The Journal of Organic Chemistry
Article
purified by flash column chromatography (silica gel, eluent dichloro-
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methane/methanol 50/1) to give 0.7 g of pure product (GC > 99%,
1
4
4% yield), identified by H NMR.
Dicumyl peroxide was of the highest commercial quality available
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and was used as received. Dibenzyl peroxide was prepared according to
a previously described procedure by reaction of KO with benzyl
2
012, 51, 5544−5555.
2
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49
bromide in dry benzene, in the presence of 18-crown-6.
5
(
(
1, 5556−5578.
Laser Flash Photolysis Studies. LFP experiments were carried
out with a laser kinetic spectrometer using the fourth harmonic (266
nm) of a Q-switched Nd:YAG laser, delivering 8 ns pulses. The laser
energy was adjusted to ≤10 mJ/pulse by the use of the appropriate
filter. A 3.5 mL Suprasil quartz cell (10 mm ×10 mm) was used in all
experiments. Nitrogen-saturated solutions of dicumyl peroxide and
dibenzyl peroxide (10 and 8 mM, respectively) were employed. All of
the experiments were carried out at T = 25 ± 0.5 °C with magnetic
stirring. The observed rate constants (kobs) were obtained by averaging
three to five individual values and were reproducible to within 5%.
Second-order rate constants for the reactions of the cumyloxyl and
benzyloxyl radicals with the amides were obtained from the slopes of
the kobs (measured following the decay of the cumyloxyl and
benzyloxyl radical visible absorption bands at 490 and 460 nm,
respectively) vs [amide] plots. Fresh solutions were used for every
amide concentration. Correlation coefficients were in all cases >0.992.
The rate constants displayed in Table 1 are the average of at least two
independent experiments, typical errors being ≤10%.
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age. Vibration frequency calculations verified the correct nature of
local minima and transition states. Several initial orientations were
used to determine the structures of prereaction complexes, from which
transition state structures were determined. The calculations did not
take into account the effects of solvent. Rate constants are calculated
from transition state theory using the free energy differences between
the free reactants and the transition state complexes and the
prereaction and transition state complexes.
1
(
9
(
03, 4657−4689.
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ASSOCIATED CONTENT
Supporting Information
Figures, tables, and texts giving plots of k vs substrate
concentration for the reactions of CumO and BnO , details of
the calculations and an input file demonstrating the use of
dispersion-correcting potentials, and potential energy surfaces
associated with laterally displacing the radical with respect to
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(
24) Kjaer, N. T.; Lund, H. Acta Chem. Scand. 1995, 49, 848−852.
*
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•
•
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1925−1928. (b) Ding, S.; Jiao, N. Angew. Chem., Int. Ed. 2012, 51,
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226−9237. (c) Yan, Y.; Zhang, Y.; Feng, C.; Zha, Z.; Wang, Z. Angew.
Chem., Int. Ed. 2012, 51, 8077−8081. (d) Xia, Q.; Chen, W. J. Org.
Chem. 2012, 77, 9366−9373. (e) Mai, W.-P.; Wang, H.-H.; Li, Z.-C.;
Yuan, J.-W.; Xiao, Y.-M.; Yang, L.-R.; Mao, P.; Qu, L.-B. Chem.
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(g) Barve, B. D.; Wu, Y.-C.; El-Shazly, M.; Chuang, D.-W.; Chung, Y.-
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AUTHOR INFORMATION
M.B.).
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*
(
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support from the Ministero dell’Istruzione dell’Uni-
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28) Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Morris, J. J.;
Taylor, P. J. J. Chem. Soc., Perkin Trans. 2 1990, 521−529.
29) (a) Salamone, M.; Martella, R.; Bietti, M. J. Org. Chem. 2012, 77,
556−8561. (b) Salamone, M.; DiLabio, G. A.; Bietti, M. J. Am. Chem.
versita
̀
e della Ricerca (MIUR) - project 2010PFLRJR (PRIN
(
8
2
010-2011) is gratefully acknowledged. We thank Prof.
Lorenzo Stella for the use of LFP equipment.
Soc. 2011, 133, 16625−16634. (c) Salamone, M.; DiLabio, G. A.;
Bietti, M. J. Org. Chem. 2011, 76, 6264−6270. (d) Salamone, M.;
Anastasi, G.; Bietti, M.; DiLabio, G. A. Org. Lett. 2011, 13, 260−263.
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(31) Evidence supporting the HBD ability of primary alkoxyl radicals
•
has been recently provided in a study of the reactions of CH
O and
3
•
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H
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