Fluorine effect chemistry

In short, the net effect of fluorine atom chemistry on ozone destruction is very small, lCL-lO4 times smaller than the effect of chlorine on a per-atom basis (Sehested et al., 1994 Ravishankara et al., 1994 Li et al., 1995b Lary, 1997). 

The repulsive destabilization of sp -bound fluorine results in peculiar reactivity which has no real counterpart in hydrocarbon chemistry. This quite unique behavior of fluorinated olefins and arenes is summarized under the term special fluorine effect (as opposed to the previously discussed general fluorine effect ). The photochemically induced (Scheme 2.36) or fluoride ion-induced (Scheme 2.37) rearrangements observed can be rationalized as the system trying to reduce the number of energetically unfavorable fluorine atoms bound to sp -hybridized carbon. 

The 1,3-dipolar cycloadditions offluonnatedallenes provide a rich and varied chemistry Allenes, such as 1,1-difluoroallene and fluoroallene, that have fluorine substitution on only one of their two cumulated double bonds are very reactive toward 1,3-dipoles Such activation derives from the electron attracting inductive and hyperconjugative effects of the allylic fluorine substituent(s) that give nse to a considerable lowering of the energy of the LUMO of the C(2)-C(3) n bond [27]... 

Although modern chemistry allows development of even more effective rocket propellants, energy efficiency is not the only consideration factor. For example, fluorine and its derivatives arc better oxidizers than oxygen, but their extreme toxicity make them environmentally dangerous. The same concerns prevent the use of beryllium hydride—an excellent fuel that combines high density with the energy efficiency comparable to liquid hydrogen. 

The reason that organic chemists are interested in compounds that contain fluorine is simple. Because of fluorine s steric and polar characteristics, even a single fluorine substituent, placed at a propitious position within a molecule, can have a remarkable effect upon the physical and chemical properties of that molecule. Discussions of the impact of fluorine on physical and chemical properties of compounds have appeared in numerous reviews and textbooks.1-8 There are also a number of recent reviews on the subject of fluorine in medicinal chemistry.9-13... 

Like nitrogen fluorides, compounds having an O—F bond are also very strong oxidants and, when utilized as such, are effective sources of electrophilic fluorine. Because the O—F bond is so weak, the chemistry of such compounds approaches that of F2 itself, and such chemistry can be free radical or electrophilic in nature, depending on the conditions and the reactants. 

A very impressive example of the synthetic utility of this chemistry is the one-pot enantioselective double G-H activation reaction of 86 to generate chiral spiran 87 (Equation (73)).172 In this case, the phthalimide catalyst Rh2(enantiotopically selective aromatic C-H insertions of diazo ketoesters (Equation (74)).216 Moreover, dirhodium(n) tetrakisIA-tetrafluorophthaloyl- )-/ /-leucinate], Rh2(hydrogen atoms of the parent dirhodium(n) complex are substituted by fluorine atoms, dramatically enhances the reactivity and enantioselectivity (up to 97% ee). Catalysis... 

In closing of this general introduction it may be said that the development of the applied chemistry of fluorine, which started with fluorination of substances has led to surface fluorination of materials, which is now an effective tool in changing of surface properties. 

Fluorinated carbonates were also used by Smart et al. as low-temperature cosolvents (Table 12), in the hope that better low-temperature performances could be imparted by their lower melting points and favorable effects on SEI chemistry. Cycling tests with anode half-cells showed that, compared with the ternary composition with nonfluorinated carbonates, these fluorinated solvents showed comparable and slightly better capacity utilizations at room temperature or —20 °C, if the cells were charged at room temperature however, pronounced differences in discharge (delithiation) capacity could be observed if the cells were charged (lithiated) at —20 °C, where one of these solvents, ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), allowed the cell to deliver far superior capacity, as Figure 63 shows. Only 50% of the capacity deliverable at room temperature was... 

D.H. Menz, Side effects of ocular endotamponades caused by surface behaviors of fluorocarbons. Poster presentation 14th European Symposium on Fluorine Chemistry, Poznan, Pologne, 11-16 juillet, (2004). 

The chemistry occurring in a plasma by an injected fluorocarbon is critically dependent upon the effective fluorine/carbon ratio in the system.. We have seen that... 

Epoxidation also proceeds (Eq. 141) under mild conditions and with high stereoselectivity (95 5 erythro threo) despite the deactivating effect of the fluorine atom [361]. At a higher oxidation level, the Lausanne group described chemistry of a metallated azomethine derived from a,/Lunsaturated-a-fluoroaldehydes [362]. Highly flexible chemistry allowed alkylation at nitrogen, or at the (fluori-nated) -position, or at the -position (Fig. 8). 

This effect cannot be explained by simply considering differences in frontier orbital energies. A useful monofluorinated dienophile has been prepared [364] using metallated difluoroenol carbamate chemistry (Eq. 143) cycloaddition occurred smoothly with a range of dienes, and desulfination could be achieved under mild conditions without loss of the fluorine atom. Wakselman and co-workers [365] synthesised a rare competent difluorinated dienophile. Lewis acid catalysed Diels-Alder reaction with furan afforded an acceptable yield of (unfortunately) unstable cycloadduct which decomposed to a phenolic product via a dehydrofluorination reaction, circumscribing its utility (Eq. 144). 

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