Bond dissociation enthalpy group 16 molecules

Consider a molecule AB, where A and B can be atoms or groups of atoms. The A-B bond dissociation enthalpy, represented by DH (A-B), is defined as the standard enthalpy of the gas-phase reaction where the only event is the cleavage of that bond at a given temperature ... 

We conclude this section by giving, for the sake of clarity, the most general definition of mean bond dissociation enthalpy. For any molecule AYmXn, where A is a central atom and X and Y are any mono- or polyatomic groups, the A-X... 

The second source of uncertainty can add a few kcal mol to the imcer-tainty estimates and will scale with the munber of bonds in the molecule. The use of different reference values would shift our calculated heats of formation as a group, with the consequence that calculated bond dissociation enthalpies and reaction enthalpies are affected less than the heats of formation. Overall, we believe that the uncertainties in the BAC-MP4 heats of formation lie in the 2-5 kcalmol" range. 

The replacement of hydrogen or methyl groups by phenyl groups induces a considerable decrease in D(Si-H). The use of Ph SiH as a reducing agent for alkyl bromides was suggested by the low silicon-hydrogen bond dissociation enthalpy in this molecule. 

The metal-methyl mean bond dissociation enthalpies in the main-group homoleptic molecules, MMe , vary from 131 kJmoF in ZnMc2 to 283kJmoF in AlMc3. Thus, the above value for Z) (M-Me) in a transition metal complex is not particularly high, suggesting that many cootdinatively unsaturated transition metal complexes would activate methane. 

Table 14.3 Some covalent bond enthalpy terms (klmoP ) the values for single bonds refer to the group 15 elements in 3-coordinate environments, and values for triple bonds are for dissociation of the appropriate diatomic molecule.

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