Dissociative bond energies for

Table 5 Gas-phase dissociative bond energies for oxygen-containing molecules...

The driving force for such a reaction is the difference between the free energy of bond formation for YO-H (-AGbf), and the enthalpy of bond dissociation for R-H (AHdbe)- Table 12 summarizes the YO-H bond-formation energies for oxygen radicals (Y0-), as well as dissociative bond energies for several R-H substrates. Reference to these data indicates that t-BuO- will react exothermally with toluene (PhCH3), but will be essentially unreactive with methane. 

Table 12 Radical strength of oxygen radicals (Y0-) in terms of their YO-H bond formation free energies, and dissociative bond energies for H-R molecules...

The value of Aleq is estimated on the basis of the Pt-H bond-formation energy from metallic platinum [A(-AGbf), 48 kcal moF ] and the dissociative bond energy for Hz ( AGdbe, 96 kcal moF ). 

Much of the enthalpy of formation data for the dialkylzincs was reported from two separate sources in 1949 . From these measurements each group derived the mean bond dissociation energies of the diaUcylzinc compounds. From Reference 12, the mean C—Zn bond energies were 172 kJmor for MeaZn and 150 kJmoU for EtaZn (and by assumption for the n-Pr2Zn and n-Bu2Zn species also). From Reference 18, the mean bond energies for the MeiZn and Et2Zn compounds were reported as 171 and 144 kJmoU, respectively. 

As a first example of the use of the d band model, consider the trends in dissociative chemisorption energies for atomic oxygen on a series of 4d transition metals (Figure 4.6). Both experiment and DFT calculations show that the bonding becomes... 

The terms AHAm and AHAy are the enthalpies of atomization of the metal and the nonmetal, respectively. For gaseous diatomic nonmetals, AHA is the enthalpy of dissociation (bond energy plus RT) of the diatomic molecule. For metals which vaporize to form monatomic gases, AHA is identical to the enthalpy of sublimation. If sublimation occurs to a diatomic molecule, M2> then the dissociation enthalpy of the reaction must also he included ... 

The hydrogen molecule-ion, H2 , can be regarded as having one electron in a vapor state by spectroscopic means and found to have a dissociation energy to H and H- of 61 kcal mole-1 compared to the 104.2 kcal mole-1 bond energy for H2. Several possible combinations of two hydrogen orbitals and from one to four electrons are shown in Figure 6-6(b). 

The RETOF technique has applications far beyond mass analysis and determination of metastable dissociation fraction. In particular, it provides a very valuable approach to determining kinetic energy release (KER) during evaporative dissociation. As shown in this section, these data also find application in determining absolute values of cluster bond energies for systems without a barrier to... 

The differences between the heat of dissociation and the bond energy for the C—H bond in propylene and toluene and for the C—C bond in butene-1 and diphenylethane are interesting. The cause lies here not so much in the bonds of the molecules in question, as can be seen from the total binding energy deduced from the heat of combustion (or heat of hydrogenation), but in the peculiar stability of the ally] and toluyl radicals formed (p. 237). 

---