Amines - Amines, Their Structure, Classification, Basicity, Uses, Practice Problems and FAQs

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Table of Contents:

Amines
Structure of Amine
Classification of Amines
IUPAC Nomenclature of Amines
Basicity of Amines
Daily Life uses of Amine
Practice Problems
Frequently Asked Questions

Amines:

An amine is often a functional group with a nitrogen atom that has a lone pair. Because nitrogen can form bonds with up to three hydrogen atoms, amines functionally mimic ammonia. Additionally, it has a variety of properties dependent on carbon connection.

In essence, they are produced by replacing one or more hydrogen atoms in ammonia with an alkyl or aryl group, giving them the names alkylamines and arylamines, respectively.

Structure of Amine:

With a lone pair and 5 valence electrons, nitrogen is trivalent in nature in amines. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the hybridisation of nitrogen in amines is sp3, The structure should be tetrahedral in nature which is the typical shape for most sp3 hybridized compounds but it is pyramidal in shape.

Each of the three sp3 hybridized nitrogen orbitals overlap with an orbital of carbon or hydrogen. The C-N-H angle in amines is less than 109o due to the existence of a lone pair, which is an optimal angle of tetrahedral geometry. Amines have an angle of roughly 107o. The reason behind this angle can be explained on the basis of steric hindrance created by bulky lone pair present in amine.

Classification of Amines:

Amines can be categorized into 5 different groups based on how an ammonia molecule replaces the hydrogen atoms.

Primary Amine
Secondary Amine
Tertiary Amine
Quaternary Amine
Cyclic Amine

Primary Amine:

When one hydrogen of ammonia is replaced by an alkyl or aryl group, it is known as Primary Amine. Primary amine contains two hydrogen atoms directly bonded to Nitrogen.

Example: Aniline, Methylamine etc.

Secondary Amine:

When two hydrogen atoms of ammonia are replaced by an alkyl or aryl group, it is known as Secondary Amine. Secondary amine contains one hydrogen atom directly bonded to Nitrogen.

Example: diphenylamine, dimethylamine etc.

Tertiary Amine:

When all three hydrogen atoms of ammonia are replaced by an alkyl or aryl group, it is known as tertiary Amine. Tertiary amine contains no hydrogen atom directly bonded to Nitrogen.

Example: methyl diphenylamine, trimethylamine etc.

Quaternary Amine:

When all three hydrogen atoms of ammonia along with lone pair are replaced by an alkyl or aryl group, it is known as Quaternary Amine.

Example: Tetramethylammonium chloride etc.

Cyclic Amines:

When the ammonia group is present in the cyclic structure, it is known as Cyclic Amine.

Example : Piperidine, Pyrrolidine etc.

IUPAC Nomenclature of Amines:

They are alkyl derivatives of ammonia. These are formed by replacing one, two or all three hydrogen atoms in ammonia with the alkyl group. They are also known as alkanamine. The name is derived by replacing e from an alkane with an addition of a suffix ‘amine’.

Amine	IUPAC Name
NH₂CH₃	Methanamine
NH₂CH₂CH₃	Ethanamine
NH(CH₃)₂	N-methylmethanamine
N(CH₃)₃	N, N-dimethylmethanamine

Basicity of Amines:

Primary and secondary amines both exhibit some acidity because they share protic hydrogens with ammonia. In contrast, tertiary amines lack protic hydrogen and do not have any acidity.

The amine molecule in an aqueous solution is extremely alkaline.

The basicity of amine depends on three factors in general and they are as follows:

Inductive Effect - More the alkyl groups, more is the inductive effect, more is the basicity of amine.

So, the order of basicity of amine is NH2R<NH(R)2<N(R)3

Steric Hindrance - More the alkyl groups, the more is the steric hindrance of an alkyl group, less is the basicity of amine.

So, the order of basicity of amine is NH2R>NH(R)2>N(R)3

Solubility - More the number of hydrogen atoms directly attached to nitrogen, more is the solubility of alkyl group, more is the basicity of amine.

So, the order of basicity of amine is N(R)3<NH(R)2<NH2R

The overall basicity of amine is when R group is methyl is: NH3<N(CH3)3<NH2CH3<NH(CH3)2

The overall basicity of amine is when R group is ethyl is: NH3<NH2CH2CH3<N(CH2CH3)3<NH(CH2CH3)2

Daily Life uses of Amine:

Amines are used often in daily life. Here are some examples of amine uses:

It is employed in the production of drugs, the purification of drinking water, and the creation of herbicides and insecticides.
It has a role in the synthesis of amino acids, which are essential for the development of proteins in living things.
Amines can also be used to create a wide range of vitamins.
It regulates the sensation of hunger and is essential for the brain's general processing speed.
Amines are used to manufacture analgesics, which are medications that relieve pain. Morphine and Demerol are examples of analgesic medicines.

Practice Problems:

Q1. Which of the following given amine is secondary amine?

Answer : (D)

Solution: Secondary amine is formed when an alkyl or aryl group replaces two of the hydrogen atoms in ammonia. One hydrogen atom is directly linked to nitrogen in a secondary amine.

In option (A), there is no hydrogen attached directly to the nitrogen atom. Hence it is not a secondary amine. It is actually a tertiary amine.

In option (B), there are two hydrogens attached directly to the nitrogen atom. Hence it is also not a secondary amine. It is actually a primary amine.

In option (C), there is no hydrogen attached directly to the nitrogen atom. Hence it is not a secondary amine. The nitrogen is sp2 hybridized and hence can not be classified under primary, secondary and tertiary amine.

In option (D), there is one hydrogen attached directly to the nitrogen atom. Hence it is a secondary amine.

Hence, the correct answer is option (D).

Q2. Which of the following given amine is primary amine?

Answer : (D)

Solution: Primary amine is formed when an alkyl or aryl group replaces one of the hydrogen atoms in ammonia. Two hydrogen atoms are directly linked to nitrogen in a secondary amine.

In option (A) and (B), there is no hydrogen attached directly to the nitrogen atom. Hence these are not secondary amines. These are actually tertiary amines.

In option (C), there is one hydrogen attached directly to the nitrogen atom. Hence it is a secondary amine.

In option (D), there are two hydrogens attached directly to the nitrogen atom. Hence it is a primary amine.

Hence, the correct answer is option (D).

Q3. Which of the following compounds has IUPAC named N-ethyl-N-methylcyclopentanamine?

Answer : (C)

Solution: In option (A), The correct IUPAC name is 2-ethyl-1-methylcyclopentanamine as ethyl substituent is present at the 2nd position and methyl substituent is present at the Ist position.

In option (B), The correct IUPAC name is 1-ethyl-2-methylcyclopentanamine as ethyl substituent is present at the Ist position and methyl substituent is present at the 2nd position.

In option (C), The correct IUPAC name is N-ethyl-N-methylcyclopentanamine as ethyl substituent and methyl substituent are present at the Nitrogen.

In option (D), The correct IUPAC name is 2-ethyl-2-methylcyclopentanamine as both the substituents are present at the 2nd position.

Hence, the correct answer is option (C)

Q4. Which of the following is the incorrect order of basicity?

a. ${N H_{3} < N (C H_{3})_{3} < N H_{2} C H}_{3} < N H (C H_{3})_{2}$
b. ${N H_{3} < N H_{2} {C H}_{2} C H}_{3} < N ({C H}_{2} C H_{3})_{3} < N H ({C H}_{2} C H_{3})_{2}$
c. $N H_{3} < {N H}_{2} C H_{3} < N H_{2} {C H}_{2} C H_{3}$
d. ${N H_{3} < N ({C H}_{2} C H_{3})_{3} > N H_{2} {C H}_{2} C H}_{3} < N H ({C H}_{2} C H_{3})_{2}$

Answer : (D)

Solution: The basicity of amine depends on three factors in general and they are as follows:

More the alkyl groups, more is the inductive effect, more is the basicity of amine.
More the alkyl groups, the more is the steric hindrance of an alkyl group, less is the basicity of amine.
More the number of hydrogen atoms directly attached to nitrogen, more is the solubility of alkyl group, more is the basicity of amine.

The overall basicity of amine is: (when R group is methyl)

${N H_{3} < N (C H_{3})_{3} < N H_{2} C H}_{3} < N H (C H_{3})_{2}$

The overall basicity of amine is: (when R group is ethyl) ${N H_{3} < N H_{2} {C H}_{2} C H}_{3} < N ({C H}_{2} C H_{3})_{3} < N H ({C H}_{2} C H_{3})_{2}$

Hence, option (A) and (B) are a correct representation of basicity order.

The basicity order NH3<NH2CH3<NH2CH2CH3 given in option (C) is also correct on the basis of the inductive effect that is more prominent over steric hindrance and solubility.

Hence, the incorrect order is in option (D) and is the correct answer for the given question.

Frequently Asked Questions-FAQs:

1. What distinguishes an amine from an amide?
Answer: Organic substances can be divided into amides and amines. The presence of a carbonyl group distinguishes amines from amides; amines lack carbonyl groups connected to the nitrogen atom and have the formula RNH2, whereas amides have a carbonyl group attached to a nitrogen atom and have the formula R-CO-NH₂.

2. Are amines toxic?
Answer: The majority of the aliphatic amines included in food are typically used to make amino acids, which are the building blocks of proteins. Therefore, compounds are not particularly harmful by nature. However, some aromatic amines might be toxic by nature and can irritate the skin.

3. How does the body react to amines?
Answer: Amines are taken in many medicines but when ingested in high amounts along with nutrients, It is seen that the biogenic amines can result in respiratory problems, headaches, tachycardia, hypo- or hypertension, and allergic responses. Amines are vasoactive substances that can affect blood pressure in both humans and animals when consumed in large doses.

4. How can be distinguished primary, secondary and tertiary amines?
Answer: The Hinsberg test is a chemical procedure that is frequently used to identify primary, secondary, and tertiary amines. A Hinsberg reagent reacts with an amine when there is an aqueous alkali present.