Thermodynamic Control Bond Dissociation Energies BDEs

Concentrated HBr is therefore a suitable reagent for converting simple alcohols to the corresponding alkyl bromides (assuming there are no other acid-sensitive groups in the molecule). 

Broadly speaking, nucleophilicity correlates with reduction potential. Thus, stronger reducing agents tend to make better nucleophiles, which makes sense because both properties are related to electron donation. The correlation, however, is best limited to a set of structurally closely related nueleophiles. For a broader correlation, Edwards and Ritchie proposed an oxibase scale, which afforded a linear correlation of the reactivity of a nucleophile with the reduction potential of its oxidized form and the of its conjugate acid. Although space doesn t permit a more detailed discussion of this scale, redox potentials are broadly important for the subject matter of this book. 

A table such as Table 1.5 provides an indication of whether an oxidant or reductant is suitable for a given redox role. Thus, with a high reduction potential (1.19 V in Table 1.5), CIO2 is clearly a strong oxidant, which underlies its wide use as a disinfectant. 

Observe that several of the reductions involve an oxidant (e.g., O2, H2O2, N03 ) in acid solution. This makes sense because protonation is expected to make an oxidant even more powerful, that is, an even more avid acceptor of electrons. 

Not much more needs to be said about redox potentials at this point. We will refer back to Table 1.5 once in a while when we make arguments based on redox potentials. 

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THERMODYNAMIC CONTROL BOND DISSOCIATION ENERGIES (BDEs)... 

In extensive experiments with molecular oxygen, rate constants and product branching ratios for the reaction of 67 atomic metal cations were measured. The reaction efficiencies are plotted as a function of metal cation oxygen affinity (OA) in Figure 8.2. A clear correlation between reaction efficiency and OA and between product channel and OA is evident. When the OA of the metal is below the bond dissociation energy (BDE) of O2 (i.e. the OA of O) inefficient O2 clustering occurs. When the OA of the metal is above the OA of O, efficient O-atom transfer to the metal cation occurs. Near the thermo-neutral threshold Mo" reacts with moderate efficiency by O-atom transfer. So it can be said that these reactions are thermodynamically controlled. 

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