Benzene, hexafluoro

At a given temperature, the cis-57/trans-55 ratio is independent of the olefin concentration over a range of 150-fold dilution with cyclohexane. Hexafluoro-benzene as diluent results in a more stereospecific reaction... 

The rhodium complex 42, containing the first example of an 2-hexafluoro-benzene ligand, has been prepared and crystallographically characterized (92). 

Figure 14.29 shows the (solid + liquid) phase diagram for (benzene + hexafluoro-benzene). A congruently melting solid molecular addition compound with the formula QFU-CeFe ) is evident in this system.26 The rounded top of the freezing curve (solid line) for the addition compound results from almost complete dissociation of the addition compound in the liquid mixture. In other words, benzene and hexafluorobenzene act as independent molecular species in the liquid state and combine together as the addition compound only in the solid state. 

One approach, which has proved revealing in the case of 9-carbena-fluorene and which may be generally applicable, is to examine the influence of additives which can deactivate electronically excited carbenes without undergoing reaction themselves (e.g. hexafluoro-benzene) or which react preferentially with carbenes of a particular spin state (e.g. oxygen and butadiene, which are both thought to react preferentially with triplet carbenes). The technique is analogous to well-... 

Although the attack of nucleophiles upon aromatic rings in the gas phase was reported more than a decade ago, not many publications on this topic have appeared since then. Thus, it was shown in earlier work that alkoxide ions react with fluorobenzene to give F and with hexafluoro-benzene to give pentafluorophenoxide anions (Briscese and Riveros, 1975), that (M + N02) adducts can be formed from reaction of N02 with < -, m-and /7-dinitrobenzenes (Bowie and Stapleton, 1977) and that (M — H + 0) ions are generated in reactions of Ot ions with benzene, naphthalene, pyridine, alkylbenzenes, methylpyridines and fluorotoluenes by displacement of a ring hydrogen atom (Bruins et al., 1978). 

Figure 13 Room-temperature reduced spectral densities for (a) acetonitrile, (b) benzene, (c) benzene-d6, (d) carbon disulfide, (e) chloroform, (f) hexafluoro-benzene, (g) mesitylene, and (h) 1,3,5-trifluorobenzene. 

The primary standard betaine dye (44) is only sparingly soluble in water and less polar solvents it is insoluble in nonpolar solvents such as aliphatic hydrocarbons. In order to overcome the solubility problems in nonpolar solvents, the more lipophilic penta-t-butyl-substituted betaine dye (45) has additionally been used as a secondary reference probe [174]. The excellent Hnear correlation between the Ej values of the two dyes allows the calculation of t(30) values for solvents in which the solvatochromic indicator dye (44) is not soluble. Introduction of electron-withdrawing substituents e.g. Cl [323], F, CF3, C6F13 [324]) in the betaine molecule reduces the basicity of its phenolate moiety, which allows the direct determination of x(30) values for somewhat more acidic solvents. Moreover, the Hpophilic and fluorophilic penta(trifluoromethyl)-substituted betaine dye (46) is more soluble in nonpolar solvents e.g. hexafluoro-benzene) than the standard dye (44) [324]. Conversely, the solubility in aqueous media can be improved through replacement of some of the peripheral hydrophobic phenyl groups in (44) by more hydrophilic pyridyl groups, to yield the more water-soluble betaine dye (47) [325]. The Ej values of these new secondary standard betaine dyes correlate linearly with the x(30) values of (44), which allows the calculation of x(30) values for solvents in which only betaine dyes (45)-(47) are sufficiently stable and soluble for the UV/Vis spectroscopic measurements [324, 325]. 

PENTANETHIOL HEXACHLORO-BENZENE HEXAFLUORO-BENZENE O-DICHLORO-BENZENE M-DICHLORO-BENZENE P-DICHLORO-BENZENE M-DIFLUORO-BENZENE O-DIFLUORO-BENZENE P-DIFLUORO-BENZENE BROMOBENZENE CHLOROBENZENE FLUOROBENZENE lODOBENZENE BENZENE PHENOL BENZENETHIOL... 

Physical Measurements and Calculations. —Reaction Kinetics and Rate Theory. The reactions of fluorinated benzenes (PhF, 1,2- and l,4-FaC6H4, lA3,4-F4C6Ha, CaFsH, and CeFe) with hydrated electrons and hydroxyl radicals In aqueous solution have been investigated by pulse radiolysis and y-irradiation experiments. Electron capture by the highly fluorinated compounds usually leads to loss of fluoride e.g. CeFe + eaq - CeFe -H F ), but radical anions formed from mono-or di-fluorobenzenes are protonated to give fluorocyclohexadienyl radicals, detected by U.V. spectroscopy fPhF -I- eaq - 7 PhF -> -CeHeF). The reaction of hexafluoro-benzene with hydroxyl radicals probably gives the pentafluorophenoxy radical... 

The Bristol group have studied the activity coefficients of benzene and fluorobenzenes in various n-alkane long-chain hydrocarbons with the aim of testing various solution theories. The activity coefficient of benzene at 323 K varies from 0.993 in hexadecane to 0.644 in dotriacontane. The trend in the fluorobenzene systems is for the activity coefficient to increase with increasing fluorocarbon substitution. For example, in the case of n-octadecane systems at 323 K, the activity coefficient for fluorobenzene is 1.130 while for hexafluoro-benzene it is 1.945. In these cases, the temperature variation of the activity coefficients was sufficiently great to warrant the determination of the infinitely dilute excess enthalpies. 

The following table gives the vapor pressure of hexafluoro-benzene (C5pg) as a function of temperature ... 

Although only the trace of the chemical shift tensor is measured in isotropic solution, in general F nuclei have large chemical shift anisotropies and in anisotropic media such as solids or liquid crystal solutions, which can include biological matrices such as membranes, the spectrum can be severely dependent on such parameters in that the observed chemical shift is dependent on the orientation of the molecule relative to the magnetic field. The definition of the chemical shift anisotropy in terms of molecule-based axes depends on the symmetry of the molecule under study but it can easily have a magnitude of tens or hundreds of ppm, for example, being 158 ppm in hexafluoro-benzene, which has an isotropic shift of — 163 ppm. 

Over short ranges, equations (16) and (18) can be adjusted to fit the best results within the precision of the measurements, and the range of high quality fit can be increased if more terms are added to equation (18). For example, terms in T and T were used by Douslin, Harrison, and Moore for the representation of their accurate measurements on hexafluoro-benzene. ... 

The photochemical introduction of a methylol group into hexafluoro benzene succeeds also with pentafluoro pyridine, yielding a mixture of the 2- and the 4-isomer [754]. 

On the other hand, it is well known that perfluoro arenes, for example, hexafluoro-benzene or octafluoronaphthalene, form some type of complex with their hydrocarbon parent compounds, having melting points higher than those of the pure components [76]. Very recently, the deuterium NMR spectra of the octafluoronaphthalene/ naphthalene system have been explained in terms of a highly ordered columnar mesophase [76 d]. However, the face-to-face stacking in such solids and also in liquids is... 

Many polyfluorobenzenes undergo photochemical valence-bond isomerization to give, in most cases, one or more para-bonded isomers. Hexafluoro-benzene gives up to 60% of hexafluorobicyclo[2,2,0]hexa-2,5-diene (111)... 

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