Heterocycles

What are three-membered heterocycles? The chemistry of three-membered heterocycles is dominated by angular tension, which leads to high reactivity. Attack by a nucleophile on a ring carbon, heating or irradiation can result in ring opening. Therefore, three-membered heterocycles are abnormally reactive molecules, and very useful as intermediates in synthesis. Oxiranes (epoxides) Oxiranes or epoxides are … Read more

What are pyrroles? Pyrroles are 5-membered heterocyclic aromatic compounds with one nitrogen atom and 4 carbons in a pentagonal ring. Apart from its interest as an aromatic system, the pyrrole is biologically important because its structure is part of the heme group, chlorophyll and other natural products related to vitamin B12 and bile pigments. Among … Read more

What are quinolines and isoquinolines? They are the fusion products of a benzene ring and a pyridine nucleus. fig-01 Both substances are obtained from coal tar. These weakly basic heterocycles resemble pyridine in their stability against chemical attack. But there are some fundamental differences in their reactivity. Both quinoline and isoquinoline can be considered as … Read more

What are six-membered rings with one heteroatom? Hexagonal heterocycles with one heteroatom are six-membered cyclic organic compounds with one atom in the ring other than carbon. A CH in the benzene can be replaced by a nitrogen atom or by another of the group 15 elements without substantially altering the character of the π-orbitals. That … Read more

What are cyclization reactions or ring formation reactions? The most common cyclization reactions are those in which a nucleophilic atom interacts with an electrophile. Therefore, the predominant reaction types are as follows: The nucleophilic shift in a saturated carbon atom. Nucleophilic addition on an unsaturated carbon. Nucleophilic addition-removal. An example of the ring formation reaction … Read more

Basic concepts Heterocyclic compounds are cyclic compounds containing one or more non-carbon atoms in the ring structure. The most frequent elements are N, S and O. They are widely found in nature. Many of them are of fundamental importance to living systems; they can be key components in biological processes. For example: chlorophyll and the … Read more

What are non-aromatic heterocycles? Non-aromatic heterocycles can be related to open-chain analogous compounds, but the size of the ring may play a relevant role between them. The existence of a ring system imposes restrictions on the molecule that may be absent in the acyclic system. The greater these constraints, the greater the difference between the … Read more

What are aromatic heterocycles? A heterocyclic compound is an organic compound in which one or more of the carbon atoms in the backbone of the molecule has been replaced by an atom other than carbon. Typical heteroatoms include nitrogen, oxygen and sulphur. Of this group, those that obey Hückel’s rule are called aromatics. Heterocycles with … Read more

What are pyrazoles, triazoles and tetrazoles? Derivatives of pyrazoles, triazoles and tetrazoles are stable aromatic compounds. Many of them have been used as pharmaceuticals, dyes and pesticides. The tetrazoles are relevant in medicinal chemistry. This is because the tetrazole group behaves similar to carboxylic acids. Both systems are planar, have comparable pKa (that of the … Read more

What are pyridines? Pyridine is a colorless liquid that boils at 115 ºC. It used to be obtained almost exclusively from coal tar. Today, it is obtained industrially from ammonia and acetylene. Pyridine like benzene has 6 π electrons (aromatic Hückel). Its structure is planar with bond angles of 120º. The heat of combustion reveals … Read more