C—F bond energy

Because of the high C - F bond energy, glycosyl fluorides are stable in comparison to the other glycosyl halides, and this character has attracted much attention. They have been prepared in many different ways. One of them, rather classical, is through addition of the elements of HF (for example, HF in benzene ), BrF, or IF to per-O-acylated glycals. ... 

The very high (C-F) bond energy makes PTFE chemically inert, therefore ideal for non-stick ovenware (1). Strong (C-Cl) bonds give PVC a useful life, but creates problems for its disposal (1). 

Halogenated aliphatic polymers such as polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC) are moderately resistant to attack by reactants. The fluorinated polymers, such as ptfe, are exceptionally resistant to attack by acids and alkalis even at elevated temperatures because of their tight packing and high C—F bond energy. 

A C-F bond energy can be computed from thermochemical studies of the... 

The scope of the photohydrodehalogenation process has been tested by an investigation of the photochemistry of pentafluorobenzene (5). Since the C-F bond energy in fluorobenzene is 124 kcal/mol, while Amai is 257 nm, suggesting a singlet energy level of less than 111 kcal/mol, one would expect direct fission to... 

Low-valent transition-element fluorides, especially those in which carbonyl and organo-ligands are incorporated, require other approaches, which are tailored to the element and the oxidation state. Here an inherent thermodynamic problem is imposed by the high C—F bond energy, which can exceed the M—F bond energy,... 

In view of the small number of resonant unperturbed modes in the observed spectra of CH3F [26,55] (Table A), usually used least-squares refinement of the six parameters of the model Hamiltonian for CX3Y molecules [4,26,28] is impractical. For estimating C-F bond energy in CH3F, only five parameters ( 1 - x,), 2, co 2, 1 ami A,2 are required. Furthermore, there are only five unperturbed stretching modes to calibrate it. Three of the five parameters are calculated with the equations obtained from Eqs. (11), (12), using the observed vi, V3, V4 [56] fundamentals ... 

The C—F bond energy is indeed very high (486 kJ mol-1 cf. C—H 415, and C—Cl 332 kJ mol"1), but organic fluorides are not necessarily particularly stable thermodynamically rather, the low reactivities of fluorine derivatives must be attributed to the impossibility of expansion of the octet of fluorine and the inability of, say, water to coordinate to fluorine or carbon as the first step in hydrolysis, whereas with chlorine this may be possible using outer d orbitals. Because of the small size of the F atom, H atoms can be replaced by F atoms with the least introduction of strain or distortion, as compared with replacement by other halogen atoms. The F atoms also effectively shield the carbon atoms from attack. Finally, since C bonded to F can be considered to be effectively oxidized (whereas in C—H it is reduced), there is no tendency for oxidation by oxygen. Fluorocarbons are attacked only by hot metals, e.g., molten sodium. When pyrolyzed, fluorocarbons tend to split at C—C rather than C—F bonds. 

The atomization energies of CH4 and CF4 yield the mean C-H and C-F bond energies listed in Table 13.6. 

I2 + Q. and potassium carbonate at ca. 310 °C (- KF + CO + Q, study of which has led to the value 448.5 kJ mol- for the C—F bond energy [the C—F bond energy in poly(carbon monofluoride) of stoichiometry CFi.ij is reported to be ca. 480 kJ mol ]. Obviously, thermal decomposition of carbon monofluoride in the presence of suitable substrates might prove an interesting, if not useful, source of some fluorinated organic, organometallic, or organometalloidal compounds. 

The enthalpy value for CH3F leads to the value 443 kJ mole" for the C—F bond energy. This value is given in Table V-1. The other fluoromethanes are stabilized by resonance with structures other than the normal valence-bond structure. 

Bond strengths can be useful guides in predicting whether proposed steps in catalytic cycles are energetically reasonable. For example, oxidative addition of a C-F bond to a metal would require that the necessary loss of the large C—F bond energy of 120 kcal/mol be compensated by the formation of sufficiently... 

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