Consider the following statements about amines.
(A) The nitrogen orbitals in amines are sp3 hybridised and the geometry of amines is pyramidal.
(B) In trimethylamine, the C–N–C bond angle is greater than 109.5° because of the unshared pair of electrons on nitrogen.
(C) Amines behave as nucleophiles due to the presence of an unshared electron pair on the nitrogen atom.
(D) Tertiary amines like trimethylamine are used as insect repellents.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B) and (D) only
Like ammonia, the nitrogen atom of an amine is trivalent and carries an unshared pair of electrons. This pair decides both the shape of amines and much of their chemistry.
(A) The nitrogen orbitals in amines are sp3 hybridised and the geometry of amines is pyramidal. — Correct statement. Three sp3 orbitals form bonds and the fourth holds the unshared pair, which gives a pyramidal shape.
(B) In trimethylamine, the C–N–C bond angle is greater than 109.5° because of the unshared pair of electrons on nitrogen. — Incorrect statement. The unshared pair pushes the bonds closer together, so the angle is less than 109.5°; in trimethylamine it is 108°.
(C) Amines behave as nucleophiles due to the presence of an unshared electron pair on the nitrogen atom. — Correct statement. The unshared pair attacks electron-poor carbon, as in the reactions of amines with alkyl halides and acid chlorides.
(D) Tertiary amines like trimethylamine are used as insect repellents. — Incorrect statement. Trimethylamine and similar tertiary amines are used as insect attractants, not repellents.
NCERT (2026-27 edition):
9.1 Structure of Amines – “…Nitrogen orbitals in amines are therefore, sp3 hybridised and the geometry of amines is pyramidal. … Due to the presence of unshared pair of electrons, the angle C–N–E, (where E is C or H) is less than 109.5°; for instance, it is 108° in case of trimethylamine…”
9.6 Chemical Reactions – “…Moreover, amines behave as nucleophiles due to the presence of unshared electron pair.”
Summary – “Tertiary amines like trimethylamine are used as insect attractants.”