Comprehension:
Amines are derivatives of ammonia obtained by replacement of one, two or all the three hydrogen atoms by alkyl and / or aryl groups. Nitrogen atom of amines like ammonia is trivalent and carries an unshared pair of electrons. Orbitals of nitrogen overlap with orbitals of hydrogen or carbon depending upon the composition of the amines. The fourth orbital of nitrogen in all amines contains an unshared pair of electrons. Due to the presence of unshared pair of electrons, the angle C-N-E (where E is C or H) is less than tetrahedral angle 109.5°. Amines are classified as primary (1°), secondary (2°) and tertiary (3°) amines. All amines are basic in nature and basicity differs between primary amines, secondary amines and tertiary amines. In aryl amines, –NH2 group is directly attached to the benzene ring. C6H5NH2 is simplest example of arylamine. Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.
Carbylamine reaction is shown by
A. ammonium salts .
B. tertiary amines.
C. secondary amines.
D. primary amines.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → D only
In the carbylamine reaction:
\( \displaystyle \ce{R-NH2 + CHCl3 + 3KOH} \xrightarrow{\text{heat}} \ce{R-NC + 3KCl + 3H2O} \)
To form the R–N≡C group, the nitrogen must lose both of its hydrogen atoms. Only a primary amine has two H atoms on nitrogen, so only it gives the reaction.
A. ammonium salts . — Incorrect. Ammonium salts contain no alkyl or aryl group on nitrogen, so no isocyanide R–NC can form.
B. tertiary amines. — Incorrect. \( \ce{R3N} \) has no H on nitrogen, so no isocyanide can form.
C. secondary amines. — Incorrect. \( \ce{R2NH} \) has only one H on nitrogen, not the two that are needed.
D. primary amines. — Correct. The –\( \ce{NH2} \) group has two hydrogens, which are replaced to give R–N≡C, e.g. aniline gives phenyl isocyanide.
NCERT (2026-27 edition):
Carbylamine Reaction
