Thermal Isomerizations of Substituted Benzyl Isocyanides: Relative Rates Controlled Entirely by Differences in Entropies of Activation

Article abstract of DOI:10.1021/jo970282u

The absolute and relative rates of thermal rearrangments of substituted benzyl isocyanides were obtained at the temperatures between 170 and 230 °C. The relative rates are independent of temperature and exhibit excellent Hammett correlations (p⁺ = -0.24). The temperature studies yielded activation parameters (ΔH_Y^? and ΔS_Y^?) and their differential counterparts (ΔΔH_Y-H^? and ΔΔS_Y-H^?). The differential terms were plotted against σ⁺. The secondary α-deuterium kinetic isotope effects (k_D/k_H = 1.11) were measured at several temperatures. The rate data can be rationalized with the cyclic TS. The substituent effects on the rates are due to the entropic contributions.

Full text of DOI:10.1021/jo970282u

J . Org. Chem. 1998, 63, 1185-1189
1185
Th er m a l Isom er iza tion s of Su bstitu ted Ben zyl Isocya n id es:
Rela tive Ra tes Con tr olled En tir ely by Differ en ces in En tr op ies of
Activa tion †
Sung Soo Kim,* Won J ung Choi, Yu Zhu,1 and J in Hyun Kim
Department of Chemistry and Center for Molecular Dynamics, Inha University,
Inchon 402-751, South Korea
Received February 14, 1997 (Revised Manuscript Received August 26, 1997)
The absolute and relative rates of thermal rearrangments of substituted benzyl isocyanides were
obtained at the temperatures between 170 and 230 °C. The relative rates are independent of
temperature and exhibit excellent Hammett correlations (F+ ) -0.24). The temperature studies
yielded activation parameters (∆HYq and ∆SYq ) and their differential counterparts (∆∆HYq -H and
∆∆SqY-H). The differential terms were plotted against σ+. The secondary R-deuterium kinetic
isotope effects (kD/kH ) 1.11) were measured at several temperatures. The rate data can be
rationalized with the cyclic TS. The substituent effects on the rates are due to the entropic
contributions.
An isonitrile2 maintains the alternative structure of 1
Sch em e 1
or 2 with 1 being responsible for the heterolytic reactions.
The thermal isomerization of methyl isocyanide3 in gas
phase is a cationotropic 1,2-shift which takes place via a
triangular transition state (TS) with concerted bond
formation and cleavage. Either ultraviolet radiation4 or
vibrationally excited ethane molecules5 also bring about
Resu lts a n d Discu ssion
the same isomerizations without intervention of radicals.
The isonitrile-nitrile rearrangements6 of several aryl and
alkyl isocyanides evidently excluded the carbocations as
reaction intermediates. The structure-reactivity rela-
tionship7 appeared, however, ambiguous for isomeriza-
tions of a number of isonitriles. The structural changes
of the isonitriles failed to produce equivalent variations
of the activation parameters.
Rela tive Ra tes, Ha m m ett Con sta n ts, Activa tion
P a r a m eter s, a n d Secon d a r y r-Deu ter iu m Kin etic
Isotop e Effects. The ampules containing a substituted
benzyl isocyanide, chlorobenzene (internal standard), 1,1-
diphenylethylene, and benzene (solvent) underwent ther-
molysis at several temperatures (170-230 °C). 1,1-
Diphenylethylene was added as a safeguard to eliminate
the possibility of radical reactions. However, the reac-
tions were unaltered even in the absence of the radical
scavenger (Scheme 1). The heating transformed the
substituted benzyl isocyanide smoothly into the substi-
tuted phenyl acetonitrile without detectable side reac-
tions, which were verified by either GLC or NMR method.
The excellent first-order plots (r g 0.98) and material
balances (g97%) again excluded other reaction pathways.
The rates at 170, 190, and 210 °C were measured by GLC
method. The absolute rate constants (kY) have been
derived from ln C0/Ct ) kY(H)t with C0 and Ct denoting
initial and final concentrations of the substituted benzyl
isocyanide, respectively. NMR method was utilized to
However, we were fortunate enough to discover small
polar substituent effects controlling rates of the isomer-
izations in previous work.6,7 The rearrangements of
substituted phenyl isocyanides6 to substituted benzo-
nitriles reveal F ) -0.21 at 200 °C. Similar reactions of
substituted benzyl isocyanides7 indicate F+ ) -0.24 at
210 °C. We report herein novel temperature effects on
the rates of the isomerizations.
† We mourn for the late Professor Glen A. Russell who passed away
on J anuary 1, 1998.
determine the rates (kY) at 230 °C employing ln[(CAt
+
CBt)/CAt] ) kYt where CAt and CBt are the concentrations
of reactant and product, respectively. The rate of isomer-
ization of benzyl isocyanide at 210 °C indicated virtually
identical value whether obtained by either NMR or GLC.
The relative rates (kY/kH) have been obtained and put into
Hammett correlations. The value of F+ ) -0.24 excel-
lently agrees with the previous one7 calculated by us.
These rate data are tabulated in Table 1. The rates (kY
× 105 s-1) of isomerization of benzyl isocyanide in three
solvents at 210 °C measured by NMR method are 45.2 (
(1) A visiting scholar under the program of the brain pool (1996-
1998) supported by the Korean Federation of Science and Technology
Societies.
(2) Ugi, I. Isonitrile Chemistry; Academic Press: New York and
London, 1971.
(3) Schneider, F. W.; Rabinovitch, B. S. J . Am. Chem. Soc. 1962,
84, 4215. Ibid. 1963, 85, 2365.
(4) Shaw, D. H.; Pritchard, H. O. J . Phys. Chem. 1966, 70, 1230.
(5) Shaw, D. H.; Dunning, B. K.; Pritchard, H. O. Can. J . Chem.
1969, 47, 669.
(6) Casanova, J ., J r.; Werner, N. D.; Schuster, R. E. J . Org. Chem.
1966, 31, 3473.
(7) Meier, M.; Mu¨ller, B.; Ru¨chardt, C. J . Org. Chem. 1987, 52, 648.
S0022-3263(97)00282-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/04/1998

1186 J . Org. Chem., Vol. 63, No. 4, 1998
Ta ble 1. Absolu te (Rela tive) Ra tes a n d Ha m m ett Cor r ela tion s of th e Th er m a l Isom er iza tion s
Kim et al.
kY × 105/s (kY/kH)a,b when Y )
c
temp (°C)
p-OCH3
p-CH3
H
p-Cl
p-NO2
F
+ (r)d
F (r)d
170e
190e
210e
230f
3.46(1.72)
16.9(1.70)
78.6(1.72)
396(1.74)
2.61(1.30)
13.0(1.31)
59.4(1.31)
2.01(1)
9.94(1)
45.2(1)g
228(1)
1.95(0.97)
9.54(0.96)
44.3(0.98)
226(0.99)
1.47(0.73)
7.26(0.73)
33.4(0.73)
166(0.73)
-0.24(0.987)
-0.24(0.986)
-0.24(0.986)
-0.24(0.987)
-0.31(0.914)
-0.31(0.919)
-0.31(0.915)
-0.31(0.911)
295(1.29)
a
The absolute rates (kY) were obtained from the plot of ln(C0/Ct) vs time. The correlation coefficients for the slope are always r > 0.98.
The error limits are far less than 5%. Substituent constants are taken from ref 29. c The relative reactivity of p-nitrobenzyl isocyanide
b
against benzyl isocyanide has been taken as kY/kH ) 0.73 from Table 1 of ref 7. Correlation coefficient. e The rates were measured by
d
GLC method. f The rates were measured by NMR method. The rates were measured in three solvents (C6H6, C6H5CN, and n-C16H34).
g
The analysis of the reaction mixture by GLC and NMR method have produced identical results.
(+)-sec-Butyl isocyanide6 undergoes isomerization with
retention of configuration at the migrating carbon atom.
Numerous anionotropic 1,2-shifts (e.g. Curtius, Hofmann,
Lossen, and Schmidt rearrangements)10 also show similar
retention of configuration, which can be due to the cyclic
TS structure. “Ch:” in 3 is a nucleophilic site. The
rearrangements can therefore be taken as an intra-
molecular nucleophilic process where breakage and for-
mation of the bonds occur concurrently on the same side.
The cyclic structure 4 introduces significant angle
strains and restricts its internal motions. 3 and 5, on
the contrary, are free of such angular distortions and
F igu r e 1. Temperature dependence of rates of the isomer-
izations.
enjoy the free rotations. If a TS were of an “intermediate
configuration” between reactant and product, the rate
should be linearly related with the equilibrium to realize
the linear free energy relationship (LFER).11,12 Therefore
the reactivity/selectivity principle11 and the Hammond
postulate13 should predict the trend of the reactivities.
However 4 resembles neither 3 nor 5 and obviously
deviates from the aforementioned “intermediacy”. The
Hammond postulate13 should be thus invalidated under
the foregoing circumstances. The perpendicular effect14
has been invoked to describe the deviation of TS occur-
ring in a variety of organic reactions.15-19 The principle
of nonperfect synchronization18 and “imbalanced TS”20
are other expressions for the deviations. The tempera-
ture studies (Table 1) indicate that the absolute rates
increase at higher temperatures, but the relative rates
(selectivities) persistently remain unaltered. Therefore,
the temperature effects disobey the classical reactivity/
selectivity principle (RSP).11
0.5 in C6H6, 45.2 ( 0.2 in C6H5CN, 47.6 ( 1.4 in n-C16H34.
Nearly idential rates may indicate that kinetic solvent
interactions hardly control cleavage and formation of the
bonds in 4. Therefore the substituent effects should
solely perturb the activation process.
The temperature studies employed the Eyring equa-
tion8 to obtain the activation parameters (∆HqY and
∆SqY) from Figure 1. Table 2 contains the activation
terms and their differential ones (∆∆HqY-H and
∆∆SqY-H). Both differential parameters were plotted
against σ+ (Figures 2 and 3). The secondary R-deuterium
kinetic isotope effects (kH/kD) were measured as kH/kD
)
1.11 ( 0.05 at 170, 190, and 230 °C. kD is a rate constant
for C6H5CD2NC f C6H5CD2CN.
Mech a n istic High ligh ts of th e Isom er iza tion s.
The Hammett constant F+ ) -0.24 of Table 1 suggests
that a modest positive charge occurs on the benzylic
carbon atom in 4. The better correlation with σ+ indi-
cates dispersion of the positive charge into the phenyl
ring. When the bond cleavage slightly outweighs the
bond formation in 4, a fractional positive charge should
be left over on the carbon atom. The secondary R-deu-
terium kinetic isotope effects show kH/kD ) 1.11 for
isomerizations of benzyl isocyanide. Typical SN2 reac-
tions frequently exhibit kH/kD < 1 with the R-deutera-
tions.9 This may suggest that 4 experiences substantial
bond cleavage, and the benzylic carbon atom undergoes
significant sp2-hybridization to promote a bending vibra-
tion of the methylene group.
(10) March, J . Advanced Organic Chemistry, 4th ed.; McGraw-Hill:
New York, 1992, Chapter 18.
(11) Leffler, J . E.; Grunwald, E. Rates and Equilibria of Organic
Reactions; Wiley: New York, 1963.
(12) Shaik, S. S.; Schlegel, H. B.; Wolfe, S. Theoretical Aspects of
Physical Organic Chemistry; Wiley: New York, 1992.
(13) Hammond, G. S. J . Am. Chem. Soc. 1955, 77, 334.
(14) Thornton, E. R. J . Am. Chem. Soc. 1967, 89, 2915.
(15) Kim, S. S. Pure Appl. Chem. 1995, 67, 791.
(16) J encks, W. P. Chem. Rev. 1985, 85, 511.
(17) Hoz, S. Acc. Chem. Res. 1993, 26, 69.
(18) Bernasconi, C. F. Acc. Chem. Res. 1992, 25, 9. Adv. Phys. Org.
Chem. 1992, 27, 119.
(8) Eyring, H. J . Chem. Phys. 1935, 3, 107.
(9) Issacs, N. S. Physical Organic Chemistry, 2nd ed.; Longman
Scientific & Technical: Essex, 1995; Chapter 10.
(19) Albery, W. J .; Kreevoy, M. M. Adv. Phys. Org. Chem. 1978, 16,
87.
(20) J encks, D. A.; J encks, W. P. J . Am. Chem. Soc. 1977, 99, 7948.

Thermal Isomerizations of Benzyl Isocyanides
J . Org. Chem., Vol. 63, No. 4, 1998 1187
Ta ble 2. Activa tion (Differ en tia l Activa tion ) P a r a m eter s of th e Th er m a l Isom er iza tion s
parametersa
p-OCH3
p-CH3
H
p-Cl
p-NO2
∆HqY(∆∆HqY-H
)
c
34.02(0.18)d
-4.25(0.34)d
33.84(0)
-5.23(-0.62)
b
33.95(0.11)
-3.30(1.31)
33.83(-0.01)
-4.10(0.51)
33.84(0)
-4.61(0)
∆SqY(∆∆SqY-H
)
q
Refer to the correlation coefficients for the substituents in Figure 1. ∆∆HY-H ) ∆HqY - ∆HHq where ∆HYq and ∆HHq are the activation
a
b
enthalpies for substituted and unsubstituted benzyl isocyanides, respectively (unit: kcal/mol). c ∆∆SYq -H ) ∆SYq - ∆SqH where ∆SYq and
∆SqH are similarly related as with the above enthalpic terms (unit: eu). The “abnormal” behavior of p-Cl has been also noted in a
d
previous work22 and attributed to the dual substituent effects. p-Cl could be electron-withdrawing via inductive effects but become electron-
donating by resonance effects.
F igu r e 2. Plot of ∆∆HYq -H vs σ+ for the thermal isomeriza-
tions.
F igu r e 3. Plot of ∆∆SYq -H vs σ+ for the thermal isomeriza-
tions.
and the Gibbs formulation reduces to ∆∆GYq -H
)
Activa tion P a r a m eter s a n d Ra tion a liza tion of
Con sta n t Selectivities. The enthalpies of activation
(∆HqY) (Table 2) stay almost invariable (ca. 33.90 kcal/
mol) so as to declare sparse substituent effects. Even
drastic structural changes of the isonitriles7 entail very
modest variations of ∆HqY. The molecular distortion of 4
should be the prime candidate to determine the magni-
tude of ∆HqY. The substituents (Y) could exercise only a
minor9 influence on ∆HqY because the requirements of
bond formation and breakage are opposite. An electron-
withdrawing group (Y) facilitates the bond-making but
retards the bond-breaking and vice versa. Accordingly
the differential terms (∆∆HqY-H) become close to zero
(Table 2), and a nearly horizontal slope is attained for
Figure 2.
-T∆∆SqY-H. The values of T∆∆SYq -H at 210 °C have been
calculated to be 0.63 and -0.30 kcal/mol for p-OCH3 and
p-NO2, respectively. Therefore the rates are delicately
controlled through the entropic term derived from the
degrees of the bond cleavages.
Figures 2 and 3 are empirical drawings to visualize
the substituent effects controlling extent of bond cleav-
ages. The differential substituent effects could be too
weak to yield significant alterations of ∆HqY. Such
feeble interactions (equivalent to less than 1 kcal) have
been however detected in ∆SqY. A similar phenomenon
concerning the substituent effects on ∆HqY and ∆SYq was
already observed with the radical reactions involving
polar TS (refer to the “Supporting Information”).22-24
Others25,26 also perceived importance of the entropies
with similar radical reactions. The cyclic TS, 4, and the
polar TS22-26 share a structural similiarity in that they
both escape from the “intermediate configuration” be-
tween reactant and product.
Entropies of activation21 (∆SqY) can be closely related
with the differences in number and character of the
degrees of freedom between 4 and 3. The cyclic structure
of 4 barely allows the internal freedom while 3 enjoys
the free rotations. The negative sign of ∆SqY of Table 2
can be accordingly understood. The small and negative
value of F+ ) -0.24 suggests that bond-breaking slightly
exceeds bond-making with net increase in the entropy.
The electron-donating substituents tend to increase the
extent of bond cleavage leading to a relatively looser TS
Solvolysis of substituted cumyl chlorides (eq 4) and
decomposition of the phosphonium chlorides (eqs 5 and
(23) Kim, S. S.; Kim, H. R.; Kim, H. B.; Youn, S. J .; Kim, C. J . J .
Am. Chem. Soc. 1994, 116, 2754.
(24) Kim, S. S.; Kim, H.; Yang, K. W. Tetrahedron Lett. 1997, 38,
5303.
structure. The differential entropy terms (∆∆SYq -H
)
should thus be a result of bond scission for a substituted
benzyl isocyanide being less than for benzyl isocyanide
itself. Figure 3 shows almost linear relations between
∆∆SqY-H and σ+ which are also featured with our radical
reactions.22-24 The values of ∆∆HYq -H are close to zero,
(25) Wagner, P. J .; Cao, Q.; Pabon, R. J . Am. Chem. Soc. 1992, 114,
346.
(26) (a) Das, P. K.; Encinas, M. V.; Steenken, S.; Scaiano, J . C. J .
Am. Chem. Soc. 1981, 103, 4162. (b) The temperature effects have not
been explicitly discussed by the above authors. We have analyzed the
data of the above literature in order to find out the entropic dominance
for the rates. p-Methoxyphenol (k ) 1.6 × 109 M-1 s-1) reacts faster
than phenol (k ) 3.3 × 108 M-1 s-1). However, the former reaction
(Ea ) 4 kcal/mol) exhibits higher activation energy than the latter (Ea
) 2.8 kcal/mol). Therefore, the entropy of activation (∆Sq) must
outweigh its enthalpic counterpart (∆Hq) to render the faster rate.
(21) Schaleger, L. L.; Long, F. A. Adv. Phys. Org. Chem. 1963, 1, 1.
(22) Kim, S. S.; Choi, S. Y.; Kang, C. H. J . Am. Chem. Soc. 1985,
107, 4234.

1188 J . Org. Chem., Vol. 63, No. 4, 1998
Kim et al.
6) were investigated by us27 to obtain the differential
activation parameters (∆∆HqY-H and ∆∆SYq -H). Both re-
actions showed enthalpy control of reactivities. The
structures of TSs must satisfy requirements of the
“intermediate configuration”. The temperature effects on
the relative rates (kY/kH) conformed to RSP. The plots
of ∆∆HqY-H vs σ+ yielded good straight lines with positive
slopes (refer to the “Supporting Information”). Therefore
the substituent effects systematically control the bond
ruptures, which is reflected in variations of ∆HqY.
Su bstitu ted ben zyl isocya n id es (YC6H4CH2NC, Y )
p-OCH3, p-CH3, H, and p-Cl) were prepared by the literature
method:31
The stretching vibration of -NtC is shown at 2184 cm-1 for
all the isonitriles (YC6H4CH2NC). The chemical shifts are
indicated as follows: 1H NMR (200 MHz, CDCl3) δ: Y ) H,
7.38 (m, 5H), 4.64 (s, 2H); Y ) p-OCH3, 7.29-7.24 (d, 2H),
6.94-6.89 (d, 2H), 4.56 (s, 2H), 3.81 (s, 3H); Y ) p-CH3, 7.19
(dd, 4H), 4.54 (s, 2H), 2.34 (s, 3H); Y ) p-Cl, 7.40-7.36 (d,
2H), 7.31-7.26 (d, 2H), 4.62 (s, 2H).
Deu ter a ted ben zyl isocya n id e (C6H5CD2NC)32 was ob-
tained via dehydration of C6H5CD2NDCHO derived from the
reaction of C6H5CD2ND2 with HCO2H. Reduction of C6H5CN
with LiAlD4 gave C6H5CD2ND2.33 The percent deuteration was
over 98%.
The selectivity (Q) can be defined as Q ) ln(kY/kH) and
ln(kY/kH) ) -(∆GqY - ∆GHq )/RT ) -∆∆GqY-H/RT. Q )
-∆∆GqY-H/RT can be divided into entropy and enthalpy
term.
Th er m a l Rea ction s. A substituted benzyl isocyanide
(YC6H4CH2NC, 0.6 M), 1,1-diphenylethylene (0.4 M), and
chlorobenzene (internal standard, 0.2 M) were dissolved in
benzene. The benzene solutions were divided into several
Pyrex ampules, which were degassed and sealed by the freeze-
pump-thaw method. Before the thermolysis, the ampules were
prewarmed at 170 °C for 5 min to shorten the time of thermal
equilibrium. The control experiment indicated no isomeriza-
tions taking place during the period of 5 min. Less than 10 s
was required for the warming up to 230 °C. The ampules were
then exposed to the thermal reactions at the temperatures and
quenched with ice/water at several intervals.
Q ) ∆∆SqY-H/R - ∆∆HqY-H/RT
(7)
Since ∆∆HqY-H/RT is close to zero, eq 7 becomes Q )
∆∆SqY-H/R which is devoid of the temperature. The
constant selectivities against the temperature gradient
are thereby verified.
An a lytica l P r oced u r es. The solutions having undergone
the thermal reactions were analyzed on 30 m DB-1 capillary
column utilizing FID and temperature programming from 40
to 210 °C. The GLC analysis provided the final concentrations
of YC6H4CH2NC and YC6H4CH3CN, which always showed
excellent material balances (g97%). The absolute rate con-
stants have been derived from plot of ln(CA0/CAt) vs t, with CA0
and CAt representing the initial and final concentration of
YC6H4CH2NC at time t, respectively. The rate constants (kY)
at 170, 190, and 210 °C were obtained as follows. Each sample
was analyzed more than two times to locate a point in the plot
of ln CA0/CAt vs time. More than four points make a straight
line with a correlation coefficient, r g 0.980. The figure (r g
0.980) should indicate that the isomerization is the sole
reaction taking place during the thermolysis. Each rate
constant (kY) was obtained from the average slopes of more
than two straight lines. The rates at 230 °C were measured
by NMR method. The NMR spectra showed the peaks only
for YC6H4CH2NC and YC6H4CH2CN which indicated that no
side reactions occurred during the reactions. The disappear-
ance of YC6H4CH2NC also matched the formation of
YC6H4CH2CN. The rate equation can be written down as
ln[(CAt + CBt)/CAt] ) kYt where CAt and CBt are concentrations
of YC6H4CH2NC and YC6H4CH2CN at reaction time t, respec-
tively. The integration of the methylene peaks of YC6H4CH2NC
and YC6H4CH2CN were used as the substitute for the concen-
trations, i.e., CAt and CBt. Therefore the rate equation exempts
employment of an internal standard and guarantees the better
precision of the data. Separate samples were measured at
various intervals to determine the location of the points in the
Con clu sion
The isomerizations belong to the cationotropic 1,2-
shifts, which have been rarely studied.10 The structure
of TS should characterize the reactivities. The cyclic TS
can be defined as an “imbalanced TS”20 which confines
the validity of Hammond postulate13 and reactivity/
selectivity principle,11 and engenders the entropy control
of reactivities. An absence of temperature effects is
rationalized and established in terms of the entropic
contribution. The entropy term is 1000 times more
sensitive than its enthalpic mate in order to recognize
the substituent effects on the bond fissions. The activa-
tion parameters fail to follow the isokinetic relationship28
and to show compensation effects.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. Substituted benzaldehydes,
5-aminotetrazole, palladium on activated carbon, triethyl-
amine, lithium aluminum deuteride, formic acid, and other
reagents were purchased from the major suppliers. Liquids
were distilled with center-cut collection, and solids were
recrystallized according to the standard procedures30 when
necessary. A Varian 3300 gas chromatograph and a Varian
Gemini 2000 NMR spectrometer were used for the analysis of
the reaction mixtures.
(31) Ho¨fle, G.; Lange, B. Organic Syntheses; Wiley: New York, 1990;
Coll. Vol. VII, p 27.
(32) Ugi, I.; Meyr, R.; Lipinskz, M.; Bodeshein, F.; Rosendahl, F.
Organic Syntheses; Wiley: New York, 1973; Coll. Vol. V, p 300.
(33) Amundsen, L. H.; Nelson, L. S. J . Am. Chem. Soc. 1951, 73,
242.
(27) Unpublished results.
(28) Leffler, J . E. J . Org. Chem. 1955, 20, 1202.
(29) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165.
(30) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. F. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: Oxford, U.K., 1980.

Thermal Isomerizations of Benzyl Isocyanides
J . Org. Chem., Vol. 63, No. 4, 1998 1189
plots. More than four points were obtained to make one
straight line. The plots of ln[(CAt + CBt)/CAt] vs time gave
straight lines with excellent correlation coefficient, i.e., r g
0.980. Several representative plots of the rate equation are
given in the Supporting Information.
Su p p or tin g In for m a tion Ava ila ble: Several plots (e.g.
∆∆HqY-H vs σ+ or σ and ∆∆SYq -H vs σ+ or σ) that compare the
reactivities controlled by the entropies and enthalpies;
ln(concn) vs time plots that indicate accuracy of the measure-
ments of the absolute rates; the examples of material balance
of the isomerizations (8 pages). This material is contained in
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, and can be ordered from the
ACS; see any current masthead page for ordering information.
Ack n ow led gm en t. We warmly thank Ministry of
Education (BSRI-97-3416) and KOSEF/OCRC for the
financial support. Grateful thanks are due to the editor
and the reviewers for the very kind efforts to improve
the manuscript. We also thank professor Bong Rae Cho
for the editorial corrections.
J O970282U