904
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 4, April, 2003
Opeida et al.
logkTEMPO
constant values and the observed changes in the selecꢀ
tivity.
12
–2
References
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[Stable Radicals], Khimiya, Moscow, 1973, 386 pp. (in
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–3
–4
–5
–6
11
7
10
8
9
4
3
6, 14
2
5
1
0.0
0.5
1.0
1.5
2.0
logkROO
•
5. K. A. Moffat, G. K. Hamer, and M. K. Georges, Macromol.,
1999, 32, 1004.
6. W. G. Skene, S. T. Belt, T. J. Connolly, P. Hahn, and J. C.
Scaiano, Macromol., 1998, 31, 9103.
Fig. 3. Correlation between the rate constants of the reaction
with alkylarenes 1—12 and 14 for the TEMPO (kTEMPO) and
peroxy radicals (kROO•).
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Nauka, Moscow, 1971, 249 pp. (in Russian).
reactive Oꢀcentered cumylperoxyl radical (ROO•).8—11
The kTEMPO(135 °C) values are by five orders of magniꢀ
tude lower than kROO•(75 °C) for the reaction with the
same hydrocarbons. This could be expected considering
the difference between the energies of the formed О—Н
bond: it is ∼70 kcal mol–1 for ТЕМРОН and about
90 kcal mol–1 for ROOH. The ratio between the logaꢀ
rithms of the reaction rate constants of the radicals under
study is presented in Fig. 3. These data show a satisfacꢀ
tory, in general, correlation of these values, considering
that the difference in temperatures at which the constants
were measured was 60 °C. It is of interest that the slope
ratio of the plot of logkTEMPO vs. logkROO for the less
•
reactive substrates is close to 1, although the radicals difꢀ
fer strongly in reactivity. This is explained by a significant
difference in temperatures at which the constants were
measured. The temperature increase suppresses substanꢀ
tially the selectivity of ROO• in H atom abstraction reacꢀ
tions. Note that the difference in the selectivity of the
action of RNO• and ROO• increases with an increase in
the reactivity of the substrate. For example, for less reacꢀ
tive hydrocarbons 1—10 (see Table 1)
(logk2 – logk10
)
•/(logk2 – logk10)ROO• ≈ 1.03,
RNO
and for more reactive molecules 11 and 12 (see Table 1)
(logk10 – logk12
)
•/(logk10 – logk12
)
• ≈ 2.5.
ROO
RNO
This can be explained by the fact that for the reactions
of alkylarenes with ROO• the transition state in the reacꢀ
tion coordinate is closer to the reactants, while for the
reaction with RNO• it is closer to the products. This
assumption agrees with both the difference in the rate
21. M. Simony and F. Tudos, Acta Chim. Acad. Sci. Hung., 1973,
77, 315.
Received April 12, 2002;
in revised form November 26, 2002