Quantitative approach to the Menschutkin reaction of benzylic systems

Article abstract of DOI:10.1002/poc.574

The quaternization reactions of substituted (Z)-benzyl (X)-benzenesulfonates with substituted (Y)-pyridines were investigated in acetonitrile at 35 °C. The magnitudes of the Hammett reaction constants ρ_X, ρ_Y and ρ_Z indicate that a stronger nucleophile leads to a lesser degree of bond breaking. In addition, a better leaving group is accompanied by a lesser degree of bond formation. Application of multi-Hammett interactions, |ρ_YZ| > |ρ_XY| >ρ_XZ|, predicts that these Menschutkin-type reactions are dissociative S_N2 reactions. In particular, the reaction of strongly activated benzyl derivatives with tertiary amines in acetonitrile reveals a more advanced bond breaking like S_N1 reactions. The predicted mechanism for the benzylation of pyridines with benzylic systems is evident from More O'Ferrall-Jencks diagram and the semi-empirical MO calculations with the AM1 method. Copyright

Full text of DOI:10.1002/poc.574

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2003; 16: 63–68
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.574
Quantitative approach to the Menschutkin reaction of
benzylic systems
Soo-Dong Yoh,1* Duk-Young Cheong1 and Oh-Seuk Lee2
1Department of Chemistry Education, Kyungpook National University, Taegu 702-701, Korea
2Department of Chemistry, Andong National University, Andong 760-749, Korea
Received 25 May 2002; revised 31 July 2002; accepted 15 August 2002
ABSTRACT: The quaternization reactions of substituted (Z)-benzyl (X)-benzenesulfonates with substituted (Y)-
pyridines were investigated in acetonitrile at 35°C. The magnitudes of the Hammett reaction constants rX, rY and rZ
indicate that a stronger nucleophile leads to a lesser degree of bond breaking. In addition, a better leaving group is
accompanied by a lesser degree of bond formation. Application of multi-Hammett interactions, jꢀYZ j >jꢀXY j >jꢀXZ
j, predicts that these Menschutkin-type reactions are dissociative SN2 reactions. In particular, the reaction of strongly
activated benzyl derivatives with tertiary amines in acetonitrile reveals a more advanced bond breaking like SN1
reactions. The predicted mechanism for the benzylation of pyridines with benzylic systems is evident from More
O’Ferrall–Jencks diagram and the semi-empirical MO calculations with the AM1 method. Copyright  2002 John
Wiley & Sons, Ltd.
KEYWORDS: benzylic systems; Menschutkin reaction; SN2 reactions; multi-Hammett interactions; semi-empirical
MO; MOFJ diagram
INTRODUCTION
where nucleophilic displacement is promoted by facile
bond formation with the nucleophile and facile bond
fission with the leaving group, in addition to stabilization
of the TS. In a detailed analysis of the mechanism, it is
important to evaluate the contributions from three
species: the substrate, nucleophile and leaving group.
This is to establish overall stabilization of the TS. The
magnitude of rXZ reflects the requirement of bond
cleavage between the centers of the leaving group (L)
and the substrate (Z) for the formation of TS. A larger
value of jrXZj leads to a need for a greater degree of bond
cleavage for TS formation (i.e. when the magnitude of
rXZ is large, C—L bond fission is not ready, hence the
bond fission of C—L needs more progress for the
formation of the TS). In the same sense, the magnitude of
There has been considerable interest in determining the
transition-state (TS) structure for SN reactions using
linear free energy relationships.1–3 The magnitudes of
Hammett r values have commonly been used as a means
of assessing relative bond tightness in the TS. However, it
has often been pointed out that the efficiency of charge
transmission among the reaction centers of the substrate,
nucleophile and leaving group in bond formation or
cleavage may differ for different reaction series. As a
result, the magnitudes of r can at most serve as a relative
measure of bond formation or cleavage within a
particular family of closely related reactions.4 In contrast,
already proposed is the correlation interaction coefficient
(CIC), rij, which reflects the demand of the changing
distance between the reaction centers of i and j in the TS.5
For example, a CIC with the three variables rZ, rX and
rY for the reaction of substituted (Z)-benzyl (X)-
benzenesulfonates with substituted (Y)-N,N-dimethyl-
anilines in acetone is expressed by Scheme 1:6,7
r
YZ reflects the requirement for bond formation between
the centers of the nucleophile (Nu) and the substrate (Z);
a larger value of jrYZj needs a greater degree of bond
formation for the formation of TS. Nevertheless,
quantitative measurement of the CIC method is not
complete in all reaction series.
logꢀkXYZ=k000† ˆ ꢀXꢁX ‡ ꢀYꢁY ‡ ꢀZꢁZ ‡ ꢀXYꢁXꢁY
‡ ꢀXZꢁXꢁZ ‡ ꢀYZꢁYꢁZ
*Correspondence to: S.-D. Yoh, Department of Chemistry Education,
Kyungpook National University, Taegu 702-701, Korea.
E-mail: sdyoh@knu.ac.kr
Contract/grant sponsor: KOSEF, Centre for Biofunctional Molecule.
Contract/grant sponsor: Brain Korea 21 Project.
Scheme 1
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 63–68

64
S.-D. YOH, D.-Y. CHEONG AND O.-S. LEE
In this paper, we present an example to demonstrate
substituent in the substrate and nucleophile indicates
that a positive charge developed on the benzylic carbon
because the reaction center of the substrate is stabilized
by electron-donating substituents in the TS. This is in
harmony with the sign of rZ in Table 2. A negative sign
of rZ indicates that the reaction center of the substrate has
developed a positive charge and the TS is stabilized by
electron-donating substituents on the substrate or nu-
cleophile. In the leaving group, however, the attracting
substituents facilitate the reaction rate as listed in Table 1.
This is also illustrated by the negative rY value as shown
in Table 3, which is consistent with an attack by the
nucleophile at the benzylic carbon being helped by
electron-attracting substituents of the leaving group.
The rY values can be regarded as relative measures of
the degree of C—N bond formation in the transition state.
The rY values vary widely from À2.43 to À1.85 as the
substituent Z changes from 4-NO2 to 4-CH3 at the leaving
group X = H. According to the above data, the order of
bond formation is 4-NO2 >4-CH3 for the benzylic
substrate. This agrees with the prediction of the
substituent effects on the SN2 transition state.
the degree of bond formation and bond fission by
comparing them with the magnitude of rij and computa-
tional analysis. As a result, rij provides a quantitative
measure of bond order in the TS of SN reactions of
substituted benzyl arenesulfonates with pyridines:
(Z)-C6H4CH2OSO2C6H4-(X) ‡ (Y)-C5H4N !
‡
À
(Z)-C6H4CH2-N C5H4-(Y) OSO2C6H4-(X)
Z ˆ 4-CH3; H; 4-Br; 3-Br; 4-NO2
X ˆ 4-CH3; H; 4-Cl; 3-NO2
Y ˆ 4-NH2; 3; 4-CH3; 3; 5-CH3; 4-CH3; H; 3-Cl; 3-CN
RESULTS AND DISCUSSION
The reaction rates were determined by monitoring the
changes in conductance through the formation of salt
from the reactions of substituted (Z)-benzyl (X)-ben-
zenesulfonates with (Y)-pyridines in acetonitrile as
described previously.8 The reactions, carried out with a
large excess of pyridine, follow pseudo-first-order
kinetics to at least 85% completion. The second-order
rate constants are summarized in Table 1.
The jrYj values being used by pyridines as nucleophile
are larger than that of N,N-dimethylanilines in this
reaction.8 This probably causes the nucleophilic nitrogen
atoms on the aromatic ring in the pyridine. The former is
Rate enhancement with a more electron-donating
Table 1. Second-order rate constants, k2 Â 104 (1 molÀ1
pyridines in acetonitrile at 35°C
s
À1), for the reactions of (Z)-benzyl (X)-benzenesulfonates with (Y)-
(Z)
(X)
(Y)
4-CH3
H
4-Br
3-Br
4-NO2
p-CH3
4-NH2
3,4-(CH3)2
3,5-(CH3)2
4-CH3
H
424.4
91.44
78.20
59.85
37.29
5.813
2.042
675.7
169.4
144.2
113.9
68.22
9.400
4.044
1901
254.3
48.22
39.59
29.53
17.78
2.560
1.132
468.9
86.98
77.00
53.31
32.66
4.230
1.470
1024
209.9
39.14
30.78
24.26
12.98
1.693
0.5171
408.8
70.69
57.21
44.70
24.90
3.300
1.095
950.2
190.4
153.4
124.1
68.90
9.802
2.927
5399
140.0
24.70
19.07
14.14
9.583
0.8355
0.2818
295.2
46.82
38.92
28.62
15.13
2.100
0.6136
629.4
120.8
97.30
85.67
44.19
5.373
1.587
3632
116.9
16.40
13.31
10.32
5.049
0.4251
0.1387
212.2
29.40
24.32
17.17
8.952
0.7300
0.2348
486.9
79.50
63.43
36.99
24.06
2.426
0.6399
3-Cl
3-CN
H
4-NH2
3,4-(CH3)2
3,5-(CH3)2
4-CH3
H
3-Cl
3-CN
4-NH2
3,4-(CH3)2
3,5-(CH3)2
4-CH3
H
3-Cl
3-CN
4-NH2
3,4-(CH3)2
3,5-(CH3)2
4-CH3
H
p-Cl
495.4
464.1
362.9
223.0
38.92
10.86
10420
2909
244.1
206.9
170.1
94.53
13.90
4.356
6582
m-NO2
2554
1581
1359
823.3
655.1
526.1
291.8
35.05
11.04
514.9
397.2
286.8
153.1
16.20
4.380
2560
1265
1056
1951
1002
819.0
533.2
63.85
23.31
1144
608.1
104.5
33.53
3-Cl
3-CN
239.8
96.67
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 63–68

MENSCHUTKIN REACTION OF BENZYLIC SYSTEMS
65
Table 2. Hammett rZ values and interaction terms for the reaction of (Z)-benzyl (X)-benzenesulfonates with (Y)-pyridines in
acetonitrile at 35°C
rZ
a
(Y)
spy
(X) = 4-CH3
(X) = H
(X) = 4-Cl
(X) = 3-NO2
rZX
4-NH2
3,4-(CH3)2
3,5-(CH3)2
4-CH3
H
À0.61
À0.18
À0.11
À0.12
0
À0.550
À0.726
À0.750
À0.742
À0.832
À1.13
À0.497
À0.733
À0.755
À0.784
À0.869
À1.07
À0.560
À0.770
À0.833
À0.957
À0.929
À1.23
À0.605
À0.758
À0.785
À0.800
À0.857
À1.17
À0.09
À0.04
À0.05
À0.07
À0.02
À0.09
À0.13
3-Cl
0.41
3-CN
rZY
0.56
À1.21
À1.19
À1.20
À1.31
À0.60
À0.58
À0.59
À0.62
a
The spy values were taken from Ref. 9.
Table 3. Hammett rY values and interaction terms for the reaction of (Z)-benzyl (X)-benzenesulfonates with (Y)-pyridines in
acetonitrile at 35°C
rY
X
sa
(Z) = 4-CH3
(Z) = H
(Z) = 4-Br
(Z) = 3-Br
(Z) = 4-NO2
rYZ
p-CH3
H
p-Br
m-NO2
rYX
À0.14
0
0.24
0.71
À1.88
À1.85
À1.81
À1.67
0.25
À1.93
À2.04
À1.94
À1.85
0.15
À2.12
À2.09
À2.04
À1.96
0.19
À2.21
À2.16
À2.12
À2.07
0.15
À2.41
À2.43
À2.34
À2.27
0.19
À0.60
À0.58
À0.56
À0.62
a
The s values were taken from Ref. 10.
À2.04 and the latter is À1.73. However, the relationship
between bond formation and bond fission in the benzylic
system cannot be explained clearly. Ballistereri et al.11
reported Hammett rY values for the reactions of benzyl
halides with substituted (Y)-anilines. The jrYj value
decreased from À1.46 to À0.87 when the leaving group
changed from iodide to chloride. Furthermore, Westaway
and Ali12 reported that more nucleophilic assistance is
required to displace a better leaving group given for the
reaction of arylbenzyldimethylammonium ions with (Y)-
thiophenoxide ions. These results suggest that changing
to a better leaving group leads to a product-like
transition-state structure. However, Table 6 (see later)
shows that the jrYj values decrease gradually as the
leaving group changes from 4-CH3 to 3-NO2. This means
that C—N bond formation decreases progressively with a
better leaving moiety. This is in complete agreement with
the result of previous work.7,8,13 In the case of the present
benzyl system, the better leaving groups thus do not yield
a ‘product-like’ transition state but rather a ‘loose’ one.
This result agrees with the prediction of the More
O’Ferrall diagram for the effects of leaving group
variation in an SN2 transition state.4,14 The variation of
jrYj, DrY, on changing the substituent of the substrate (Z)
is larger than DrX of rX for leaving group (X), as shown
in Tables 3 and 4. For example, the values of DrY
(X = H) and DrX (Y = H) are 0.55 and 0.15, respectively.
This means that a larger value of jrYZj requires a greater
Table 4. Hammett rX values and interaction terms for the reaction of (Z)-benzyl (X)-benzenesulfonates with (Y)-pyridines in
acetonitrile at 35°C
rX
Z
sa
(Y) = 4-NH2 (Y) = 3,4-(CH3)2 (Y) = 3,5-(CH3)2 (Y) = 4-CH3 (Y) = H (Y) = 3-Cl (Y) = 3-CN rXY
4-CH3 À0.14
1.65
1.64
1.76
1.78
1.78
1.75
1.78
1.80
1.75
1.80
1.94
1.92
1.90
1.79
0.27
0.16
0.16
0.17
0.20
H
0
4-Br
3-Br
4-NO2
rXZ
0.24
0.37
0.78
1.63
1.81
1.80
1.79
1.89
1.84
1.92
1.62
1.56
À0.09
1.78
1.76
À0.01
1.78
1.73
À0.04
1.83
1.70
À0.08
1.77
1.74
À0.03
1.85
1.88
À0.07
1.84
1.77
À0.14
a
The s values were taken from Ref. 10.
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 63–68

66
S.-D. YOH, D.-Y. CHEONG AND O.-S. LEE
Table 5. Charges of atoms relevant to the reaction center in the transition state for the reaction of (Z)-substituted benzyl (X)-
benzenesulfonates with pyridinea
(X)
(Z)
Charge
4-CH3O
4-CH3
3-CH3
H
4-Cl
3-Cl
4-NO2
4-CH3O
N
C
O
N
C
O
N
C
O
N
C
O
N
C
O
N
C
O
N
C
O
À0.205
0.315
À1.087
À0.203
0.315
À1.078
À0.202
0.315
À1.073
À0.202
0.313
À1.072
À0.200
0.308
À1.066
À0.200
0.307
À1.063
À0.197
0.292
À1.052
À0.205
0.315
À1.087
À0.203
0.315
À1.077
À0.202
0.315
À1.073
À0.202
0.313
À1.072
À0.201
0.309
À1.066
À0.200
0.308
À1.063
À0.198
0.293
À1.052
À0.205
0.316
À1.087
À0.203
0.316
À1.078
À0.202
0.315
À1.073
À0.202
0.314
À1.072
À0.201
0.309
À1.066
À0.200
0.308
À1.063
À0.198
0.293
À1.052
À0.205
0.316
À1.087
À0.203
0.316
À1.078
À0.202
0.315
À1.074
À0.202
0.314
À1.073
À0.201
0.310
À1.067
À0.201
0.308
À1.063
À0.198
0.294
À1.052
À0.207
0.316
À1.093
À0.206
0.319
À1.085
À0.205
0.318
À1.076
À0.205
0.317
À1.075
À0.205
0.314
À1.074
À0.204
0.313
À1.070
À0.200
0.297
À1.052
À0.208
0.316
À1.094
À0.207
0.319
À1.086
À0.206
0.319
À1.081
À0.206
0.318
À1.080
À0.205
0.315
À1.075
À0.205
0.314
À1.071
À0.201
0.298
À1.055
À0.212
0.314
À1.096
À0.212
0.322
À1.089
À0.212
0.324
À1.086
À0.212
0.324
À1.085
À0.211
0.322
À1.080
À0.211
0.322
À1.076
À0.204
0.301
À1.050
4-CH3
3-CH3
H
4-Cl
3-Cl
4-NO2
a
The values for reactants and products, where (Z) = (X) = H, are N À0.161, C 0.065, O À0.703 and N À0.022, C À0.030, O À1.094, respectively.
degree of bond formation in the TS formation while
varying the substituent of the substrate or nucleophile
(i.e. the formation of the C—Nu bond progresses poorly
in the TS). On the other hand, the smaller the value of
jrXZj, the more the C—L bond fission progresses in the
TS. This is reasonable since bond breaking has already
progressed much further than bond formation in the TS of
a dissociative SN2 reaction, so further increases in bond
breaking will be small.
reaction center, i.e. N of the nucleophile, benzylic C of
the substrate and O of the leaving group in the transition
state of the reaction between (Z)-benzyl (X)-benzene-
sulfonates and pyridine, are listed in Table 5. Distances
between atoms and the reaction center in the transition
state for these reactions are listed in Table 6.
In Table 5, when (Y) = H and (Z) changes from 4-NO2
to 4-CH3O, the charge values of C increase, but those of
N and O decrease in all of the (X) substituents. In
addition, when (X) = (Y) = H and (Z) changes from 4-
NO2 to 4-CH3O, the C—N and C—O are bond lengths
These results also agreed with those of semi-empirical
AM1 calculations. The charges of atoms relevant to the
Ê
Table 6. Distances (A) between atoms and reaction center in the transition state for the reaction of (Z)-substituted benzyl (X)-
benzenesulfonates with pyridinea
(X)
(Z)
Distance
4- CH3O
4-CH3
3-CH3
H
4-Cl
3-Cl
4-NO2
4-CH3O
D(N—C)
D(C—O)
D(N—C)
D(C—O)
D(N—C)
D(C—O)
D(N—C)
D(C—O)
D(N—C)
D(C—O)
D(N—C)
D(C—O)
D(N—C)
D(C—O)
2.045
2.234
2.024
2.181
2.013
2.158
2.008
2.152
1.986
2.119
1.979
2.104
1.924
2.022
2.045
2.235
2.025
2.183
2.014
2.160
2.010
2.154
1.988
2.120
1.980
2.106
1.925
2.023
2.047
2.238
2.027
2.185
2.016
2.162
2.012
2.157
1.991
2.123
1.983
2.108
1.927
2.024
2.048
2.240
2.028
2.187
2.018
2.164
2.013
2.158
1.992
2.124
1.984
2.109
1.928
2.024
2.067
2.266
2.049
2.210
2.034
2.182
2.029
2.175
2.014
2.144
2.005
2.127
1.937
2.028
2.070
2.271
2.053
2.216
2.043
2.191
2.039
2.185
2.019
2.150
2.010
2.133
1.944
2.031
2.101
2.323
2.090
2.263
2.081
2.236
2.077
2.228
2.060
2.195
2.050
2.173
1.966
2.049
4-CH3
3-CH3
H
4-Cl
3-Cl
4-NO2
a
The values for reactants and products, where (Z) = (X) = H, are D(N—C) 4.038, D(C—O) 1.411 and D(N—C) 1.474, D(C—O) 3.107, respectively.
J. Phys. Org. Chem. 2003; 16: 63–68
Copyright  2002 John Wiley & Sons, Ltd.

MENSCHUTKIN REACTION OF BENZYLIC SYSTEMS
67
Table 7. Hammett and Brùnsted constants for the reaction
of substituted (Z)-benzyl (X)-benzenesulfonates with sub-
stituted (Y)-pyridines in acetonitrile at 35°C
reaction. This agrees with the above-mentioned CIC
treatment and the reaction of substituted (Z)-benzyl (X)-
benzenesulfonates with (Y)-pyridines in acetonitrile will
lead to a dissociative SN2 mechanism.
The magnitude of rij dependent on the changes in
distance between the reaction centers of i and j, which
can express the sensitivity of risj (or rjsi) (i.e. rXZ and
a
a
b
b
(Z)
rY
bNu
rX
bLg
4-CH3
H
4-Br
3-Br
4-NO2
À1.85
À2.04
À2.09
À2.16
À2.43
0.25
0.27
0.28
0.29
0.33
1.87
1.76
1.85
1.72
1.70
À0.62
À0.59
À0.61
À0.58
À0.57
r
YZ indicate the degrees of Ca—L bond fission and Nu—
Ca bond formation, respectively). The sign of rZ is
negative in Table 2, indicating that the reaction center of
the substrate has developed a positive charge and thus a
greater degree of bond breaking than bond formation in
the TS for the reaction series. In Tables 2–4, the
magnitude of jrXZj is smaller than that of jrYZj. The
change in the substituent of substrates indicates that the
leaving moiety is already away from the reaction center
of the substrate, so the variation in the distance from the
a
The r and b values are evaluated for (X) = H and pKas were taken from
Ref. 15.
b
The r and b values are evaluated for (Y) = H and pKas were taken from
Ref. 16.
longer, as shown in Table 6. These results agree well with
the experimental results for the reaction of (Z)-benzyl
(X)-benzenesulfonates with (Y)-pyridine in acetonitrile.
The parameter of nucleophilic participation, jrYj,
decreases but the facility of the leaving moiety, jrXj,
increases with electron-donating substituents in the
substrate, as shown in Tables 3 and 4. These results
show that the more electron-donating substituents in the
substrate, the weaker is bond formation between the
nucleophile and reaction center, but the looser it is
between the leaving group and substrate. When (Z) = 4-
CH3O, the nucleophilic attack is less advanced. However,
bond breaking progresses greatly. Therefore, its TS
stands like an SN1 mechanism.
reaction center is small, but is large in the case of rYZ
.
Therefore, from the sign of rZ and the comparison of rij
(jꢀYZj >jꢀXZj), this reaction will lead to a dissociative
SN2 mechanism:
logꢀkXYZ=k000† ˆ 1:8ꢁX À 2:0ꢁY À 0:86ꢁZ ‡ 0:15ꢁXꢁY
À 0:58ꢁYꢁZ À 0:02ꢁXꢁZ ‡ 0:04ꢁXꢁYꢁZ
Table 7 shows that the value of jbLgj is about twice that
of bNu and the More O’Ferrall–Jencks diagram (Fig. 1)
for this reaction also is above that for a concerted SN2
EXPERIMENTAL
Materials. Purification of acetonitrile, substrate prepara-
tion and product analysis have been described pre-
viously.5 Pyridines were commercially available and
further purified by distillation or recrystallization before
use.
Kinetic measurements. The reaction rates of substituted
(Z)-benzyl (X)-benzenesulfonates with (Y)-pyridines in
acetonitrile at 35°C were measured by a conductimetric
method.8 Conductance measurements were performed in
a cell with platinum electrodes and conductivity readings
were carried out by using a conductivity meter (CM-60S,
equipped with an interval time unit and printer; TOA
Electric).
The typical procedure for kinetic measurements is as
follows. A 50 ml volume of a stock solution of pyridine
(0.12 M) in acetonitrile, which was prepared at 35°C, was
equilibrated in the reaction cell at 35.0 Æ 0.02°C in a
thermostated bath for 30 min and then 10 ml of benzyl
ester solution (ca 0.003 M) were added. The resulting
solution of ester and pyridine in the cell was shaken
thoroughly. The reactions were generally followed by
taking at least 80 points at appropriate time intervals for
2.5 half-lives and the infinity reading was taken after
eight half-lives. All kinetic runs were under pseudo-first-
order conditions with 0.01–0.30 M final concentrations of
pyridine, which were 20–600 times larger than that of the
Figure 1. MOFJ diagram based on structure-reactive
coef®cient for the reaction of substituted (Z)-benzyl (X)-
benzenesulfonates with (Y)-pyridines in acetonitrile. The
energy contours are not shown. The transition state * moves
toward *' with the lowering of the energy of the TS when the
substituent (Z) changed from 4-CH3 to 4-NO2
Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 63–68

68
S.-D. YOH, D.-Y. CHEONG AND O.-S. LEE
4. Jencks WP. Chem. Rev. 1985; 85: 511.
substrate. The pseudo-first-order rate constants were
determined by a least-squares computer program.
Duplicate kinetic runs showed that the rate constant
was reproducible to within Æ2.0%. The precision of the
fit to pseudo-first-order kinetics was generally satisfac-
tory, with a correlation coefficient >0.99995 over three
half-lives of the reaction. Second-order rate constants, k2,
were determined by dividing kobs by the initial amine
concentration.
5. (a) Yoh S-D, Cheong DY. J. Phys. Org. Chem. 1996; 9: 701; (b)
Yoh S-D, Park HY, Cheong DY, Park JH, Lee YD, Howang KT. J.
Phys. Org. Chem. 1999; 12: 319.
6. (a) Yoh S-D. PhD Dissertation, Osaka University, 1973; 6(b) Yoh
S-D, Sawada M, Yukawa Y. In Abstracts of the 28th Spring
Meeting of the Chemical Society of Japan, Tokyo, 1974; 1128;
6(c) Tsuno Y, Fujio M, Yoh S-D, Sawada M, Yukawa Y. In
Abstracts of the 25th Symposium on Reaction Mechanisms,
Chemical Society of Japan, Tokyo, 1974; 119; 6(d) Yoh S-D. J.
Korean Chem. Soc. 1975; 19: 449; (e) Yoh S-D, Tsuno Y, Yukawa
Y. J. Korean Chem. Soc. 1984; 28: 433; (f) Yoh S-D, Cheong DY,
Park JH, Kim SH, Howang KT. Bull. Korean Chem. Soc. 1998; 19:
434.
Calculations. All calculations were performed with the
AM1 method by using MOPAC93.17 Transition states
were located by using the eigenvector following
procedure18 and characterized by confirming the pre-
sence of only one negative eigenvalue in the Hessian
matrix.
7. Yoh S-D, Tsuno Y, Fujio M, Sawada M, Yukawa Y. J. Chem. Soc.,
Perkin Trans. 2 1989; 7.
8. (a) Kim SH, Yoh S-D, Fujio M, Imahori H, Mishima M, Tsuno Y.
Bull. Korean Chem. Soc. 1995; 16: 760; (b) Kim SH, Yoh S-D,
Lim C, Mishima M, Fujio M, Tsuno Y. J. Phys. Org. Chem. 1998;
11: 254.
9. Cheong DY, Kweon JM, Yoh S-D, Park S, Lee OS. J. Korean
Chem. Soc. 1995; 16: 604.
10. Isaacs NS. Physical Organic Chemistry (2nd edn). Longman:
Harlow, 1995; 151.
11. Ballistereri FP, Maccaron E, Mamo A. J. Org. Chem. 1976; 41:
Acknowledgements
3364.
This work was supported by the KOSEF through the
Center for Biofunctional Molecules and partly financially
supported by the Brain Korea 21 Project.
12. Westaway KC, Ali SF, Can. J. Chem. 1979; 57: 1354.
13. (a) Cheong DY, Kim SH, Lee MH, Yoh S-D, Fujio M, Tsuno Y. J.
Korean Chem. Soc. 1995; 39: 643; (b) Tsuji Y, Saeki Y, Yatsugi K,
Kim SG, Fujio M, Tsuno Y. Mem. Fac. Sci. Kyushu Univ. Ser. C
1992; 18: 267.
14. (a) More O’Ferrall RA. J. Chem. Soc. 1970; 274; (b) Harris JM,
Shafer SG, Moffatt JR, Becker AR. J. Am. Chem. Soc. 1979; 101:
3295.
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Copyright  2002 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 63–68