Supporting Information

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1 Supporting Information Quinone 1 e and 2 e /2 H + Reduction Potentials: Identification and Analysis of Deviations from Systematic Scaling Relationships Mioy T. Huynh, Colin W. Anson, Andrew C. Cavell, Shannon S. Stahl,*, and Sharon Hammes-Schiffer*, Department of Chemistry, University of Illinois at Urbana Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States Department of Chemistry, University of Wisconsin Madison 1101 University Avenue, Madison, Wisconsin 53706, United States *corresponding authors: shs3@illinois.edu and stahl@chem.wisc.edu Table of Contents Experimental Page 1. Experimental 1 e and 2 e /2 H + Reduction Potentials... S2 2. Chart of Quinones used in Benchmarking Study... S3 3. Experimental 2 e /2 H + Reduction Potentials... S4 4. Experimental 1 e Reduction Potentials... S5 5. Cyclic Voltammograms of Quinones... S6 S13 Computational Page 6. Reference (Isodesmic) Reactions... S14 7. Calculated Reduction Potentials Using Different Functionals... S15 8. Table of Hammett Constants (σ)... S16 9. Hammett Correlation Plots for Electron-Donating Quinones... S Hammett Correlation Plots for Different Substitution Schemes... S E [Q, 2H + /H2Q], E [Q/Q 2 ], and pka vs. E [Q/Q ]... S E [Q, H + /HQ ], E [Q/Q 2 ], and pka vs. E [Q/Q ]... S Analysis of Tautomers for Select Quinones... S E [Q/Q ] vs. Effective Hammett Constant ( )... S Experimental and Calculated E [Q/Q ] in Different Solvents... S Experimental and Calculated E [Q /Q 2 ] in Water... S Experimental and Calculated pka of H2Q... S Experimental and Calculated pka of HQ... S Experimental and Calculated E [Q, 2H + /H2Q] in Water... S List of Quinones that Deviate from Linear Correlations... S All Calculated Reduction Potentials and pka Values in Water... S29 S References... S34

2 Table S1. Experimental 1e and 2 e /2 H + E Values for Quinones Presented in Figure 1. Complex 1 e E (V vs. Fc 0/+ ) 2 e /2 H + E (V vs. NHE) 1,4-benzoquinone (1) phenyl-1,4-benzoquinone (2) methyl-1,4-benzoquinone (3) tert-butyl-1,4-benzoquinone (4) methoxy-1,4-benzoquinone (5) ,6-dimethyl-1,4-benzoquinone (69) ,3-dimethyl-1,4-benzoquinone (25) Trimethyl-1,4-benzoquinone (91) ,6-dimethoxy-1,4-benzoquinone (71) Tetramethyl-1,4-benzoquinone (113) DDQ (134) Tetrafluoro-1,4-benzoquinone (121) ,5-dichloro-1,4-benzoquinone (56) Tetrachloro-1,4-benzoquinone (122) chloro-1,4-benzoquinone (12) S2

3 Chart S1. Quinones Used in Benchmarking Study S3

4 Table S2. Experimental 2 e /2 H + E Values and Peak-to-peak Separation for Studied Quinones. Complex a E red a E ox E a E 1,4-benzoquinone (1) phenyl-1,4-benzoquinone (2) methyl-1,4-benzoquinone (3) tert-butyl-1,4-benzoquinone (4) methoxy-1,4-benzoquinone (5) ,6-dimethyl-1,4-benzoquinone (69) ,3-dimethyl-1,4-benzoquinone (25) b Trimethyl-1,4-benzoquinone (91) ,6-dimethoxy-1,4-benzoquinone (71) Tetramethyl-1,4-benzoquinone (113) DDQ (134) Tetrafluoro-1,4-benzoquinone (121) ,5-dichloro-1,4-benzoquinone (56) Tetrachloro-1,4-benzoquinone (122) b chloro-1,4-benzoquinone (12) ,4-naphthoquinone ,10-Anthraquinone ,8-dichloro-9,10-anthraquinone ,3-dichloro-1,4-naphthoquinone ,5-di-tert-butyl-1,2-benzoquinone tert-butyl-1,2-benzoquinone Phenanthrenequinone ,2-naphthoquinone ,10-phenanthroline-5,6-dione Tetrachloro-1,2-benzoquinone a Values given in mv vs. NHE. b Species used as the hydroquinone form. S4

5 Table S3. Experimental 1 e E Values and Peak-to-peak Separation for Studied Quinones. Complex E 1 red a E 1 ox a E 1 a E 1 1,4-benzoquinone (1) phenyl-1,4-benzoquinone (2) methyl-1,4-benzoquinone (3) tert-butyl-1,4-benzoquinone (4) methoxy-1,4-benzoquinone (5) ,6-dimethyl-1,4-benzoquinone (69) ,3-dimethyl-1,4-benzoquinone (25) Trimethyl-1,4-benzoquinone (91) ,6-dimethoxy-1,4-benzoquinone (71) Tetramethyl-1,4-benzoquinone (113) DDQ (134) Tetrafluoro-1,4-benzoquinone (121) ,5-dichloro-1,4-benzoquinone (56) Tetrachloro-1,4-benzoquinone (122) chloro-1,4-benzoquinone (12) ,4-naphthoquinone ,10-Anthraquinone ,8-dichloro-9,10-anthraquinone ,3-dichloro-1,4-naphthoquinone ,5-di-tert-butyl-1,2-benzoquinone tert-butyl-1,2-benzoquinone Phenanthrenequinone ,2-naphthoquinone ,10-phenanthroline-5,6-dione Tetrachloro-1,2-benzoquinone a Values given in mv vs. Fc 0/+. S5

6 Figure S1. Cyclic Voltammograms of 1 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S2. Cyclic Voltammograms of 1 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S3. Cyclic Voltammograms of 2 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S4. Cyclic Voltammograms of 2 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S6

7 Figure S5. Cyclic Voltammograms of 4 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S6. Cyclic Voltammograms of 4 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S7. Cyclic Voltammograms of 5 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S8. Cyclic Voltammograms of 5 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S7

8 Figure S9. Cyclic Voltammograms of 71 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S10. Cyclic Voltammograms of 71 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S11. Cyclic Voltammograms of 3 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S12. Cyclic Voltammograms of 3 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S8

9 Figure S13. Cyclic Voltammograms of 25 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S14. Cyclic Voltammograms of 25 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S15. Cyclic Voltammograms of 69 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S16. Cyclic Voltammograms of 69 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S9

10 Figure S17. Cyclic Voltammograms of 91 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S18. Cyclic Voltammograms of 91 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S19. Cyclic Voltammograms of 113 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S20. Cyclic Voltammograms of 113 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S10

11 Figure S21. Cyclic Voltammograms of 12 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S22. Cyclic Voltammograms of 12 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S23. Cyclic Voltammograms of 56 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S24. Cyclic Voltammograms of 56 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S11

12 Figure S25. Cyclic Voltammograms of 121 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S26. Cyclic Voltammograms of 121 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. Figure S27. Cyclic Voltammograms of 122 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S28. Cyclic Voltammograms of 122 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S12

13 Figure S29. Cyclic Voltammograms of 134 in 1 M p-tsoh. Scan Rate = 50 mv/s. Figure S30. Cyclic Voltammograms of 134 in CH3CN with 0.1 M TBAPF6. Scan Rate = 50 mv/s. S13

14 Reference (Isodesmic) Reactions In our implementation, the reference reaction always pertains to the reaction involving our reference species (1). An example of the use of a reference reaction for the calculation of a reduction potential is depicted in Scheme S1. In this case, the reaction of interest is the 1 e reduction of benzoquinone (2) from [2] 0 to [2], and the reference reaction is the oxidation of [1] to [1] 0. Scheme S1. Calculation of Reduction Potentials Using a Reference Reaction [2] 0 + e [2] FE o [1] ref [1] ref 0 [1] ref + [2] 0 0 [1] ref + e o FE ref + [2] o G r The reduction potential for the system of interest (2) can then be expressed as o o Gr o E E ref F where G o r is the free energy change associated with the reaction shown at the bottom of o Scheme S1 and E ref is the reduction potential of the reference species (1), which is known from experimental measurements. A reference reaction can also be used to calculate pka values, which is shown in Scheme S2. In this case, the reaction of interest is the deprotonation of [H2] + to form [2] 0, and the reference reaction is the protonation of [1] 0 to form [H1] +. Scheme S2. Calculation of pka Values Using a Reference Reaction [H2] + [2] 0 + H + ln(10)rtpka + H + [H1] ref ln(10)rtpka,ref 0 [1] ref 0 [1] ref + [H2] [H1] ref + [2] 0 G r o The pka for the system of interest (2) can then be expressed as o Gr p Ka ([H 2 ] ) pka,ref ln(10) RT where G o r is the free energy change associated with the reaction shown at the bottom of Scheme S2 and pk a,ref is the pka value of the reference species [H1] +, which is known from experimental measurements. Note that in practice, we only calculated the pka values for the reduced benzoquinone species using analogous reference reactions. S14

15 Figure S31. Plots correlating calculated and experimental 1 e reduction potentials in acetonitrile (top) and 2 e /2 H + reduction potentials in water, (bottom) using different functionals. The structures of the quinones studied are shown in Chart S1. S15

16 Table S4. Hammett Constants (σ) for Substituents a,b Substituent σ p σ m σ p H C6H CH C(CH3) OCH N(CH3) NH CH2CH OH OCH2CH F Cl Br SH n/a SiH n/a CHO COOCH CF CN COOH SO NO COCH a All Hammett constants (σ) were taken from Ref 1. b The bolded Hammett constants were used for the correlation plots. The σm values were used for halogen substituents, the σp values were used for substituents capable of conjugating with the reaction center, and the σp values were used for all other substituents. S16

17 Figure S32. Plots of the 1 e reduction potentials and pka values as functions of the sum of the effective Hammett constants ( p) for the electron-donating quinones shown in Chart S1 for which experimental values are known. The selected quinones and corresponding values are provided in Tables S5-S9. S17

18 Figure S33. Plots of the 2 e /2 H + reduction potentials (darkly filled circles), the sum of the pka values (lightly filled circles), and the average of the two 1 e reduction potentials (open circles) as functions of the sum of the effective Hammett constants ( ) for different quinone substitution schemes. The quinones studied are in Chart 2 of the main text. S18

19 Figure S34. Plots of the E [Q/Q ] reduction potential versus (a) the 2 e /2 H + reduction potentials, (b) the average of the two 1 e reduction potentials, and (c) the sum of the two pka values for all of the quinones given in Chart 2 of the main text. S19

20 Figure S35. Plots of the E [Q/Q ] reduction potential versus (a) the 2 e /1 H + reduction potentials (hydride transfer), (b) the average of the two 1 e reduction potentials, and (c) the pka values for all of the quinones given in Chart 2 of the main text. S20

21 Figure S36. Analysis of tautomers for select quinones with NH2, OH, SH, and CO2H substituents for the neutral quinone (Q), quinone radical anion (Q ), and quinone dianion (Q 2 ) states. Relative free energies in kcal/mol are given in parentheses when more than one tautomer for a given state is given. For the CO2H substituents, the dianion species exhibit spontaneous intramolecular proton transfer for hydrogen-bonding conformations. Quinones with multiple protic substituents could display enhanced effects but are unlikely to alter the qualitative trends for the 1 e versus 2 e /2 H + reduction potentials. S21

22 Figure S37. Correlations between the 1 e reduction potentials, E [Q/Q ], of quinones and their effective Hammett constants ( ). The gray data points were used to generate the linear fit, and the colored data points were found to exhibit deviations from these linear fits and are defined in the legend, with the specific substituents in each group given in the SI (Table S10). S22

23 Table S5. Experimental and Calculated E [Q/Q ] in Different Solvents Water Acetonitrile Complex Expt. E a Calc. E a Expt. E b Calc. E b Lit. E b,c 1,4-benzoquinone (1) d e e phenyl-1,4-benzoquinone (2) n/a methyl-1,4-benzoquinone (3) d tert-butyl-1,4-benzoquinone (4) f methoxy-1,4-benzoquinone (5) n/a n/a 2,6-dimethyl-1,4-benzoquinone (69) g ,3-dimethyl-1,4-benzoquinone (25) d n/a Trimethyl-1,4-benzoquinone (91) d n/a 2,6-dimethoxy-1,4-benzoquinone (71) n/a Tetramethyl-1,4-benzoquinone (113) d,h ,3-dichloro-5,6-dicyano-1,4- n/a n/a benzoquinone (134) Tetrafluoro-1,4-benzoquinone (121) n/a ,5-dichloro-1,4-benzoquinone (56) n/a Tetrachloro-1,4-benzoquinone (122) n/a chloro-1,4-benzoquinone (12) n/a ,4-naphthoquinone i Anthraquinone ,8-dichloroanthraquinone n/a 2,3-dichloronaphthoquinone n/a n/a 1,8-dinitroanthraquinone n/a n/a n/a 3,5-di-tert-butyl-1,2-benzoquinone j n/a 4-tert-butyl-1,2-benzoquinone n/a n/a Phenanthrenequinone i n/a 1,2-naphthoquinone i n/a 1,10-phenanthroline-5,6-dione n/a n/a Tetrachloro-1,2-benzoquinone n/a n/a a Units of V vs. NHE. b Units of V vs. Fc 0/+. c Ref. 2. d Ref. 3. d This is the reference reaction and agrees by construction. e Ref. 4. f Ref. 5. g Refs. 6 and 7. h Ref. 8. i Ref. 9. S23

24 Table S6. Experimental and Calculated E [Q /Q 2 ] in Water Complex Expt. E a Calc. E a 1,4-benzoquinone (1) b c 2-tert-butyl-1,4-benzoquinone (4) d methoxy-1,4-benzoquinone (5) b Tetramethyl-1,4-benzoquinone (113) b a Units of V vs. NHE. b Ref. 10. c This is the reference reaction and agrees by construction. d Ref. 4. S24

25 Table S7. Experimental and Calculated pka of H2Q in Water Complex Expt. pk a Calc. pk a 1,4-benzoquinone (1) 9.85 a 9.85 b 2-methyl-1,4-benzoquinone (3) c tert-butyl-1,4-benzoquinone (4) d methoxy-1,4-benzoquinone (5) 9.91 a ,6-dimethyl-1,4-benzoquinone (69) a ,3-dimethyl-1,4-benzoquinone (25) a Trimethyl-1,4-benzoquinone (91) a Tetramethyl-1,4-benzoquinone (113) c ,5-dichloro-1,4-benzoquinone (56) 7.90 a chloro-1,4-benzoquinone (12) 8.90 a ,4-naphthoquinone 9.35 c ,5-di-tert-butyl-1,2-benzoquinone e 6.28 a Ref. 11. b This is the reference reaction and agrees by construction. c Ref. 12. d Ref. 4. e Ref. 9. S25

26 Table S8. Experimental and Calculated pka of HQ in Water Complex Expt. pk a Calc. pk a 1,4-benzoquinone (1) a b 2-methyl-1,4-benzoquinone (3) c tert-butyl-1,4-benzoquinone (4) d methoxy-1,4-benzoquinone (5) a ,6-dimethyl-1,4-benzoquinone (69) a ,3-dimethyl-1,4-benzoquinone (25) a Trimethyl-1,4-benzoquinone (91) a Tetramethyl-1,4-benzoquinone (113) c ,5-dichloro-1,4-benzoquinone (56) a chloro-1,4-benzoquinone (12) a ,4-naphthoquinone c a Ref. 11. b This is the reference reaction and agrees by construction. c Ref. 12. d Ref. 4. S26

27 Table S9. Experimental and Calculated E [Q, 2H + /H2Q] in Water Complex Expt. E a Calc. E a,b Lit. E a 1,4-benzoquinone (1) c d 2-phenyl-1,4-benzoquinone (2) n/a 2-methyl-1,4-benzoquinone (3) d 2-tert-butyl-1,4-benzoquinone (4) n/a 2-methoxy-1,4-benzoquinone (5) n/a 2,6-dimethyl-1,4-benzoquinone (69) n/a 2,3-dimethyl-1,4-benzoquinone (25) d Trimethyl-1,4-benzoquinone (91) d 2,6-dimethoxy-1,4-benzoquinone (71) d Tetramethyl-1,4-benzoquinone (113) e 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (134) n/a Tetrafluoro-1,4-benzoquinone (121) n/a 2,5-dichloro-1,4-benzoquinone (56) d Tetrachloro-1,4-benzoquinone (122) e 2-chloro-1,4-benzoquinone (12) d 1,4-naphthoquinone d Anthraquinone n/a 1,8-dichloroanthraquinone n/a 2,3-dichloronaphthoquinone n/a 3,5-di-tert-butyl-1,2-benzoquinone n/a 4-tert-butyl-1,2-benzoquinone n/a Phenanthrenequinone n/a 1,2-naphthoquinone n/a 1,10-phenanthroline-5,6-dione n/a Tetrachloro-1,2-benzoquinone d a Units of V vs. NHE. b Calculated using equation (2) in main text. c Reference reaction, agrees by construction. d Ref. 13. e Ref. 14. S27

28 Table S10. All Quinones that Deviate from Linear Correlations a Hydrogen- Hydrogen- Sterically Bonding (H2Q) b Bonding (Q) c Halogenated Charged Bulky d a The reduction potentials and pka values are given in Table S11. b The substituent acts as a hydrogen bond acceptor to the hydroquinone (H2Q) OH. c The substituent acts as a hydrogen bond donor to the neutral quinone (Q) C=O. d The substituents were chosen by examining the hydroquinone structures for either a nonplanar six-membered quinone core or protons which were oriented out of the plane of the planar quinone core. S28

29 Table S11. All Calculated Reduction Potentials and pka Values in Water a R2 R3 R5 R6 E b E b E b pka pka pka E a E b,c [Q/Q ] [Q /Q 2 ] [HQ/HQ ] [HQ ] [H2Q] [HQ] [Q, H + /HQ ] [Q, 2H + /H2Q] 1 H H H H d,e d,e e,g e,h 9.85 e,h 4.10 e,i e e 2 C6H5 H H H CH3 H H H C(CH3)3 H H H OCH3 H H H N(CH3)2 H H H NH2 H H H CH2CH3 H H H OH H H H OCH2CH3 H H H F H H H Cl H H H Br H H H SH H H H SiH3 H H H CHO H H H COOCH3 H H H CF3 H H H CN H H H COOH H H H SO3 H H H NO2 H H H COCH3 H H H C6H5 C6H5 H H CH3 CH3 H H C(CH3)3 C(CH3)3 H H OCH3 OCH3 H H N(CH3)2 N(CH3)2 H H NH2 NH2 H H CH2CH3 CH2CH3 H H S29

30 31 OH OH H H OCH2CH3 OCH2CH3 H H F F H H Cl Cl H H Br Br H H SH SH H H SiH3 SiH3 H H CHO CHO H H COOCH3 COOCH3 H H CF3 CF3 H H CN CN H H COOH COOH H H SO3 SO3 H H NO2 NO2 H H COCH3 COCH3 H H C6H5 H C6H5 H CH3 H CH3 H C(CH3)3 H C(CH3)3 H OCH3 H OCH3 H N(CH3)2 H N(CH3)2 H NH2 H NH2 H CH2CH3 H CH2CH3 H OH H OH H OCH2CH3 H OCH2CH3 H F H F H Cl H Cl H Br H Br H SH H SH H SiH3 H SiH3 H CHO H CHO H COOCH3 H COOCH3 H S30

31 62 CF3 H CF3 H CN H CN H COOH H COOH H SO3 H SO3 H NO2 H NO2 H COCH3 H COCH3 H C6H5 H H C6H CH3 H H CH C(CH3)3 H H C(CH3) OCH3 H H OCH N(CH3)2 H H N(CH3) NH2 H H NH CH2CH3 H H CH2CH OH H H OH OCH2CH3 H H OCH2CH F H H F Cl H H Cl Br H H Br SH H H SH SiH3 H H SiH CHO H H CHO COOCH3 H H COOCH CF3 H H CF CN H H CN COOH H H COOH SO3 H H SO NO2 H H NO COCH3 H H COCH C6H5 C6H5 C6H5 H CH3 CH3 CH3 H C(CH3)3 C(CH3)3 C(CH3)3 H S31

32 93 OCH3 OCH3 OCH3 H N(CH3)2 N(CH3)2 N(CH3)2 H NH2 NH2 NH2 H CH2CH3 CH2CH3 CH2CH3 H OH OH OH H OCH2CH3 OCH2CH3 OCH2CH3 H F F F H Cl Cl Cl H Br Br Br H SH SH SH H SiH3 SiH3 SiH3 H CHO CHO CHO H COOCH3 COOCH3 COOCH3 H CF3 CF3 CF3 H CN CN CN H COOH COOH COOH H SO3 SO3 SO3 H NO2 NO2 NO2 H COCH3 COCH3 COCH3 H C6H5 C6H5 C6H5 C6H CH3 CH3 CH3 CH C(CH3)3 C(CH3)3 C(CH3)3 C(CH3) OCH3 OCH3 OCH3 OCH N(CH3)2 N(CH3)2 N(CH3)2 N(CH3) NH2 NH2 NH2 NH CH2CH3 CH2CH3 CH2CH3 CH2CH OH OH OH OH OCH2CH3 OCH2CH3 OCH2CH3 OCH2CH F F F F Cl Cl Cl Cl Br Br Br Br S32

33 124 SH SH SH SH SiH3 SiH3 SiH3 SiH CHO CHO CHO CHO COOCH3 COOCH3 COOCH3 COOCH CF3 CF3 CF3 CF CN CN CN CN COOH COOH COOH COOH SO3 SO3 SO3 SO NO2 NO2 NO2 NO COCH3 COCH3 COCH3 COCH CN CN Cl Cl a This data table is also provided as an Excel spreadsheet. b Units of V vs. NHE. c Calculated using equation (2) in Main Text. d Ref. 3. e This is the reference reaction and agrees by construction. f Ref. 10. g Ref. 15. h Ref. 11. i Ref. 16. S33

34 References (1) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165. (2) Frontana, C.; Vázquez-Mayagoitia, Á.; Garza, J.; Vargas, R.; González, I. J. Phys. Chem. A 2006, 110, (3) Ilan, Y. A.; Czapski, G.; Meisel, D. Biochim. Biophys. Acta 1976, 430, 209. (4) Dohrmann, J. K.; Bergmann, B. J. Phys. Chem. 1995, 99, (5) Meisel, D.; Fessenden, R. W. J. Am. Chem. Soc. 1976, 98, (6) Wood, P. M. FEBS Lett. 1974, 44, 22. (7) Wardman, P. Free Radic. Res. Commun. 1991, 14, 57. (8) Butler, J.; Hoey, B. M. Free Radic. Biol. Med. 1986, 2, 77. (9) Jovanovic, S. V.; Kónya, K.; Scaiano, J. C. Can. J. Chem. 1995, 73, (10) Steenken, S.; Neta, P. J. Phys. Chem. 1982, 86, (11) Bishop, C. A.; Tong, L. K. J. J. Am. Chem. Soc. 1965, 87, 501. (12) Baxendale, J. H.; Hardy, H. R. Trans. Faraday Soc. 1953, 49, (13) Evans, D. H. Chapter XII-1. Carbonyl Compounds in Encyclopedia of Electrochemistry; Eds.: Bard, A. J.; Marcel Dekker, Inc.: New York, 1978; pp (14) Warren, J. J.; Tronic, T. A.; Mayer, J. M. Chem. Rev. 2010, 110, (15) Lind, J.; Shen, X.; Eriksen, T. E.; Merenyi, G. J. Am. Chem. Soc. 1990, 112, 479. (16) Adams, G. E.; Michael, B. D. Trans. Faraday Soc. 1967, 63, S34