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16-394: Para - Methoxy ethyl amphetamine ( PMEA ), is a stimulant drug related to PMA . PMEA reputedly produces similar effects to PMA, but is considerably less potent and seems to have slightly less tendency to produce severe hyperthermia , at least at low doses. At higher doses however the side effects and danger of death approach those of PMA itself, and PMEA should still be considered

32-611: A potentially dangerous drug. Investigation of a drug-related death in Japan in 2005 showed PMEA to be present in the body and was thought to be responsible for the death. Stimulants: Phenylethanolamine Para isomer The toluidines serve as an example for these three types of substitution. Electron donating groups, for example amino , hydroxyl , alkyl , and phenyl groups tend to be ortho / para -directors, and electron withdrawing groups such as nitro , nitrile , and ketone groups, tend to be meta -directors. Although

48-503: A third large family of organic compounds. Analogs of the previously mentioned heterocycles for this third family of compounds are acridine , dibenzothiophene , carbazole , and dibenzofuran , respectively. Heterocyclic organic compounds can be usefully classified based on their electronic structure. The saturated organic heterocycles behave like the acyclic derivatives. Thus, piperidine and tetrahydrofuran are conventional amines and ethers , with modified steric profiles. Therefore,

64-440: A variety of common and systematic names. For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is quinoline or isoquinoline . For azepine, benzazepine is the preferred name. Likewise, the compounds with two benzene rings fused to the central heterocycle are carbazole , acridine , and dibenzoazepine. Thienothiophene are

80-502: Is a six-membered ring with three nitrogen heteroatoms and three boron heteroatoms. In a 7-membered ring, the heteroatom must be able to provide an empty π-orbital (e.g. boron) for "normal" aromatic stabilization to be available; otherwise, homoaromaticity may be possible. Borazocine is a eight-membered ring with four nitrogen heteroatoms and four boron heteroatoms. Heterocyclic rings systems that are formally derived by fusion with other rings, either carbocyclic or heterocyclic, have

96-531: Is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles . Examples of heterocyclic compounds include all of the nucleic acids , the majority of drugs, most biomass ( cellulose and related materials), and many natural and synthetic dyes. More than half of known compounds are heterocycles. 59% of US FDA -approved drugs contain nitrogen heterocycles. The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and

112-597: Is the class of dithiazoles , which contain two sulfur atoms and one nitrogen atom. The 6-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azines . Thiazines contain a sulfur and a nitrogen atom in the ring. Dithiines have two sulfur atoms. Six-membered rings with five heteroatoms The hypothetical chemical compound with five nitrogen heteroatoms would be pentazine . Six-membered rings with six heteroatoms The hypothetical chemical compound with six nitrogen heteroatoms would be hexazine . Borazine

128-580: The Hantzsch-Widman nomenclature for naming heterocyclic compounds. Although subject to ring strain , 3-membered heterocyclic rings are well characterized. The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azoles . Thiazoles and isothiazoles contain a sulfur and a nitrogen atom in the ring. Dithioles have two sulfur atoms. A large group of 5-membered ring compounds with three or more heteroatoms also exists. One example

144-412: The nitrogen atom is considered one of the substituents. For example, nicotinamide and niacin , shown meta substitutions on a pyridine ring, while the cation of pralidoxime is an ortho isomer. Heterocycle 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). Heterocyclic organic chemistry

160-431: The ortho isomer catechol , the meta isomer resorcinol , and the para isomer hydroquinone : There are three arene substitution isomers of benzenedicarboxylic acid (C 6 H 4 (COOH) 2 ) – the ortho isomer phthalic acid , the meta isomer isophthalic acid , and the para isomer terephthalic acid : These terms can also be used in six-membered heterocyclic aromatic systems such as pyridine , where

176-464: The racemic form of tartaric acid "paratartaric acid" (another obsolete term: racemic acid ) in 1830. The use of the prefixes ortho , meta and para to distinguish isomers of disubstituted aromatic rings starts with Wilhelm Körner in 1867, although he applied the ortho prefix to a 1,4-isomer and the meta prefix to a 1,2-isomer. It was the German chemist Karl Gräbe who, in 1869, first used

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192-431: The current meaning is perhaps not obvious. The ortho description was historically used to designate the original compound, and an isomer was often called the meta compound. For instance, the trivial names orthophosphoric acid and trimetaphosphoric acid have nothing to do with aromatics at all. Likewise, the description para was reserved for just closely related compounds. Thus Jöns Jakob Berzelius originally called

208-599: The prefixes ortho -, meta -, para - to denote specific relative locations of the substituents on a disubstituted aromatic ring (namely naphthalene ). In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene . The current nomenclature was introduced by the Chemical Society in 1879. Examples of the use of this nomenclature are given for isomers of cresol , C 6 H 4 (OH)(CH 3 ): There are three arene substitution isomers of dihydroxybenzene (C 6 H 4 (OH) 2 ) –

224-455: The preponderance of work and applications involves unstrained organic 5- and 6-membered rings. Included are pyridine , thiophene , pyrrole , and furan . Another large class of organic heterocycles refers to those fused to benzene rings . For example, the fused benzene derivatives of pyridine, thiophene, pyrrole, and furan are quinoline , benzothiophene , indole , and benzofuran , respectively. The fusion of two benzene rings gives rise to

240-629: The specifics vary depending on the compound, in simple disubstituted arenes, the three isomers tend to have rather similar boiling points. However, the para isomer usually has the highest melting point, and the lowest solubility in a given solvent, of the three isomers. Because electron donating groups are both ortho and para directors, separation of these isomers is a common problem in synthetic chemistry. Several methods exist in order to separate these isomers: The prefixes ortho , meta , and para are all derived from Greek, meaning correct , following , and beside , respectively. The relationship to

256-421: The study of organic heterocyclic chemistry focuses on organic unsaturated rings. Some heterocycles contain no carbon. Examples are borazine (B 3 N 3 ring), hexachlorophosphazenes (P 3 N 3 rings), and tetrasulfur tetranitride S 4 N 4 . In comparison with organic heterocycles, which have numerous commercial applications, inorganic ring systems are mainly of theoretical interest. IUPAC recommends

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