Hexafluorobenzene, effect

The choice of solvent may have a critical impact on efficiency too. In metathesis, dichloromethane, 1,2-dichloroethane and toluene are the solvents most commonly used. There are examples that show much higher yields in ring closing metathesis (RCM) when using fluorinated solvents [150]. An impressive effect of hexafluorobenzene as a solvent for CM is the modification of the steroid 93 the use of 1,2-dichloroethane leads to a very low yield and significant amounts of dimerisa-tion while the same reaction proceeds in 90% yield in C F (Scheme 3.14) [151]. 

Figure 3. Effect of water on the reaction of hexafluorobenzene and bisphenol-A in chlorobenzene in the presence of 18 crown-6 catalyst. Products of the catalyzed reaction were oligomeric materials. No reaction is observed under the experimental conditions in the absence of the 18-crown--6 catalyst. (Reproduced with permission from reference 14, Copyright 1985 John Wiley.)...

Neelakandan M, Pant D, Quitevis EF. Reorientational and intermolecular dynamics in binary liquid mixtures of hexafluorobenzene and benzene femtosecond optical Kerr effect measurements. Chem Phys Fett 1997 265 283-292. 

The combination of these three factors could explain why hexafluorobenzene (F/C =1.0) is the fastest polymerizing monomer among hydrocarbons and perfluorocarbons, and the effect of pulsed radio frequency discharge is significantly different in hydrocarbons and perfluorocarbons. 

Rule 4 The number of anti-fluorous functional groups capable of attractive in-termolecular interactions, via electrostatic forces, hydrogen bonds, or dispersion interactions must be minimized [16]. An example of such an anti-fluorous effect is the low fluorophilicity of hexafluorobenzene (12) and pentafluorobenzene (13) despite their high relative fluorine content. Both compounds can participate in specific electrostatic interactions with electron-rich hydrocarbons, for example the toluene component of the biphasic test mixture. 

Note that the fit of the AC model for hexafluorobenzene (11.0%) is better than the AC model for s-tetrazine (16.6%, Table 8), and also that the improvement in fit given by the LP model is less in hexafluorobenzene (4.3%) than in s-tetrazine (1.6%). So, contrary to expectation based on the larger electronegativity of fluorine, lone-pair effects as modeled here are less important in hexafluorobenzene than in s-tetrazine. In fact. Table 11 shows that a better fit to the electric potential of these fluorocarbons can be obtained by placing sites at the centers of the C—F bonds. 

The kinetic data in Figure 2.2 indicate that carbene 10, under the conditions of our TRIR experiments, does not form ketene 11, in contrast to the observed reactivity of acyclic carbene 7. Platz and co-workers [94] determined that carbene 7 is separated from ketene 8 by a 3.4 kcal/mol barrier in hexafluorobenzene. It is likely that the higher singlet/triplet gap for carbene 10 relative to that of 7 raises the effective barrier to rearrangement. We find, by monitoring the lifetime of carbene 10 as a function of concentration of diazoester 9, that 10 is effectively quenched by 9 with /tdiazo=(5.0 0.5) x 10 M s in Freon-113. This observation suggests that a major decay route of the carbene under the conditions of our experiment is formation of azine 16. 

The centroid-to-anion distance varies from 2.554 to 3.230 A (see Table 1). The effects of the complexation of the anion to the CeFe molecule are shortening of the C - C bonds (0.004 A) and a lengthening of the C - F bonds (0.006 A). On complexation, the fluorine atoms move slightly towards the anion and the plane formed by the carbon atoms is about 0.02 A further away from the anion than that formed by the fluorine atoms. The hexafluorobenzene molecule adopts a cup conformation. 

Besides the earlier demonstrated possibilities for the polyfluorinated aromatic compounds to add the electrophiles Cl" and CHj, the addition of F and Br" has also been effected Thus the interaction of hexafluorobenzene with the... 

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