Fluoroalkane bonding

A nucleophile is a species that attacks electron-deficient sites and donates a lone pair of electrons to form a covalent bond. Halogenoalkanes get more reactive as the C-X bond gets longer and therefore weaker. Iodoalkanes therefore react fastest and fluoroalkanes slowest. 

Tertiary polyfluoro alcohols, l,l,l,3,3,3-hexafluoro-2-methylpropan-2-ol, 1,1,1,3,3-penta-fluoro-2-methylpropan-2-ol and l,l,3,3-tetrafluoro-2-methylpropan-2-ol, on treatment with sulfur tetrafluoride undergo dehydration to give the respective alkenes 7, but not fluoroalkanes small amounts of byproducts resulting from the addition of hydrogen fluoride to the C = C bond of the resultant alkcncs are also formed.54... 

Several examples of telomerisation of fluoroalkanes with various telogens are reported in Table 1. All the telogens employed in telomerisation of hydrogenated olefins [21-24] are also efficient for fluoroalkenes and the system of initiator also works well with these telogens. Consequently, a large variety of cleavages of X-Y bonds is possible these bonds can be located at the chain end or in the... 

The magnitude of one-bond fluorine coupling to carbon in a simple fluorohydrocarbon can vary from 151 to 280 Hz, depending again on whether one, two, or three fluorines are bound to the carbon. Scheme 2.22 demonstrates these trends in the fluoromethanes and fluoroalkanes. The scheme also includes mention of the one-bond H-C... 

The equilibrium position of the reaction depends on the nucleophilicity of the anion, whether a good leaving group is present, and whether one anion is better stabilized than the other in a given solvent. For example, reactions with KF will thus lead cleanly to fluoroalkanes, because fluoride is such a poor leaving group due to the stability of the C-F bond. 

Note n, a and are normalized in such a way that their sum gives 1.00 and therefore are only relative numbers. These so-called solvatochromic parameters are useful for the characterization of the selectivity properties of a solvent, see Section 5.2. Solvents of low polarity, from fluoroalkanes to carbon tetrachloride, do notinteract with solutes by dipoles or hydrogen bonds, therefore no solvatochromic parameters can be I isted for them. 

Because of the extraordinary strength of the carbon-fluorine bond, transition metal-mediated activation of fluoroalkanes and arenes is not easy to achieve. Nevertheless, activation of the C-F bond in highly electron-deficient compounds such as 2,4,6-trifluoropyrimidine, pentafluoropyridine, or hexafluorobenzene is possible with stoichiometric amounts of bis(triethylphosphano) nickel(O) [101] (Scheme 2.45). More recently Herrmann and coworkers [102] have described a variant of the Kumada-Corriu cross-coupling reaction [103] between fluorobenzene and aryl Grignard compounds which uses catalytic amounts of nickel carbene complexes. Hammett analysis of the relative kinetic rate constants indicated that the reaction proceeds via initial oxidative addition of the fluoroaromatic reactant to the nickel(O) species. 

Unsaturated halogenated compounds with a central C = C or C = C bond undergo cleavage on oxidation in the middle of the molecule and form two carboxylic acids without loss of a carbon atom. The reaction mechanism of the oxidation of internal fluoroalkenes by potassium permanganate includes hydroxylation of the C = C bond in 2 by permanganate, accompanied by dehydrofluorination of the geminal fluoroalkane-1,2-diol 3 and formation of an intermediate fluorocarbonyl compound 4 oxidative cleavage of the C-C bond in 4 leads to the final products 5.1... 

Oxidative addition of C-F bonds to low-valent metal complexes constitute one of the routes in activation of fluoroalkanes and fluoroarenes [71, 72], The chemical activation of carbon-fluorine bonds has attracted much attention since functionalization of C-F compounds gives various fluoroorganic derivatives, which have many technological applications. Typical examples of oxidative addition of C-F bonds [73] are shown in Scheme IV.36. 

We classify the fundamental processes of intermolecular G-F bond activation in the following six categories (i) oxidative addition of fluorocarbon, (ii) M-G bond formation with HF elimination, (iii) M-G bond formation with fluorosilane elimination, (iv) hydrodefluorination of fluorocarbon with M-F bond formation, (v) nucleophilic attack on fluorocarbon, and (vi) defluorination of fluorocarbon (Scheme 4). Table 2 shows the occurrence of these processes for intermolecular G-F activation, classified according to the type of G-F bond. For instance, oxidative addition is a characteristic process for fluoroaromatics but not for fluoroalkanes, while defluorination is characteristic of fluoroalkanes but not fluoroaromatics. We include processes as intermolecular even if they involve coordination of the fluorocarbon in one of the modes in Section 1.26.1.1 prior to G-F bond breaking. Notice that processes (ii), (iii), and (iv) could be described as cr-bond metatheses we have avoided this descriptor, since it has mechanistic connotations that are only appropriate in some cases. It should also be recognized that secondary processes may make some reactions awkward to classify under this scheme. 

The confonnation of fluoroalkane derivatives is of considerable contemporary interest. The influence of fluorine on the conformation of vicinally substituted compounds is based on a stabilizing gauche interaction that relies upon hyperconjugation between a C-H bond and the low lying a orbital of the C-F bond. The energy of this interaction is estimated to be 0.8 kcal mol", modest but... 

Hydrolysis of polyfluoroalkylsilicon di- or trihalides with water affords polyfluoroalkylsilicon polymers (66). However, even dilute aqueous alkali cleaves the silicon-carbon bonds of these polymers at room temperature when fluorine is in either the a- or the j8-positions. Fluorocarbon groups in nonpolymeric compounds like CHF2CF2SiCl3 or (CH3)2Si(C3F7)2 are also easily removed as fluoroalkanes with aqueous base. Nucleophilic attack on silicon is evidently favored by the electronegative polyfluoroalkyl groups. When fluorine is not in the a- or j8-positions, as in (CF3CH2CH2SiOt.s] , strong aqueous alkali fails to cleave silicon-carbon bonds even at elevated temperatures. 

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