Heterocycles thiophenes

Heterocoagulation Heterocyclic Heterocyclic amines Heterocyclic azo dyes Heterocyclic compounds Heterocyclic dyes Heterocyclic polymers Heterocyclic thiophenes Heteroepitaxy Heterogeneous catalysis Heterogemte Heteroglycan Heterojunction... 

This subject will be restricted almost exclusively to consideration of the fragmentation behavior of the parent heterocycle, thiophene (1). This approach is dictated chiefly by the fact that only for thiophene is a large enough information pool available for a reasonable analysis of the fragmentation pattern. For benzothiophenes there is very little systematic information available (8lAHC(29)l7l). 

A different explanation was identified in the quenching properties of these heterocycles. Thiophene and mono methyl derivatives are efficient quenchers of triplet benzophenone. The Stem-Volmer plot showed a linear relationship [104, 105]. On the contrary, 2,5-dimethylthiophene (a compound able to give the cycloaddition reaction) is not a good quencher of benzophene [106]. N-Benzoylpyrrole also does not act as a quencher of the triplet benzophenone [106]. On the contrary, pyrrole and selenophene are quenchers of the excited benzophenone [106]. In this case, the Stern-Volmer plot is not linear. This situation is commonly encountered when the quencher employed quenches two excited states. It seems reasonable that pyrrole acts as quencher of both triplet benzophenone and the exciplex between triplet benzophenone and pyrrole [106]. 

In the 7] -(S)-coordinated thiophenes, the sulfur appears to be sp -hybridized the metal does not lie in the plane of the thiophene. They are all weakly coordinating compared to THT (a dialkyl sulfide type of molecule) consequently, such complexes can be isolated only in some special cases. The tendency to coordinate to metal ions in the 77-(S) mode generally increases in the order T < BT < DBT. (As per the normal convention, the unstarred symbols T, BT, and DBT refer to the unsubstituted heterocycles thiophene, benzo[. ]thiophene, and diben-zo[i, . thiophene, respectively, while a star indicates the inclusion of substituted thiophenes as well. Cp and Cp refer to the 77 - bound CsHs and CsMcs, respectively.)... 

The formation of borylated heterocyclic componnds has attracted mnch interest with regard to their use as starting materials for cross-conpling reactions, the possible formation of interesting macrocyclic species, and their applications in optoelectronic materials. Several synthetic routes are available for the borylation of the five-membered heterocycles thiophene, furan, pyrrole, and related componnds (101-103 ... 

Molybdenum disulfide catalysts, promoted by cobalt or nickel, are used to remove organosulfur compoimds from crude petroleum by hydrogenolysis— hydrodesulfurisation or HDS [124,125,126], These compounds are imdesirable because they poison motor vehicle autoexhaust catalysts and bum to sulfur dioxide, an environmental pollutant. The most difficult compounds to desulfurise are sulfur heterocyclics thiophene, benzothiophene, dibenzothiophene and their methyl substituted derivatives. A typical reaction is the removal of sulfiir from thiophene ... 

The unsaturated phosphorus compounds depicted in Fig. 5.12 show a quinoidal structure, and resonate in the normal range for a P=C double bond. The thienyl derivative has an electron-rich heterocycle (thiophene) as parent compound. The... 

Resonance energies have been determined for the three heterocycles thiophene has the highest value (29.1 kcal/mol), which is similar to that for pyridine (27.9 kcal/mol), whereas pyrrole has the value 21.6 kcal/mol, and furan 16.2 kcal/mol. These values clearly are consistent with the view that these rings possess the extra stabilization associated with the presence of high electron delocalization. 

Five-membered aromatic heterocycles, thiophenes, furans, pyrroles, and other jt-excessive systems are reluctant, of course, to react with nucleophilic reagents. Contrary to that, nitro- or aza-activated derivatives of azoles undergo nucleophilic displacement of hydrogen rather smoothly. A great deal of both oxidative Sn (AO) and eliminative Sn (AE) reactions in the series of nitroazoles (nitropyrrole, nitrofuran, nitrothiophene) or aza-activated azoles (imidazoles, thia-zoles, oxazoles), as well as their benzo analogues, have been documented in the literature [10-18, 45, 123-128]. 

J. K. Winkler, W. Karow, and P. Rademcher, Gas-phase pyrolysis of heterocyclic compounds, part 1 and 2 flow pyrolysis and annulation reactions of some sulfur heterocycles thiophene, benzo[6]thiophene, and dibenzothiophene. A product-oriented study, J. Anal. Appl. Pyrolysis 62(1), 123-141 (2002). 

Thiophene is an aromatic heterocycle thiophene-1-oxide (or thiophene-S-oxide) is stiU aromatic, whereas thiophene-1,1-dioxide (or thiophene-S,S-dioxide), having both electron pairs engaged in the formation of sulfur-oxygen bonds, is no longer aromatic [1-3]. 

Sulfolane is the most common commercially available sulfone solvent. The solvent, also known as tetrahydrothiophene-1,1-dioxide, is a colorless, highly polar liquid consisting of a fully hydrogenated five-member sulfur-carbon heterocyclic thiophene ring. The solvent is available as both anhydrous sulfolane and as sulfolane containing 3 wt% deionized water. Sulfolane is used as a reaction medium, as a solvent for a wide variety of organic chemicals and polymers, and as an extraction solvent. 

S- from S,N-Heterocyclics Thiophenes from 2-methyl-J -thiazolines... 

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