Generation and Reactivity toward Oxygen of Carbon-Centered Radicals Containing Indane, Indene, and Fluorenyl Moieties

Abstract

Resonance-stabilized radicals containing indane, indene, and fluorenyl moieties exhibit attenuated reactivity toward oxygen. Rate constants of approximately 10(5) M(-1) s(-1) were observed for the most stabilized radicals. The dependence of k(OX) (rate constant for radical trapping by oxygen) on the corresponding bond dissociation energies revealed that stereoelectronic effects are more important than steric effects in determining the low radical reactivity with oxygen. Scavenging by the nitroxide TEMPO was also examined, and revealed that in this case steric effects are more important than in the case of oxygen. The rate constants for the hydrogen abstraction by cumyloxyl and tert-butoxyl radicals generated thermally and photochemically have been determined in benzene, and were in the range of ca. (1-13) x 10(6) M(-1) s(-1), showing that benzylic stabilization has a modest effect on substrate reactivity as a hydrogen donor toward alkoxyl radicals.

LoneSelectivity of the Decatungstate-Sensitized Photooxidation of 1-Substituted Cycloalkenes

“…Thus, RI 2 will be less stable than the intermediate corresponding to RI 1 , in which the conjugation between the phenyl group and the double bond is preserved (relative yield of secondary hydroperoxide a 63% and 64%, respectively). 17 It is clearly demonstrated by the present results that alkyl or phenyl substituents activate the C-H bond in the loneposition roughly by a factor of 1.7-7.3, depending on the It is interesting to note that when the substituent R was tbutyl-or phenyl- (substrates 1-4), a small amount, 2-5% of tertiary hydroperoxide b was formed (Table 1). However, when R was methyl or benzyl (substrates 5 and 6) the amount of tertiary hydroperoxide b increased substantially (relative yields of 36% and 20%, respectively).…”

Aromatic Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical

“…At 5 × 10 –7 M, the accumulation of 4 • was not detectable, a behavior previously observed for other benzylic π radicals. 57 Instead of 4 • , a different species was formed, characterized by an absorption spectrum resembling that of 4 2 and a somewhat enhanced fluorescence ( Figure S4C ). This intermediate, which we presume to be the peroxide R–O–O–R ( Scheme 2 ), subsequently decayed to produce ketone 7 as the final oxidation product.…”

New Insights into the Chemistry of gem‐Bis(phosphonates): Unexpected Rearrangement of Michael‐Type Acceptors

“…The stable radical TEMPO is often used to scavenge free radical pairs that escape the initial solvent cage and appeared applicable to the study of this reaction. [38,39] When this reaction was accordingly conducted in the presence of TEMPO, a significant impairment of formation of 8 was observed, CG-MS analysis showing the presence of TEMPO, TEMPO-H, and a small amount of compound 8. In addition, no trapping products formed from radical species and TEMPO were detected, but some other random free radical coupling products -such as tetraethyl ethane-1,1-diylbis(phosphonate), tetraethyl 2-hydroxyethane-1,1-diylbis(phosphonate), [(EtO) 2 P(O)] 2 , etc.…”

“…A lack of ability of TEMPO for radical trapping, in spite of producing an inhibitory effect on the course of the reaction, has already been described. [38][39][40] These findings may be due either to steric hindrance of the TEMPO radical [38] or to thermal instability [39,40] of the coupling products. The addition of TEMPO or quinhydrone retards the formation of compound 8, which suggests that a radical mechanism was involved in this reaction.…”