What will be the increasing order of basic strength of the following compounds: \(\text{C}_2\text{H}_5\text{NH}_2, (\text{C}_2\text{H}_5)_2\text{NH},(\text{C}_2\text{H}_5)_3\text{N},\text{C}_6\text{H}_5\text{NH}_2\)
- \(\text{C}_2\text{H}_5\text{NH}_2 < (\text{C}_2\text{H}_5)_2\text{NH} < (\text{C}_2\text{H}_5)_3\text{N} < \text{C}_6\text{H}_5\text{NH}_2\)
- \(\text{C}_6\text{H}_5\text{NH}_2 < \text{C}_2\text{H}_5\text{NH}_2 < (\text{C}_2\text{H}_5)_3\text{N} < (\text{C}_2\text{H}_5)_2\text{NH}\)
- \((\text{C}_2\text{H}_5)_3\text{N} < (\text{C}_2\text{H}_5)_2\text{NH} < \text{C}_6\text{H}_5\text{NH}_2 < \text{C}_2\text{H}_5\text{NH}_2\)
- \((\text{C}_2\text{H}_5)_2\text{NH} < (\text{C}_2\text{H}_5)_3\text{N} < \text{C}_2\text{H}_5\text{NH}_2 < \text{C}_6\text{H}_5\text{NH}_2\)
The Correct Option is B
Solution and Explanation
To determine the increasing order of basic strength, we need to consider the factors that affect the basicity of amines:
- Aliphatic vs. Aromatic Amines: Aliphatic amines (like C2H5NH2, (C2H5)2NH, (C2H5)3N) are generally more basic than aromatic amines (like C6H5NH2). This is because in aromatic amines, the lone pair of electrons on the nitrogen is delocalized into the benzene ring, making it less available for protonation.
- Alkyl Groups: Alkyl groups are electron-donating, which increases the electron density on the nitrogen atom, making it more basic.
- Steric Hindrance: In tertiary amines, the bulky alkyl groups can hinder the approach of a proton, reducing basicity.
- Solvation Effects: In aqueous solutions, solvation of the protonated amine plays a significant role. Secondary amines are generally more solvated than tertiary amines.
Let's analyze the given compounds:
C2H5NH2 (Ethylamine): A primary aliphatic amine.
(C2H5)2NH (Diethylamine): A secondary aliphatic amine.
(C2H5)3N (Triethylamine): A tertiary aliphatic amine.
C6H5NH2 (Aniline): An aromatic amine.
Based on these factors:
Aniline (C6H5NH2) is the least basic due to resonance delocalization.
Among the aliphatic amines, secondary amines are generally the most basic due to a combination of inductive and solvation effects.
Primary amines are less basic than secondary amines but more basic than tertiary amines due to steric hindrance in tertiary amines.
Therefore, the increasing order of basic strength is:
C6H5NH2 < C2H5NH2 < (C2H5)3N < (C2H5)2NH
The correct answer is:
Option 2: C6H5NH2 < C2H5NH2 < (C2H5)3N < (C2H5)2NH
Top Questions on Amines
- Identify correct statements: (A) Primary amines do not give diazonium salts when treated with \({NaNO}_2\) in acidic condition.
(B) Aliphatic and aromatic primary amines on heating with \({CHCl}_3\) and ethanolic \({KOH}\) form carbylamines.
(C) Secondary and tertiary amines also give carbylamine test.
(D) Benzenesulfonyl chloride is known as Hinsberg’s reagent.
(E) Tertiary amines react with benzenesulfonyl chloride very easily.
Choose the correct answer from the options given below: Amines have a lone pair of electrons on the nitrogen atom, due to which they behave as Lewis bases. Greater the value of \( K_b \) or smaller the value of \( pK_b \), stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. However, it does not occur in a regular manner, as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron-releasing groups such as \( -CH_3 \), \( -NH_2 \), etc., increase the basicity, while electron-withdrawing substituents such as \( -NO_2 \), \( -CN \), halogens, etc., decrease the basicity of amines. The effect of these substituents is more pronounced at the para-position than at the meta-position.
(a) Arrange the following in increasing order of their basic character. Give reason:
\[ \includegraphics[width=0.5\linewidth]{ch29i.png} \]- Amines have a lone pair of electrons on nitrogen atom due to which they behave as Lewis base. Greater the value of \( K_b \) or smaller the value of \( pK_b \), stronger is the base. Amines are more basic than alcohols, ethers, esters, etc. The basic character of aliphatic amines should increase with the increase of alkyl substitution. But it does not occur in a regular manner as a secondary aliphatic amine is unexpectedly more basic than a tertiary amine in aqueous solutions. Aromatic amines are weaker bases than ammonia and aliphatic amines. Electron releasing groups such as \(–CH_3\), \(–NH_2\), etc., increase the basicity while electron-withdrawing substituents such as \(–NO_2\), –CN, halogens, etc., decrease the basicity of amines. The effect of these substituents is more at the p₊ than at m₋ position.
- Assertion (A): Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis. Reason (R): Aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide.
- Give plausible explanation for each of the following:
Amides are less basic than amines.
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