Fluorobenzene radical

TABLE 22. Isotropic coupling constants (gauss) for fluorobenzene radical anions and radical cations... 

Table 4 Summary of important electronic energies, for the interacting states of the fluorobenzene radical cations including the quadratic coupling terms (QVC). The diagonal values represent the minima of the diabatic potential energies, off-diagonal entries are minima of the corresponding intersection seams. Three dots (...) indicate missing results...

A mechanism analogous to that of equation 14 has been proposed to account for the observation by ESR of the predominant production of phenoxyl radical on reaction of OH with fluorobenzene at pH 1.8, where the fluorobenzene radical cation is assumed to be an intermediate (equation 15). 

This idea is based on the assumption that hydration of the radical cation occurs predominantly at the ipso position. This is reasonable on the basis of estimates" of the charge distribution in fluorobenzene radical cation. The mechanism in equation 15 is, however, not likely for oxidative dehalogenation of halophenols" at pH 4.5 since the halophenol radical cations would deprotonate before they had a chance to react with water. With substituted phenols, therefore, the observed semiquinones are probably produced via equation 14. 

Gindensperger E, Baldea 1, Franz J, Koppel H (2007) Multi-state vibronic interactions in the fluorobenzene radical cation the importance of quadratic coupling terms. Chem Phys 338 207... 

Figure 8 Multiphoton excitation and ion spectroscopy Bottom spectrum cold, mass selected UVspectmm (S, <- So transition) of fluorobenzene, providing wavelengths for efficient and selective ionization. Middle spectra photoelectron spectra induced by UV-resonance enhanced two-photon absorption. Choosing different intermediate states [S,(0,0) or S,(6b )] results in different populations of the final fluorobenzene radical cations. Top spectrum spectroscopy of the excited ionic state of the fluorobenzene radical cation measured by muKiphoton dissociation spectroscopy. The ions have been prepared via the neutral 0°o transition. A special excitation scheme has been used to optimize cation spectroscopy (for further details see text).

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

Fluorescence was observed for the TMB family such as 3,5-dimethoxyphenol, l,3-dihydroxy-5-methoxybenzene (5-methoxyresorcinol), l-acetoxy-3,5-dimethoxyben-zene, and l,3,5-trimethoxy-2-methylbenzene. These results indicated that complete symmetry of the substitution on O atoms is not necessary to observe fluorescence from the TMB family, and that the variation of parent molecules of fluorescent radical cation is possibly performed [153]. Fluorescence was also detected from hexamethxybenzene as an example of pseudo-Dgh molecules. The discussion of the symmetry has been described here on the fluorescence from fluorobenzenes in the vapor-phase or noble gas matrices. 

Reaction of CF with benzene generates the 7-fluoronorcaradien-7-ly radical (39), which abstracts hydrogen (from added isobutane) and opens to 7-fluorocyclohepta-triene (40). Cycloheptatriene (10) is trapped as tropylium fluoroborate (41) by the addition of BF3 (Eq. 21)P An additional product of CF + benzene is fluorobenzene (42), in which labeling studies demonstrate that the attacking carbon contains the fluorine in 42. The interesting transfer of CH in Eq. 28 is proposed to account for the formation of 42. " ... 

Table 3 shows that the fluoroarene yield increases with the irradiation power and is dependent again on the hydrogen fluoride/pyridine ratio (cf. 2-methoxy-4-nitroaniline). An optimum ratio must, most probably, be determined for each substrate. It should also be noted that photochemical fluorodediazoniation does not occur in pure hydrogen fluoride. This observation probably implies that not only light is involved in the weakening of the C-N bond. On the other hand, benzene is formed together with fluorobenzene when pyridine is replaced by 2,4,6-trimethylpyridine such a phenomenon is consistent with the occurrence of aryl radicals."... 

Direct fluorination of aromatic rings is so exothermic that a tarry mixture of products is obtained. Reaction of benzene with the xenon fluorides, XeF2 or XeF4, does give fluorobenzene, but the mechanism is probably free radical rather than polar.137... 

For some of these compounds, the protonic hyperfine coupling constants are known. The isotopic A /Ap ratio is 1.21 for radicals produced by addition to C6H6 and to the ortho position of C6H5CH3 and 1.15-1.18 for several fluorobenzenes (133). Quantum chemical calculations that include averaging over 33 vibrational modes in CeH7-C6H6Mu have shown that the dynamics account quantitatively (A /Ap = 1.16) for the... 

Figure 15 shows the extrapolated fluorine enhancement for the case of different fluorobenzenes as a function of the degree of fluorine substitution, for two different radicals DPPH and Galvinoxyl. The behaviour for the two radicals is markedly different and indicates that when scalar coupling is present, care must be taken in generalizing conclusions obtained from measurements with only one radical. 

When substitution takes place, the relation between the amounts of the isomers formed is influenced by (1) the group present, (2) the group introduced, (3) the temperature, and (4) the catalyst, if one is used. (1) In the classification given above all the groups in the first division send an entering element or radical to the para and ortho positions, but the groups differ among themselves in their effect on the relative proportion of the two isomers formed. For example, when fluorobenzene and chlorobenzene are nitrated at 0 , the mixture of ortho and para nitro-derivatives obtained contains in the first case 12.4 per cent and m the second, 30.1 per cent of the ortho compound. (2) While the... 

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