Derived Bond Dissociation Energies

Group increments for silicon compounds based on the data reviewed here, and derived in accordance with the group additivity scheme29-31, are shown in Table 27. Radical and atomic heats of formation for non-silicon-containing species used in this chapter to derive bond dissociation energies are shown in Table 28. Miscellaneous inorganic silane heats of formation are included in Table 29. 

The determination of Eo from visible onsets introduces considerable error in the derived bond dissociation energies. This problem is primarily attributed to experimental kinematic broadening introduced through the ion beam energy distributions and the thermal motion of the target gas in the case of beam cell experiments. Armentrout et have fit various functional... 

Heats of formation of halogen-suhstituted alkyl radicals, and derived bond dissociation energies,... 

The Morse oscillator model is often used to go beyond the harmonic oscillator approximation. In this model, the potential Ej(R) is expressed in terms of the bond dissociation energy Dg and a parameter a related to the second derivative k of Ej(R) at Rg k = ( d2Ej/dR2) = 2a2Dg as follows ... 

Because these stability measurements pertain to the gas phase, it is important to consider the effects that solvation might have on the structure-stability relationships. Hydride affinity values based on solution measurements can be derived from thermodynamic cycles that relate hydrocarbon p T, bond dissociation energy and electrochemical potentials. The hydride affinity, AG, for the reaction... 

However, the fact that the derived S—O bond dissociation energy in sulfuric acid is identical to that found in the acid derivatives, strongly supports the estimated enthalpy of formation for gas-phase sulfurous acid given by Benson18. 

Sulfones are thermally very stable compounds, diaryl derivatives being more stable than alkyl aryl sulfones which, in turn, are more stable than dialkyl sulfones allyl and benzyl substituents facilitate the homolysis by lowering the C-—S bond dissociation energy. Arylazo aryl sulfones, on heating in neutral or weakly basic media at 100 °C, yield an aryl and arenesulfonyl radical pair via a reversible one-bond fission followed by dediazoni-ation of the aryldiazenyl radical (see Scheme 2 below) °. However, photolysis provides a relatively easy method for generating sulfonyl radicals from compounds containing the SO2 moiety. 

More than just a few parameters have to be considered when modelling chemical reactivity in a broader perspective than for the well-defined but restricted reaction sets of the preceding section. Here, however, not enough statistically well-balanced, quantitative, experimental data are available to allow multilinear regression analysis (MLRA). An additional complicating factor derives from comparison of various reactions, where data of quite different types are encountered. For example, how can product distributions for electrophilic aromatic substitutions be compared with acidity constants of aliphatic carboxylic acids And on the side of the parameters how can the influence on chemical reactivity of both bond dissociation energies and bond polarities be simultaneously handled when only limited data are available ... 

---