19.4
Nomenclature of Aryl and Heterocyclic Amines
The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated…
Phenylamine—the simplest aryl amine, and its derivatives are known by their common names, with prefixes o-, m- , and p- used to indicate the point of substitution.
Systematic nomenclature refers to them as derivatives of aniline. The ring is numbered from the carbon atom bearing the –NH2 group and continues in the direction to give the lowest locant to the substituent.
For more substituted aryl amines, the first point of difference is assigned the lowest locant, and the substituents are listed alphabetically.
Secondary and tertiary aryl amines are named N-substituted anilines.
Saturated and unsaturated heterocyclic amines have specific names based on the ring size and the heteroatoms present.
The numbering starts at the N atom or the heteroatom with the highest atomic weight and continues in the direction to give the lowest locant to the other heteroatom.
Alternatively, prefixes aza- or diaza- along with the locants, indicate the number of N atoms in the ring.
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Q1: What is phenylamine and how is it named?
Phenylamine is the simplest aryl amine, containing an –NH2 group directly attached to an aromatic ring. It is also called aniline, which designates this fundamental skeleton. Phenylamine and its derivatives are commonly named using prefixes ortho-, meta-, and para- to indicate substitution position on the ring.
Q2: How are substituted anilines numbered in systematic nomenclature?
The ring is numbered starting from the carbon bearing the –NH2 group, continuing in the direction that gives the lowest locant to the substituent. For multiple substituents, the first point of difference receives the lowest locant, and substituents are listed alphabetically. This systematic approach ensures consistent naming across all substituted aniline derivatives.
Q3: How are secondary and tertiary aromatic amines named?
Secondary and tertiary aromatic amines are named as N-substituted anilines, with the N- prefix indicating substitution on the nitrogen atom. The parent name derives from aniline, and the substituents attached to nitrogen are listed with the N- designation before the parent amine name. This nomenclature system follows the nomenclature of secondary and tertiary amines conventions.
Q4: What are the naming rules for saturated heterocyclic amines?
Saturated and unsaturated heterocyclic amines have specific names based on ring size and heteroatoms present. Common examples include pyrrolidine, pyrrole, piperidine, pyridine, and imidazole. These biological amines are recognized by their established trivial names rather than systematic nomenclature conventions in most contexts.
Q5: How is numbering determined in heterocyclic amines with multiple heteroatoms?
Numbering starts at the heteroatom with the highest atomic weight, continuing in the direction that gives the lowest locant to other heteroatoms. For example, in thiazole, sulfur is numbered one, and numbering continues to give nitrogen the lowest possible number. This priority system ensures consistent nomenclature across mixed-heteroatom rings.
Q6: What are aza- and diaza- prefixes used for in amine nomenclature?
The prefixes aza- or diaza- along with locant numbers indicate nitrogen atoms replacing carbons in the parent alkane structure. This nomenclature approach is particularly common in bicyclic fused ring systems, such as DBU and DBN, where nitrogen is part of a fused ring system.
Q7: What is the difference between common and systematic names for aniline derivatives?
Common names use ortho-, meta-, and para- prefixes to indicate substitution positions and often have trivial names. Systematic nomenclature numbers the ring from the nitrogen-bearing carbon and lists substituents alphabetically. Both approaches describe the same compounds but follow different naming conventions based on context and tradition.