Question:
Which from following amines has lowest \(\mathrm{pK}_b\) value?
Which from following amines has lowest \(\mathrm{pK}_b\) value?
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Lowest pKb means the strongest base, so compare basic strength of these amines.
Updated On: Nov 13, 2026
- \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{NH}_{2}\)
- \((\mathrm{CH}_{3})_{3}\text{ }\mathrm{N}\)
- \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NH}_{2}\)
- \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{NH}_{2}\)
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept
A lower \(\text{p}K_b\) value means a higher \(K_b\), that is a stronger base.
Step 2: Compare basic strength
Aliphatic amines are stronger bases than aromatic amines because the aniline lone pair is delocalised into the ring.
In aqueous solution, ethylamine (\(\text{p}K_b \approx 3.3\)) is stronger than trimethylamine (\(\approx 4.2\)) because of better solvation and less steric hindrance.
Benzylamine has \(\text{p}K_b \approx 4.7\) and aniline about 9.4.
Step 3: Conclude
Ethylamine has the lowest \(\text{p}K_b\).
Final Answer:
Ethylamine has the lowest pKb. \[ \boxed{\text{(A) }\text{C}_2\text{H}_5\text{NH}_2} \]
A lower \(\text{p}K_b\) value means a higher \(K_b\), that is a stronger base.
Step 2: Compare basic strength
Aliphatic amines are stronger bases than aromatic amines because the aniline lone pair is delocalised into the ring.
In aqueous solution, ethylamine (\(\text{p}K_b \approx 3.3\)) is stronger than trimethylamine (\(\approx 4.2\)) because of better solvation and less steric hindrance.
Benzylamine has \(\text{p}K_b \approx 4.7\) and aniline about 9.4.
Step 3: Conclude
Ethylamine has the lowest \(\text{p}K_b\).
Final Answer:
Ethylamine has the lowest pKb. \[ \boxed{\text{(A) }\text{C}_2\text{H}_5\text{NH}_2} \]
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