Thiophene, structure

For the reaction with u-heptane, Friedmann again postulated the hydrocarbon isomerization. He obtained two products, C HjoS (A) and C7HJS2 (B). The structure of methylthieno[2,3-6]thiophene was ascribed to product B, though again there seems to be no reason to neglect the isomeric methylthieno[3,2-t]thiophene structure. 

Potential fuel stability problems especially if sulfur exists in thiophene structure. 

The synthesis of other poly(arylene ether)s containing thiophene units concerned the reaction of two activated halides containing thiophene (structures 8 and 9) with bisphenol A [44,45]. The polymers from the monomers of structures 8 and 9 and bisphenol A had intrinsic viscosities (NMP, 25 °C) of 1.23 and 0.43 dL/g and Tgs of 158 and 120°C, respectively. 

Though it has long been known that the more highly condensed thiophene structures, such as dibenzothiophene and especially their alkyl-substituted derivatives, have low HDS reactivity (21, 25-29), it is only recently that study in this area has intensified. Researchers throughout the world are now actively seeking understanding of the fundamental causes of low reactivity and attempting to find means to circumvent the problems (29-33). 

Calculation results on a possible unified approach fit the experimental data (Figure 2) (99H(50)1115). Ab initio calculations showed a different level in the Dewar thiophene (02JPP(A)(149)31). More recently, the possible presence of a cage thiophene structure into the photoisomerization has been studied in order to explain some results that cannot be rationalized by using the above-described approach (09H(78)737). 

Figure 2 shows the results of the pyrolysis experiments conducted with the Spanish lignite at 750-960°C at residence times of 0.52-0.72 sec. It is seen that under the pyrolysis conditions used, 60 - 70% of the sulfur in this coal appears in the gaseous products as H2S, COS, and CS2. As in the previous sulfur study (1), the principal sulfur gaseous product at all temperatures is H2S, with some CS2 formed at T >840°C. The CS2 is apparently formed at the expense of the H2S, by any of several reactions H2S may react with the carbon of the coal and/or the methane evolved in the pyrolysis of the coal to form CS2- A small amount of COS is detected at all temperatures trace amounts of SO2 are also detected. Moreover, the total sulfur yield appears to reach a maximum about 900°C. The decrease in sulfur volatilization as pyrolysis temperature is increased above 900°C is attributed to sulfur retention in the char due to the reaction of H2S with coke or char to form more stable thiophenic structures (2). GC/MS analysis of the tars (diluted to 10 ml) from the pyrolysis at 750 and 850°C did not reveal any sulfur-containing structures. Tars from the pyrolysis at 900 and 950°C, however, contain dibenzothiophene. 

Pharmaceuticals and Agrochemicals. ThioglycoHc acid and its esters are useful as a raw material to obtain biologically active molecules. In cephalosporine syntheses, (4-pyridyl)thioacetic acid [10351-19-8] (65) and trifluoromethane (ethyl) thioglycolate [75-92-9] (66) are used as intermediates. Methyl-3-amino-2-thiophene carboxylate can be used as intermediate for berbicidal sulfonylureas (67) and various thiophenic structures (68). 

The nature of vibronic coupling in fused polycyclic benzene-thiophene structures, including benzodithiophene 45, naphthodithiophene 111, and anthradithiophene 112, has been studied using an approach that combines high-resolution gas-phase photoelectron spectroscopy measurements with first-principles quantum-mechanical calculations <2006CEJ2073>. 

The Dewar thiophen structure (232) of the photoproduct of tetrakis(trifluoro-methyl)thiophen (233) has been confirmed.188 The possible intermediacy of a... 

In an open system some isotopic discrimination between the rubber-like polymer (PCLM) and the H2S formed is expected. This is due to two stages (1) attack to form the C-Sx bonds and (2) the extraction of hydrogens to form the H2S leading to the aromatic stable thiophenes structure. This discrimination for the open systems was lately demonstrated by us also for the reaction of elemental sulfur with unsaturated hydrocarbons (unpublished results). Nevertheless, since the system described above is totally closed (hydrocarbons and elemental sulfur in ampoule), remixing of the sulfur reservoir and its isotope ratio occurs. The above results support the suggested high temperature re-reaction of previously released reduced sulfur with no isotopic discrimination under closed vessel reactions. 

Kiebooms, R., et al. 1996. Poly(tetrafluorobenzo[c]thiophene). Structure analysis of oligomers and model compound based on ID and 2D NMR spectroscopy. Macromolecules 29 5981. 

Alkylation of Thiophene Poly(3,4-Ethylenedioxythiophene) and Sulfur Derivatives Reduced Bandgap Polymers Based on Chalcogen 3,4-Substituted Thiophenes Structural Modifications of EDOT Functionalized EDOT Derivatives... 

Dewar thiophenes are thiiranes fused to cyclobutene rings. While the reversion of the tetrakis(trifluoromethyl) derivative to the normal thiophene structure requires a high temperature (r 1/2 160 , C Hg] 5.1 hr), the transformation can be achieved at room temperature by phosphines (86) such as Ph3P. A 1 1 adduct can be isolated when PhjPCl is added to the Dewar thiophene. However, the harder PhPCl2 and PCI3 and pentacovalent phosphorus compounds are totally ineffective for the isomerization. 

Several nematicidal acetylenic compounds have been isolated most possess thiophene structures and are from members of the Asteraceae family. Another recently isolated compound with this activity is (8/ ,9jR,10S)-9,10-epoxyhep-tadec-16-ene-4,6-diyne-8-ol (16) from Cirsium japonicum (Kawazuetal, 1980) (Fig. 3.13). l-Phenylhepta-l,3,5-triyne and 2-phenyl-5-(l -propynyl)-thiophene from Coreopsis lanceolata and Z-dehydromatricaria ester (5) from Solidago altissima have been shown to be fly ovicidal substances (Seigler, 1983). 

Since this book deals with thiophenes, we will not dwell on the more estabUshed small molecular organic semiconductors but will focus on oligo(thiophenes) and poly(thiophenes). Oligo(thiophenes) can be viewed both as materials with great potentials for devices, partly because of their high field-effect mobilities, and also as finite model systems for the poly(thiophenes). Structures of some oligo(thio-phenes) are shown in Fig. 2. 

The employment of substituted 2-aminothiophenes in such areas represents the latest discovery showing a great promise in materials chemistry for the generation of novel oligo- and poly- thiophene structures. 

Schematically show and compare the results of n-doping of a conventional semiconductor (e.g. Si with P) and a CP (e.g. poly(thiophene) with tetrafluo-roborate), using band structure diagrams, and molecular (for Si) and chain (for poly(thiophene)) structures. 

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