Azoles: pentagonal heterocycles with two or more heteroatoms

What are azoles? The azoles are five-membered cyclic organic compounds having one or more non-carbon atoms in the ring, at least one of the heteroatoms being nitrogen. This is the largest and most diverse group of aromatic heterocycles. They are derived from furan, thiophene and pyrrole, by replacement of one or more CH groups by … Read more

Nucleophilic substitution of pyridines

What is nucleophilic substitution of pyridines? The nucleophilic substitution reaction is not a common process in benzene chemistry, but it is much easier in pyridines, and particularly at the C2 and C4 positions which are activated by nitrogen. Nucleophilic displacement of a good leaving group, via addition-elimination, occurs most easily for groups at C2 and … Read more

Oxadiazoles and thiadiazoles

What are oxadiazoles and thiadiazoles? There are 4 types of isomers of these compounds. The 1,2,3-oxadiazoles exist in the open form of diazoketone (CN2O). For the 1,2,3-thiadiazoles, however, the cyclic tautomer is the preferred structure. Also, there are the benzofused analogs of 1,2,3-thiadiazole and 1,2,5- isomers. The 1,2,5-oxadiazole is also known as furazan and the … Read more

Furans

What are furans? Furans are heterocyclic organic compounds consisting of a 5-membered aromatic ring with four carbon atoms and one oxygen atom. furan is a colorless, highly volatile and flammable liquid with a boiling point of 31 ºC. It is also slightly soluble in water, soluble in common organic solvents, and with a dipole moment … Read more

Isoxazoles, isothiazoles and their benzoderivatives

What are isoxazoles, isothiazoles and their benzoderivatives? Isoxazole and isothiazole are liquids of boiling point 95 and 113 ºC, respectively. There are several natural isoxazoles with significant pharmacological activity, for example, muscimol, which is a fungus (Amanita muscaria) with psychotropic effects. Two types of isoxazoles and benzofused isothiazoles can occur. Thus, monocyclic systems and their … Read more

Benzo-fused 5-membered heterocycles

What are benzo-fused 5-membered heterocycles? Condensed 5-membered heterocycles are the heteroatoms resulting from the fusion of a benzene ring and a 5-membered heterocycle. The main ones are those where the fusion is performed on the 2-3 bond of the heterocycle. The description of these 3 heterocycles (indole, benzofuran and benzothiophene), from the point of view … Read more

Five-membered rings with one heteroatom

What are five-membered rings with one heteroatom? Five-membered rings with one heteroatom are pentagonal heterocycles that have one atom in the ring other than carbon. It is one of the most relevant groups of heterocyclic compounds, and the three most notable are: pyrrole, furan and thiophene. fig-01 These heterocycles can be considered as aromatic, to … Read more

Oxazoles and thiazoles

What are oxazoles and thiazoles? Oxazole and thiazole are heterocycles that are closely related to furan and thiophene. The oxazole ring system is almost not found in nature and has no significant natural derivatives. In contrast, thiazole is very common in natural products, for example, vitamin B1 (thiamine) contains a pyridine ring and a thiazole ring. … Read more

Thiophenes

What are thiophenes? Thiophenes are heterocyclic organic compounds, consisting of a 5-membered aromatic ring with four carbon atoms and a sulfur atom. Thiophene is a liquid with a boiling point of 84 °C, found in coal tar. It occurs as a contaminant of benzene, when obtained from coal tar. fig-01 Thiophene is an electron-rich aromatic … Read more

Six-membered rings with one oxygen

What are hexagonal heterocycles with one oxygen? Because the neutral divalent oxygen atom cannot replace the CH group of the benzene ring (it would need valence 3). Therefore, the existence of neutral oxygenated compounds with a constitution analogous to pyridine is not possible. The cyclic, unsubstituted, uncharged system with two double bonds is called a … Read more

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