Of carbon-fluorine bonds

The presence of carbon—fluorine bonds in organic polymers is known to characteristically impart polymer stabiUty and solvent resistance. The poly(fluorosibcones) are siloxane polymers with fluorinated organic substituents bonded to siUcon. Poly(fluorosibcones) have unique appHcations resulting from the combination provided by fluorine substitution into a siloxane polymer stmcture (see Silicon compounds, silicones). 

Richmond TG (1999) Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds. 3 243-269... 

Ribaudo F, van Leeuwen PWNM, Reek JNH (2006) Supramolecular Dendritic Catalysis Noncovalent Catalyst Anchoring to Fimctionalized Dendrimers. 20 39-59 Richmond TG (1999) Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds. 3 243-269... 

Let us now look at some examples to illustrate what we have discussed so far to get a feeling of how structural moieties influence the mechanisms, and to see some rates of nucleophilic substitution reactions of halogenated hydrocarbons in the environment. Table 13.6 summarizes the (neutral) hydrolysis half-lives of various mono-halogenated compounds at 25°C. We can see that, as anticipated, for a given type of compound, the carbon-bromine and carbon-iodine bonds hydrolyze fastest, about 1-2 orders of magnitude faster than the carbon-chlorine bond. Furthermore, we note that for the compounds of interest to us, SN1 or SN2 hydrolysis of carbon-fluorine bonds is likely to be too slow to be of great environmental significance. 

Catalytic Hydrogenolysis of Carbon-Fluorine Bonds rc-Bond Participation Mechanism Hudlicky, M. J. Fluorine Chem. 1989, 44, 345-359. 

Detection of Carbon-Fluorine Bonds in Organofluorine Compounds by Raman Spectroscopy Using a Copper-Vapor Laser ... 

When hexafluorocyclobutene is treated with aluminum chloride, all fluorine atoms are replaced by chlorine. On treatment with aluminum bromide, all are replaced by bromine. The products are hexachlorocyclo-butene and hexabromocyclobutene, respectively. The reason for this quite unexpected reaction may be the difference in the strength of carbon-fluorine bond and aluminum-fluorine bond. As the aluminum-fluorine bond (595 kJ/mol, 142 kcal) is stronger than the carbon-fluorine bond (443 kJ/mol, 106 kcal), the lower reaction enthalpy may be the driving force for the halogen exchange [40]. 

One of the major activities of chemists in industry and academia is the search for special-effect chemicals, i.e. systems with new chemistry and with novel properties that can be exploited by industry. There are, of course, many ways of creating novel systems but the introduction of carbon-fluorine bonds into organic compounds has led to spectacular industrial developments, together with an exciting field of organic chemistry and biochemistry. 

Part of the interest in fluorocarbon systems lies in a comparison of the chemistry, and particularly reaction mechanisms, of fluorocarbon derivatives with those of the corresponding hydrocarbon compounds. Indeed, such comparisons pose quite a strenuous test on our theories of organic chemistry. As will be seen, our understanding of the influence of carbon-fluorine bonds on reaction mechanisms has made considerable progress. Nevertheless, it must be emphasised that fluorocarbon derivatives present much more complicated systems than their corresponding hydrocarbon compounds because, in addition to effects arising from different electronegativities, the effect of the lone pairs of electrons of fluorine that are not involved in o-bonds must be taken into consideration. Furthermore, the relative importance of these effects seems to be very dependent on the centre to which the fluorine is attached. 

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