Nomenclature of Amines: Important Notes, Questions

Nomenclature of Amines: Amines are organic compounds in which one or more hydrogen atoms are replaced by an alkyl/aryl group in ammonia molecules (s). Proteins, vitamins, alkaloids, and hormones are all examples of them in nature.

Synthetic materials include polymers, dyestuffs, and medicines. Two physiologically active compounds, adrenaline and ephedrine, both of which contain secondary amino groups, increase blood pressure. Novocain, a synthetic amino molecule, is used as an anaesthetic in dentistry. Benadryl, a well-known antihistaminic drug, has a tertiary amino group. Quaternary ammonium compounds are used as surfactants. Diazonium salts are used as a starting point for making a variety of aromatic compounds, including colours. In this article, let us learn everything about the Nomenclature of Amines in detail.

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Structure of Amines

Like ammonia, the nitrogen atom of amines is trivalent and carries an unshared pair of electrons.

Nitrogen orbitals in amines are, therefore, \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybridised, and the geometry of amines is pyramidal.

Each of the three \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybridised orbitals of nitrogen overlap with orbitals of hydrogen or carbon depending upon the composition of the amines. The fourth orbital of nitrogen in all amines contains an unshared pair of electrons. Due to the presence of unshared pair of the electron, the angle of \({\rm{C – N – E}}\) (where \({\rm{E}}\) is \({\rm{C}}\) or \({\rm{H}}\) is less than \({\rm{109}}{\rm{.}}{{\rm{5}}^{\rm{^\circ }}}\); for instance, it is \({\rm{10}}{{\rm{8}}^{\rm{^\circ }}}\) in the case of trimethylamine, as shown in fig.

Classification of Amines

Amines are ammonia-based organic compounds that have one or more hydrogen atoms replaced by alkyl or aryl groups. They are classed as primary, secondary, or tertiary depending on whether alkyl groups replace one, two, or all three hydrogen atoms in ammonia (R). Amines can be considered derivatives of ammonia, obtained by replacing one, two, or all the three hydrogen atoms with alkyl and/or aryl groups.

For example,

Preparation of Amines

Some of the important methods of preparation of amines are:

1. Alkylation of Ammonia
2. Alkylation of Azide Ion and Reduction
3. Gabriel Phthalimide Synthesis
4. Reduction of Nitro Compounds
5. Reduction of Nitriles, Isonitriles, and Oximes
6. Reductive Amination of Carbonyl Compounds
7. From Amides
8. Hoffmann Bromamide Degradation

Nomenclature of Amines

Amines are commonly named alkylamines. The alkyl groups attached to N-atom are named in alphabetical order, followed by amine. They are known as Alkanamine in the IUPAC system of nomenclature. The parent compound is chosen as the one with the longest carbon atom chain connected to the N-atom, and the suffix amine replaces the last letter “e” in the name of the parent hydrocarbon. The substituents are named as prefixes in alphabetical order. In the case of mixed amines, the name of the alkyl groups is written in alphabetical order. When two or three identical alkyl groups are attached to a nitrogen atom, the prefix di- or tri- is added to the name of the alkyl group. The IUPAC names (in the bold letter) and common names (in parenthesis) of some well-known amines are given below.

(a) Primary Amines

When one of the three hydrogen atoms in ammonia is replaced by an alkyl or aromatic group, primary amines form. Important primary alkylamines include methylamine, most amino acids, while primary aromatic amines include aniline.

Most secondary and tertiary amines are named in the same general way. In common terminology, we either designate the organic groups individually if they are different or use the prefixes di- or tri- if they are the same. In systematic nomenclature, we use the locant N to designate substituents attached to a nitrogen atom.

(b) Secondary Amines

Secondary amines are nitrogen-bound compounds containing two organic substituents (alkyl, aryl, or both) and one hydrogen. Important representatives include ethylmethylamine, while an example of an aromatic amine would be diphenylamine.

(c) Tertiary Amines

Nitrogen has three organic substituents in tertiary amines. Trimethylamine, which has a strong fishy odour, and EDTA are two examples.

(d) Arylamines

Arylamines have \(\mathrm{NH}_{2}\) a group directly attached to the benzene ring. In the common name system, the aromatic amines are called arylamines and named by adding the suffix amine to the name of the aryl group. They may also be named as derivatives of the simplest aromatic amine, i.e., aniline.

In the IUPAC system, the simplest aromatic amine is called benzenamine, and the other amines are named as derivatives of benzenamine. The complete name of an amine is always written as one word. The common and IUPAC names of some aromatic amines are given below.

(e) Heterocyclic Amines

Heterocyclic amines (HCAs) are chemical compounds that have at least one heterocyclic ring, which has atoms from at least two different elements and at least one amine (nitrogen-containing) group by definition. IUPAC names of heterocyclic amines have prefixes aza, diaza, or triaza to indicate that one, two, or three nitrogen atoms have replaced carbon atoms in the corresponding hydrocarbons. The numbering of the ring starts from the heteroatom. The names of some of the well-known heterocyclic amines are as follows.

Summary

1. Amines are a type of organic compound in which an alkyl/aryl group replaces one or more hydrogen atoms in ammonia molecules (s).
2. Like ammonia, the nitrogen atom of amines is trivalent and carries an unshared pair of electrons. Nitrogen orbitals in amines are, therefore, \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybridised, and the geometry of amines is pyramidal.
3. They are classed as primary, secondary, or tertiary depending on whether alkyl groups replace one, two, or all three hydrogen atoms in ammonia (R). 
4. According to the IUPAC system of nomenclature, they are named Alkanamine.
5. The parent compound is chosen as the one with the longest carbon atom chain connected to the N-atom, and the suffix amine replaces the last letter “e” in the name of the parent hydrocarbon.
6. In the case of mixed amines, the name of the alkyl groups is written in alphabetical order. When two or three identical alkyl groups are attached to a nitrogen atom, the prefix di- or tri- is added to the name of the alkyl group.
7. Arylamines have a \(\mathrm{NH}_{2}\) group directly attached to the benzene ring.
8. In the common name system, the aromatic amines are called arylamines and named by adding the suffix amine to the name of the aryl group. They may also be named as derivatives of the simplest aromatic amine, i.e., aniline.
9. Heterocyclic amines (HCAs) are chemical compounds that have at least one heterocyclic ring, which has atoms from at least two different elements and at least one amine (nitrogen-containing) group by definition.
10. IUPAC names of heterocyclic amines have prefixes aza, diaza, or triaza to indicate that one, two, or three nitrogen atoms have replaced carbon atoms in the corresponding hydrocarbons.

FAQs on Nomenclature of Amines

Q.1.  Describe the structure of amines.
Ans: In the structure of amine, the nitrogen atom of amines is trivalent and carries an unshared pair of electrons. Nitrogen orbitals in amines are, therefore, \({\rm{s}}{{\rm{p}}^{\rm{3}}}\) hybridised, and the geometry of amines is pyramidal. Depending on the amine composition, each of the three hybridised orbitals of nitrogen overlaps with orbitals of hydrogen or carbon. All amines have an unshared pair of electrons in the fourth orbital of nitrogen. The angle of \({\rm{C – N – E}}\) (where \({\rm{E}}\) is \({\rm{C}}\) or \({\rm{H}}\) is less than \({\rm{109}}{\rm{.}}{{\rm{5}}^{\rm{^\circ }}}\) due to the presence of an unshared pair of electrons; for example, it is \({\rm{10}}{{\rm{8}}^{\rm{^\circ }}}\) in the case of trimethylamine.

Q.2.  Describe the classification of amines?
Ans: Amines can be classified into different types. Amines are ammonia-based organic compounds that have one or more hydrogen atoms replaced by alkyl or aryl groups. They are classed as primary, secondary, or tertiary depending on whether alkyl groups replace one, two, or all three hydrogen atoms in ammonia (R). Amines can be considered derivatives of ammonia, obtained by replacing one, two, or all the three hydrogen atoms with alkyl and/or aryl groups.

Q.3. How the naming of amines is done?
Ans: There are various ways to name the amines. Amines are commonly named alkylamines. The alkyl groups attached to N-atom are named in alphabetical order, followed by amine. They are known as Alkanamine in the IUPAC system of nomenclature. The parent compound is chosen as the one with the longest carbon atom chain connected to the N-atom, and the suffix amine replaces the last letter “e” in the name of the parent hydrocarbon. The substituents are named prefixes in alphabetical order. 

Q.4. What are primary amines?  Give IUPAC names and common names of some common amines.
Ans: When one of the three hydrogen atoms in ammonia is replaced by an alkyl or aromatic group, primary amines form.  Important primary alkylamines include methylamine, most amino acids, while primary aromatic amines include aniline.

Q.5. How the name of some heterocyclic amines is done?
Ans: In the IUPAC naming, heterocyclic amines have prefixes aza, diaza or triaza to indicate that one, two or three nitrogen atoms have replaced carbon atoms in the corresponding hydrocarbons. The numbering of the ring starts from the heteroatom. The names of some of the well-known heterocyclic amines are as follows. 

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