INTERACTIVE FREE-ENERGY RELATIONSHIPS ON RUTHENIUM(III) CATALYZED OXIDATION
587
Table IV Significance of q in Oxidation and
Reduction Reactions
in ring Y and for a particular substituent in ring X are
p-CH3 (Ϫ0.950); H (Ϫ0.525); p-Cl (Ϫ0.550); m-Cl
(Ϫ0.310), and p-NO2 (Ϫ0.275). The negative values
obtained in all the cases indicate the formation of an
electron-deficient transition state as expected for an
electron transfer reaction. It is clear from the values of
Nature of
Transition
State
Sign of
Hammett’s
Value
Sign of
q Value
Process
oxidation
reduction
electron deficient
electron rich
Ϫve
ϩve
ϩve
Ϫve
X(Y) or Y(X) that the magnitude of for various sub-
stituents in any particular ring is a function of the na-
ture of substituents present in the other ring.
The results were analyzed in terms of interactive
free-energy relationships for multiple substituent ef-
fects as discussed by Ruasse et. al [17,18] in their work
on bromination of stilbenes. The most probable site
ative for the reduction process (Table III). This shows
that the sign of q could be used for distinguishing
whether the reaction center is electron deficient (oxi-
dation: q ϭ ϩve) or electron rich (reduction: q ϭ Ϫve)
in the transition state (Table IV).
of attack suggested there was
, which is be-
C"C
tween the two phenyl rings. For this type of reaction,
the following equation was found to be applicable:
Ϫ
X(Y)
Ϫ
X(Y0)
Y(X)
Y(X0)
ϭ
ϭ q
One of the authors (S.R.A.) is grateful to University Grants
Commission for the award of a Senior Research Fellowship.
x
y
where
and
are reaction constants for var-
X(Y0)
Y(X0)
ious substituents in ring X and ring Y, respectively,
with H in the other ring. x and y are the substituent
constants of substituents in ring X and Y, respectively.
This equation must be true whatever the nature of the
substituent in ring X or Y, i.e., q (which is called the
cross-interaction constant) is expected to be the same.
In the case of oxidation of aromatic anils by acid bro-
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, q
C"N9
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x
and qy are expected to be same. In fact, the values
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same, suggesting that the site of attack is indeed
. Similarly in the case of Os(VIII) cata-
C"N9
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the site of attack suggested was
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considered as , q and q were 0.550 and
. But in the
C"C
C"O
x
y
8. Vogel, A. I. Practical Organic Chemistry, Addison Wes-
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one-electron transfer from
present work, where the site of attack is considered
as , q and q are not expected to be the same.
The cross-interaction constants were calculated at four
different temperatures: 298, 303, 308, and 313 K. The
qx values were 0.575, 0.600, 0.625, and 0.600 (Fig. 4)
and qy values were 0.850, 0.900, 0.950, and 1.00, re-
spectively, at these temperatures, suggesting the site
group. In the
C"O
C"O
x
y
of attack is at
for oxidation of PSKs by different oxidants and neg-
. q and q values were positive
C"O
14. Cady, H. H.; Connick, R. E. J Am Chem Soc 1958, 80,
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x
y