This note is concerned with an esrstudy of intermediateradicals formed by UV and gamma irradiation of the perfluoropolyethers A,D and their peroxidic precursors B,C obtained by perfluoroolefines photooxidation2 CF3(O-CF2CF(CF3) )n (OCF2)m OCF3 (A) Y(OCF2CF(CF3) )n (OCF2)m (O)p Y′ (B) Z(OCF2CF2)n (OCF2)m (O)p Z′ (C) CF3(OCF2CF2)n (OCF2)m OCF3 (D) Y = −CF3, −COF; Y′ = −OCF3, −OCOF; Z = −CF3, CF2COF; Z′ = −OCF3, OCF2COF The UV irradiation at 4.2 K of B leads to the formation of the radicals CF3·, −OCF2· and −O(CF3)CF·. The same species are detected folling UV irradiation at higher temperatures with the samples in the liquid state. Above 400 K, the esr spectrum of −OCF2· and, partially, of −O(CF3)CF·, are replaced by that of −0CF2(CF3)CF·. The UV irradiation of C always leads to the exclusive formation of −OCF2·.The analysis of the esr spectra obtained following gamma irradiation at 77 K of the peroxides B,C point to the major process for neutral radical production being based on the peroxidic OO bond rupture followed by the β scission of secondary fluoroalkoxyls. In the case of the neutral polyethers A,D the rupture of the ether CO bonds seems to be of prominent importance. In all cases, strong singlets centred at g∼ 2.003 are observed; these signals are tentatively assigned to radical anions or trapped electrons on the basis of the results of irradiation experiments with charge scavengers and with samples of B prepared by 17O2 photooxidation of perfluoropropene. Informations regarding the electronic structures and the geometries of the alkoxyfluoralkyl radicals identified have been obtained from the anisotropies of α −F tensors and from INDO SCF MO calculations. The computed energy minima and the best agreement between computed and experimental esr data are obtained by assuming pyramidal configurations of the radical centres with degrees of bending equal to ∼ 11° and ∼ 17° for −OCF2(CF3)CF· and −OCF2· respectively. Such large deviations from the planarity are considered diagnostic of a destabilizing π conjugative interaction with the α O atoms. The esr investigation has been extended also to the peroxyl radicals RO2· obtained by reaching −OCF2(CF3)CF· and −OCF2· with 17O2. The species R16O17O and R17O17O have been identified and characterized.
Esr study of intermediate radicals in UV and gamma irradiated perfluoropolyethers and their related polyperoxidic precursors
FAUCITANO, ANTONIO;BUTTAFAVA, ARMANDO;MARTINOTTI, FAUSTA;
1980-01-01
Abstract
This note is concerned with an esrstudy of intermediateradicals formed by UV and gamma irradiation of the perfluoropolyethers A,D and their peroxidic precursors B,C obtained by perfluoroolefines photooxidation2 CF3(O-CF2CF(CF3) )n (OCF2)m OCF3 (A) Y(OCF2CF(CF3) )n (OCF2)m (O)p Y′ (B) Z(OCF2CF2)n (OCF2)m (O)p Z′ (C) CF3(OCF2CF2)n (OCF2)m OCF3 (D) Y = −CF3, −COF; Y′ = −OCF3, −OCOF; Z = −CF3, CF2COF; Z′ = −OCF3, OCF2COF The UV irradiation at 4.2 K of B leads to the formation of the radicals CF3·, −OCF2· and −O(CF3)CF·. The same species are detected folling UV irradiation at higher temperatures with the samples in the liquid state. Above 400 K, the esr spectrum of −OCF2· and, partially, of −O(CF3)CF·, are replaced by that of −0CF2(CF3)CF·. The UV irradiation of C always leads to the exclusive formation of −OCF2·.The analysis of the esr spectra obtained following gamma irradiation at 77 K of the peroxides B,C point to the major process for neutral radical production being based on the peroxidic OO bond rupture followed by the β scission of secondary fluoroalkoxyls. In the case of the neutral polyethers A,D the rupture of the ether CO bonds seems to be of prominent importance. In all cases, strong singlets centred at g∼ 2.003 are observed; these signals are tentatively assigned to radical anions or trapped electrons on the basis of the results of irradiation experiments with charge scavengers and with samples of B prepared by 17O2 photooxidation of perfluoropropene. Informations regarding the electronic structures and the geometries of the alkoxyfluoralkyl radicals identified have been obtained from the anisotropies of α −F tensors and from INDO SCF MO calculations. The computed energy minima and the best agreement between computed and experimental esr data are obtained by assuming pyramidal configurations of the radical centres with degrees of bending equal to ∼ 11° and ∼ 17° for −OCF2(CF3)CF· and −OCF2· respectively. Such large deviations from the planarity are considered diagnostic of a destabilizing π conjugative interaction with the α O atoms. The esr investigation has been extended also to the peroxyl radicals RO2· obtained by reaching −OCF2(CF3)CF· and −OCF2· with 17O2. The species R16O17O and R17O17O have been identified and characterized.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
