Carbon-fluorine bond energy

The exceptional thermal and chemical stability of PTFE originate in the strength of its primary chemical bonds. The carbon-fluorine bond energy is the highest currently known among organic compounds [3, 4]. In addition, the fluorine atoms... 

A consideration of the cyclobutene ring-opening reactions [34, 35] (Table 7.4) reveals that the changes in hybridisation of carbon bonded to fluorine are the same for both compounds T7.4A and T7.4B, and so any changes in carbon-fluorine bond energies must also be the same. Consequently, as A// for T.7.4A is more endothermic than for T7.4B,... 

Fluoropolymers are technical polymers with very special properties and apphcations. Their properties are derived mainly from the strong carbon-fluorine bond energy of 507 kJ moU compared with typical energies of 415 kJ moU for C-H or 348 kJ moU for C-C bonds. The most important fluoropolymer is polytetrafluoroethylene (PTFE). In... 

Bromine and chlorine are two reactive halogens that have worked well for flame retardant purposes. Organo-fluorine compounds have not been as effective as flame retardant additives because the carbon-fluorine bond energy is so high that other events dominate at temperatures where halogenated flame retardants operate. ... 

Estimate the carbon-fluorine bond energy given that the 0—0 bond energy Is 347 kJ/mol, the 0=0 bond energy Is 614 kJ/mol, and the F—F bond energy Is 154 kJ/mol. 

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

The last example represents a fairly rare elimination of hydrogen fluoride in preference to hydrogen chloride, a reaction that deserves a more detailed discussion A comparison of bond dissociation energies of carbon-halogen bonds shows that the carbon-fluorine bond is much stronger than the carbon-chlorine, carbon-bromine, and carbon-iodme bonds 108-116, 83 5, 70, and 56 kcal/mol, respec-... 

Carbon-hydrogen bonds, such as those in hydrocarbons like methane and ethane, have dissociation energies close to 400 kj-mol whereas single bonds between carbon and fluorine have dissociation energies close to 500 kj-mol-1. The greater strength of a carbon-fluorine bond helps to explain why fluorocarbon polymers are very resistant to chemical attack. They are used to construct valves for corrosive gases and to line the interiors of chemical reactors. 

Many fluorinated polymers have been prepared using free-radical processes and the intensity of interest in this field stems from the number of rmique properties that are bestowed on the polymer by the presence of the carbon-fluorine bonds in a system. For example, excellent resistance to chemically aggressive environments, high thermal stability, low dielectric constant, low flammability and very low surface energies are just some of the properties of fluorinated materials that have been exploited. Uses range from... 

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