Radical anions of acyclic vicinal oligoketones: An electron spin resonance study

The Chemistry of Vicinal Polycarbonyl Compounds

“…Photoirradiation of open chain tetraketones 106 provided a delightful contrast to the reactions of tri- (198) or zwitterionic (199)…”

“…The inverse correlation between g-values and the amount of spin population on the terminal substituents prove that the unpaired electron in the radical anions up to five CO units is fully delocalized. 198 For the sake of completeness, we mention the reports on the radical anions of R,β-diketoesters such as dimethyl mesoxalate 195 and the methyl and ethyl esters of R,β-diketobutyric acid. 195 In contrast to the few investigations on acyclic polyketones there are several reports on the radical anions of cyclic triketones.…”

“…ESR data of cyclic and acyclic triketones have been summarized recently . To the best of our knowledge, there are only three reports of ESR investigations of acyclic vic -polyketones. − The radical anions of 1,3-diphenyl-1,2,3-propanetrione ( 1a ) 195 and dimesityltetraketone ( 2c ) 197 exist as free ions in dimethyl sulfoxide. In the case of 2c , the contact ion pairs with Na + , Cs + , and Ba 2+ were characterized by their ESR/ENDOR spectra showing temperature-dependent metal couplings of a Na + = 0.061 mT (190 K), a Cs + = 0.021 mT (190 K) and a Ba 2+ = 0.145 mT (295 K).…”

“…Di( tert -butyl)diketone, -triketone ( 1i ), -tetraketone ( 2i ), and -pentaketone ( 3i ) as well as the benzil, diphenyl triketone ( 1a ), and diphenyl tetraketone ( 2a ) were reduced with potassium metal in dimethoxyethane in the presence of Kryptofix 222 (see Table ) . The coupling constants obtained decrease steadily, from the α-diketones to the vic- tetra- and pentaketones while the g -values increase.…”

“…The increase of the g -values is related to the growing spin−orbit coupling due to the interaction of the unpaired electron with the lone pairs at the oxygen atoms. The inverse correlation between g -values and the amount of spin population on the terminal substituents prove that the unpaired electron in the radical anions up to five CO units is fully delocalized 16 Hyperfine Coupling Constants a (H) and g -Factors Derived from ESR Spectroscopic Investigations of the Radical Anions of Di- tert -butyldiketone, -triketone ( 1i ), -tetraketone ( 2i ), and -pentaketone ( 3i ) as well as Diphenyldiketone, -triketone ( 1a ), and -tetraketone ( 2a ) (Data from ref ) compound T [K] a (H)[G] a (H m )[G] a (H p )[G] g t -buCOCO t -bu •- 300 0.27 (18H) 2.0050 1i •- 300 0.14 (18H) 2.0053 2i •- 265 0.08 (18H) 2.0055 3i •- 240 0.063 (18H) 2.0058 PhCOCOPh •- 300 0.101 (4H) 0.034(4H) 0.115 (2H) 2.0050 1a •- 300 −0.060 (4H) 0.019(4H) −0.065 (2H) 2.0052 2a •- 260 0.017 (4H) 0.006(4H) 0.017 (2H) 2.0056 17 Hyperfine Coupling Constants a (H) from ESR Spectroscopic Investigations of the Radical Anions of Indanetrione ( 4 a ), o -Tropoquinone ( 62 ), and Cyclopentane-1,2,3-trione ( 243 ) (All values recorded at 298 K) compound a (H) [G]ref 4 a 0.097 200 62 H(4,7) 0.109 199 H(5,6) 0.205 243 H(4,5) 0.600(2) 198 …”