Can. J. Chem. 67, 1628 (1989). Electron affinities for aza-substituted polycyclic aromatics were determined from measurements of electron transfer equilibria in the dilute gas phase with a pulsed electron high pressure mass spectrometer (PHPMS). These are (in kcall mol): quinazoline (12.7), quinoxaline (15.8), cinnoline (l6.0), acridine (20.3), benzo[c]cinnoline (20.6), pyrido[2,3-blpyrazine (22.5), phenazine (29.5). Solvation energies of the corresponding radical anions in acetonitrile and dimethylformamide are derived from the gas phase data and literature on electron reduction potentials in solution. An observed linear relationship between the electron affinities and the reduction potentials allows estimates of electron affinities to be made for 12 aza compounds whose EA's are too low to be measured with the present method.

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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)

The electron affinities of 14 substituted nitrobenzenes including nitrobiphenyls were determined by measurement of electron transfer equilibria [1] in the gas phase with a pulsed high pressure mass spectrometer: A− + B = A + B− [1]. These data, when combined with previous determinations from this laboratory, lead to electron affinities for 35 substituted nitrobenzenes and provide a comprehensive data set for the examination of substituent effects. The data are used to derive Taft gas-phase substituent parameters. A qualitative discussion based on frontier orbital molecular theory examines the substituent effect on the benzene and nitrobenzene LUMOs. The lifetimes for electron autodetachment from excited nitrobenzene negative ions, (A−)*, studied earlier by Christophorou, are examined in light of the present electron affinity data. Keywords: electron affinities, substituent effects, frontier orbital treatment, electron autodetachment from nitrobenzene radical anions.

Oxidation of dexamethasone in an aqueous suspension by air during prolonged storage produces the 17alpha-formyloxy-17beta-carboxylic acid 4. A pathway to 4 is proposed that involves Baeyer-Villiger-type oxidation of keto aldehyde 1 to mixed anhydride 5, followed by intramolecular formyl transfer. Synthetically, acid 3 was reacted with N,N'-carbonyldiimidazole followed by triethylammonium formate in order to generate the transient anhydride 5 en route to an authentic sample of 4.