Electron spin resonance study of a stable benzo[b]furanyl radical

Abstract

The structure of radicals of type (11) formed by the thermal decomposition of 2,2 '-dioxo-3,3'-diphenyl-2,2',3,3'tetrahydrobibenzo[b]furan-3-y1 (I) has been studied. The approximate values of the coupling constants were determined using methyl or deuterium substitution and the e.s.r. spectra of (11) and some of its derivatives were computer-simulated. Spin densities were calculated by the IN DO and McLachlan-Honeybourne methods. The calculated coupling constants were compared with those obtained by computer simulation.'THE benzo[b]furan ring is present in many naturally occurring oxygen-containing heterocycles. Information on free-radical reactions in this system is very limited and no e.s.r. study of the benzo[b]furanyl radical has been published so far.The present work is devoted to a study of stable free radicals of type ( 11), with 2,2'-dioxo-3,3'-diphenyl-2,2',3,3'-tetrahydrobibenzo[b]furan-3-y1 (DTDB) (I) as precursor. The structure of the latter suggests that the 3,3'-bond will be easily broken thermally due to steric hindrance. The radicals thus formed are expected to be stabilized by delocalization. Thus, e.g. a xylene solution of (I) becomes blue when heated to 70 "C. This colour disappears when the solution is cooled. The presence of

Lactone-Derived Carbon-Centered Radicals: Formation and Reactivity with Oxygen

“…The resonance delocalization of the unpaired electron on the carbonyl oxygen atom in this type of radicals could be provided by ESR data. It is known that 3,3′-diphenyl-3,3′dibenzofuran-2,2′-dione 17 dissociates readily on heating in an inert solvent to form 2 radical. The ESR spectrum for 2 radical [a H ortho (2H) ) 2.51 G, a H meta (2H) ) 0.97 G, a H para -(1H) ) 2.74 G] suggests less interaction between the unpaired electron and the protons of the phenyl group than that reported for the diphenylmethyl radical 18 From a different perspective, carbon-centered radicals are known to have greatly reduced reactivity toward oxygen in cases of extensive resonance stabilization, such as triphenylmethyl and 9-phenylfluorenyl.…”

Base-Catalyzed Ship-in-a-Bottle Synthesis of a Prefluorescent, Zeolite-Incorporated Sensor for Monitoring Radical Processes in Zeolites

“…To accomplish this we monitored the fluorescence evolution of a slurry composed of 1.0 mg mL -1 of DT@NaY in a hexane solution of 3,3‘-diphenyl-3 H ,3 H ‘-[3,3‘]bibenzofuranyl-2,2‘-dione, 7 , which was chosen as the radical precursor. The ability of 7 to yield 3-phenyl-2-coumaranone radicals, 8 , (Scheme ) via homolytic C−C bond cleavage upon heating and the fate of the resulting radicals is well documented in the literature . Depending on the nature of the solvent and the temperature, the favored process is either recombination to form the starting dimer, coupling affording head-to-tail dimers and tetramers, or hydrogen atom abstraction from a donor medium to yield 3-phenyl-2-coumaranone 9 …”

Radicals and Polymers

“…His synthesis [29] consisted of the condensa tion of phenol with mandelic acid in 73% H 2 SO 4 and afforded 10 in a modest 22% yield. In 1977 Karafiloglou et al [30] re ported the electron spin resonance (ESR) study of the blue persistent benzofuranyl radical 11, which is in thermal equilibrium with its dimer 12. The radical 11 was read ily prepared via deprotonation of 10 and subsequent oxidation with iodine.…”

“…Fig. 2 shows the 1 mM CH 2 Cl 2 solu tions of the radical dimers (both colorless in solid state) from the major (30) and mi nor (31) isomer of Irganox ® HP136 after 1 h at room temperature under air.…”