Nomenclature Of Amines Chemistry Note For Class 12
Amines are derived from ammonia in which one or more of the hydrogens are replaced by an alkyl or aryl group. The nomenclature of amines is complicated because several different nomenclature systems exist, and there is no clarity on which system is to be considered. Additionally, the terms primary (1°), secondary (2°) & tertiary (3°) are used during the classification of amines, these terms refer to the number of alkyls (or aryl) substituents bonded to the nitrogen atom.
The compounds shown in the top row of the following diagram are all C4H11N isomers. The first two are classified as primary amines since only one alkyl group is bonded to the nitrogen; however, the alkyl group is primarily in the first example and tertiary in the second. The third and fourth compounds in the row are secondary and tertiary amines respectively. Whereas, nitrogen bonded to four alkyl groups is necessarily a positively charged entity, called a quaternary (4°)ammonium cation. For example, (CH3)4N(+) Br(–) is tetramethylammonium bromide.
In the above image, the IUPAC names are listed in a blue colour. In this system of naming amines, the amines function as substituents on the largest alkyl group. The most simple -NH substituent found in 1° amine is called an amino group. For 2°and 3°amines, a compound prefix (e.g. dimethylamino in the fourth example) includes the names of all but the root alkyl group.
The Chemical Abstract Service (it is a body of the American Chemical Society and a source of chemical information). This has adopted a nomenclature system in which the suffix -amine is attached to the root alkyl name. For primary amines like butanamine, see the first example in the above image. The additional nitrogen substituents in the case of secondary and tertiary amines, the prefix N- before the group name. These CAS names are mentioned in magenta colour, in the above-given image.
Lastly, in the common name system for simple amines, the names of each alkyl substituent on nitrogen are given in alphabetical order, followed by the suffix -amine. These are mentioned in the last row in black colour in the above image.
Many aromatic and heterocyclic amines are known by particular common names, which have no connection with their structures.
Some Common Rules of Nomenclature of Amines
i. The naming of aliphatic amines is done by putting the name of the alkyl group as a prefix to the amines. Therefore, the names of aliphatic amines are like alkylamine. For example, CH3NH2 is named as methylamine (alkyl part + amine = methylamine).
ii. Prefixes like, di and tri are added before the names of the alkyl group if two or more identical groups are present.
iii. If more than one amino group is present in the amine (is called a diamine, triamine, tetramine, etc.), then the parent chain and the position of amino groups is determined by numbering the carbon atoms in the parent chain. The numbering is done such that the carbon atom bearing the –NH2 groups get the lowest numbers.
Prefixes di, tri, tetra etc. along with the numbers are then used to denote the number of amino groups and their position in the molecule. For example, H2N-CH2-CH2-NH2 is named as ethane 1, 2-diamine.
iv. In the compounds like, mixed amines, the names of alkyl groups are arranged in alphabetical order. The amines are named as N-substituted derivatives of the largest group of primary amines.
(C2H5)2NCH2CH2CH2CH3 – N, N – diethyl butylamine
v. If –NH2 group is attached to a benzene ring then it is called as arylamines.
vi. When we name arylamines according to the IUPAC system, the ‘e’ of the arene is replaced by the amine, for example, C6H5-NH2 is named as benzenamine.
vii. In the case of diamines the ending -e of the hydrocarbon name is used as it is and the suffix diamine is added, the name of H2N-(CH2)5-NH2 is 1,5 – Pentane-di-amine.
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