In organic chemistry, non-carbon atoms are collectively referred to as heteroatoms, and the most common heteroatoms are nitrogen, sulfur, and oxygen. The organic matter that contains heteroatoms on the ring is called a heterocyclic compound. They are the most abundant group of organic matter.

Heterocyclic compounds can be divided into two categories: lipid heterocycles and aromatic heterocycles. Heterocyclic compounds that do not have aromatic characteristics are called aliphatic heterocyclic compounds. For example, lactones, lactides, cyclic ethers, cyclic amides, lactams, etc., are similar in nature to the corresponding open-chain compounds.

The heterocyclic compounds discussed here mainly refer to the relatively stable ring system, the ring including heteroatoms is planar, and there are 4n+2 π electrons in the ring in the closed conjugated system, which are collectively called aromatic (aromatic) heterocyclic compounds. Other heterocyclic compounds that are not aromatic are collectively referred to as non-aromatic heterocyclic compounds or heteroalicyclic compounds.

1. Classification of heterocyclic compounds

Second, the nomenclature of heterocyclic compounds

(1) The naming of heterocyclic mother rings

1. Transliteration method: based on the common names of 45 heterocyclic compounds. China uses the transliteration method: on the left side of the homophone Chinese character + the word "mouth".

2. Systematic nomenclature

The heterocyclic is regarded as a heteroatom replacing the carbon atom in the corresponding carbon ring, and the corresponding carbon ring is used as the parent body when naming, and the name of the heteroatom is added before the name of the carbon ring, which is called "a certain miscellaneous". Note: In the absence of misunderstanding, the word "miscellaneous" can be omitted.

(2) The numbering principle of heterocyclic mother rings

1. A heteroring containing one heteroatom is numbered "1". The carbon atoms in the ortho-heteroatomic position can also be used in α, β, γ... Numbering.

2. If two or more identical heteroatoms are contained, the heteroatom number should be the smallest, and the number of heteroatoms connected with hydrogen atoms or substituents should be set as No. 1; when different heteroatoms are contained, they should be numbered in the order of O→S→NH→N.

3. The numbering of the heterocyclic rings starts with the heteroatoms and is numbered one week in sequence (common carbon is not numbered). Some have a specific number.

4. Some heterocycles have tautomerism, and in order to distinguish the heteromers, the location of one or more hydrogen atoms is often indicated in capital italics "H".

(3) Common heterocyclic mother nucleus

1. Five-membered heterocyclic compounds

1. 1 Pyrrole, furan, thiophene

1.2 Pyrazole, imidazole, thiazole

A five-membered monoheterocyclic containing two heteroatoms and at least one of them being a nitrogen atom is called azole.

2. Six-membered heterocyclic compounds

2.1. Pyridine (C5H5N)

2.2. Pyrimidine (C4H4N2) and its derivatives

3. Thick heterocyclic compounds

3.1. Indole

Indole is a white crystal with a melting point of 52.5 °C. The extremely dilute solution has a fragrance and can be used as a spice, and the thick indole solution has a fecal odor. Frangipani and citrus flowers contain indole. The derivatives of indole ring are widely found in animals and plants, and have a close relationship with human life and life.

3.2 Quinoline and isoquinoline

3.3. Purines

The pyrimidine ring is fused with the imidazole ring

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