The reaction of amines with mineral acids to form ammonium salt shows that these are basic in nature. Amines have an unshared pair of electron on nitrogen atom due to which they behave as lewis base. Basicity of amines is related to their structure. Basic character of an amine depends upon the ease of formation of cation by accepting a proton from the acid. The more stable the cation is relative to the amine. more basic is the amine.
Structure of anunoniuin salt when ethylamine reacts with one mole of HCl?
- \(C_2H_5 - NH_3^+ Cl^-\)
- \((C_2H_5)_2 - NH_2^+Cl^-\)
- \((C_2H_5)_3 - NH^+Cl^-\)
- \((C_2H_5)_4 - N^+Cl^-\)
The Correct Option is A
Solution and Explanation
In this reaction, ethylamine \((C_2H_5NH_2)\) acts as a base and accepts a proton (H+) from HCl to form an ammonium ion \((C_2H_5NH_3^+)\).
The chloride ion (Cl-) is the counterion in the salt. Therefore, the correct structure of the ammonium salt formed is \(C_2H_5^-NH_3^+Cl^-\).
Among the following amines, which one is most basic (in aqueous solution)?
- \(NH_3\)
- \(C_2H_5NH_2\)
- \((C_2H_5)_2NH\)
- \((C_2H_5)_3N\)
The Correct Option is A
Solution and Explanation
Ammonia \(NH_3\) has a lone pair of electrons on the nitrogen atom, which can easily accept a proton \((H^+)\) from water to form the ammonium ion \((NH_4^+)\). This protonation reaction makes \(NH_3\) a strong base in aqueous solution.
In comparison, the alkylamines such as \(C_2H_5NH_2\) (ethylamine), \((C_2H_5)_2NH\) (diethylamine), and \((C_2H_5)_3N\) (triethylamine) also have lone pairs of electrons on the nitrogen atoms, but the presence of alkyl groups decreases the basicity compared to NH3. The alkyl groups in these amines can donate electron density towards the nitrogen atom, reducing its ability to accept a proton and decreasing their basicity relative to NH3.
Therefore, among the given options, \(NH_3\) (ammonia) is the most basic amine in aqueous solution.
The correct order of basicity of amines in gas phase.
- \(1°<3°<2°\)
- \(3°<1°<2°\)
- \(2°<3°<1°\)
- \(1°<2°<3°\)
The Correct Option is D
Solution and Explanation
The correct order of basicity of amines in the gas phase is:
\(1° < 2° < 3°\)
In general, the basicity of amines increases with the degree of substitution of the nitrogen atom. Primary amines \((1°)\) have one alkyl group attached to the nitrogen, secondary amines \((2°)\) have two alkyl groups, and tertiary amines \((3°)\) have three alkyl groups.
The presence of alkyl groups in amines can donate electron density towards the nitrogen atom, making it less available to accept a proton. As a result, primary amines, having the least steric hindrance and the most accessible nitrogen lone pair, are generally more basic than secondary and tertiary amines.
Therefore, the correct order of basicity in the gas phase is \(1° < 2° < 3°\).
Among the following, which one has the highest \(pK_b\) value?
- \(C_2H_5NH_2\)
- \(C_6H_5NHCH_3\)
- \((C_2H_5)_2NH\)
- \(C_6H_5NH_2\)
The Correct Option is A
Solution and Explanation
To determine which amine has the highest \(pK_b\) value, we need to compare their basicities. The higher the \(pK_b\) value, the weaker the base and the lower the basicity.
In general, the basicity of amines is influenced by various factors including electron-donating groups, steric hindrance, and resonance effects.
Among the given options:
\(C_2H_5NH_2\) (ethylamine) is a primary amine.
\(C_6H_5NHCH_3\) (methylbenzylamine) is a secondary amine.
\((C_2H_5)_2NH\) (diethylamine) is a secondary amine.
\(C_6H_5NH_2\) (aniline) is a primary amine.
In terms of basicity, primary amines are generally more basic than secondary amines. Additionally, electron-donating alkyl groups can increase basicity.
Based on this information, we can conclude that \(C_2H_5NH_2\) (ethylamine) has the highest \(pK_b\) value among the given options.
Among the following, which one has the highest \(K_b\) value?
- \(C_2H_5NH_2\)
- \(C_6H_5N(CH_3)_2\)
- \((C_2H_5)_2NH\)
- \(CH_3NH_2\)
The Correct Option is D
Solution and Explanation
Among the given options:
\(C_2H_5NH_2\) (ethylamine) is a primary amine.
\(C_6H_5N(CH_3)_2\) (dimethylbenzylamine) is a secondary amine.
\((C_2H_5)_2NH\) (diethylamine) is a secondary amine.
\(CH_3NH_2\) (methylamine) is a primary amine.
In general, primary amines are more basic than secondary amines.
Additionally, electron-donating alkyl groups can increase basicity.
Based on this information, we can conclude that \(CH_3NH_2\) (methylamine) is expected to have the highest \(K_b\) value among the given options.
Top Questions on Amines
- Give plausible explanation for the following: (a) Diazonium salts of aromatic amines are stable.
(b) Aniline does not undergo Friedel–Crafts reaction.
(c) Aniline on nitration gives a substantial amount of meta product. - Assertion (A): Acetamide (structure: \(\text{C}_6\text{H}_5\text{NHCOCH}_3\)) is less basic than aniline.
Reason (R): Acetylation of aniline results in decrease of electron density on nitrogen. - The chemical test which can be used to distinguish between ethanamine and aniline is:
- If amines are arranged in increasing order of their basic strength in gaseous phase, the correct order will be:
Which of the following amines does not give foul smell of isocyanide on heating with chloroform and ethanolic KOH ?
