)3 > NH3Correct
Explanation. In aqueous solution, the basicity of methyl-substituted amines depends on inductive, solvation, and steric effects. These combined factors result in secondary dimethylamine being the strongest base, followed by methylamine, trimethylamine, and finally ammonia.
Q12
In the reaction,
[3-bromo-4-nitrobenzenediazonium chloride] --A--> [1-bromo-2-nitrobenzene]
the reagent 'A' is:
- A. H3PO2 and H2OCorrect
- B. H+ / H2O
- C. HgSO4 / H2SO4
- D. Cu2Cl2
Explanation. Hypophosphorous acid (H3PO2) in water is used to deaminate the diazonium salt by replacing the diazonium group with a hydrogen atom.
Q13
In the following reaction sequence,
C6H5NO2 --Fe/HCl--> A --NaNO2/HCl, 273K--> B --H2O, 283K--> C
the product 'C' is:
- A. C6H5-OHCorrect
- B. C6H5-CH2OH
- C. C6H5-CHO
- D. C6H5NH2
Explanation. Nitrobenzene is reduced to aniline (A) using Fe/HCl. Diazotization of aniline with NaNO2 and HCl at 273 K yields benzene diazonium chloride (B), which on hydrolysis with warm water at 283 K yields phenol (C).
Q14
Nitrobenzene on reaction with concentrated \(\text{HNO}_3 / \text{H}_2\text{SO}_4\) at \(80\text{-}100^\circ\text{C}\) forms which one of the following products?
- A. 1,4-dinitrobenzene
- B. 2,4,6-trinitrobenzene
- C. 1,2-dinitrobenzene
- D. 1,3-dinitrobenzeneCorrect
Explanation. The nitro group in nitrobenzene is an electron-withdrawing group that deactivates the benzene ring and directs electrophilic substitution to the meta-position, leading to the formation of 1,3-dinitrobenzene.
Q15
A compound with molecular formula \(\text{C}_5\text{H}_{13}\text{N}\) reacts with \(\text{HNO}_2\) to give an optically active compound. The compound is:
- A. pentan-1-amine
- B. pentan-2-amineCorrect
- C. N,N-dimethylpropan-2-amine
- D. diethyl methyl amine
Explanation. Pentan-2-amine is a primary amine with a chiral carbon atom. It reacts with nitrous acid to yield pentan-2-ol, which preserves the chiral center and remains optically active.
Q16
Secondary nitroalkanes react with nitrous acid to form:
- A. red solution
- B. blue solutionCorrect
- C. green solution
- D. yellow solution
Explanation. Secondary nitroalkanes react with nitrous acid to produce pseudonitroles, which contain a characteristic blue color in solution.
Q17
Which of the following amines does not undergo acetylation?
- A. t-butylamine
- B. ethylamine
- C. diethylamine
- D. triethylamineCorrect
Explanation. Triethylamine is a tertiary amine. Because it lacks any acidic hydrogen atoms bonded directly to the nitrogen atom, it cannot undergo acetylation.
Q18
Which one of the following is most basic?
- A. 2,4-dichloroaniline
- B. 2,4-dimethylanilineCorrect
- C. 2,4-dinitroaniline
- D. 2,4-dibromoaniline
Explanation. Methyl groups exert a electron-donating inductive (+I) effect, raising the electron density on the nitrogen's lone pair and increasing basicity. Halogens and nitro groups are electron-withdrawing.
Q19
When \(\text{C}_2\text{H}_5\text{ONO}\) is reduced with \(\text{Sn} / \text{HCl}\), the pair of compounds formed are:
- A. Ethanol, hydroxylamine hydrochlorideCorrect
- B. Ethanol, ammonium hydroxide
- C. Ethanol, hydroxylamine
- D. Ethylamine, water
Explanation. Reduction of ethyl nitrite cleaves the oxygen-nitrogen single bond, yielding ethanol and hydroxylamine, which exists as hydroxylamine hydrochloride in an acidic HCl medium.
Q20
What is the IUPAC name for the amine with structure \(\text{(CH}_3)_2\text{N-C(CH}_3\text{)(CH}_2\text{CH}_3)_2\)?
- A. 3-dimethylamino-3-methylpentane
- B. 3-(N,N-diethyl)-3-aminopentane
- C. 3-N,N-trimethylpentanamine
- D. N,N-dimethyl-3-methylpentan-3-amineCorrect
Explanation. The longest continuous carbon chain containing the nitrogen atom has five carbons (pentane). The nitrogen and a methyl substituent are located on carbon-3, yielding N,N-dimethyl-3-methylpentan-3-amine.
Q21
Identify the product 'P' in the following reaction sequence:
- A. (figure A)
- B. (figure B)Correct
- C. (figure C)
- D. (figure D)
Explanation. Grignard reagents react with nitriles through nucleophilic addition followed by acidic hydrolysis to form ketones.
Q22
Ammonium salt of benzoic acid is heated strongly with \(\text{P}_2\text{O}_5\) and the product so formed is reduced and then treated with \(\text{NaNO}_2 / \text{HCl}\) at low temperature. The final compound formed is:
- A. Benzene diazonium chloride
- B. Benzyl alcoholCorrect
- C. Phenol
- D. Nitrosobenzene
Explanation. Ammonium benzoate dehydrates with phosphorus pentoxide to yield benzonitrile. Reduction yields benzylamine, which reacts with nitrous acid at low temperatures to produce unstable diazonium ions that hydrolyze into benzyl alcohol.
Q23
Identify X in the sequence given below:
- A. (figure A)Correct
- B. (figure B)
- C. (figure C)
- D. (figure D)
Explanation. Primary arylamines undergo the carbylamine reaction to form isocyanides. Subsequent acidic hydrolysis breaks down the isocyanide group to regenerate the original primary amine.
Q24
Among the following, the reaction that proceeds through an electrophilic substitution, is:
- A. (figure A)
- B. (figure B)Correct
- C. (figure C)
- D. (figure D)
Explanation. The halogenation of benzene using chlorine in the presence of an anhydrous Lewis acid catalyst is a classical electrophilic aromatic substitution reaction.
Q25
The major product of the following reaction is:
- A. (figure A)
- B. (figure B)Correct
- C. (figure C)
- D. (figure D)
Explanation. Strong heating of a dicarboxylic acid like phthalic acid with ammonia promotes dehydration and stable ring closure, yielding a cyclic imide known as phthalimide.
