The heterocyclic compound is a type of cyclic organic compound that has one heteroatom in the cyclic ring structure. Sulfur, oxygen, and nitrogen are the most common heteroatoms.
Heterocyclic compounds constitute half of the natural organic compounds mainly found in plenty in animal and plants products. Natural heterocyclic compounds include drugs, alkaloids, proteins, natural dyes, and enzymes.
The classification of heterocyclic compounds is based on their electronic system, classified as either saturated or unsaturated. The saturated heterocyclic compounds have tendencies such as the acyclic derivatives but with an adjustment of steric properties. This category has tetrahydrofuran and piperidine, which are the standard amines and ethers. However, there has been an extensive study of unsaturated heterocyclic compounds of 5 and 6 member rings due to their unstrained nature.
Some unstrained unsaturated heterocyclic compounds include pyrrol, pyridine. Furan thiophene and benzo fused derivatives. Some benzo-fused heterocycles are benzofuran, indole, quinoline, benzothiophene, and isoquinoline.
Uses of heterocyclic compounds
They are widely used in veterinary products, agrochemicals, and pharmaceuticals. Quite a number of heterocyclic compounds are essential and valuable to human life. The heterocyclic structure can be found in hormones, essential amino acids, vitamins, alkaloids, hemoglobin, antibiotics, pigments, and dyes.
Classification of heterocyclic compounds.
Given the electronic and structural arrangement, the heterocyclic compounds are two types.
- Aliphatic heterocyclic compounds
These compounds comprise cyclic amides, cyclic thioethers, cyclic amides, and cyclic ethers. The aliphatic heterocyclic without double bonds is known as saturated heterocyclic. The ring strain affects the properties of aliphatic heterocyclic.
Examples of aliphatic heterocyclic compounds include Thiirane, Azetidine Aziridine, Ethylene oxide, Thietane,and piperidine.
- Aromatic heterocyclic compounds
These compounds are analogous to benzene and are subject to Huckel’s rule. This rule state that the aromatic compounds are cyclic with planar geometry due to connecting double bonds that must contain electrons. The Furan Indole Cabazole Thiophene, Quinoline Pyridine, Isoquinoline, Pyridazine, Pyrazole Purine, and Pyrimidine are aromatic heterocyclic compounds.
A heterocyclic ring may be made up of three or more atoms that are either saturated or unsaturated. Also note, the heterocyclic ring may have more than one heteroatom, which may be similar or different. Due to the diversity of the structure, the heterocyclic compounds may be divided into:
- Five membered heterocyclic compounds
These compounds are obtained from benzene by replacing a C=C bond of a hetero atom with a single pair of electrons. Considering how many heteroatoms are present in the cyclic ring, this five-membered class may have further subdivisions. Such as:
- Heterocyclic compounds with one heteroatom. Examples include pyrrole, furan, and thiophene.
- Heterocyclic compounds with more than one heteroatom may be similar or different. Examples in this group are triazole, thiazole, pyrazole, tetrazole, oxazole, and imidazole.
- Six membered heterocyclic compounds.
This class is obtained by replacing a carbon atom of benzene with an iso-electronic atom. Similarly, this class is further subdivided into:
- Heterocyclic compounds with one heteroatom. Examples include thiopyran, pyridine, and pyran.
- Heterocyclic compounds with more than one heteroatom. Examples include pyrazine, pyridazine, and pyrimidine.
- Condensed or fused heterocyclic compounds. This category has two or more fused rings, partly carbocyclic and heterocyclic. Examples in this group include carbazole, indole, isoquinoline, and quinine.