Carbon tetrafluoride bonding

Representing a two electron covalent bond by a dash (—) the Lewis structures for hydrogen fluoride fluorine methane and carbon tetrafluoride become... 

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

Caibon has eight electrons in its valence shell in both methane and carbon tetrafluoride. By forming covalent bonds to four other atoms, carbon achieves a stable electron configuration analogous to neon. Each covalent bond in methane and carbon tetrafluoride is quite strong—comparable to the bond between hydrogens in Fl2 in bond dissociation energy. 

Carbon tetrafluoride and all polyfluorinated hydrocarbons are very stable and inert molecules. This inertness can be attributed to the strength of the CF bonds and the close packing of the inert fluoride-like ligands around the carbon atom, which effectively prevent attack by a nucleophile on the carbon atom. In contrast, even though BF3 has stronger bonds than CF4, it is more reactive, forming adducts such as BF3-NH3 because the boron atom is only three-coordinated and there is space around it for an additional ligand. 

The bonding in SiF4 is exactly as in carbon tetrafluoride (CF4). The geometry of silicon tetrafluoride is tetrahedral. 

The interaction of fluorine with an organic compound liberates a quantity of energy which is frequently of the order of magnitude of, or greater than, the energy which binds the carbon atoms in chains. It is estimated 63 that the addition of fluorine to a double bond liberates ldS calories per mole, whereas chlorine liberates only 30 calories. Careful control qf the temperature throughout the reacting masses is therefore essential. Even in the most favorable cases, much decomposition occurs and carbon tetrafluoride is frequently the main reaction product.62-6 ... 

Carbon tetrafluoride, CF4, shown in Figure 3.38, is another example of a non-polar molecule that contains polar bonds. 

Carbon tetrafluoride, CF4, contains four polar bonds. Because of its symmetry, however, it is a non-polar molecule. 

Perfluorocarbons are essentially inert to hydrolysis unless heated to very high temperatures, although it has been calculated that the free energy of hydrolysis of carbon tetrafluoride is exothermic by 304kJmoP [12], and the inertness therefore stems from a high activation barrier. The carbon backbone in a perfluorocarbon is shielded towards attack by nucleophiles by the non-bonding electron pairs associated with the many adjacent fluorine atoms, and this is undoubtedly a major factor contributing to the relative inertness of fluorocarbons. 

E G F) may be derived as a primary bond energy term from the heat of formation of carbon tetrafluoride. Unfortunately this quantity is not certainly known. The heat of formation ( - Hf)... 

For a polyvalent atom the partial charge builds up every time another highly electronegative substituent is added. Thus the partial charge on the carbon atom in carbon tetrafluoride is considerably larger than it is in the methyl fluoride molecule, and so all of the C—F bonds shrink, though the effect is not as great for the last fluorine as for the first ... 

The Group IVA atom contributes four electrons to the bonding in a tetrahedral AB4 molecule, and the other four atoms contribute one electron each. The Lewis formulas for methane, CH4, and carbon tetrafluoride, CF4, are typical. 

Carbon tetrafluoride (CE ), also called Ereon-14, is used as a low temperature refrigerant and as a gaseous insulator. Are the bonds in CE polar or nonpolar Is CE a polar molecule Explain. 

FIGURE 12-10 (a) In methyl fluoride, the polar C—F bond is not canceled by the C—FI bonds, making the molecule polar, (b) In carbon tetrafluoride, the four polar C—F bonds cancel each other, making the molecule nonpolar. 

Reactions of alkane-1,1-dicarboxylic acids, e.g. la, alkane-1,4-dicarboxylic acids, e.g. lb, and their longer-chain homologs with sulfur tetrafluoride afford mixtures of bis(trifluoromethyl)-alkanes, bis(pentafluoroalkyl) ethers and small amounts of polyethers.118 Total yields, generally, decrease with increasing length of the carbon chain and in the presence of C = C bonds. 

---