Thermolysis kinetics of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates

Article abstract of DOI:10.1002/poc.1950

An experimental approach was developed to determine the intrinsic thermolysis rate constants of the central carbon-carbon bond during the dl/meso isomerization of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates (G=H, Me, OMe, Cl, and NO₂

Full text of DOI:10.1002/poc.1950

Research Article
Received: 07 September 2011,
Revised: 11 October 2011,
Accepted: 16 October 2011,
Published online in Wiley Online Library:2011
(wileyonlinelibrary.com) DOI: 10.1002/poc.1950
Thermolysis kinetics of diethyl 2,3-dicyano-2,
3-di(p-substituted phenyl)succinates
Chenze Qia, Linjun Shaoa, Yueqing Lua, Chen Wanga and Xian-Man Zhanga*
An experimental approach was developed to determine the intrinsic thermolysis rate constants of the central
carbon–carbon bond during the dl/meso isomerization of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates
(G=H, Me, OMe, Cl, and NO2) at temperatures ranging from 80 to 120 ꢀC. The obtained rate constants are significantly
affected by the polarity of the para substituents, in sharp contrast to their negligible effects on the dl/meso
isomerization equilibrium constants. Moreover, the substituent effects on the activation enthalpies can be linearly
correlated with the Hammett substituent resonance constants and the homolytic dissociation enthalpies (bond
dissociation energies) of the benzylic C–H bonds of ethyl 2-cyano-2-(p-substituted phenyl)acetates. Copyright © 2011
John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this paper.
Keywords: activation enthalpy and entropy; dl/meso thermal isomerization; hexasubstituted ethane; thermolysis kinetics,
polymerization initiators
The thermolysis rate constants of the central C–C bond
INTRODUCTION
homolysis are important for the applications of hexasubstituted
ethanes as polymerization initiators. Ruchardt and Beckhaus[3,4]
The central carbon–carbon (C–C) bond strength (reactivity) of
have developed
a series of methods to determine the
hexasubstituted ethane is significantly influenced by the size
and electronic structures of the substituents. For example, the
C–C bond dissociation enthalpy (BDE) of ethane is well
established to be 377.4 ꢁ 0.8 kJ/mol,[1,2] while the central C–C
BDE of the hypothetical hexaphenylethane is estimated only in
the range of 50–70 kJ/mol.[3,4] The difference of ~310 kJ/mol in
bond strength corresponds to a reactivity difference of 1054
times at 25 ꢀC. The tremendous difference explains why
hexaphenylethane is thermodynamically unstable even at room
temperature, while the decomposition of ethane into methyl radi-
cals with t1/2 = 1.0 h occurs only at a temperature of around
690 ꢀC,[3–5] although the true structure of the hypothetical
hexaphenylethane is 3-triphenylmethyl-6-diphenylmethylidene-1,
4-cyclohexadiene, which could be further isomerized into
1-diphenylmethyl-4- triphenylmethylbenzene.[5]
The reactivities (stabilities) of hexasubstituted ethanes can be
tuned by a variation of the substituents.[3,4,6] Aiming at the
synthesis of polymerization initiators, we have synthesized a
series of hexasubstituted ethanes from the copper-mediated
oxidative coupling of ethyl 2-cyano-2-(p-substituted phenyl)
acetates as shown in Scheme 1. The dl and meso diastereomeric
mixtures of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)
succinates (1) were separated and then characterized by nuclear
magnetic resonance (NMR), infrared, ultraviolet and mass
spectrometry analyses,[7,8] and their stereochemical structures
were confirmed by X-ray crystal structure analysis.[9] Although
the central C–C bond lengths are longer (~1.60 Å) than the
standard (1.54 Å),[9] the dl and meso diastereomers are both
stable, indicating that the corresponding homolysis into
diradicals is negligible at room temperature. However, these dl
and meso diastereomers have been demonstrated as excellent
polymerization initiators at ~100 ꢀC for various alkene monomers
such as styrene, acrylonitrile, methyl mathacrylate, etc.[8–10]
thermolysis rate constants of the central C–C bond homolysis
for hexasubstituted ethanes and some of their meso and dl
diastereomers. Bennett et al.[11] have employed a similar
approach to determine the thermolysis rate constants for the
meso and dl diastereomers resulting from the photoreduction
of 5,6-dihydro-3,5,5-trimethyl-1,4-oxazin-2-one. However, these
thermolysis rate constants were exclusively obtained by the
addition of radical scavengers, followed by the quantification
of the hydrogen abstract products as shown in Scheme 2.
Weiner[12] has demonstrated that the addition of radical
scavengers could significantly affect the thermolysis rate
constants and the differences could be over 30 times. Moreover,
small or even negative activation entropies were generally
observed from the central C–C bond homolysis studies,[3,4,11,12]
suggesting that the added radical scavenger may involve the
C–C bond thermolysis because a unimolecular reaction should
have a substantial positive activation entropy because of the much
looser transition state.[13] This is not unexpected because the
radical scavengers can only trap the escaped radical intermediates
rather than the radical intermediates in the solvent cages. In the
present paper, we present a unique experimental approach to
determine the intrinsic thermolysis rate constants without the
need for any radical scavengers for the central C–C bond
* Correspondence to: X.-M. Zhang, Institute of Applied Chemistry and
Department of Chemistry, University of Shaoxing, Shaoxing, Zhejiang
312000, China.
E-mail: xian-man.zhang@usx.edu.cn
a C. Qi, L. Shao, Y. Lu, C. Wang, X.-M. Zhang
Institute of Applied Chemistry and Department of Chemistry, University of
Shaoxing, Shaoxing, Zhejiang, 312000, China
J. Phys. Org. Chem. (2011)
Copyright © 2011 John Wiley & Sons, Ltd.

C. QI ET AL.
CN
C
CN
C
CN
were confirmed by the well-resolved electron spin resonance spec-
trum.[8] The formation of radical intermediates is further supported
by the fact that diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)suc-
cinates can all be used as radical initiators for various alkene
polymerizations.[10]
Cu(I)/O2
G
G
2
G
CH
CO2Et CO2Et
CO2Et
1
G = p-H; p-Me; p-OCH3; p-Cl and p-NO2
Scheme 1. Synthesis of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)
succinates
Kinetic method for dl/meso isomerization
The dl/meso isomerization of Scheme 3 can be simply expressed
as Eqn (2)
k1
⇌ ⇌1dl
k3
1meso
2 Inꢄ
(2)
k2
k4
Scheme 2. Kinetics of the carbon-carbon bond homolysis
where k1, k2, k3 and k4 are the rate constants for the designated
elementary step reactions.
homolysis of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)
succinates (G=H, Me, OMe, Cl and NO2) at various reaction
temperatures.
The analytic solutions for the reversible first-order consecutive
reaction (A⇌ B ⇌ C) are known, but they are clearly too complex
to process any experimental data without approximation.[16]
To the best of our knowledge, no analytic solutions for the
reversible bimolecular consecutive reaction (Eqn (2)) have ever
been reported in the literature. Nevertheless, we expect that such
analytic solutions will be more complex even if the related differ-
ential equations could be solved. Thus, it is necessary to develop
an approximate approach to process the experimental results.
The rate differential equations for the reactant 1meso and
RESULTS AND DISCUSSION
The dl/meso isomerization of diethyl 2,3-dicyano-2,3-diphenyl-
succinate (G=H, Scheme 1) was examined using a simple
reversible reaction model (Eqn (1)) by quantification of the
dl and meso diastereomeric concentrations because the dl
and meso diastereomers have differently well-resolved high-
performance liquid chromatography (HPLC) peak retention
times, which are summarized together with the retention
times of other substituted substrates in Table S1.[8,14]
However, the obtained activation entropies from the apparent rate
constants were found to be different from negative to positive
(ꢂ46 to + 30 J/molꢃK) in different solvents,[8,14] suggesting that
the over-simplified kinetic approach (Eqn (1)) may not be suitable
to model the dl/meso isomerization of diethyl 2,3-dicyano-2,
3-diphenylsuccinate.
•
intermediate In of Eqn (2) are given
d½1meso
dt
ꢅ
2
¼ ꢂk1½1mesoꢅ þ k2½Inꢄꢅ
(3)
d½Inꢄꢅ
dt
2
2
¼ k1½1mesoꢅ þ k4½1dlꢅ ꢂ k2½Inꢄꢅ ꢂ k3½Inꢄꢅ
(4)
•
•
where [1meso], [In ] and [1dl] are the concentrations of 1meso, In
and 1dl at time t, respectively.
Electron spin resonance studies showed that the concentra-
tions of the radical intermediates were found to be less than
10–5 M at temperatures below 120 ꢀC, indicating that the radical
concentrations are negligible relative to the meso and dl diaste-
reomeric concentrations (0.2 ~ 0.3 M) (also refer to the Experi-
mental Section). Thus, the derivative of the radical intermediate
concentration (Eqn (4)) should also be negligible. After applying
k1
⇌
1meso
1dl
(1)
k2
Dl/meso isomerization
•
the steady-state approximation to the radical intermediate In ,
Homolytic cleavage of the central C–C bond is the major and usually
the sole pathway for the thermolysis of hexasubstituted
ethanes.[3,4,15] The dl/meso isomerization of diethyl 2,3-dicyano-2,
3-di(p-substituted phenyl)succinates has been proposed to
proceed via the central C–C bond homolysis to yield two radical
intermediates (In.) followed by their recombination as shown in
Scheme 3.[8,9] Ethyl 2-cyano-2-(p-substituted phenyl)acetates were
found as the only observed products from the thermolysis of either
meso or dl diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates
in the presence of a radical scavenger such as thiophenol.[8,9] The
radical intermediates derived from the central C–C bond homolysis
•
that is, d[In ]/dt = 0, rearrange Eqn (4) to yield
k1½1mesoꢅ þ k4½1dlꢅ
2
½Inꢄꢅ ¼
(5)
k2 þ k3
Substitution of Eqn (5) into Eqn (3) gives
d½1meso
dt
ꢅ
k2k4½1dlꢅ ꢂ k1k3½1meso
k2 þ k3
ꢅ
¼
(6)
Because the radical intermediate concentrations are negligible,
Scheme 3. DL/MESO Isomerization
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2011)

KINETICS OF C–C BOND HOMOLYSIS
À
Á
the concentration of the product dl diastereomer ([1dl]) can be
obtained from Eqn (7).
1 ꢂ k1=k4
kobs ꢂ k1
1
Δk ¼
¼
<
(14)
kobs
1 þ K
1 þ K
½1dlꢅ ꢆ ½1mesoꢅo ꢂ ½1meso
ꢅ
(7)
where [1meso]o and [1meso] are the meso diastereomeric concen-
trations at times 0 and t.
Substitution of Eqn (7) into Eqn (6) yields
Because the dl diastereomers are predominant at equilibrium,
the meso diastereomers were used for all of the kinetic studies.
Figure 1 shows the dl and meso concentration time courses
for the dl/meso isomerization of diethyl 2,3-dicyano-2,3-di
(p-methylphenyl)succinate at temperatures of 80, 90, 100, 110,
and 120 ꢀC. The dl and meso concentration time courses for the
rest of the diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)
succinates are summarized in the supplementary material. These
concentration time courses show that the product dl’s concen-
trations increase as the reactant meso’s concentrations decrease
and each substrate has its own characteristic isoconcentration at
different temperatures. Nice linear correlations were obtained
after these concentration time courses were processed
according to Eqn (11). The representative linear correlations
are summarized in Fig. 2 for diethyl 2,3-dicyano-2,3-di
d½1meso
dt
ꢅ
k2k4½1mesoꢅo ðk1k3 þ k2k4Þ½1meso
ꢅ
¼
ꢂ
(8)
k2 þ k3
k2 þ k3
Integration of Eqn (8) gives[1b]
È
À
ÁÉ
k1k3 þ k2k4
k2 þ k3
ln k1k3½1mesoꢅ ꢂ k2k4 ½1mesoꢅo ꢂ ½1meso
ꢅ
¼
t (9)
The dl/meso isomerization equilibrium constant (Keq) can
be obtained either by forward/backward rate constants or by
equilibrated concentrations as shown in Eqn (10).
eq
k1k3
k2k4
½1dlꢅ
0.225
0.200
0.175
0.150
Keq
where [1dl]eq and [1meso
¼
¼
(10)
eq
½1meso
ꢅ
]
eq are the equilibrated concentrations of
1
dl and 1meso, respectively.
]
eq + [1dl]eq, Eqn (9) can be rewritten
80 oC
80 oC
Because [1meso]o ꢆ [1meso
0.125
0.100
0.075
0.050
0.025
0.000
90 oC
90 oC
as
100 oC
110 oC
120 oC
100 oC
110 oC
120 oC
k1k3 þ k2k4
eq
lnf½1dlꢅ ꢂ ½1dlꢅg ¼
t ¼ kobst
(11)
k2 þ k3
where
k1k3 þ k2k4
k2 þ k3
kobs
¼
(12)
0
50
100
150
200
250
300
Interestingly, Bennett et al.[11] derived similar kinetic equations
and used them to validate their thermolysis rate constants as
determined by the addition of the radical scavenger for the meso
and dl diastereomers.
Time (min)
Figure 1. Concentration time courses for diethyl 2,3-dicyano-2,3-di
(p-methylphenyl)succinate at different reaction temperatures. The lines
with unfilled labels are for the meso diastereomer and the lines with filled
labels are for the dl diastereomer
Thermolysis rate constants for the central C–C
bond homolysis
6
For a complex chemical reaction, it is usually difficult to deter-
mine the rate-determining step, resulting in the difficulty to
correlate the apparent rate constant with any given elementary
step reaction.[17]
The dl diastereomers are 11.5 ꢁ 1.3 times more stable than the
corresponding meso counterparts for diethyl 2,3-dicyano-2,3-di
(p-substituted phenyl)succinates regardless of the substituent
polarity,[7–9] suggesting that the forward rate constants k1 and
k3 should be larger than the backward k2 and k4 in a similar
magnitude. Thus, the apparent rate constant (kobs) should be
approximately equal to the thermolysis rate constant k1 for the
central C–C bond homolysis.
80oC
90oC
5
100oC
110oC
120oC
4
3
2
1
0
k1k3 þ k2k4
kobs
¼
ꢆ k1
(13)
k2 þ k3
0
2000 4000 6000 8000 10000 12000 14000 16000 18000
Time (s)
Figure 2. Linear plots of Ln{[1dl]eq ꢂ [1dl]} versus reaction time for
diethyl 2,3-dicyano-2,3-di(p-methylphenyl)succinate at different reaction
temperatures
The experimental error introduced by this approximation can
be estimated by Eqn (14) to be less than about 8% because K
is 11.5 ꢁ 1.3.[8]
J. Phys. Org. Chem. (2011)
Copyright © 2011 John Wiley & Sons, Ltd.
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C. QI ET AL.
(p-methylphenyl)succinates, and the rest of the linear
correlations are summarized in the supplementary material.
The resultant thermolysis rate constants (k1) from the linear
correlations are summarized in Table 1 for all diethyl 2,
3-dicyano-2,3-di(p-substituted phenyl)succinates at tempera-
tures of 80, 90, 100, 110 and 120 ꢀC.
rate constants (Table 1) according to the Eyring equation
(Eqn (15)),[18] and the related results are summarized in Table 2.
¼
¼
lnðk1=TÞ ¼ lnðkB=hÞ þ ΔS =R ꢂ ΔH RT
(15)
An examination of Table 2 shows that the activation
entropies are all similarly positive (53.4 ꢁ 5.8 J/molꢃK), which
are in good agreement with the unimolecular reaction
mechanism for the thermal dl/meso isomerization (Scheme 3
and Eqn (2)) because a loose transition state is usually
characterized by a substantial positive activation entropy.[13]
Most intriguingly, the para-substituents exert noticeable
effects on the activation enthalpies in contrast to their
negligible effects on the dl/meso isomerization equilibrium
constants. For example, the introduction of the p-NO2 group
increases the activation enthalpy by ~2 kJ/mol, whereas the
introduction of the p-CH3, p-CH3O, and p-Cl groups decreases
the activation enthalpy by 38.5, 41.4 and 19.4 kJ/mol,
respectively. The para-substituents should have similar steric
and inductive effects for the central C–C bond homolysis
because they are far away from the reaction centers. Thus,
the activation enthalpy differences must be primarily associ-
ated with the electronic (resonance) effects of the para-
substituents through the aromatic ring, which are similar to
the substituent effects on the thermolysis rate constants.
Indeed, the resultant activation enthalpies are best linearly
correlated with the corresponding substituent resonance
constants (sR), as shown in Fig. 3.
An examination of Table 1 shows that the introduction of
p-Me, p-MeO, and p-Cl groups increase the rate constants by
3–10 times, whereas the introduction of p-NO2 group
decreases the rate constants by about two times. At the
same reaction temperature, the relative thermolysis rate
constants for the five substrates are best correlated with
the Hammett resonance constants of the para-substituents.
Most interestingly, the thermolysis rate constants increase
with the reaction temperature by 20–80 times. These results
are in sharp contrast to the negligible effects of reaction
temperature and p-substituents on the dl/meso isomerization
equilibrium constants.[8,9] It is worth noting that the
thermolysis rate constants (Table 1) are all much larger than
the rate (10–4 min–1
) of radical formation required for
efficient polymerization initiators,[19] suggesting that these
hexasubstituted ethanes can be used as polymerization
initiators.[10]
Activation parameters for the central C–C bond homolysis
The activation enthalpies and entropies for the central C–C bond
homolysis of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)
succinates were obtained from the temperature-dependent
Homolytic bond dissociation enthalpies of the benzylic C–H
Table 1. Thermolysis rate constants (k1) for the central C–C
bond of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)suc-
cinates at various reaction temperaturesa
bonds
The activation enthalpy reflects the stability of the transition
state[13] and BDE has long been considered as the best quantita-
tive measure of the radical thermodynamic stability.[21] The
linear Hammett correlation of the kinetic results (Fig. 3)
prompted us to examine whether the activation enthalpies can
be correlated with the thermodynamic stabilities of the radical
intermediates. Theoretical calculations have been widely used
to obtain BDEs of various chemical bonds.[22] The GAUSSIAN
(Pittsburgh PA USA) package with the density function theory
was used in this study to calculate the benzylic C–H BDEs
(Scheme 4) and the related results are summarized in Table 3.
Table 3 shows that the benzylic C–H BDE of ethyl 2-cyano-
2-phenylacetate is 332.5 kJ/mol, which is in excellent agree-
ment with the experimental result (334.5 kJ/mol) that was
determined from the equilibrium acidity and oxidation
Temperature
80 ꢀC
90 ꢀC 100 ꢀC 110 ꢀC 120 ꢀC
p-H
0.163
1.99
2.06
0.615 2.07
6.66
24. 7
24.9
12.7
3.42
13.3
43.4
43.3
33.6
p-CH3
p-OCH3
p-Cl
4.48
5.37
1.98
9.24
9.63
5.50
0.723
p-NO2
0.0839 0.300 0.877
7.23
aFirst-order rate constants in min–1. The dl/meso isomerization
reactions were performed in 1,1,2,2-tetrachloroethane solution.
Table 2. Activation enthalpies and entropies for the central
C–C bond homolysis for diethyl 2,3-dicyano-2,3-di(p-substi-
tuted phenyl)succinatesa
140.0
= 67.8 + 118
R
H
p-NO
2
p-H
130.0
120.0
110.0
100.0
90.0
R = 0.86
¼
¼
Substrate
ΔH
ΔS
Correlation coefficient (r2)
p-Cl
(kJ/mol) (J/molꢃK)
p-Me
p-H
126
87.9
85.0
107
128
59.2
48.4
47.6
54.0
59.0
0.994
0.996
0.994
0.999
0.996
p-OMe
p-CH3
p-OCH3
p-Cl
80.0
70.0
-0.60 -0.50 -0.40 -0.30 -0.20 -0.10
0.00
0.10
0.20
p-NO2
Hammett R constant
aActivation enthalpies and entropies obtained from the
thermolysis rate constants according to Eqn (15).
Figure 3. Correlation of the activation enthalpies with the substituent
resonance constants (sR)[20]
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. (2011)

KINETICS OF C–C BOND HOMOLYSIS
scavengers. The activation enthalpies of the central C–C bond
homolysis can be linearly correlated with the Hammett substitu-
ent resonance constants and the homolytic dissociation enthal-
pies of the benzylic C–H bonds of ethyl 2-cyano-2-(p-substituted
phenyl)acetates, which provide the additional evidences to
support the reliability of the novel kinetic approach reported in
this paper.
Scheme 4. Benzylic C-H bond dissociation enthalpies
EXPERIMENTAL SECTION
Table 3. Homolytic bond dissociation enthalpies of benzylic
C–H bonds of ethyl 2-cyano-2-(p-substituted phenyl)
acetatesa
Chemicals and instruments
All solvents were of analytical grade, or the highest grade commercially
available. 1,1,2,2-Tetrachloroethane (Aldrich, Milwaukee, WI, USA) was
soaked in anhydrous MgSO4 overnight and then distilled under a re-
duced pressure. NMR spectra were recorded on a Bruker AM (Madison,
WI, USA) 400 MHz instrument. HPLC analysis was carried out on a Hitachi
model (Tokyo, Japan) liquid chromatograph. The quantitative HPLC anal-
ysis was employed by the internal standard technique with a calibration
against authentic reference compounds.
Substrates
BDEC–H (kJ/mol)
p-H
332.5
318.3
325.9
329.1
335.1
p-OCH3
p-CH3
p-Cl
p-NO2
aObtained from the theoretical calculations at the Becke,
General synthesis procedure
three-parameter, Lee–Yang–Parr/6-31G* level.
Diethyl 2,3-dicyano-2,3-diphenylsuccinate, diethyl 2,3-dicyano-2,3-di
(p-methylphenyl)succinate, diethyl 2,3-dicyano-2,3-di(p-chlorophenyl)-
succinate and diethyl 2,3-dicyano-2,3-di(p-methoxyphenyl)succinate
340
were synthesized using
a protocol adapted from the literature
procedure, that is, from the reactions of the corresponding para-
substituted benzylcyanide carbanions with diethyl carbonate, fol-
lowed by the copper-mediated oxidative coupling reactions.[7,25]
Diethyl 2,3-dicyano-2,3-di(p-nitrophenyl)-succinate was synthesized
from the nucleophilic substitution of p-nitrochlorobenzene with ethyl
cyanoacetate carbanion, followed by the copper-mediated oxidative
coupling reaction.[7,26] The meso and dl diastereomers were
p -NO
p -Cl
2
BDE = 0.293
R=0.92
H + 297
335
330
325
320
315
p -H
p -Me
separated by fractional crystallization using
a mixed solvent of
p -OMe
carbon tetrachloride and ethyl acetate and they were characterized
by NMR, mass spectrometry, and HPLC analyses.[7,8]
80
90
100
110
120
130
Kinetic measurements for dl/meso isomerization
H
(kJ/mol)
Flasks containing 0.2–0.30 M of the meso diastereomers in a 1,1,2,2-
tetrachloroethane solution were purged with nitrogen for about 10 min
before heating in a pre-equilibrated thermostat (80, 90, 100, 110, or
120 ꢀC). Aliquots were taken and were immediately quenched in a dry
ice–acetone bath at different time intervals then subjected to the HPLC
analysis.
Figure 4. Correlation of the benzylic C–H BDEs with the activation
enthalpies
potential measurements.[23] The introduction of the p-NO2
group increases the benzylic C–H BDE, whereas introduction
of the p-CH3, p-CH3O, and p-Cl groups decreases the benzylic
C–H BDEs. These effects are similar to the substituent effects
on the activation enthalpies. We have shown that the BDEs of
the benzylic C–H, phenolic O–H, and thiophenolic S–H bonds
can be linearly correlated with Hammett constants of the
substituent on the aromatic ring.[24] Nevertheless, the ther-
modynamic benzylic C–H BDEs can also be linearly correlated
with the kinetic activation enthalpies derived from the central
C–C bond homolysis as shown in Fig. 4. These linear
correlations confirm that the measured rate constants are
the thermolysis rate constants for the central C–C bond
homolysis.
THEORETICAL CALCULATIONS
Density function theory calculations were performed using the
GAUSSIAN-03 program at the Becke, three-parameter, Lee–Yang–
Parr/6-31G* level.[27,28]
SUPPORTING INFORMATION
Kinetic concentration time courses and linear correlations for the
dl/meso isomerization and Cartesian coordinates and absolute
energies for the calculated structures.
CONCLUSIONS
Acknowledgements
In summary, we have determined the thermolysis rate constants
for diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates
(G = H, Me, OMe, Cl, and NO2) without the need for any radical
We greatly appreciate the financial support from the Shaoxing
medical and chemical engineering projects and Shaoxing
University.
J. Phys. Org. Chem. (2011)
Copyright © 2011 John Wiley & Sons, Ltd.
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C. QI ET AL.
[19] G. Moad, D. H. Solomon, The Chemistry of Radical Polymerization,
2nd edn, Elsevier, Oxford, 2006, p. 64.
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