Question

The increasing order of pK_b values of the following compounds is:

• A. $\mathrm{I}<\mathrm{II}<\mathrm{III}$$<\mathrm{IV}$
• B. $\mathrm{II}<\mathrm{IV}<\mathrm{III}<\mathrm{I}$
• C. $\mathrm{I}<\mathrm{II}<\mathrm{IV}<\mathrm{III}$
• D. $\mathrm{II}<\mathrm{I}<\mathrm{III}<\mathrm{IV}$

Answer 1

The correct option is C

$\mathrm{I}<\mathrm{II}<\mathrm{IV}<\mathrm{III}$

The correct options are (c)

The Explanation for the correct options:

(c)

• Explanation: Finding the compound with the highest basic strength is the first step because it will have the highest ${\mathrm{K}}_{\mathrm{b}}$ value and lowest ${\mathrm{pK}}_{\mathrm{b}}$ and, and vice versa. Solve it now.
• Knowing a compound's fundamental strength will help us determine which compound has the highest value of pK_b. The compound with the highest basic strength will also have the highest $\mathrm{k}$ value, and vice versa, resulting in the lowest value of ${\mathrm{pK}}_{\mathrm{b}}$.
• Therefore, the person with the lowest basic strength will also have the lowest value of ${\mathrm{pK}}_{\mathrm{b}}$ and a larger value of ${\mathrm{K}}_{\mathrm{b}}$.
  1. The quantity of electron-donating groups present in the chemical itself determines its fundamental strength.
  2. The electron pairs or single electrons of the group that is donating should not be in conjugation or resonance.
  Now, taking into account the claim;
• Diagram:

The Explanation for the incorrect options:

(a)

• Explanation: Intermolecular hydrogen bonds exist in all of the compounds listed. Despite the fact that there are two ${\mathrm{NH}}_2$groups, the nitrogen atoms' lone pairs are conjugated. Therefore, it loses basic strength and has a lower ${\mathrm{K}}_{\mathrm{b}}$ value.
• The molecular weight ${\mathrm{CH}}_3$is lower than that of $\mathrm{N}{\left({\mathrm{CH}}_2\right)}_3$. $\mathrm{NHCH}$ has a lower concentration than${\mathrm{NH}}_2$, and ${\mathrm{NH}}_2$ has a lower concentration than$\mathrm{OH}$.

(b)

• Explanation: It has the highest basic strength of all and the highest $\mathrm{kb}$value because it contains three electron-donating nitrogen groups with lone electrons that are neither in conjugation nor in resonance with one another.
• The molecular weight ${\mathrm{OCH}}_3$is lower than that of$\mathrm{N}{\left({\mathrm{CH}}_2\right)}_3$. ${\mathrm{CH}}_3$has a lower density than$\mathrm{N}$, and $\mathrm{N}$ has a lower density than${\mathrm{NH}}_2$.

(d)

• Explanation: There is only one ${\mathrm{NH}}_2\mathrm{CH}$ group, but the nitrogen atom's single pair is conjugated. Therefore, it loses fundamental strength, which contains two groups.
• ${\mathrm{NHCH}}_3$molecular weight is lower than that of $\mathrm{OH}$. The density ${\mathrm{CH}}_3$is lower than that of $\mathrm{N}$, and the density of is lower than that of$\mathrm{OH}$.
• $\mathrm{OH}$ has the strongest hydrogen bonding because the $\mathrm{O}$is more electron negative than the $\mathrm{CN}$ other compounds.

Hence, the correct option is C