Bond dissociation energy peroxides

This stems from the weakness, i.e. ease of thermal fission, of the Pb—R bond, and radicals may be generated in solution in inert solvents, as well as in the vapour phase, through such thermolysis of weak enough bonds, e.g. those with a bond dissociation energy of < w 165 kJ (40kcal)mol 1. Such bonds very often involve elements other than carbon, and the major sources of radicals in solution are the thermolysis of suitable peroxides (O+O) and azo compounds (C+N). Relatively vigorous conditions may, however, be necessary if the substrate does not contain substituents capable of stabilising the product radical, or... 

The similarity of the structure of peroxynitrous acid to the simplest peroxy acid, per-oxyformic acid, immediately raised the question as to its relative reactivity as an oxygen atom donor. This became particularly relevant when it was recognized that the 0—0 bond dissociation energy (AG° = 21 kcalmoR ) of HO—ONO was much lower than that of more typical peroxides. Consequently, peroxynitrous acid (HO-ONO) can be both a one- and two-electron oxidant. Since the 0-0 bond in HO-ONO is so labile, its chemistry is also consistent in many cases with that of the free hydroxyl radical. 

Acetyl peroxynitrate (18) and perfluoroacetyl peroxynitrate (19), two important atmospheric oxidation products of hydrocarbons (formation of 18) or chlorofluorocarbon replacements, such as CF3CH3 (formation of 19), preferentially adopt a gauche conformation (C—O—O—N = 84.7° for 18 and 85.8° for 19 electron diffraction). The two peroxides are characterized by comparatively short 0—0 bonds on one side and long 0°—N connectivities (Table 5) on the other. The observed O —N distances may be explained on the basis of an no ct od-n orbital overlap. This type of interaction lowers the 0°—N bond order and could explain the low bond dissociation energies of this connectivity in peroxides 18 and 19 (118 4 klmol for both compounds). It should be noted that this interpretation does not reflect a possible r-type interaction between a lone pair at 0° and virtual orbitals of the nitro group and therefore requires future investigation. 

The standard state of fluorine is the difluorine molecule, F2, which has an electronic configuration identical with that of the peroxide ion. The two species are isoelectronic. The bond order is 1, and the bond dissociation energy of 155 kj mol-1 and bond length of 144 pm are very similar to the values for 022-. 

The bond dissociation energy of hydrogen peroxide has been accurately predicted by high-level ah initio theory16. It was disclosed very early that Hartree-Fock theory, in the absence of electron-correlation correction, simply cannot be applied to problems involving 0—0 bond dissociation. For example, the predicted 0—0 bond energy in peroxyformic acid is only 1.0 kcalmol-1 by Hartree-Fock theory, whereas at the... 

Dihydro-5,10-disilanthracene and AIBN can reduce xanthates and thiocarbonates in refluxing cyclohexane solution. Reduction of xanthates with monosilanes such as PhSiH3 and Ph2SiH2 initiated by AIBN does not work effectively because of their strong Si-H bond dissociation energies. However, the same reactions using either dibenzoyl peroxide or triethylborane as an initiator do induce the effective reduction of xanthates. 

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