Substituent effects on the reactions of aromatic triflones with para-X-anilines in methanol: Low intrinsic reactivity and transition state imbalances

Article abstract of DOI:10.1002/kin.20545

A kinetic study is reported for S_NA_r reactions of 2,4,6-tris(trifluoromethanesulfonyl) anisole 1a with a series of para-X-substituted anilines 2a-e in a methanol solution at various temperatures. The substituent effects on free energy (δ^≠G), enthalpy (δ^≠H), and entropy (δ^≠S) of activation are examined. Aniline addition to triflone 1a is characterized by a β_X=0.57, α_Z=0.31, and an imbalance of I = α_Z-β_X=-0.26. The imbalance shows that resonance development lags behind C-N bond formation at the transition state. Interestingly, analysis of the results in terms of Marcus theory reveals that these S_NAr are associated with some extremely low intrinsic reactivity (log k_o=-1.25

Full text of DOI:10.1002/kin.20545

Substituent Effects on the
Reactions of Aromatic
Triflones with
Para-X-Anilines in
Methanol: Low Intrinsic
Reactivity and Transition
State Imbalances
NIZAR EL GUESMI, TAOUFIK BOUBAKER
Department of Chemistry, Faculty of Sciences of Monastir, Avenue de l’Environnement, Monastir 5019, Tunisia
Received 17 September 2010; revised 29 November 2010; accepted 30 November 2010
DOI 10.1002/kin.20545
Published online 23 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: A kinetic study is reported for SNAr reactions of 2,4,6-tris(trifluoromethanesulfonyl)
anisole 1a with a series of para-X-substituted anilines 2a–e in a methanol solution at various
ꢀ
ꢀ
temperatures. The substituent effects on free energy (ꢀ=G), enthalpy (ꢀ= H), and entropy
(ꢀꢀ=S) of activation are examined. Aniline addition to triflone 1a is characterized by a βX = 0.57,
αZ = 0.31, and an imbalance of I = αZ –βX = −0.26. The imbalance shows that resonance
development lags behind C N bond formation at the transition state. Interestingly, analysis
of the results in terms of Marcus theory reveals that these SNAr are associated with some
ꢁ
C
extremely low intrinsic reactivity (log ko = −1.25). 2011 Wiley Periodicals, Inc. Int J Chem
Kinet 43: 255–262, 2011
temperatures. An aromatic nucleophile substitution
SNAr mechanism is suggested based on the second-
order kinetics and the dependence of rates on the nature
of the aniline [1].
We have now extended our study to the reaction
of 2,4,6-tris(trifluoromethanesulfonyl)anisole 1a with
various para-X-substituted anilines 2a–e in methanol,
in the temperature range 288–328 K. We investigated
the mechanism by comparing the data obtained in
this study with those for the corresponding reactions
with triflone 1b. The substituent effects on the kinetic
INTRODUCTION
Recently, we have kinetically studied the reaction
of 2,6-bis(trifluoromethanesulfonyl)-4-nitroanisole 1b
with some substituted anilines in methanol at various
Correspondence to: Taoufik Boubaker; e-mail: boubaker
taoufik@yahoo.fr.
Supporting information is available in the online issue at
www.wileyonlinelibrary.com.
c
ꢀ
2011 Wiley Periodicals, Inc.

256
EL GUESMI AND BOUBAKER
ꢀ
parameters k, ꢀ=G, ꢀꢀ=H, and ꢀꢀ=S are discussed.
As will be seen, our results of linear free energy re-
lationships are analyzed in terms of imbalanced tran-
sition states. Possible explanations accounting for the
inequality between the Bro¨nsted αZ and βX values and
imbalanced transition states will be suggested. The in-
trinsic rate constant ko for triflones 1a and 1b has been
determined and compared with the corresponding pa-
rameters for other compounds.
RESULTS AND DISCUSSION
Kinetic Studies
Kinetic runs were performed by the methods previ-
ously reported [1,3–9], following the appearance of
the reaction product 350 < λ < 370 nm. All reac-
tions in this study obeyed pseudo-first-order kinetics
under conditions of excess p-X-aniline 2a–e. Pseudo-
first-order rate constants, kobsd, were obtained from the
correlation ln (A –At ) against time, where A refers
∞
∞
to the absorbance of the product 3a–e at the comple-
tion of the reaction and At refers to the absorbance
at time t. The kobsd values obtained are summarized
in Tables S1–S5 in the Supporting Information. The
pseudo-first-order rate constants, kobsd, for all the re-
actions obeyed Eq. (1) [1]. (Correlation coefficients of
the linear regressions were usually higher than 0.99.)
EXPERIMENTAL
2,4,6-Tris(trifluoromethanesulfonyl)anisole 1a was
prepared as reported previously [2]. Anilines 2a–e
(Aldrich products) were available of the highest quality
and were recrystallized or distilled before use when-
ever necessary. Methanol was used without further pu-
rification.
kobsd = k1 [para-X-aniline]o
(1)
From the slopes of these plots, exemplified in Fig. 1,
the second-order rate constants, k1, were readily de-
rived. Table I summarizes the second-order rate con-
stants, k1, which were measured at 10 K intervals
with the temperatures range 288–328 K for the re-
action of para-X-substituted anilines 2a–e with 2,4,6-
tris(trifluoromethanesulfonyl)anisole 1a in methanol.
All the available data for reactions (2) are consistent
with the SNAr mechanism in which the formation of
the zwitterionic intermediates ZH is rate limiting.
In this regard, we note that El Hegazy and coworkers
have studied the coupling of meta- and parasubstituted
anilines with 2-chloro-3,5-dinitropyridine in methanol
and found that the initial attack of the electrophile is
also rate limiting [10].
A stock solution of triflone 1a was prepared (5 ×
10−3 mol dm−3) and diluted before use to 5 × 10−5 mol
dm−3. Solutions of various substituted anilines 2a–e
(5 × 10−3 to 10−1 mol dm−3) wereprepared, just before
use by dissolving a weighed amount of the required
aniline in a known volume of solvent.
UV–visible spectra and kinetic measurements were
made on a Shimadzu spectrophotometer equipped
(model 1650 PC) with a Peltier temperature controller
(model TCC-240 A), which is able to keep to tem-
perature within 0.1 K. The kinetic constants measured
in the range 288–328 K were reproducible to within
ꢀ
5%; the maximum error ofꢀ ꢀ=H is 2.1 kJ mol−1
,
.
and the maximum error of ꢀ=S is 4.9 J mol−1 K−1
+
NH2C6H4X
CH3O
CF3O2S
OCH3
NH2
SO2CF3
SO2CF3
CF3O2S
k
k
1
+
–1
Z
X
Z
+
-
1
2
ZH
X = OCH3 (2a), CH3 (2b),
H (2c), F (2d), Cl (2e)
(a) Z = SO2CF3
(b) Z = NO2
(2)
NHC6H4X
CF3O2S
SO2CF3
k
2
+
CH3OH
Z
3
International Journal of Chemical Kinetics DOI 10.1002/kin

SUBSTITUENT EFFECTS ON THE REACTIONS OF AROMATIC TRIFLONES
257
0.01
0.008
0.006
0.004
0.002
0
CH
3
OCH
3
H
k
Cl
F
0
0.02
0.04
0.06
0.08
0.1
0.12
[para-X-Aniline] (mol dm-3)
o
Figure 1 Influence of the concentration of anilines 2a–e on the observed first-order rate constant for addition to 2,4,6-
tris(trifluoromethanesulfonyl)anisole 1a in methanol at 25◦C.
Table I Substituent and Temperature Effects on the
Second-Order Rate Constants, k1, for Reactions of
2,4,6-Tris(trifluoromethanesulfonyl)anisole 1a with
Para-X-Substituted Anilines 2a–e in Methanol
tion) based on the data acquired in experiments run
at 15, 25, 35, 45, and 55◦C as reported in Table II.
ꢀ
We found highly negative activation entropy ꢀ=S and
ꢀ
positive activation enthalpy ꢀ=H. The lower activa-
k1 (×10−2 dm3 mol−1 s−1
15◦C 25◦C 35◦C 45◦C 55◦C
)
tion enthalpy and high free energy of activation sup-
port the formation of highly solvated transition state.
It is interesting to note that the negative activation en-
tropy agrees with accepted addition–elimination mech-
anism. As can clearly be seen, the overall reactions to
give substitution products 3a–e are enthalpy controlled
Para-X-Substituted
Anilines (X)
2a (OCH3)
2b (CH3)
2c (H)
2d (F)
2e (Cl)
ρ
0.61 1.19 2.03 4.02 6.93
0.44 0.93 1.61 3.45 6.08
0.22 0.46 1.01 1.97 4.00
0.14 0.34 0.73 1.52 3.07
0.03 0.22 0.54 1.13 2.42
−1.74 −1.54 −1.19 −1.16 −0.91
ꢀ
ꢀ
(ꢀ=H > –T ꢀ=S).
Substituent Effects
Comparison of the rate constants k1 (see Table I)
to the couplings of para-X-substituted anilines
2a–e with 2,4,6-tris(trifluoromethanesulfonyl)anisole
1a obtained in methanol at different temperatures re-
veals that the rates of the reactions are notably sensitive
ꢀ
The activation parameters ꢀ=H (enthalpy of acti-
vation), ꢀ=S (entropy of activation), and ꢀ=G (free
energy of activation) were obtained from the linear
Eyring plots [11] (Fig. S1 in the Supporting Informa-
ꢀ
ꢀ
Table II Activation Parameters for the Reactions of 2,4,6-Tris(trifluoromethanesulfonyl)anisole1a with
Para-X-Substituted Anilines 2a–e in Methanol
Para-X-Substituted Anilines (X)
Activation Parameters
2a (OCH3)
2b (CH3)
2c (H)
2d (F)
2e (Cl)
ꢀꢀ=H(kJ mol−1
)
45.1
−111.1
78.2
49.0
−100.3
78.9
54.5
−87.3
80.5
57.8
−78.7
81.3
62.2
−67.7
82.4
ꢀꢀ=S(J mol−1 K−1
ꢀꢀ=G (298 K)(kJ mol−1
)
)
Calculated by using the Eyring equation (log k1/T vs. 1/T ) [11].
International Journal of Chemical Kinetics DOI 10.1002/kin

258
EL GUESMI AND BOUBAKER
0.5
0
–0.5
55 °C
45 °C
35 °C
–1
k
–1.5
–2
25 °C
15 °C
–2.5
H
p-F
p-Cl
0.2
p-OCH3 p-CH3
–0.3 –0.2
–3
–0.4
–0.1
0
0.1
0.3
0.4
σ
para
Figure 2 Substituent effect on the rate for reactions of 2,4,6-tris(trifluoromethanesulfonyl)anisole 1a with anilines 2a–e in
methanol at various temperature. The σ values were taken from [11].
ꢀ
change of ꢀ=S with the substituents is caused by the
to the inductive effects of the X-substituent in the ani-
line molecule. This behavior is illustrated in Fig. 2,
which shows that five different straight lines are ob-
tained by plotting the log k1 values measured at the
different temperatures studied versus the appropriate
Hammett σpara [11].
change in solvation and by the reorganization of the
solvent [12–14]. Interestingly, the free energy of
the transition state ꢀ=G is essentially insensitive to
ꢀ
the substituent effect.
A significant feature of the results is that a plot of
log kX/kH for the reaction of 1a against log kX/kH
for the reaction of 1b in methanol [1] exhibits a
linear relationship with a slope very close to unity
(Fig. 4). This suggests that the structure of the transition
state is not significantly altered by the change in the
X-substituent in the aniline.
The ρ values deduced from the slopes of the log
k1 versus σpara (Table I, line 6) for reactions of 1a
increase from −1.74 to −0.91 as the temperature in-
creases. A similar result is obtained for the correspond-
ing reactions of 2,6-bis(trifluoromethanesulfonyl)-4-
nitroanisole 1b [1]. On the other hand, the ρ values are
clearly consistent with significant development of pos-
itive charge at the nitrogen atom of the aniline moiety
in the transition state for formation of the zwitterionic
intermediate ZH .
Intrinsic Reactivity of Triflones 1
ꢀ
A plot of ꢀꢀ=H against ꢀ=S for the reactions in
Information about the transition state of the first step for
methanol (Fig. S2 in the Supporting Information) gave
a good straight line of slope 402 K, which is the value of
isokinetic temperature for these reactions. This linear
relationship between the enthalpy and entropy contri-
butions implies that the susceptibility of a reaction to
substituent effects would be reversed simply by chang-
ing the temperature. The observation of isokinetic
relationships is evident in favor of an identical reac-
tion mechanism.
¨
our SNAr reactions can be obtained from the Bronsted-
type relationships [15–17]. In fact, the rates of reaction
(2) may be modified by changing substituents in two
ways: (a) The basicity of the aniline can be varied by
changing X (e.g., to give a Bronsted βX) and (b) the
acidity of the triflone can be varied by changing Z (e.g.,
¨
to give a Bronsted αZ) [18,19]. We describe now how
the rates of this reaction are affected by each of these
variables and compare the results with predictions of
the transition state imbalances.
In this study, when the logarithm of the second-order
rate constants k1 measured in methanol for the re-
actions of 2,4,6-tris(trifluoromethanesulfonyl)anisole
¨
In some cases, the changes in activation param-
eters with theꢀ substituents are also illustrated by
ꢀ
ꢀ=G/ꢀꢀ=H/ꢀ=S versus σpara plots (Fig. 3). We
note that the majority of the experimentally observed
International Journal of Chemical Kinetics DOI 10.1002/kin

SUBSTITUENT EFFECTS ON THE REACTIONS OF AROMATIC TRIFLONES
259
100
80
60
40
20
0
–60
Δ#S
Δ#G
–70
Δ#H
–80
–90
–100
–110
–120
–0.4
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
0.4
σ
para
ꢀ
ꢀ
Figure 3 ꢀ=G/ꢀꢀ=H/ꢀ=S versus σ plots of the coupling of 2,4,6-tris(trifluoromethanesulfonyl) anisole 1a with para-X-
substituted anilines 2a–e in methanol.
1
log ( k X / k H) (1a) = 0.03 + 1.03 log ( k X / k H) (1b)
1
1
1
1
R = 0.99418
0.5
0
k
k
15°C
25°C
35°C
45°C
55°C
-0.5
-1
-0.5
0
0.5
log ( k1X / k1H) (1b)
Figure 4 Linear correlation between the log kX/kH for the reaction of 1a versus log kX/kH for the reaction of 1b in methanol
at various temperatures. R is the regression coefficient. k1H is the rate constant for X = H, and k1X is the rate constant for the
substituent X.
1a with para-X-substituted anilines 2a–e was plotted
against the pKa(X) values of the conjugate acids of
the anilines 2a–e in an aqueous solution [20], a linear
correlation is obtained (Fig. 5) with a slope represent-
ing the Bro¨nsted value of 0.57. The value of βX for
these reactions (2) reported in the present study is pre-
sented in Table III, together with the corresponding
βX data obtained for para-X-substituted anilines 2a–e
with triflone 1b [1]. As can be seen, the same values
of βX have been obtained in the present study for the
charge transfer from the aniline to triflone. The impli-
cation of this finding is that both triflones 1a and 1b
demonstrated the same amount of bond formation in
the TS of their reactions. On the other hand, the val-
ues of βX are close to 0.55, suggesting that the degree
of carbon-nitrogen bond formation is approximately
International Journal of Chemical Kinetics DOI 10.1002/kin

260
EL GUESMI AND BOUBAKER
0
1a, βX = 0.57
1b, = 0.54
log ko = -0.55
βX
–0.5
–1
log ko = -1.25
–1.5
–2
k
–2.5
–3
K
3
4
5
6
7
8
9
pK
a
Figure 5 Bro¨nsted-type plots for the reaction of triflone 1a and 1b with para-X-substituted anilines 2a–e in methanol at 25◦C.
half complete in the transition state and falling in the
domain recognized as typical of polar SNAr [6,21].
Most importantly, Fig. 5 can be used for estimat-
ing the intrinsic rate constants, ko, of Marcus theory
[22,23], defined as ko = k1 when pKa(X) = pKa(Z),
where Ka(Z) is the thermodynamic constant for the
reversible formation of the methoxy σ-adduct 4 (see
Table III and Eq. (3)) [4,24]. The values of the intrinsic
rate constants for 1a and 1b, as determined from the
Bro¨nsted plots, are presented in Table III.
tivity log ko = −0.80 of the reactions of 4,6-dinitro-7-
methoxybenzofurazan 6 with methanol at 20◦C [27].
OCH3
O2N
NO2
O2N
N
N
O
NO2
NO2
5
6
CH3O
CF3O2S
OCH3
OCH3
SO2CF3
SO2CF3
CF3O2S
Ka
+
+
+
CH3OH
H
Z
(3)
Z
1
4
(a) Z = SO2CF3
(b) Z = NO2
As we can observe, these rate constants are remark-
ably low compared with those reported for a number of
electron-deficient nitro-substituted aromatic and het-
eroaromatic substrates [25,26]. For example, log ko
values of 0.18 and 0.22 have been found for reac-
tions of 1,3,5-trinitrobenzene 5 with nitroalkane an-
ions in methanol at 25◦C [26]. Interestingly, the log ko
value measured for 1a (log ko = −1.25) in methanol
reflects one of the highest intrinsic barriers ever ob-
served for SNAr reactions. We note particularly that
Terrier et al. have also reported a low intrinsic reac-
Our results show that the replacement of NO2 by
SO2CF3 is accompanied by an appreciable decrease
in intrinsic reactivity (ꢀlog ko = −0.70). This is cer-
tainly a reflection of the preferential stabilization of
the negative charge of the transition state by a para-
SO2CF3 group [28,29]. On the other hand, a re-
cent study of the σ-complexation of 1a and 1b and
other anisole series 2,4,6-trinitro- and 4-SO2CF3–2,6-
dinitro- has revealed that the especially high capacity
of resonance stabilization of the negative charge of
International Journal of Chemical Kinetics DOI 10.1002/kin

SUBSTITUENT EFFECTS ON THE REACTIONS OF AROMATIC TRIFLONES
261
Table III Comparison of βX, log ko, and I Values for Para-X-Substituted Anilines Attachment to Triflones 1a and 1b
in Methanol at 25◦C.
pKaCH OH
pKaH O
βX
log k
Imbalance I = αZ–βX
3
2
Triflone
o
1a (Z = SO2CF3)
1b (Z = NO2)
7.32a
10.48b
4.80c
7.96c
0.57d
0.54e
−1.25d
−0.55d
−0.26d
−0.23d
aFrom El Guesmi et al. [24].
bFrom El Guesmi et al. [4].
cCalculated from the equation: pKa (H2O) = pKa (CH3OH) – 2.52 [4].
d This work.
e
From El Guesmi et al. [1].
+
+
+
NH2C6H4X
CH3O
CF3O2S
NH2C6H4X
CH3O
CF3O2S
NH2C6H4X
SO2CF3
CH3O
CF3O2S
SO2CF3
SO2CF3
SO2CF3
SO2CF3
SO2CF3
Ia
IIa
IIIa
+
+
+
NH2C6H4X
CH3O
CF3O2S
NH2C6H4X
CH3O
CF3O2S
NH2C6H4X
SO2CF3
CH3O
CF3O2S
SO2CF3
SO2CF3
NO2
NO2
NO2
Ib
IIIb
IIb
the adducts through an Fπ–type polarization effect is
a major factor that accounts for the strong activation
provided by SO2CF3 groups [4].
However, we suggest that the high intrinsic barri-
ers associated with reactions (2) have been attributed
to increased resonance stabilization as illustrated by
resonance structures Ia–IIIa and Ib–IIIb (see next
section).
at 25◦C. Bro¨nsted αZ value close to 0.31 is found. As
can be seen, the αZ value is markedly smaller than βX.
The large inequality between the Bronsted βX and αZ
values is known to be good evidence for a consider-
able lag in structural-electronic and solvational reorga-
nization behind charge transfer in the transition state.
The difference I = αZ-βX (see Table III) suggests that
our SNAr reactions are characterized by imbalanced
transition state structures in which development of
resonance and solvation at the aromatic ring of tri-
flone 1 lags behind C N bond formation or lags behind
charge transfer the aniline to the triflone [19,30]. Imbal-
ance values of the order of 0.25 have also been recently
found for the reactions of substituted benzylidene Mel-
drum’s acids and methyl thiobenzylidene Meldrum’s
acids with OH−, CF3CH2O−, and HOCH2CH2S− in
50% Me2SO in 50% H2O [31]. On the other hand, it
is interesting to note that negative I values obtained in
this work reflects a situation where the Z substitutent
is located closer to the negative charge in the zwitteri-
onic intermediates ZH than in the transition state.
A convenient way to visualize structure–reactivity
relationships is to consider the transition state to be
Transition State Imbalances
If we assume that the both triflones 1a and 1b are
structurally similar, then we can estimate a value of αZ
directly from Eq. (4) using the values of δpKa (Z) and
δ log k1
δ log k1
αZ =
(4)
δpKa
In this equation, k1 represent the values of the second-
order rate constants for the couplings of triflones 1a–b
with a given aniline 2a–e, e.g., aniline (2c, X = H), and
δpKa (Z) is the differing thermodynamic acidity con-
stants values of the two triflones measured in methanol
International Journal of Chemical Kinetics DOI 10.1002/kin

262
EL GUESMI AND BOUBAKER
situated on a More O’Ferrall-Jencks diagram [32]
(Fig. S3 in the Supporting Information). We suggest
that the transition state for anilines addition to the tri-
flone 1 is imbalanced in the sense that charge delo-
calization into the 2,4,6-(SO2CF3) or 2,6,-(SO2CF3)-
4-NO2 phenyl ring lags somewhat behind C N bond
formation. This finding is consistent with the fact that
the intrinsic rate constants log ko for these reactions
are substantially lower.
3. (a) Bunnett, J. F.; Zahler, R. E. Chem Rev 1951, 49, 273–
412; (b) Bunnett, J. F.; Sekiguchi, S.; Smith, L. A. J Am
Chem Soc 1981, 103, 4865–4871; (c) Bunnett, J. F.;
Cartano, A.V. J Am Chem Soc 1981, 103, 4861–4865.
4. El Guesmi, N.; Boubaker, T.; Goumont, R.; Terrier, F.
Org Biomol Chem 2008, 6, 4041–4052.
5. Orvik, J. A.; Bunnett, J. F. J Am Chem Soc 1970, 92,
2417–2427.
6. Terrier, F. Nucleophilic Aromatic Displacement. The In-
fluence of the Nitro Group; Wiley-VCH: New York,
1991.
7. Thomas, A. E.; Chukwuemeka, I. Int J Chem Kinet 2002,
34, 645–650.
CONCLUSIONS
8. Buncel, E.; Dust, J. M.; Terrier, F. Chem Rev 1995, 95,
2261–2280.
9. Boubaker, T.; Goumont, R.; Jean, E.; Terrier, F. Org
Biomol Chem 2003, 1, 2764–2770.
10. El Hegazy, F. M.; Abdel Fattah, S. Z.; Hamed, S. A.;
Sharaf, S. M. J Phys Org Chem 2000, 13, 549–554.
11. Hammett, L. P. Reaction Rates, Equilibria and Mecha-
nism, 2nd ed.; McGraw-Hill: New York, 1970.
12. Parker, A. J. Adv Phys Org Chem 1967, 5, 173.
13. Alexander, J.; Ko, E. C. F.; Parker, A. J.; Broxton, T. J.
J Am Chem Soc 1968, 90, 5049–5069.
ꢀ
ꢀ
Activation parameters, ꢀ=H, ꢀ=S, and ꢀꢀ=G, are ob-
tained for five anilines by para-X-substituted anilines
(X = OCH3, CH3, H, F, Cl) from the second-order
rate constants at 15, 25, 35, 45, and 55◦C. All the
available data for reactions (2) are consistent with the
SNAr mechanism with addition of the aniline being a
rate-limiting step. The overall reactions are enthalpy
controlled in methanol. The inequality between the
Bro¨nsted αZ and βX values provides further evidence
for the imbalance transition state. The intrinsic reactiv-
ity value measured for 1a in methanol reflects one of the
lowest intrinsic reactivity ever observed for SNAr re-
actions. Another significant feature emerges from this
study, namely, that there is also a clear relationship
between the intrinsic reactivity log ko values and the
extent of resonance stabilization of the resulting nega-
tive charge.
14. Kapinus, E. I.; Rau, H. J Phys Chem A 1998, 102, 5569–
5576.
15. Finn, M.; Friedline, R.; Suleman, N. K.; Wohl, C. J.;
Tanko, J. M. J Am Chem Soc 2004, 126, 7578–7584.
16. Lakhdar, S.; Westermaier, M.; Terrier, F.; Goumont, R.;
Boubaker, T.; Ofial, A. R.; Mayr, H. J Org Chem 2006,
71, 9088–9095.
17. Grunwald, E. J Am Chem Soc 1985, 107, 4710–4715.
18. Jencks, W. P. Chem Rev 1985, 85, 511–527.
19. Bernasconi, C. F. Adv Phys Org Chem 1992, 27, 119.
20. Crampton, M. R.; Rabbit, L. J Chem Soc, Perkin Trans
2 1999, 1669–1674.
SUPPORTING INFORMATION
Rate constant determinations at different temper-
atures in methanol for the reactions of anilines
2a–e with 2,4,6-tris(trifluoromethanesulfonyl)anisole
1a (Tables S1–S5), Eyring plots (Fig. S1), plot of
ꢀꢀ=H against ꢀꢀ=S (Fig. S2), and More O’Ferrall-
Jencks structure-reactivity diagram (Fig. S3) are avail-
able as Supporting Information in the online issue at
www.wileyonlinelibrary.com.
21. Bordwell, F. G.; Hughes, D. L. J Am Chem Soc 1986,
108, 5991–5997.
22. Bernasconi, C. F.; Ketner, R. J. J Org Chem 1998, 63,
6266–6272.
23. Marcus, R. A. J Phys Chem 1968, 72, 891–899.
24. El Guesmi, N.; Boubaker, T.; Goumont, R.; Terrier, F.
Chem Eur J 2009, 15, 12018–12029.
25. Asghar, B. H. M.; Crampton, M. R. Org Biomol Chem
2007, 5, 1646–1654.
26. Cox, J. P. L.; Crampton, M. R.; Wight, P. J Chem Soc,
Perkin Trans 2 1988, 25–29.
27. Terrier, F.; Chatrousse, A. P.; Soudais, Y.; Hlaibi, M. J
Org Chem 1984, 49, 4176–4181.
The authors are thankful to Profs. Franc¸ois Terrier and Re´gis
Goumont, University of Versailles, France, for providing lab-
oratory facilities.
28. Goumont, R.; Magnier, E.; Kizilian, E.; Terrier, F. J Org
Chem 2003, 68, 6566–6570.
BIBLIOGRAPHY
29. Terrier, F.; Magnier, E.; Kizilian, E.; Wakselman, C.;
Buncel, E. J Am Chem Soc 2005, 127, 5563–5571.
30. Bernasconi, C. F. Acc Chem Res 1987, 20, 301–308.
31. Bernasconi, C. F.; Ketner, R. J.; Chen, X.; Rappoport,
Z. ARKIVOC 2001, 161–178.
1. El Guesmi, N.; Boubaker, T.; Goumont, R. Int J Chem
Kinet 2010, 42, 203–210.
2. Boiko,V. N.; Shchupak, G. M.; Ignat’ev, N. V.;
Yagupol’skii, L. M. J Org Chem USSR (Engl. Transl.)
1979, 15, 1111–1112.
32. (a) More O’Ferrall, R. A. J Chem Soc (B) 1970, 274;
(b) Jencks, W. P. Chem Rev 1972, 72, 705.
International Journal of Chemical Kinetics DOI 10.1002/kin