Substituent effects on the electron affinities of perfluorobenzenes C6F5X

Abstract

The electron attachment free energy and enthalpy AGa°a nd AHa°corresponding to the reaction e" + = B" was determined by measuring electron-transfer equilibria, A~+ B = A + B', with a pulsed electron high-pressure mass spectrometer (PHPMS), involving compounds A whose attachment energies are known. Values were obtained for C6F5X (X = F, Cl, C6F5, CF3, COCH3, CHO, CN, Br, I, N02, COC6F5). The substituent effects for the -acceptor/Tr acceptor substituents were found to be very similar to those observed for the electron attachment energies of substituted nitrobenzenes: N02C6H4X. This correspondence shows that the extra electron in both systems enters a 7r*-orbital. The substituent effects for the -acceptor/ir-donor substituents, X = Cl, Br, I, were found to be very much larger for the C6F5X, relative to the nitrobenzenes, and to increase greatly in the order F, Cl, Br, I. These results indicate that the extra electron enters a CT*-orbital, which is localized on the C-X atoms.Recent workla from this laboratory reported electron affinities of perfluorobenzene C6F6 and substituted perfluorobenzenes C6F5X determined via gas-phase measurements of electron-transfer(1) (a)

Pentafluorobenzaldehyde and its utilizing in organic synthesis

“…If utilizing the difluorobromotriphenylphosphonium bromide and metal cadmium for ylide formation, according to Burton [274] the difluorovinylpentafluorobenzene is formed in Wittig reaction (56,Scheme 36).…”

Electron attachment and detachment: C6F6

“…Shortly afterwards, in 1986, Chowdhury et al used high-pressure mass spectrometry to measure EACCgFe) and found 0.52±0.10eV [9][10][11] and noted that thermal detachment would take place at modest temperatures. In 1992, Knighton et al [12] confirmed the electron detachment explanation of the previous experiments and measured rate constants for the detachment process over the temperature range 307-349 K. Much of the Knighton et al work regarded the role of unavoidable oxygen impurities in high-pressure experiments; they concluded that high-pressure experiments carried out without mass spectrometric analysis of the ions, such as those of Spyrou and Christophorou [5] and Chen et al [6], were unlikely to be correctly interpreted.…”

Electron capture by pentafluoronitrobenzene and pentafluorobenzonitrile

“…8 However, recent values obtained from electron transfer equilibria converge to a value of 0.53 eV. 8,13,14 We find that pentafluoronitrobenzene does not form a metastable parent anion, while in pentafluorobenzonitrile the parent anion (C 6 F 5 CN À ) is observed within a narrow resonance near 0 eV which is by far the dominant ion formed in electron attachment to C 6 F 5 CN. A metastable C 6 F 5 CN À ion has, in fact, already been observed in an early time of flight (TOF) experiment.…”

“…19 In SF 6 , all DEA channels are endothermic and hence not accessible at 0 eV, provided that the temperature of the target molecule is low (no thermal activation). 20 Experimental values for the electron affinities of the compounds under investigation are available from electron transfer equilibria, namely 1.08 eV (C 6 F 5 CN 21 ) and 1.45 eV (C 6 F 5 NO 2 13 ). Fig.…”