Diketone Radical Cations:  Ketonic and Enolic Forms As Revealed by Matrix EPR Studies and DFT Calculations

Abstract

Radical cations of 2,3-butanedione, 2,4-pentanedione, 3-methylpentane-2,4-dione, 2,5-hexanedione, and 2,3-pentanedione were investigated by electron paramagnetic resonance (EPR) spectroscopy in a solid Freon matrix and density functional theory (DFT) quantum chemical calculations. All the diketone radical cations in ketonic form show small proton hyperfine couplings (typically unresolved in the EPR spectra). In the cases of 2,4-pentanedione and 3-methylpentane-2,4-dione, enolic forms of the radical cations (pi-type species with main spin population at carbon atom) were characterized. Preferential stabilization of the enolic form of 3-methylpentane-2,4-dione radical cation was explained by trap-to-trap positive hole migration rather than monomolecular relaxation of the ionized ketonic form through H atom transfer.

Communication: Stabilization of radical anions with weakly bound electron in condensed media: A case study of diacetonyl radical anion

“…Therefore, both experiment and theory prove formation of delocalized state of the diacetonyl radical anion that can be compared to delocalized state of the corresponding radical cation reported previously. 15 In summary, our results suggest that the stabilization of the diacetonyl radical anion in glassy matrices is determined by the intermolecular interactions within the first solvation shell. In a wider sense, it implies that the capture of excess electron by molecules with zero or slightly negative electron affinity may be effectively controlled by the environment.…”

“…Furthermore, it belongs to a specific class of "bridged" bifunctional molecules of the X(CH 2 ) n Y type, which can be used for probing excess electron and hole delocalization and switching between localized and delocalized states. [15][16][17][18] An earlier study performed in our laboratory 15 revealed symmetrical delocalization of positive hole between the functional groups for a number of radical cations of small "bridged" diketones (n = 0 to 2). Meanwhile, the corresponding data for radical anions are unavailable.…”

Large Nonstatistical Branching Ratio in the Dissociation of Pentane-2,4-dione Radical Cation: An Ab Initio Direct Classical Trajectory Study

“…The formation of pentane-2,4-dione radical cation has been studied experimentally, , but its dissociation has not been investigated. Similar to our previous studies on acetone radical cation, , we have used ab initio classical trajectory calculations to study the nonstatistical dissociation of 2,4-pentanedione radical cation.…”

Photochemistry of Radical Cations of Some Organic Oxygen-Containing Compounds in Frozen Matrices

“…Попытка изучить фотопревращения более сложных по структуре КР дикетонов оказалась практически безуспешной из-за их высокой стабильности к действию видимого света. Авторы [17] наблюдали лишь незначительное снижение общей концентрации парамагнитных центров при действии света с λ = 380-510 нм и, в отдельных случаях, образование дистонических КР, что связывали с возможностью внутримолекулярного переноса протона.…”