Hybrid DFT calculations of the potential energy surface (PES) relative to the O-neophyl rearrangement of a series of ring-substituted 1,1-diarylalkoxyl radicals have been carried out at the UB3LYP/6-31G(d) level of theory. On the basis of the computational data, the rearrangement can be described as a consecutive reaction of the type a reversible arrow b -> c (see above graphic), and the steady-state approximation could be applied in all cases to the intermediate b. The first-order rearrangement rate constants [k(obs) = k(1)k(2)/(k(-1) + k(2))] were thus obtained from the computed activation free-energies and were compared with the experimental rate constants measured previously in MeCN solution by laser flash photolysis. An excellent agreement is observed along the two series, which strongly supports the hypothesis that the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals proceeds through the formation of the reactive 1-oxaspiro [2,5]octadienyl radical intermediate. This is in contrast to previous hypotheses that involve either a long-lived intermediate or the absence of this intermediate along the reaction path. The calculated rearrangement free-energies decrease upon going from the methoxy-substituted radical (Delta G degrees = -16.4 kcal center dot mol(-1)) to the nitro-substituted one (Delta G degrees = -21.8 kcal center dot mol(-1)), which follows a trend that is similar to the one observed for the C-Ar-O bond dissociation enthalpies (BDEs) of ring-substituted anisoles. This evidence indicates that in the O-neophyl rearrangement the effect of ring substituents on the strength of the newly formed C-Ar-O bond plays an important role.
Bietti, M., Ercolani, G., & Salamone, M. (2007). DFT evidence for a stepwise mechanism in the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. JOURNAL OF ORGANIC CHEMISTRY, 72(12), 4515-4519.
|Tipologia:||Articolo su rivista|
|Citazione:||Bietti, M., Ercolani, G., & Salamone, M. (2007). DFT evidence for a stepwise mechanism in the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals. JOURNAL OF ORGANIC CHEMISTRY, 72(12), 4515-4519.|
|IF:||Con Impact Factor ISI|
|Settore Scientifico Disciplinare:||Settore CHIM/06 - Chimica Organica|
|Revisione (peer review):||Sì, ma tipo non specificato|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1021/jo070125n|
|Stato di pubblicazione:||Pubblicato|
|Data di pubblicazione:||2007|
|Titolo:||DFT evidence for a stepwise mechanism in the O-neophyl rearrangement of 1,1-diarylalkoxyl radicals|
|Autori:||Bietti, M; Ercolani, G; Salamone, M|
|Appare nelle tipologie:||01 - Articolo su rivista|