Fluorocarbons groups

Fluorinated Acids. This class of compounds is characterized by the strength of the fluorocarbon acids, eg, CF COOH, approaching that of mineral acids. This property results from the strong inductive effect of fluorine and is markedly less when the fluorocarbon group is moved away from the carbonyl group. Generally, their reactions are similar to organic acids and they find apphcations, particularly trifluoroacetic acid [76-05-1] and its anhydride [407-25-0] as promotors in the preparation of esters and ketones and in nitration reactions. 

Release agents function by either lessening intermolecular interactions between the two surfaces in contact or preventing such close contact. Thus, they can be low surface-tension materials based on aUphatic hydrocarbon, fluorocarbon groups, or particulate soHds. The principal categories of material used are waxes, fatty acid metal soaps, other long-chain alkyl derivatives, polymers, and fluorinated compounds. 

The chemical shifts of secondary CF2 groups within perfluorocarbons decrease modestly (less shielding) as the neighboring fluorocarbon groups become more branched, i.e., change from CF3 to CF2Rf to CF(Rf)2, as exemplified by the examples in Scheme 6.24. 

Jarvis, N.L. and Zisman, W.A. "Surface Activity of Fluorinated Organic Compounds at Organic-Liquid/Ari Interfaces Part III. Equation of State of Adsorbed Monolayers and Work of Adsorption of a Fluorocarbon Group," Naval Research Labs Report 5401, Surface Chemistry Branch, Chemistry Division, November 17, 1959. 

Fluorocarbon groups, containing titanium complexes, 25 98 Fluorocarbon industry, 18 303 Fluorocarbon production, 11 869 Fluorocarbons... 

In this context, by the term fluorosilicone are meant polymers containing C-F bonds and Si-O bonds with hydrocarbon entities between them. Thus, the repeating structure may be generally written as [RfX (CH J (CH,)vSiOz, where Rf is the fluorocarbon group.59 Commercially available fluorosilicones are based on polymethyltri-fluoropropylsiloxane (PMTFPS), or more accurately poly[methyl (3,3,3-trifluoropropyl)siloxane]. In some cases PMTFPS is copolymerized with polydim-ethyl siloxane (PDMS) for cost/benefit balance.60 The manufacture of monomers for fluorosilicones is discussed in some detail in Reference 60. Fluorosilicone elastomers... 

The Influence of Fluorine or Fluorocarbon Groups on some Reaction Centres... 

The Influence of Fluorine or Fluorocarbon Groups on some Reaction Centres Table 4.2 pKa values of some organic acids and alcohols [7]... 

It is the aim of this chapter to develop a model for the very broad spectrum of reactivity of fluorine-containing systems towards nucleophiles. Substiment effects of fluorine and fluorocarbon groups on the SnI process were considered earlier, in a more general discussion of carbocations (see Chapter 4, Section VI) effects on the Sn2 process will now be examined. Then the broader principles of displacement of fluorine, as fluoride ion, from carbon in different environments will be discussed to emphasise why, for example, nucleophilic displacement of fluoride ion from perfluoroalkenes occurs extremely rapidly while, in contrast, perfluoroalkanes are characterised by extreme inertness. 

In contrast, fluorine or fluorocarbon groups directly attached to the reaction centre have a much more pronounced effect [4] for example, the hydrolytic displacement of chloride from PhCHFCl appears to be activated with respect to benzyl chloride [10], although the situation is complicated by concomitant SnI and Sn2 processes. 

Conversely, fluorine or fluorocarbon groups have a major effect in reducing the base strength of amines, ethers and carbonyl compounds for example, 2,2,2-trifluoroethylamine (pKb = 3.3) is ca. 10 times less basic than ethylamine. Also, pentafluoropyridine is only protonated in strong acid [6], whereas hexafluoroacetone is not protonated even in superacids [7-9] and perfluorinated tertiary amines and ethers are sufficiently non-basic for them to be used as inert fluids interchangeably with perfluorocarbons. 

Let us consider the possible effects of fluorine or fluorocarbon groups as substituents on the transformation of a benzene derivative to a para-bonded species 9.100A, a benzvalene 9.100B or a prismane 9.100C (Figure 9.100). 

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