The Journal of Organic Chemistry
Article
Laser Flash Photolysis. Nanosecond laser flash photolysis
experiments were carried out with a laser kinetic spectrometer using
the third harmonic (355 nm) of a Q-switched Nd:YAG laser delivering
7 ns pulses. The laser energy was <3 mJ per pulse. In all the
experiments a 3 mL quartz cell containing a solution of 1−7 (1.0 ×
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−
10−2 M), 3-CN-NMQ+ClO4 (7 × 10−4 M), and the cosensitizer
toluene (1 M) in N2-saturated CH3CN was flashed at 22 2 °C. The
transient spectra were obtained by a point-to-point technique,
monitoring the ΔA values after the laser flash at 10 nm intervals,
averaging at least 10 decays at each wavelength. The estimated error
for the decay rate constants was 10%.
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Computational Details. Harmonic vibrational frequencies were
calculated, at the B3P86/6-311+G(d,p) level of theory, to check that
the stationary points found for neutral sulfoxides and radicals
correspond to local minima and to evaluate the zero-point vibrational
energy (ZPVE) corrections. The ZPV energies were scaled by a 0.9845
factor.30 When, for a given compound, more than one minimum was
found, its energy (Eel + EZPVE) was obtained by Boltzmann averaging
the energy (Eel + EZPVE) of all the corresponding minima. It was
verified that the stationary points found for sulfoxide radical cations
correspond to local minima by calculating the harmonic vibrational
frequencies at the B3LYP/6-311G(d,p) level of theory. The atomic
charges were evaluated by natural population analysis (NPA).31
Electron spin densities were evaluated using the Mulliken population
analysis. In Supporting Information are reported the Cartesian
coordinates, the electronic energy, and the zero-point vibrational
energy of all the minima found.
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(10) The reduction potential of 3-CN-NMQ+ (−0.60 V vs SCE in
CH3CN)11 is much lower than that of PhSO• (1.08 V vs SCE in
CH3CN, calculated at 25 °C on the basis of a thermochemical cycle).6
Given the remarkable difference in the redox potential values for the
two species, reaction 2 is expected to be very exergonic even in the
presence of electron-donating substituents in the arylsulfinyl ring (4-
MeO-C6H4SO• and 4-Me-C6H4SO•).
ASSOCIATED CONTENT
* Supporting Information
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S
Time-resolved absorption spectra after LFP of the 3-CN-
NMQ+/toluene/2−7 systems in CH3CN. Decay kinetics of
1+•−7+•, LFP of the 3-CN-NMQ+/toluene/1−7 systems, and
structures, dihedral angles, and bond lengths of the most stable
conformers of 1+•−7+•. Cartesian Coordinates, energies, ZPVE
from DFT calculations for neutral sulfoxides 1, 3−7, for
arylsulfinyl and alkyl radicals, for sulfoxide radical cations 1+•−
7+•, and for the transition state of the C−S bond cleavage in the
radical cations 1+•−7+•. Linear correlation between the decay
rate constants for the radical cations 1+•−4+• and 2+•, 5+•−7+•
with the total benzylic product yields. Second-order plot for the
decay of 2+• as a function of water concentration. This material
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AUTHOR INFORMATION
Corresponding Authors
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was funded by MIUR (Ministero dell’Istruzione,
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dell’Universita
2011, grant number 2010FM738P).
̀
e della Ricerca Scientifica), Italy (PRIN 2010-
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