Furan molecular structure

Furano( 1,4)naphthalenophane conformation, 4, 538 Furanonaphthalenophanes molecular structure, 4, 5 Furan-2-one, tetrahydro-reactions, 4, 656... 

The most extensive research on furanic polyamides is recent (33) and deals essentially with furanic-aromatic structures, although an important effort was also devoted to all-fiiranic compositions. The reaction of the diacid 11a with various aromatic diamines leads to high-molecular weight polymers with good thermal stability and ciystallinity. Structure 23, obtained with p-phenylenediamine, exhibited features resembling closely those of polyaramides ... 

PBDEs are a class of chemicals widely used as flame retardants in a variety of applications. They are ubiquitous in the environment and have been detected in various environmental media including air [76, 77], water [78], biota [1, 79], soil [80], sediments [81, 82], house dust [83,84], cars [85], humans [86] and sewage sludge [87]. PBDEs are similar in molecular structure to several well-known POPs such as PCBs and dioxins/furans. They have very similar physicochemical properties and, like these compounds, PBDEs are of environmental concern because of their high lipophilicity, persistence and resistance to degradation [88-90]. 

The optical absorption spectrum of the solvated electron presents a broad, featureless, but very intense band with a maximum ranging from the visible (500-700 nm for alcohols and aqueous solutions) to the infrared (above 2000 nm for tetrahydro-furan or diethylether, for instance) depending on the medium (Fig. 2). On the whole, the maximum of the absorption band of the solvated electron shifts to higher wavelengths as the dielectric constant of the solvent diminishes. However, the absence of a simple correlation between the maximum and the dielectric constant or the dipolar moment of the solvent suggests that the position of the absorption spectrum is mostly governed by the molecular structure of the liquids. 

A consideration of the results of molecular structural determinations of furan,194 pyrrole,196 thiophene,196 and selenophene197-198 shows that bond alternation as exemplified by the ratio (R) of the C-2-C-3 to C-3-C-4 bond lengths decreases in the order, furan (R = 0.950), selenophene (R = 0.956), pyrrole (R = 0.959), and thiophene (R=0.964). Whether this corresponds to an aromaticity scale,189 considering that the bond angles at the heteroatom are widely divergent, is a matter for debate. The X-ray structure determination199 of 1,2,5-triphenylphosphole is discussed later. 

Information about molecular dimensions may be obtained by liquid-crystal NMR spectroscopy. Molecular structure determined thus for furan <830MR(21)143, 85MRC725, 89JST(I96)1> is in fair agreement with the results derived from the microwave spectrum for benzo[6]furan <820MR(18)157> and for dibenzofuran <840MR(22)547>. For the latter compounds, deviation from planarity has been observed in agreement with the crystal structures. 

These conjugated oligomers are likely to form organized molecular assemblies if coupled with suitable complementary structures. The dimers la and Ila-IId were made to react with various aromatic mono- and diamines in order to build mesogenic molecular structures capable of giving rise to thermotropic liquid ciystals ( ). When the dimer moiety was entirely furanic, no mesophase appeared, whereas the thiophenic and mixed moieties produced clear-cut nematic phases. 

Figure 57 (a) Molecular structures of thiophene and furane-appended fuUerene derivatives I-III (b) schematic illustration of the... 

Furan resin is a generic term for a thermoset resinous product that contains a heterocyclic unsaturated furan ring in its molecular structures. Pentosans from com cobs and rice hulls are the main sources for the key ingredient, furfural. Commercially, the furfural alcohol polymer is the most important. All furan resins are dark in color and have a reddish-black appearance when catalyzed to cure they become black. 

Tricarbonyl(vinylketene)iron(0) complexes were shown to react with dimethyl maleate, dimethyl fumarate, ( )-methyl 4-oxopent-2-enoate and ( )-ethyl 4,4,4-trifluorobut-2-enoate to give decarbonylated adducts. " New (77 -azadiene)Fe(CO)3 complexes containing furan, thiophene or ferrocenyl moieties at the G terminus of the heterodiene complexes have been prepared.X-ray crystal structures and extended Hiickel calculations of the new materials have been reported. Gomplexation of Fe2(GO)9 with iV,iV -bis(3-phenylallylidene)hydrazine in refluxing THF affords new ( 7" -azadiene)Fe(GO)3 complexes.Molecular structures of the new complexes have been confirmed by X-ray diffraction studies. 

A series of alkyl-substituted anthracenes (14,18, and 24) were prepared from Diels-Alder reactions of bis(benzyne) equivalent 4 or dehydronaphthalene equivalent 8 with alkyl-substituted furans (11 or 27). The structural features of the crystals were characterized by X-ray crystallographic analysis. Depending on the length, position, and number of alkyl side chains, the molecular structures (alkyl conformations) and packing arrangements of the alkyl-substimted anthracenes changed drastically. Consequently, such modifications led to diffaent fluorescait properties for the anthracenes in the solid-state. 

FIGURE 142.4 Molecular structure of mono- and diadducts between psoralen and thymidine. 1 furan side monoadduct involving the 4, 5 double bond of psoralen and the 5,6 double bond of thymidine 2 Pyrone side monoadduct involving the 3,4 double bond of psoralen and the 5,6 double bond of thymidine 3 diadduct involving... 

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