Electron paramagnetic resonance spectra of aliphatic ketyl radical anions in fluid solution

Abstract

Improved methods have been developed for generating aliphatic ketyl radical anions in solution for study by EPR spectroscopy. These methods involve either photolysis of a solution of potassium in the corresponding alcohol (which probably proceeds by initial electron transfer to the solvent), or abstraction of a hydrogen atom from the corresponding alcohol by photolytically generated tertbutoxyl radicals under strongly basic conditions. The EPR spectra of a number of new aldehyde and ketone radical ions are described, and compared with the spectra of their conjugate acids. The

Stability, Properties, and Electronic g Tensors of the H2COH Radical

“…Because of the rather small inversion barrier, Johnson and Hudgens 1 concluded that H 2 COH effectively belongs to the C s (yz) point group having the inversion geometry, for which the electronic ground state corresponds to X 2 A′′. Experimental information about the structure and bonding of H 2 COH has been gained by analyzing the vibrational, 1,6 electronic, 1,7,8 photoionization, 9,10 and electron spin resonance (ESR) [11][12][13][14] spectra. The electronic spectrum, measured up to 6.0 eV, consists of Rydberg transitions only, assumed to be of type π* f 3s, 3p.…”

“…The ∆g av value of H 2 CO -, a radical isoelectronic with H 2 COH, is ∼500 ppm larger. 14 Krusic et al 12 studied the temperature dependence (from 148 to 215 K) of the β-proton hfcc and corresponding line shapes. On the basis of this information, they estimated a barrier height of ∼4.3 kcal/mol for the hindered rotation of OH about the CO bond, a value confirmed by ab initio results (see above).…”

“…Experimental information about the structure and bonding of H 2 COH has been gained by analyzing the vibrational, , electronic, ,, photoionization, , and electron spin resonance (ESR) − spectra. The electronic spectrum, measured up to 6.0 eV, consists of Rydberg transitions only, assumed to be of type π* → 3s, 3p. , The adiabatic ionization potential (IP) of H 2 COH (π* → ∞, 7.56 eV 9 ) is relatively low when compared with that of H 2 CO (n → ∞, 10.88 eV), reflecting the low excitation energies of the Rydberg states in the radical.…”

“…ESR studies for H 2 COH in solution reported hyperfine coupling constants (hfcc) and the average electronic g factor, the latter parameterizing the electron-spin magnetic moment. Three independent experimental values of Δ g av = g av − g e are available, namely 1031, 970 ± 30, and 981 ppm, the first two from measurements in aqueous and the last one in tert- pentyl alcohol solutions. The Δ g av value of H 2 CO - , a radical isoelectronic with H 2 COH, is ∼500 ppm larger …”

“…Three independent experimental values of Δ g av = g av − g e are available, namely 1031, 970 ± 30, and 981 ppm, the first two from measurements in aqueous and the last one in tert- pentyl alcohol solutions. The Δ g av value of H 2 CO - , a radical isoelectronic with H 2 COH, is ∼500 ppm larger …”