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Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated polymeric chains, which show significant electrical conductivity. [page needed] [17] The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins.
Pyridine, the parent compound of the pyridine alkaloids. Pyridine alkaloids are a class of alkaloids , nitrogen-containing chemical compounds widely found in plants, that contain a pyridine ring. Examples include nicotine and anabasine which are found in plants of the genus Nicotiana including tobacco .
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). [1] Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles .
First, the nucleophilic NH 2 − group adds to the δ+ ring carbon atom, pushing electrons onto the ring nitrogen atom and forming the anionic σ-adduct, which is stabilized by sodium. Electrons from the N atom are then pushed towards the ring to regain aromaticity , forming a C=N bond and ejecting a hydride ion in the process.
Simple aromatic rings can be heterocyclic if they contain non-carbon ring atoms, for example, oxygen, nitrogen, or sulfur. They can be monocyclic as in benzene, bicyclic as in naphthalene, or polycyclic as in anthracene. Simple monocyclic aromatic rings are usually five-membered rings like pyrrole or six-membered rings like pyridine.
Typical examples of basic aromatic rings are pyridine or quinoline. Several rings contain basic as well as non-basic nitrogen atoms, e.g. imidazole and purine. In non-basic aromatic rings the lone pair of electrons of the nitrogen atom is delocalized and contributes to the aromatic pi electron system.
The alkaloids content in plants is usually within a few percent and is inhomogeneous over the plant tissues. Depending on the type of plants, the maximum concentration is observed in the leaves (for example, black henbane ), fruits or seeds ( Strychnine tree ), root ( Rauvolfia serpentina ) or bark ( cinchona ). [ 174 ]
Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoquinoline is used to make reference to isoquinoline derivatives. 1-Benzylisoquinoline is the structural backbone in many naturally occurring alkaloids such as papaverine.