Heteroaromatic compounds definition

Other Organic Substances. Spectral data on other organic substances detected in samples of the Paleozoic rocks treated with dilute hydrochloric acid and distilled, are given in Table VI. The substances possibly represent aromatic and heteroaromatic compounds such as anthracene, naphthalene, pyridines, and phenols, but a more definite characterization has not been completed. The compounds seem to be present in only a few parts per million. 

Interconversion between two tautomeric structures can occur via discrete cationic or anionic intermediates (scheme 24, where T is an anion capable of reacting with a proton at a minimum of two distinct sites). Alternatively, interconversion can occur by simultaneous loss and gain of different protons (scheme 25, w here T has the same definition as in scheme 24). These mechanisms are well established for acyclic compounds, but they have been much less thoroughly investigated for heteroaromatic systems. The rate of interconversion of two tautomers is greatest when both of the alternative atoms to which the mobile proton can be attached arc hetero atoms, and isolation of the separate isomers is usually impossible in this case. If one of the alternative atoms involved in the tautomerization is carbon, the rate of interconversion is somewhat slower, but still fast. When both of the atoms in question are carbon, however, interconversion is... 

For this review, heterophanes are considered to contain one or more heteroaromatic ring(s) bridged by a non-aromatic chain of atoms. Although a certain arbitrariness identifies (1) but not (2), as a heterophane, this definition focuses attention on the chemistry appropriate for this review and makes the volume of literature to be reviewed more manageable. Different nomenclature approaches for heterophanes have been proposed (70T5847,72T5183, 72TL2109) as alternatives for the currently accepted, complex IUPAC or Chemical Abstracts names, which actually obscure the phane structural element in these compounds. A proposal... 

Heteroaromatic A-imines are photochemically active compounds (see Table III) On irradiation they generally yield products of (a) N-N bond cleavage, (b) ring enlargement, (c) rearrangement. However, the available data do not permit definition of the conditions necessary for selective reactions. Apparently unimportant changes in the substituents and the solvent may lead to different results. Therefore, the photochemical reactions will be discussed separately for the individual A-imines. 

A detailed study was carried out on the radical anion derived from (10c) (Table 2) in connection with the conformational analysis of heteroaromatic carbonyl compounds. Notably different ESR signals could be observed originating from distinct rotational isomers. Unfortunately no information on the interconversion of the rotamers of (10c) could be definitely derived since these radicals were highly unstable at the temperature necessary for interconversion <74JCS(P2)562>. 

The aromatic cyanates are of much more importance. If phenols are treated with cyano halides in such a way as to definitely prevent an excess of the corresponding phenolate, aryl cyanates can be isolated in up to quantitative yields. To achieve this, triethylamine is slowly added to an equimolar mixture of the phenol and the cyano halide in a nonprotic solvent, preferably acetone or n-pentane/diethyl ether (equation 27). ° Heteroaromatic hydroxy compounds can be treated in the same way. The method fails, however, if various electron-attracting substituents are present, as for instance with 2,4-dinitrophenol or polyhalophenols. ° ... 

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