Ozonation of 1,1,2,2-Tetraphenylethene Revisited: Evidence for Electron-Transfer Oxygenations

Computational Studies of Rubber Ozonation Explain the Effectiveness of 6PPD as an Antidegradant and the Mechanism of Its Quinone Formation

“…For each of the classes of reactions discussed above, a number of authors argue that ozonation reactions are initiated by one-electron charge transfer (CT) to form biradical, zwitterionic prereaction complexes (Figure ). Examples for alkenes, − amines, − ,, aromatics, , and PPDs ,,, can be found at the indicated references. Such proposals are defended on the basis of a strong correlation between substrate ionization potential and O 3 reaction rates, , electron spin resonance (ESR) spectra that indicate the presence of radicals in the reaction mixture, or details of product distributions. , Some have expressed skepticism about these CT intermediates, which have not been isolated experimentally, though theoretical literature analyzing such proposals is sparse. ,, Within the CT mechanism, one-electron transfer is taken to be the rate-determining step of ozonation, so the existence of these complexes for olefins and PPDs is of present interest.…”

“…For each of the classes of reactions discussed above, a number of authors argue that ozonation reactions are initiated by one-electron charge transfer (CT) to form biradical, zwitterionic prereaction complexes ( Figure 1 ). Examples for alkenes, 76 − 79 amines, 55 − 57 , 59 , 80 aromatics, 67 , 69 and PPDs 73 , 74 , 81 , 82 can be found at the indicated references. Such proposals are defended on the basis of a strong correlation between substrate ionization potential and O 3 reaction rates, 74 , 76 electron spin resonance (ESR) spectra that indicate the presence of radicals in the reaction mixture, 73 or details of product distributions.…”

Computational studies of rubber ozonation explain the effectiveness of 6PPD as an antidegradant and the mechanism of its quinone formation

“…The mechanistic work in this report has dispelled a number of reports in the literature that suggest the ozonation of both alkene and PPD systems is initialized by one-electron transfer from the subtrate to ozone. [74][75][76][77] This provides theoretical backing to the perhaps obvious conclusion that predicting ozonation capacity is more complicated than determining ionization potentials, even if this parameter is relatively predictive within a single class of molecules. 71 Instead, the subtlety of the mechanistic results above indicate that atomistic details of reactivity must be taken into account.…”

“…For each of the classes of reactions discussed above, a number of authors argue that ozonation reactions are initiated by one-electron charge transfer (CT) to form biradical, zwitterionic pre-reaction complexes (Figure 1). Examples for alkenes, [74][75][76][77] amines, [52][53][54]56,78 aromatics, 64,66 and PPDs 70,71,79,80 can be found at the indicated references. Such proposals are defended on the basis of a strong correlation between substrate ionization potential and O 3 reaction rates, 71,74 electron spin resonance (ESR) spectra that presence of radicals in the reaction mixture, 70 or details of product distributions.…”

“…Such proposals are defended on the basis of a strong correlation between substrate ionization potential and O 3 reaction rates, 71,74 electron spin resonance (ESR) spectra that presence of radicals in the reaction mixture, 70 or details of product distributions. 56,77 Some have expressed skepticism about these CT intermediates, which have not been isolated experimentally, though theoretical literature analyzing this proposal is sparse. 4,54,81 Often, these proposals posit that electron transfer is the rate determining step of ozonation, so the existence of these complexes for olefins and PPDs is of present interest.…”