Question

Rank each set of compounds in order of increasing basicity

(a) NaOH, NH₃, CH₃NH₂, Ph-NH₂

(b) aniline, p-methylaniline, p-nitroaniline

(c) aniline, pyrrole, pyridine, piperidine

(d) pyrrole, imidazole, 3-nitropyrrole

Short answer

(a)

Basicity (pK_b) of NaOH is 0.2

Basicity (pK_b) of NH₃ is 4.74

Basicity (pK_b) of CH₃NH₂ is 3.38

Basicity (pK_b) of Ph-NH₂ is 9.38

Order of increasing basicity = Ph-NH₂ < NH₃ <CH₃NH₂ < NaOH

(b)

Basicity (pK_b) of aniline is 9.38

Basicity (pK_b) of p-methylaniline is 9.21

Basicity (pK_b) of p-nitroaniline is 12.99

Order of increasing basicity = p-nitroaniline< aniline < p-nitroaniline

(c)

Basicity (pK_b) of aniline is 9.38

Basicity (pK_b) of pyrrole is 13.6

Basicity (pK_b) of pyridine is 8.77

Basicity (pK_b) of piperidine is 4

Order of increasing basicity = pyrrole < aniline < pyridine < piperidine

(d)

Basicity (pK_b) of pyrrole is 13.6

Basicity (pK_b) of imidazole is 7.0

3-nitropyrrole is formed by adding nitric acid to pyrrole i.e. nitration of pyrrole group.

Therefore it is less basic than pyrrole.

Order of increasing basicity = 3-nitopyrrole< pyrrole < imidazole

Step-by-step solution

Concept

pKb is the negative base -10 loh of the base dissociation constant (Kb) of the solution, which is used to determine the strength of base. Lower pkb value indicates a stronger base.

(a) NaOH, NH3, CH3NH2, Ph-NH2:

Basicity (pK_b) of NaOH is 0.2

Basicity (pK_b) of NH₃ is 4.74

Basicity (pK_b) of CH₃NH₂ is 3.38

Basicity (pK_b) of Ph-NH₂ is 9.38

Order of increasing basicity = Ph-NH₂ < NH₃ <CH₃NH₂ < NaOH

(b)  aniline, p-methylaniline, p-nitroaniline

Basicity (pK_b) of aniline is 9.38

Basicity (pK_b) of p-methylaniline is 9.21

Basicity (pK_b) of p-nitroaniline is 12.99

Order of increasing basicity = p-nitroaniline< aniline < p-nitroaniline

(c) aniline, pyrrole, pyridine, piperidine

Basicity (pK_b) of aniline is 9.38

Basicity (pK_b) of pyrrole is 13.6

Basicity (pK_b) of pyridine is 8.77

Basicity (pK_b) of piperidine is 4

Order of increasing basicity = pyrrole < aniline < pyridine < piperidine

(d) pyrrole, imidazole, 3-nitropyrrole

Basicity (pK_b) of pyrrole is 13.6

Basicity (pK_b) of imidazole is 7.0

3-nitropyrrole is formed by adding nitric acid to pyrrole i.e. nitration of pyrrole group.

Therefore it is less basic than pyrrole.

Order of increasing basicity = 3-nitopyrrole< pyrrole < imidazole