Arrange the following: (i) In decreasing order of the pKb values: C₂H₅NH₂, C₆H₅NHCH₃, (C₂H₅)₂NH and C₆H₅NH₂ (ii) In increasing order of basic strength: C₆H₅NH₂, C₆H₅N(CH₃)₂, (C₂H₅)₂NH and CH₃NH₂ (iii) In increasing order of basic strength: (a) Aniline, p-nitroaniline and p-toluidine (b) C₆H₅NH₂, C₆H₅NHCH₃, C₆H₅CH₂NH₂. (iv) In decreasing order of basic strength in gas phase: C₂H₅NH₂, (C₂H₅)₂NH, (C₂H₅)₃N and NH₃ (v) In increasing order of boiling point: C₂H₅OH, (CH₃)₂NH, C₂H₅NH₂ (vi) In increasing order of solubility in water: C₆H₅NH₂, (C₂H₅)₂NH, C₂H₅NH₂.
C₆H₅NH₂ > C₆H₅NHCH₃ > C₂H₅NH₂ > (C₂H₅)₂NH
C₆H₅NH₂ < C₆H₅N(CH₃)₂ < CH₃NH₂ < (C₂H₅)₂NH
(a) p-nitroaniline < Aniline < p-toluidine (b) C₆H₅NH₂ < C₆H₅NHCH₃ < C₆H₅CH₂NH₂
(C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃
(CH₃)₂NH < C₂H₅NH₂ < C₂H₅OH
C₆H₅NH₂ < (C₂H₅)₂NH < C₂H₅NH₂
Explanation
This question tests understanding of factors affecting basic strength, pKb values, boiling points, and solubility of amines. The key concepts involve: (1) Arylamines are weaker bases than alkylamines due to resonance stabilization where the lone pair on nitrogen conjugates with the benzene ring, making it less available for protonation. (2) In gas phase, basic strength follows the order: R₂NH > R₃N > RNH₂ > NH₃ due to inductive effect and steric factors without solvation. (3) Boiling points depend on hydrogen bonding capability - O-H bonds form stronger H-bonds than N-H bonds. (4) Solubility depends on H-bonding with water - primary amines are more soluble than secondary, and alkylamines are more soluble than arylamines.