Silver bromide, bond energy

As can be noted, all the iodides studied so far (circles) are almost equivalently reactive on silver, while exhibit on GC a secondary modulation effect chained to the organic moiety structure. On Ag, to appreciate the influence of bulky molecular structures (as in the case of haloadamantanes), or poorly activated C-X bonds (as in the case of long linear alkyl chain halides), it is necessary to consider the less reactive bromide (squares) and chloride (full triangles) derivatives. The difference between the reduction potentials on Ag and on GC ranges from 0.3 to 1.4 V, thus implying a substantial saving in the specific energy consumption. The remarkable... 

Boldyrev et al. [46], from quantum mechanical calculations of bond strengths in the oxalate anion, and from observations [38] of the decomposition of this species in potassium bromide matrices, concluded that the most probable controlling step in the breakdown of the oxalate ion is rupture of the C-C bond. This model is (again) based on the observation that the magnitudes of the activation energies for decompositions of many metal salts of oxalic acid are comparable. This model was successfiilly applied [46,68] to the decompositions of many oxalates, with the possible exception of silver oxalate where the strengths of the C-C and Ag-0 bonds are similar. 

Irradiation of methyl bromide, again on a silver(lll) surface, follows the same pattern. The principal photochemical event is the fission of the C—Br bond with the bromide being retained on the surface and with expulsion of the methyl fragment. The study reports that the threshold energy for the C—Br bond fission was higher for multilayer systems... 

In contrast, the less strained four-7r-electron cyclopentadienyl cation is very unstable. Its p r+ has been estimated as --40, using an electrochemical cycle. The heterolytic bond dissociation energy to form the cation from cyclopentadiene is 258 kcal/mol, which is substantially more than for formation of an allylic cation from cyclopentene but only slightly more than the 252 kcal/mol for formation of an unstabilized secondary carbocation. " Solvolysis of cyclopentadienyl halides assisted by silver ion is extremely slow, even though the halide is doubly allylic. When the bromide and antimony pentafluoride react at -78°C, the EPR spectrum observed indicates that the cyclopentadienyl cation is a triplet. Similar studies indicate that pentachlorocyclopentadienyl cation is also a triplet, but the ground state of the pentaphenyl derivative is a singlet. 

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