KINETICS AND MECHANISM OF THE REACTION OF N-CHLOROSUCCINIMIDE WITH I− AND OH−
Table V Values of the Activation Parameters
251
Calculated as Much for the Reaction with Iodide Ion as
for the Reaction with the Hydroxide Ion
Reaction with
Iodide Ion
Reaction with
Hydroxide Ion
k2
20
k3/K1
kOH
Ea (kJ mol−1
ꢀH# (kJ mol−1
ꢀS# (J mol−1
)
2
2
29
26
2
2
57
54
5
5
)
K
19
−1) −153 20 −130 10 −49 12
on the basis of the experimental results that the rate
constants comply with the Arrhenius equation and the
equation derived from the theory of the transition state,
using these constants to calculate the energy values,
enthalpy values, and entropy activation values for the
processes of the reactions studied, which are shown in
Table V.
The enthalpy values calculated show that the pro-
cess corresponds with a chemical control of the reac-
tion. With regard to the entropies, they present negative
values, which show that the transition state is more or-
derly than the reactives. Besides, the high values found
for the reaction with iodide ion show that the transition
state is highly solvated.
Figure 8 Bro¨nsted correlation obtained for the reaction of
NCS with different bases.
hypothesis of solvation effects of the alkoxides, it is
important to emphasize that this effect can be used to
explain almost anything. Hupe and Wu’s [29] conclu-
sion is that most of the curvatures in Bro¨nsted plots of
oxygen anions depends on the basicity of the oxygen
bases rather than the difference in energies of the reac-
tants and products. The same curvature is observed for
correlations of several reactions of oxygen anions and
elimination reactions [28,30].
If we observe the resulting correlation, it seems that
the data for bases of pKa between 8 and 12.45 fall
close to a straight line with a greater slope than those
which are between the pKa values of 12.45 and 16,
which would form another line with a less pronounced
slope. This curvature might be interpreted as a dramatic
example of the Hammon postulate in which the transi-
tion state structure becomes the reactant-like for higher
pKa.
On the other hand, given that the hydroxide ion
seems to have a smaller reactivity than we would ex-
pect, we could also interpret these results as an “anoma-
lous” behavior of this ion. However, given that there
exist studies carried out with similar systems in which
it has been found that the hydroxide ion correlates
with bases with a similar pKa, we could discard this
interpretation.
BIBLIOGRAPHY
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The simplest explanation of the above observation
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Activation Parameters. We have carried out the study
of the influence of the temperature on the rate constant
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tion parameters, for the reaction studied. We have seen
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