Question:
Which of the following amine has the highest \(pK_b\) value in aqueous phase?
Which of the following amine has the highest \(pK_b\) value in aqueous phase?
Show Hint
Mnemonic: High \(pK_b\) = Poor Base. Aniline (Benzenamine) is always a poor base compared to alkyl amines because its electrons are "busy" dancing in the benzene ring (resonance).
Updated On: Jun 24, 2026
- Methanamine
- N-methylmethanamine
- Ethanamine
- N-Methylbenzenamine
- Benzenamine
Show Solution
Verified By Collegedunia
The Correct Option is
Solution and Explanation
Step 1: Understanding the Concept:
Basicity of amines is measured by the base dissociation constant \(K_b\). A higher \(pK_b\) value indicates a weaker base.
Basicity in aqueous phase is influenced by the inductive effect, solvation effect (hydration), and steric hindrance.
Step 2: Detailed Explanation:
1. Aliphatic amines (Methanamine, Ethanamine) are significantly more basic than aromatic amines because alkyl groups are electron-releasing (\(+I\) effect).
2. Aromatic Amines (Benzenamine/Aniline): The lone pair of electrons on the nitrogen atom is involved in resonance with the benzene ring. This makes the lone pair less available for protonation.
3. Therefore, aromatic amines are very weak bases.
4. Between Benzenamine (\(1^\circ\) aromatic) and N-methylbenzenamine (\(2^\circ\) aromatic), the latter is slightly more basic due to the \(+I\) effect of the methyl group.
5. Thus, Benzenamine is the weakest base in the list and has the highest \(pK_b\).
Step 3: Final Answer:
Benzenamine has the highest \(pK_b\) value.
Basicity of amines is measured by the base dissociation constant \(K_b\). A higher \(pK_b\) value indicates a weaker base.
Basicity in aqueous phase is influenced by the inductive effect, solvation effect (hydration), and steric hindrance.
Step 2: Detailed Explanation:
1. Aliphatic amines (Methanamine, Ethanamine) are significantly more basic than aromatic amines because alkyl groups are electron-releasing (\(+I\) effect).
2. Aromatic Amines (Benzenamine/Aniline): The lone pair of electrons on the nitrogen atom is involved in resonance with the benzene ring. This makes the lone pair less available for protonation.
3. Therefore, aromatic amines are very weak bases.
4. Between Benzenamine (\(1^\circ\) aromatic) and N-methylbenzenamine (\(2^\circ\) aromatic), the latter is slightly more basic due to the \(+I\) effect of the methyl group.
5. Thus, Benzenamine is the weakest base in the list and has the highest \(pK_b\).
Step 3: Final Answer:
Benzenamine has the highest \(pK_b\) value.
Was this answer helpful?
0
0
Top KEAM Chemistry Questions
- The pH of a solution obtained by mixing 60 mL of 0.1 M BaOH solution at 40m of 0.15m HCI solution is
- $4\, g$ of copper was dissolved in concentrated nitric acid. The copper nitrate solution on strong heating gave $5\, g$ of its oxide. The equivalent weight of copper is :
- Green chemistry deals with
- Neopentyl bromide undergoes dehydrohalogenation to give alkenes even though it has no $\beta$- hydrogen. This is due to
- Plot of $ log\text{ }x/m $ against log $p$ is a straight line inclined at an angle of $ 45{}^\circ $ . When the pressure is $ 0.5 \,arm $ and Freundlich parameter. $ k $ is $ 10 $ , the amount of solute adsorbed per gram of adsorbent will be $ (log\text{ }5=0.6990) $
View More Questions
Top KEAM Amines Questions
- In the Hofmann rearrangement of primary amides having optically active group with S-configuration, the product amine has
- The product formed in the below reaction is
- Which one of the following reagent will convert acetamide to ethanamine?
- Which one of the following isomeric amines has the highest boiling point?
- Which of the following compounds is most basic?
View More Questions
Top KEAM Questions
- i.$\quad$ They help in respiration ii.$\quad$ They help in cell wall formation iii.$\quad$ They help in DNA replication iv. $\quad$They increase surface area of plasma membrane Which of the following prokaryotic structures has all the above roles?
- A body oscillates with SHM according to the equation (in SI units), $x = 5 cos \left(2\pi t +\frac{\pi}{4}\right) .$ Its instantaneous displacement at $t = 1$ second is
- The pH of a solution obtained by mixing 60 mL of 0.1 M BaOH solution at 40m of 0.15m HCI solution is
Kepler's second law (law of areas) of planetary motion leads to law of conservation of
- If $\int e^{2x}f' \left(x\right)dx =g \left(x\right)$, then $ \int\left(e^{2x}f\left(x\right) + e^{2x} f' \left(x\right)\right)dx =$
View More Questions