Spectroscopy of Thiophenes

J3 4 = 3.45-4.35 J2-4 = 1.25-1.7 and J2-5 = 3.2-3.65 Hz. The technique can be used quantitatively by comparison with standard spectra of materials of known purity. C-nmr spectroscopy of thiophene and thiophene derivatives is also a valuable technique that shows well-defined patterns of spectra. C chemical shifts for thiophene, from tetramethylsilane (TMS), are 127.6, C 125.9, C 125.9, and C 127.6 ppm. 

Synthesis, Determination of Physical Properties, Molecular Structure and Spectroscopy of Thiophene and its Homologs. 

Ch. 2 Biological and Pharmacological Activities of Thiophene and Its Derivatives Ch. 3 Syntheses and Physical Properties of Thiophene and Its Derivatives Ch. 4 Molecular Structure and Spectroscopy of Thiophene and Its Derivatives Ch. 5 Factors Affecting Substitution Reactions in the Thiophene Nucleus... 

The example of B5H9 serves to show how the chemical shift may be used as an aid to determining the stmcture of a molecule and, in particular, in deciding between alternative stmctures. There are many examples in the literature of this kind of application which is reminiscent of the way in which the chemical shift in NMR spectroscopy may be employed. However there is one important difference in using the two kinds of chemical shift. In XPS there are no interactions affecting closely spaced lines in the spectmm, however close they may be. Figure 8.15 illustrates this for the C lx lines of thiophene. In NMR spectroscopy the spectmm becomes more complex, due to spin-spin interactions, when chemical shifts are similar. 

Ir Spectroscopy. Significant absorptions can be identified as characteristic of particular substitutions within families of thiophene derivatives. The most widely studied in this connection are probably the halothiophenes, where absorption bands have been characterized. This is usehil for qualitative analysis, but has also been used quantitatively in association with the standard spectmm of materials of known purity. 

The precise geometrical data obtained by microwave spectroscopy allow conclusions regarding bond delocalization and hence aromaticity. For example, the microwave spectrum of thiazole has shown that the structure is very close to the average of the structures of thiophene and 1,3,4-thiadiazole, which indicates a similar trend in aromaticity. However, different methods have frequently given inconsistent results. 

The tautomerism of 2- and 3-aminothiophenes was mentioned by Hartough in his review of thiophenes/ but the first definite evidence became available in 1961 when Hoffman and Gronowitz showed conclusively by nuclear magnetic resonance spectroscopy that these compounds both exist in the amino form. In agreement with this finding, 3-aminothiophene generally behaves as an aromatic amine. ... 

The reaction of tetrafluorobenzyne with iV-methylpyrrole leads to a good yield of the adduct (106), and with thiophen to tetrafluoro-naphtha-ene 56>. That this latter reaction was the first example of a Diels-Alder reaction of thiophen was shown by following the reaction by XH n.m.r. spectroscopy. Evidence for the intermediacy of the episulphide (107) was obtained. 

The use of organic polymers as conductors and semiconductors in the electronics industry has led to a huge research effort in poly(thiophenes), with a focus on the modification of their electronic properties so that they can behave as both hole and electron conductors. Casado and co-workers [60] have performed combined experimental and theoretical research using Raman spectroscopy on a variety of fluorinated molecules based on oligomers of thiophene, an example of one is shown in Figure 7. 

The potentially tautomeric side-chain thiol systems exist mainly in the thiol form in liquid solution and in the gas phase, as found by IR and NMR spectroscopy and by a study of ionization potentials.126 Upon alkylation using the ion-pair extraction method, only the S-alkylated compounds were obtained. The synthesis, reactions, and properties of some selenides of thiophene, furan, and selenophene have been reviewed.127... 

Modelli and coworkers126 studied by PES and ETS (electron transmission spectroscopy) some silicon and tin derivatives of thiophene and furan, with the aim of following the energy gap between the HOMO and the LUMO as a function of the substituents. In particular they investigated the following tin derivatives ... 

J.K. Herrema, P.F. van Hutten, R.E. Gill, J. Wildeman, R.H. Wieringa, and G. Hadziioannou, Tuning of the luminescence in multiblock alternating copolymers. 1. Synthesis and spectroscopy of poly[(silanylene)thiophene]s, Macromolecules, 28 8102-8116, 1995. 

Proton NMR spectroscopy is an ubiquitous tool for the structural elucidation and study of properties of thiophenes. Both the chemical shifts and the coupling constants provide... 

In view of the existing confusion on the IR spectroscopy of benzo[6]-thiophenes, it is evident that problems of orientation are best approached by the joint application of IR and other spectroscopic techniques. 

Since the ionization potential of thiophene is relatively high, the electric fields required for its anodic polymerization are rather steep (= 20V vs SCE). In addition, the simplest supporting electrolyte for this operation is Li BE- and deposition of Li at the cathode (usually Pt) is also energetically unfavorable. Recently, Druy (13) reported that substitution of 2,2 -bithiophene for thiophene gave better quality films, probably due to the lower ionization potential of the dimer relative to thiophene. An additional improvement consisted in replacing the Pt counter electrode by A1 (9). Spectroscopy revealed that dedoped PT films produced with the above improvements were indistinguishable in quality from the chemically coupled PT. 

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