Reactivity of ether radical cations: An ESR study and quantum chemical analysisстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Местоположение издательства:Road Town, United Kingdom
Первая страница:77
Последняя страница:86
Аннотация:The electronic, spin, and energetic characteristics of the radical cations of diethyl and diisopropyl ethers, tetrahydrofuran, oxirane, trimethylene oxide, and pentamethylene oxide were calculated using the MNDO-UHF semiempirical method. The results of the quantum chemical analysis are in agreement with the most probable mechanisms of proton and H atom transfer, rearrangements, and fragmentation, as suggested by the experimental data. Efficient deprotonation (proton transfer) occurs if a particular atom bears a positive charge and a considerable spin population. Such conditions are observed in the case of proton transfer from the a-position with respect to the oxygen atom. The C-H bonds corresponding to these protons are much weaker (longer) in the resulting radical cations than in the neutral precursors. For this reason, the reaction sites under consideration show the most pronounced tendency to deprotonation yielding neutral radicals, which is confirmed by the ESR data obtained in X-ray irradiated freonic matrices. Strong elongation of C-O and C-C bonds in the ether radical cations indicate high probability of fragmentation and rearrangement reactions resulting in formation of . CH3 and RO. radicals or distonic radical cations from the primary radical cations for the linear ether radical cations. The products of ring cleavage are formed in the case of cyclic ether radical cations. The results of the calculations agree well with the ESR data obtained for freonic matrices and liquid ethers studied by spin trapping technique and with mass-spectrometric data.