618
E. Baciocchi et al. / Tetrahedron 59 (2003) 613–618
solutions containing the substrate (0.1–1.0 mM), peroxydi-
sulfate (2–10 mM) and 2-methyl-2-propanol (0.1 M).
Alternatively, N O saturated aqueous solutions (pH #3.5)
7. Schwarz, H. A.; Dodson, R. W. J. Phys. Chem. 1984, 88,
3643–3647.
8. Asmus, K.-D.; Bonifacic, M.; Toffel, P.; O’Neill, P.; Schulte-
Frohlinde, D.; Steenken, S. J. Chem. Soc., Faraday Trans.
1978, 74, 1820.
2
containing the substrate (0.1–0.4 mM) and thallium(I)
sulfate (0.5–2.0 mM) were employed. The pH of the
solutions was adjusted with NaOH or HClO . The
9. Bietti, M.; Baciocchi, E.; Steenken, S. J. Phys. Chem. A 1998,
102, 7337–7342.
4
temperature of the solutions was kept constant at
2
1
5^0.28C. Rate constants were obtained by averaging 8 to
4 values, each consisting of the average of 10 to 30 shots
10. Bally, T.; Borden, W. T. Reviews in Computational Chemistry;
Lipkowitz, K. B., Boyd, D. B., Eds.; Wiley-VCH: New York,
1999; Vol. 13, pp 1–97.
and were reproducibile to within 5%.
1
1. It is sometimes stated that because it is not the wavefunction
that is variationally optimized in the Kohn-Sham (KS) DFT
calculations, KS orbitals are meaningless. Although this is true
in principle, the KS orbitals should nevertheless be at least as
useful for discussions of chemical reactivity and of other
properties of molecules as HF MOs. Koch, W.; Holthausen,
M. C. A Chemist’s Guide to Density Functional Theory;
Wiley-VCH: Weinheim, 2000; pp 49–50.
The second order rate constants for reaction of the radical
2
cations with 2OH (k
OH) were obtained from the slopes of
the plots of the observed rates (kobs) vs concentration of
NaOH. For these experiments the solution containing 0.5–
1
0
.0 mM substrate, 10 mM potassium peroxydisulfate and
.1 M 2-methyl-2-propanol was saturated with argon or
oxygen and 1 mM sodium tetraborate was added to avoid
undesired pH variations upon irradiation.
12. (a) Fleming, I. Frontier Orbitals and Organic Chemical
Reactions; Wiley: London, 1976. (b) Rauk, A. Orbital
Interactions Theory of Organic Chemistry; 2nd ed. Wiley:
New York, 2000.
3
.5. DFT calculations
Hybrid DFT calculations (UB3LYP) and appropriate
geometry optimizations were carried out with the GAUS-
SIAN 98 series of programs using the 6-31G(d) basis set
13. (a) Bietti, M.; Lanzalunga, O. J. Org. Chem. 2002, 67,
2632–2638. (b) Baciocchi, E.; Bietti, M.; Lanzalunga, O. Acc.
Chem. Res. 2000, 33, 243–251. (c) Baciocchi, E.; Del Giacco,
T.; Elisei, F. J. Am. Chem. Soc. 1993, 115, 12290–12295. (d)
Amatore, C.; Kochi, J. K. Adv. Electron Transf. Chem. 1991,
1, 55–148.
1
8
implemented therein. The calculated spin-squared expec-
2
tation values (,S .) were #0.762 in all cases, in good
agreement with the theoretically expected value of 0.75 for
a pure doublet state.
14. An estimate of the HOMO energy of water is 20.4630 a.u.
Robin, M. B. Higher Excited States of Polyatomic Molecules;
Academic: New York, 1975.
Acknowledgements
15. Bellanova, M.; Bietti, M.; Ercolani, G.; Salamone, M.
Tetrahedron 2002, 58, 5039–5044.
This work was carried out within the framework of the EU
project ‘Towards Efficient Oxygen Delignification’ (Con-
tract No. QLK5-CT-1999-01277).
16. Jagannadham, V.; Steenken, S. J. Am. Chem. Soc. 1984, 106,
6542–6551.
17. Schuler, R. H.; Hartzell, A. L.; Behar, B. J. Phys. Chem. 1981,
8
5, 192–199.
1
8. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Mont-
gomery, J. A., Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich,
S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.;
Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski,
J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K. D.;
Malick, K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.;
Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts,
R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe,
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Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.;
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