NEET2026ChemistryChapterActual
Arrange the following compounds in the increasing order of their pK_b values in aqueous medium: (I) C₆H₅NH₂ (II) NH₃ (III) (C₂H₅)₂NH (IV) (C₂H₅)₃N
Options
- A(I) < (II) < (IV) < (III)
- B(IV) < (III) < (II) < (I)
- C(III) < (IV) < (II) < (I)
- D(III) < (IV) < (I) < (II)
Correct answer
C. (III) < (IV) < (II) < (I)
Step-by-step solution
The basic strength of amines in aqueous medium depends on the combined effect of the +I effect of alkyl groups, steric hindrance, and the hydration effect. For ethylamines, the order of basic strength is 2^ > 3^ > 1^ > NH₃ . Thus, (C₂H₅)₂NH > (C₂H₅)₃N > NH₃ . Aniline ( C₆H₅NH₂ ) is a weaker base than ammonia because the lone pair of electrons on the nitrogen atom is delocalized over the benzene ring due to resonance. The overall decreasing order of basic strength is (C₂H₅)₂NH > (C₂H₅)₃N > NH₃ > C₆H₅NH₂ , which corr