Relative Yields of Excited Ketones from Self-Reactions of Alkoxyl and Alkylperoxyl Radical Pairs

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We have measured the ratios of excited ketones that arise from the self-reactions of alkoxyl (2R1R2CHO·) and peroxyl (2R1R2CHO·) radicals. This was accomplished by measuring the chemiluminescence emission from solutions of R1R2CHO2H, or R1R2CH2 and O2, in the presence of a free-radical initiator trans-RON—NOR, in which R = t-Bu or R1R2CH in paired experiments. The excited states were trapped with 2-tert-butyl-9,10-dibromoanthracene or another fluorescent derivative of anthracene. The peroxyls were less efficient sources by 17%, 48%, 36%, and 42% than the alkoxyls for the cases in which R1R2C=O was acetophenone in ethylbenzene, cyclohexanone in cyclohexane, and 1-tetralone in t-BuPh and in t-BuOH, respectively. The activation energy for formation of excited 1-tetralone (To and/or S1) from two 1-tetralylperoxyl radicals was 6 ± 3 kcal/mol higher than for production of the excited state from the corresponding pair of alkoxyl radicals. The results are consistent with but do not demand the hypothesis that excited carbonyl states arise in peroxyl terminations by way of alkoxyl pairs. © 1988, American Chemical Society. All rights reserved.

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Journal of the American Chemical Society