15 extra multiple-choice questions for Organic Nitrogen Compounds (12th Standard Chemistry, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which of the following compounds does not exhibit nitro-aci-nitro tautomerism?
- A. Nitromethane
- B. Nitroethane
- C. 2-Nitropropane
- D. 2-Methyl-2-nitropropaneCorrect
Explanation. Tautomerism in nitroalkanes requires the presence of an alpha-hydrogen atom. Since 2-methyl-2-nitropropane is a tertiary nitroalkane, it lacks an alpha-hydrogen and cannot form the aci tautomer.
Q2
Arrange the following nitroalkanes in the increasing order of their acidic strength: Nitromethane (I), Nitroethane (II), 2-Nitropropane (III).
- A. III < II < ICorrect
- B. I < II < III
- C. II < I < III
- D. III < I < II
Explanation. The acidic strength of nitroalkanes decreases as the number of electron-releasing alkyl groups on the alpha-carbon increases. This is due to the positive inductive effect (+I effect) destabilizing the conjugate base.
Q3
What is the product formed when tert-butylamine is oxidised with aqueous KMnO4?
- A. 2-Methyl-2-nitropropaneCorrect
- B. 2-Nitropropane
- C. tert-Butyl alcohol
- D. Isobutylene
Explanation. Oxidation of tertiary alkyl amines with aqueous potassium permanganate directly converts the amino group into a nitro group, yielding tertiary nitroalkanes such as 2-methyl-2-nitropropane.
Q4
Which of the following reducing systems reduces nitrobenzene to N-phenylhydroxylamine in a neutral medium?
- A. Sn and concentrated HCl
- B. Zn dust and ammonium chlorideCorrect
- C. Tin(II) chloride and KOH
- D. Lithium aluminium hydride in ether
Explanation. Reduction of nitroarenes using zinc dust in a neutral medium like ammonium chloride yields the corresponding alkyl or aryl hydroxylamines, such as N-phenylhydroxylamine from nitrobenzene.
Q5
Boiling nitroethane with concentrated hydrochloric acid yields which of the following organic compounds?
- A. Acetaldehyde
- B. Acetic acidCorrect
- C. Ethylamine
- D. Acetamide
Explanation. Acid hydrolysis of primary nitroalkanes using mineral acids like hydrochloric acid cleaves the molecule to produce carboxylic acids. Boiling nitroethane under these conditions produces acetic acid.
Q6
Which of the following represents the correct decreasing order of basic strength of methyl substituted amines in aqueous solution?
- A. (CH3)2NH > CH3NH2 > (CH3)3N > NH3Correct
- B. (CH3)3N > (CH3)2NH > CH3NH2 > NH3
- C. CH3NH2 > (CH3)2NH > (CH3)3N > NH3
- D. (CH3)2NH > (CH3)3N > CH3NH2 > NH3
Explanation. In aqueous solution, the basicity of methyl-substituted amines is determined by inductive, steric, and solvation effects. This makes secondary dimethylamine the strongest base, followed by methylamine and tertiary trimethylamine.
Q7
In the Hofmann-Mustard oil reaction, methylamine is treated with carbon disulphide followed by heating with which reagent to produce methyl isothiocyanate?
- A. Mercuric chloride (HgCl2)Correct
- B. Cuprous chloride (Cu2Cl2)
- C. Thionyl chloride (SOCl2)
- D. Phosphorus pentachloride (PCl5)
Explanation. Primary amines react with carbon disulphide to form dithiocarbamic acids, which undergo decomposition upon subsequent treatment with mercuric chloride to yield alkyl isothiocyanates with a mustard-like odour.
Q8
At what temperature range is the diazotisation of aniline carried out to obtain stable benzene diazonium chloride?
- A. 273 K - 278 KCorrect
- B. 298 K - 303 K
- C. 313 K - 318 K
- D. 353 K - 358 K
Explanation. Diazotisation of primary aromatic amines is highly temperature-sensitive. It must be performed at low temperatures, specifically between 273 K and 278 K (0 to 5 degrees Celsius), to prevent decomposition.
Q9
Why does the direct nitration of aniline with a strong acid mixture produce a substantial amount of meta-nitroaniline?
- A. The amino group undergoes oxidation to a meta-directing group.
- B. Aniline is protonated to form the strongly deactivating, meta-directing anilinium ion.Correct
- C. The nitrating mixture steric hindrance prevents ortho and para substitution.
- D. Nitration occurs via a free-radical mechanism in acidic medium.
Explanation. In strongly acidic nitration conditions, the basic amino group of aniline is protonated to form the positively charged anilinium ion. This ion is highly deactivating and directs incoming electrophiles to the meta position.
Q10
Which of the following pH ranges is ideal for the coupling reaction between benzene diazonium chloride and phenol to form p-hydroxyazobenzene?
- A. 1 - 2
- B. 4 - 5
- C. 9 - 10Correct
- D. 12 - 13
Explanation. The coupling reaction of diazonium salts with phenol is carried out in a mildly alkaline medium (pH 9 to 10). This converts phenol into the more nucleophilic phenoxide ion, facilitating electrophilic attack.
Q11
Which reagent is used in the Sandmeyer reaction to introduce a cyano group into the benzene ring from a diazonium salt?
- A. Potassium cyanide and silver powder
- B. Cuprous cyanide (CuCN)Correct
- C. Hydrogen cyanide in pyridine
- D. Sodium cyanide in DMSO
Explanation. In the Sandmeyer reaction, benzenediazonium chloride is treated with cuprous cyanide (CuCN) to produce benzonitrile (cyanobenzene), effectively substituting the diazonium group with a cyano group.
Q12
Partial hydrolysis of acetonitrile (ethanenitrile) using alkaline hydrogen peroxide yields which organic compound?
- A. Acetic acid
- B. AcetamideCorrect
- C. Ethylamine
- D. Methylamine
Explanation. Acetonitrile undergoes partial hydrolysis when treated with alkaline hydrogen peroxide, stopping at the intermediate stage to form acetamide. Complete hydrolysis would yield acetic acid.
Q13
What is the product formed by the self-condensation of two molecules of propandinitrile or propanenitrile in the presence of sodium?
- A. 3-Imino-2-methylpentanenitrileCorrect
- B. 2-Methyl-2-pentenenitrile
- C. Propionamide
- D. Diethyl ketone
Explanation. Under the Thorpe nitrile condensation, two molecules of propanenitrile containing alpha-hydrogens undergo self-condensation in the presence of sodium to produce the iminonitrile compound, 3-imino-2-methylpentanenitrile.
Q14
What is the major organic product obtained when ethyl bromide is heated with an ethanolic solution of silver cyanide?
- A. Ethyl cyanide
- B. Ethyl isocyanideCorrect
- C. Nitroethane
- D. Ethylamine
Explanation. Silver cyanide is covalent in nature, meaning the lone pair on nitrogen acts as the nucleophile. Heating ethyl bromide with silver cyanide therefore yields ethyl isocyanide as the major product.
Q15
What are the hydrolysis products of methyl isocyanide when treated with a dilute mineral acid?
- A. Methylamine and formic acidCorrect
- B. Acetic acid and ammonia
- C. Methanol and methanamine
- D. Dimethylamine and carbon dioxide
Explanation. Alkyl isocyanides are hydrolysed by dilute mineral acids to yield a primary amine and formic acid. For methyl isocyanide, this acid-catalyzed hydrolysis produces methylamine and formic acid.
