Question

Which among the following amines is most basic in aqueous medium?

• A. $(C_2H_5)_2NH$
• B. $(C_2H_5)_3N$
• C. $C_2H_5NH_2$
• D. $NH_3$
• A. \((CH_3)_2NH\)
• B. \(CH_3NH_2\)
• C. \((CH_3)_3N\)
• D. \(NH_3\)
• A. \((CH_3)_2NH\)
• B. \(H_3NH_2\)
• C. \((CH_3)_3N\)
• D. \(NH_3\)
• A. Conjugation factor
• B. Inductive effect
• C. Solvation effect
• D. Steric hindrance
• A. 2,4-dinitrophenol
• B. NaNO₂ + HCl mixture
• C. HNO₃ + H₂SO₄ mixture
• D. Benzenesulphonyl chloride

Answer 1

The Correct Option is C

Amines exhibit basicity due to the presence of a lone pair of electrons on the nitrogen atom, which can accept protons (H⁺). The basicity of an amine in an aqueous medium is influenced by several factors, including the inductive effect from alkyl groups, solvation effects, and steric hindrance.

Let's analyze each given amine: 

• $(C_2H_5)_2NH$ (Diethylamine): This is a secondary amine. It has two ethyl groups that can provide an inductive effect, enhancing basicity. However, increased steric hindrance reduces the effectiveness of solvation by water.
• $(C_2H_5)_3N$ (Triethylamine): This is a tertiary amine with three ethyl groups. The inductive effect is strong, but the steric hindrance is significant, greatly reducing solvation and thus basicity.
• $C_2H_5NH_2$ (Ethylamine): This is a primary amine. It has one ethyl group providing some inductive effect, but solvation is better compared to secondary and tertiary amines due to minimal steric hindrance.
• $NH_3$ (Ammonia): No alkyl group is present, leading to low inductive effect, but excellent solvation due to its small size.

Considering these factors, in aqueous solution, $C_2H_5NH_2$ (Ethylamine) is more basic compared to the other options. Ethylamine strikes a balance between having sufficient inductive effect from an alkyl group and allowing effective solvation without too much steric hindrance.

Answer 2

In aqueous medium, the basicity of amines is influenced by several factors, including steric hindrance and the ability to stabilize the positive charge on the ammonium ion formed upon protonation. The relative basicity of various amines can be explained as follows:

• Primary amine (C₂H₅NH₂): Has two hydrogen atoms available for bonding, allowing for effective solvation and stabilization when protonated. This leads to a higher basicity in aqueous medium.
• Secondary amine ((C₂H₅)₂NH): Has some steric hindrance due to the two ethyl groups, but it remains relatively basic due to its ability to accept protons.
• Tertiary amine ((C₂H₅)₃N): Although it can stabilize a positive charge well, steric hindrance prevents effective interaction with protons in aqueous solution, making it less basic compared to primary and secondary amines.
• Ammonia (NH₃): Less basic than primary amines due to the lack of alkyl groups, which provide electron-donating effects that enhance basicity.

Thus, in aqueous medium, the most basic amine is the primary amine, C₂H₅NH₂. The presence of alkyl groups in primary amines allows for better solvation and protonation, enhancing their basicity.

Answer 3

To determine the least basic amine among the options provided, we analyze the effects of alkyl groups on basicity in aqueous medium: 

• Methylamine (CH₃NH₂) : A primary amine that is relatively basic due to less steric hindrance and effective solvation.
• Dimethylamine ((CH₃)₂NH) : A secondary amine that is basic, but steric hindrance starts to affect its basicity.
• Trimethylamine ((CH₃)₃N) : A tertiary amine where steric hindrance is significant, leading to reduced basicity compared to primary and secondary amines.
• Ammonia (NH3) : Though not an amine with alkyl groups, it serves as a reference for basicity.

In conclusion, trimethylamine ((CH₃)₃N) is the least basic in aqueous medium due to significant steric hindrance, which limits effective solvation and protonation.

Answer 4

To determine the least basic amine among the options provided, we analyze the effects of alkyl groups on basicity in aqueous medium:

• Methylamine (CH₃NH₂): A primary amine that is relatively basic due to less steric hindrance and effective solvation, allowing for better protonation.
• Dimethylamine ((CH₃)₂NH): A secondary amine where basicity is still strong, but steric hindrance from the two methyl groups begins to affect its reactivity.
• Trimethylamine ((CH₃)₃N): A tertiary amine where steric hindrance is significant, leading to reduced basicity compared to primary and secondary amines. This makes it less effective in interacting with protons in aqueous medium.
• Ammonia (NH₃): Not an amine with alkyl groups, but it serves as a reference for basicity. Its basicity is lower than primary amines due to the lack of alkyl groups that would stabilize the protonated form.

Conclusion: In aqueous medium, trimethylamine ((CH₃)₃N) is the least basic due to significant steric hindrance, which limits effective solvation and protonation.

Answer 5

In the gaseous phase, the basicity of amines is primarily determined by the availability of the lone pair of electrons on the nitrogen atom, without much influence from the solvation effects or steric hindrance as in the aqueous phase. The options given are:

• Dimethylamine: $(CH_3)_2NH$
• Methylamine: $CH_3NH_2$
• Trimethylamine: $(CH_3)_3N$
• Ammonia: $NH_3$

In the gaseous phase, the presence of alkyl groups enhances the electron density on the nitrogen atom through the +I inductive effect. More alkyl groups lead to increased electron availability, heightening basicity. Consequently, tertiary amines, with three electron-donating groups, often show greater basicity compared to secondary and primary amines. Among the options:

• Methylamine ($CH_3NH_2$) has one methyl group.
• Dimethylamine ($(CH_3)_2NH$) has two methyl groups.
• Trimethylamine ($(CH_3)_3N$) has three methyl groups.
• Ammonia ($NH_3$) has none.

Therefore, in the gaseous phase, trimethylamine ($(CH_3)_3N$) is the most basic due to the electron-donating effects of its three methyl groups, which maximize the availability of the lone pair on nitrogen.

Thus, the most basic amine in the gaseous medium is $(CH_3)_3N$.

Answer 6

In the gaseous phase, trimethylamine ((CH₃)₃N) is the most basic amine due to the strong electron-donating effect of the three methyl groups, which increase the electron density on the nitrogen atom. This makes the nitrogen more likely to donate electrons to a proton, enhancing its basicity.

Despite the presence of steric hindrance from the bulky methyl groups, which can prevent efficient protonation in some environments, trimethylamine still exhibits greater basicity compared to primary and secondary amines in the gaseous phase. This is because the electron-donating groups (methyl groups) play a more significant role in enhancing the nucleophilicity of the nitrogen atom.

In contrast, in aqueous solutions, steric hindrance becomes a more prominent factor, reducing the ability of trimethylamine to interact effectively with protons. As a result, its basicity decreases in comparison to primary amines, such as methylamine (CH₃NH₂).

Overall, while trimethylamine’s steric hindrance can limit its protonation in certain conditions, its strong electron-donating effect in the gaseous phase makes it the most basic amine in that environment.

Answer 7

The basic strength of amines in aqueous medium is influenced by factors such as: 

1. Inductive Effect: The electron-donating or withdrawing properties of alkyl groups impact the availability of the nitrogen's lone pair for protonation.
2. Solvation Effect: Better solvation with water molecules enhances basicity by stabilizing the protonated amine.
3. Steric Hindrance: Larger alkyl groups hinder proton access to the nitrogen, reducing basicity.
4. Conjugation Factor: This does not significantly affect the basic strength of amines, as conjugation involves pi bonds and does not influence protonation directly.

Thus, conjugation is not responsible for the basic strength of amines.

Answer 8

The basic strength of amines in aqueous medium is influenced by various factors, each contributing to the overall reactivity of the nitrogen atom in the amine group. These factors include:

1. Inductive Effect: The electron-donating or withdrawing properties of alkyl groups attached to the nitrogen atom significantly affect the availability of the nitrogen's lone pair for protonation. Alkyl groups, which are electron-donating, increase the electron density on nitrogen, enhancing its ability to accept protons and thus increasing basicity.
2. Solvation Effect: The interaction between the amine and water molecules plays a crucial role in determining its basicity. Better solvation of the protonated amine, where water molecules stabilize the positive charge on nitrogen, enhances basicity. More solvation allows for more effective protonation, making the amine more basic.
3. Steric Hindrance: The size of the alkyl groups attached to the nitrogen atom impacts the basicity of amines. Larger alkyl groups create steric hindrance, which prevents efficient protonation by obstructing the approach of protons to the nitrogen atom, thereby decreasing basicity.
4. Conjugation Factor: While conjugation with pi bonds (such as in aniline or other conjugated amines) can influence other chemical properties, it does not significantly affect the basic strength of amines. Conjugation typically involves interactions with p orbitals, which do not directly impact the nitrogen's ability to accept a proton, making it less relevant in determining basicity.

Thus, the conjugation effect does not contribute significantly to the basic strength of amines in aqueous medium, unlike inductive and solvation effects.

Answer 9

Hinsberg's reagent is a reagent commonly used in organic chemistry to separate primary, secondary, and tertiary amines. The correct answer for this question is Benzenesulphonyl chloride.

When benzenesulphonyl chloride reacts with an amine, the following observations can help distinguish the types of amines:

• Primary amines: Form a sulphonamide which is soluble in alkali. This occurs because the sulphonamide is formed through the reaction of the amine with the reagent, and this product is acidic enough to dissolve in aqueous NaOH.
• Secondary amines: Form a sulphonamide which is insoluble in alkali. This results in a precipitate that does not dissolve in NaOH due to the absence of an acidic hydrogen atom.
• Tertiary amines: Do not react with benzenesulphonyl chloride and thus are unchanged and remain in the reaction mixture.

This method effectively helps in distinguishing and separating the different classes of amines based on their chemical behavior with Hinsberg’s reagent, which is benzenesulphonyl chloride.

Answer 10

Hinsberg's reagent, which is benzenesulphonyl chloride (C₆H₅SO₂Cl), is a crucial chemical used to differentiate primary, secondary, and tertiary amines based on their distinct reactivity patterns. The reaction outcomes are as follows:

1. Primary Amines: When primary amines react with benzenesulphonyl chloride, they form soluble sulfonamides, which are characterized by their solubility in aqueous solutions. This is due to the ability of the amine group to effectively react and form a stable bond with the sulfonyl group.
2. Secondary Amines: Secondary amines can form soluble or insoluble sulfonamides depending on the conditions, such as the solvent used. The reaction is less straightforward compared to primary amines, and the solubility of the resulting product can vary.
3. Tertiary Amines: Tertiary amines do not react significantly with Hinsberg's reagent, as they lack the required hydrogen atom attached to the nitrogen for the reaction to proceed. As a result, no sulfonamide formation occurs in this case.

Thus, benzenesulphonyl chloride is an effective reagent for distinguishing primary, secondary, and tertiary amines based on the solubility and nature of the products formed.