Heterocyclic Numbering
Heterocyclic Numbering - Related Videos
01:25
Basicity of Heterocyclic Aromatic Amines
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2023
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8). Figure 1. The comparison of the basicity of piperidine and pyridine. This difference in basicity may be...
01:10
Nomenclature of Aryl and Heterocyclic Amines
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2025
The simplest aromatic amine is phenylamine, which contains an –NH2 functionality directly attached to an aromatic ring. The name aniline is designated for this skeleton. As shown in Figure 1, the common names of the functionalized anilines involve prefixes ortho-, meta-, and para- to indicate the substitution position. Different functionalized aniline derivatives also have notable trivial names. Figure 1. Common names for functionalized anilines based on substitution. For the systematic...
05:17
Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay
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Cited by 2 •
2021
Here, we describe a bioassay using 3-(4′,5′-dimethylthiazol-2′-yl)-2,5- diphenyltetrazolium bromide (MTT) to test previously synthesized spirocyclic oximes.
01:13
Five-Membered Heterocyclic Aromatic Compounds: Overview
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2023
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom, respectively.
12:19
Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Cited by 2 •
2018
We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.
FAQs
Locant selection follows a priority sequence rather than the apparent position of a substituent. The numbering starts at the highest-priority heteroatom, then favors the direction that assigns the lowest appropriate locants to other heteroatoms, indicated hydrogen, double bonds, and substituents. This sequence prevents a convenient drawing orientation from producing an inconsistent name.
Reversing the numbering direction can change the locants assigned to double bonds, indicated hydrogen, or substituents without changing the underlying ring structure. The accepted direction is the one that gives the relevant features the lowest appropriate locants after the starting heteroatom has been selected. Thus, two drawings of one compound should converge on the same systematic numbering.
Fused systems cannot always be numbered by applying the rules for an isolated ring mechanically. They follow additional conventions that account for the complexity of the fused framework and maintain consistent atom assignments. Recognizing when these conventions apply helps chemists produce unambiguous names, compare related structures, and communicate the positions of features accurately.
First identify the heterocyclic ring or fused system and its heteroatoms. Select the starting atom according to the applicable priority convention, then examine the possible numbering directions. Choose the direction producing the lowest appropriate locants for the remaining heteroatoms, indicated hydrogen, double bonds, and substituents, while applying fused-system rules whenever the structure requires them.
Numbering provides a stable positional framework for distinguishing constitutional isomers and describing substitution patterns. A locant identifies where a heteroatom, indicated hydrogen, double bond, or substituent occurs within the ring framework. Chemists can therefore compare structures, interpret reported names, and organize records in databases without depending on how a structure was drawn.
In medicinal, synthetic, and materials chemistry, consistent locants make structural reports precise across drawings, names, and comparisons. They help researchers communicate substitution patterns and relate a reported position to the ring framework when discussing reactivity or recording compounds. Correct numbering therefore supports reliable chemical communication, interpretation of structures, and consistent organization of research information.