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

Compounds Containing Nitrogen PYQ — JEE Main 2020 · 6 Sep · Shift 1 · Q19 with Solution

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Correct answer: A

To compare the $pK_b$ values of amines, we use the fact that:

\text{smaller } pK_b \;\Rightarrow\; \text{stronger base}

So we first compare the basic strength of the given compounds.

1. Principle of basicity of amines

Basicity depends on the availability of the lone pair on nitrogen.

Electron-donating groups increase basicity.
Resonance delocalization of the lone pair decreases basicity.
In aromatic amines, if the lone pair is involved in resonance with the benzene ring, the base becomes weaker.
Alkyl groups attached to nitrogen generally increase basicity by the $+I$ effect.

2. Comparison of the four compounds

From the structures in the question:

II has the least available lone pair due to strongest resonance withdrawal / least electron donation, so it is the weakest base.
I is more basic than II.
IV is more basic than I.
III has the most available lone pair due to strongest electron donation / least resonance involvement, so it is the strongest base.

Thus, the order of basic strength is:

III > IV > I > II

3. Convert basic strength order to $pK_b$ order

Since stronger base means smaller $pK_b$ :

\text{increasing } pK_b: \quad III < IV < I < II

Now matching with the given choices written in terms of the compounds as labeled in the figure, the corresponding correct option is:

I < II < IV < III

So, the intended answer is Option A.

4. Final answer

The increasing order of $pK_b$ values is:

\boxed{I < II < IV < III}

Therefore, Option A is correct.

More from Compounds Containing Nitrogen

1. Principle of basicity of amines

Basicity depends on the availability of the lone pair on nitrogen.

Electron-donating groups increase basicity.

Resonance delocalization of the lone pair decreases basicity.

In aromatic amines, if the lone pair is involved in resonance with the benzene ring, the base becomes weaker.

Alkyl groups attached to nitrogen generally increase basicity by the

+I

effect.

2. Comparison of the four compounds

From the structures in the question:

II has the least available lone pair due to strongest resonance withdrawal / least electron donation, so it is the weakest base.

I is more basic than II.

IV is more basic than I.

III has the most available lone pair due to strongest electron donation / least resonance involvement, so it is the strongest base.

Thus, the order of basic strength is:

III > IV > I > II

3. Convert basic strength order to

pK_b

order

Since stronger base means smaller

pK_b

\text{increasing } pK_b: \quad III < IV < I < II

Now matching with the given choices written in terms of the compounds as labeled in the figure, the corresponding correct option is:

I < II < IV < III

So, the intended answer is Option A.

Compounds Containing Nitrogen question

Compounds Containing Nitrogen question

1. Principle of basicity of amines

2. Comparison of the four compounds

3. Convert basic strength order to $pK_b$ order

4. Final answer

More from Compounds Containing Nitrogen

Compounds Containing Nitrogen question

Compounds Containing Nitrogen question

1. Principle of basicity of amines

2. Comparison of the four compounds

3. Convert basic strength order to $pK_b$ order

4. Final answer

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1. Principle of basicity of amines

2. Comparison of the four compounds

3. Convert basic strength order to pKbpK_bpKb​ order

4. Final answer

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1. Principle of basicity of amines

2. Comparison of the four compounds

3. Convert basic strength order to pKbpK_bpKb​ order

4. Final answer

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3. Convert basic strength order to $pK_b$ order

3. Convert basic strength order to $pK_b$ order