Radical Lifetimes
FULL PAPER
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Experimental Section
The samples of 1–6 were prepared according to procedures described in
references [7,8]. Acetophenone was purchased from Nacalai Tesque Inc.
and recrystallized twice from ethanol before use. Acetonitrile (spectral
grade) and benzene (spectral grade) were purchased from Nacalai
Tesque Inc. and used directly. Sample solutions were freshly prepared
and deoxygenated by bubbling with argon (Ar) gas before irradiation.
All experiments were carried out at room temperature.
The laser flash at 308 nm (5 mJpulseꢀ1, 25 ns) was obtained from a XeCl
excimer laser (Lambda Physik, COMPex). The probe light was obtained
from a 450 W Xe-lamp (Osram XBO-450). The probe beam was passed
through an iris with a diameter of 0.3 cm and sent into the sample with a
perpendicular intersection of the laser beam. The probe beam was then
focused on a monochromator (Nikon G250). The output of the mono-
chromator was monitored using a PMT (photomultiplier tube; Hamamat-
su Photonics R928). The signal from the PMT was recorded on a transi-
ent digitizer (TDS 580D four channel digital phosphor oscilloscope,
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[28] X-ray data for compound 5: C12H16O4S, a=8.5593(10), b=7.0317(5),
c=11.0776(14) ꢂ, b=107.615(4)8, monoclinic, P21, reflections meas-
ured: 3269, independent reflections: 2555, reflections with I>2s(I):
2043, R=0.0443, Rw=0.0816, residual electron density: 0.224/
ꢀ0.327.
1 GHz, Tektronix).
A Hamamatsu Photonics multichannel analyzer
(C5967) system was used for measurement of the transient absorption
spectra. The whole system was controlled with a personal computer by
means of a GP-IB interface. To avoid any damage of the sample solution
by the probe light, a suitable cutoff filter was used in front of the sample.
The quantum yields for the photodecomposition of substrates 3 and 4
were determined by using a merry-go-round apparatus with valerophe-
none as an actinometer.[34] The product composition was measured as a
function of time by gas chromatography and the total quantum yields FT
for substrate photodecomposition were separated into quantum yields for
cyclization FC and quantum yields for Norrish-Type-II fragmentation FF
from the total product analysis after complete conversion.
[29] Due to lone pair conjugation, a-hydroxyl or alkoxyl radicals are
rather nucleophilic, as it is apparent from B3LYP/6–31G*-NBO
SOMO energies of CH3 (D3h), ꢀ0.22427 au and HO-CH2 (planar,
Cs, i496), ꢀ0.20961 au, cf.: I. Fleming, Frontier Orbitals and Organic
Chemical Reactions, Wiley, New York 2004, p. 182.
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y, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyen-
gar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford CT, 2004.
Acknowledgements
This work has been partly supported by a Grant-in-Aid for Scientific Re-
search (Project 17105005, Priority Area (417), 21st Century COE Re-
search, and others) from the Ministry of Education, Culture, Sports, Sci-
ence and Technology (MEXT) of Japanese Government, and Deutsche
Forschungsgemeinschaft.
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Received: January 4, 2006
[16] P. Wessig, O. Muhling, Helv. Chim. Acta 2003, 86, 865.
Published online: March 24, 2006
Chem. Eur. J. 2006, 12, 4662 – 4667
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4667