物理化学学报(Wuli Huaxue Xuebao)
Acta Phys. ⁃Chim. Sin. 2012, 28 (5), 1120-1126
1120
[Article]
May
www.whxb.pku.edu.cn
doi: 10.3866/PKU.WHXB201203082
F-+CH3Cl→CH3F+Cl-反应过程中的分子形貌变化
张明波 1,2
(1 辽宁中医药大学药学院, 辽宁 大连 116600;
摘要:
宫利东 2,*
2
辽宁师范大学化学化工学院, 辽宁 大连 116029)
双分子亲核(SN2)反应是重要的基本有机反应之一, 其中电子从亲核基团向离去基团的转移发挥着关键
作用. 利用从头计算方法 CCSD(T)/aug-cc-pVDZ 和我们发展的分子形貌理论, 对反应 F-+CH3Cl→CH3F+Cl-进
行了研究, 给出了反应过程中分子形状和电子转移的动态变化图像. 结果表明, 沿内禀反应坐标, 从反应开始到
生成反应前复合物, 亲核试剂 F-的分子内禀特征轮廓在缓慢收缩, 而其上的电子密度在缓慢增大. 此后, F 的轮
廓迅速膨胀, 电子密度急剧下降, 尤其是从过渡态到产物复合物的过程中. 而在反应过程中, 离去基团 Cl 的轮
廓一直在收缩, 其上的电子密度一直在增大. 对反应过程中电子所受到作用势的研究表明, 随着反应的进行, 电
子在 F 与 C 间受到的作用势逐渐降低, 而在 C 与 Cl 间受到的作用势逐渐升高, 清楚地展现反应过程中 F 与 C 间
化学键生成和 C 与 Cl 间化学键断裂的动态过程.
关键词:
从头计算; 分子形貌理论; SN2 反应; 电子转移; 反应机理
中图分类号:
O641
Evolution of the Molecular Face during the Reaction Process of
F-+CH3Cl→CH3F+ClZHANG Ming-Bo1,2
GONG Li-Dong2,*
( College of Pharmacy, Liaoning University of Traditional Chinese Medicine, Dalian 116600, Liaoning Province, P. R. China;
School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, Liaoning Province, P. R. China)
1
2
Abstract:
Bimolecular nucleophilic substitution (SN2) reactions are among the fundamental organic
reactions, in which electron transfer from the nucleophilic group to the leaving group plays an essential
role. We use a high-level ab initio CCSD(T)/aug-cc-pVDZ method in conjunction with our previouslydeveloped molecular face (MF) theory, to investigate the SN2 reaction F-+ CH3Cl→CH3F + Cl-. Dynamic
representations of molecular shape evolution and electron transfer features throughout the reaction are
vividly presented. It is found that along the intrinsic reaction coordinate (IRC), from the beginning of the
reaction to the prereaction complex, the molecular intrinsic characteristic contour (MICC) of the nucleophile
(F-) contracts slowly, while the electron density on the MICC increases slowly. The MICC of F then expands
quickly, and the electron density decreases sharply, especially from the transition state to the product
complex. However, for the leaving group (Cl), the MICC contracts, and the electron density increases all
along the reaction. Investigations of the potential acting on an electron in a molecule (PAEM) show that, as
the reaction progresses, the PAEM gradually decreases between fluorine and carbon, while it gradually
increases between carbon and chlorine. This study enhances our understanding of the dynamic processes
of bond-forming between F and C atoms and bond-breaking between C and Cl atoms.
Key Words: Ab initio calculation; Molecular face theory;
mechanism
SN2 reaction;
Electron transfer; Reaction
Received: December 27, 2011; Revised: March 7, 2012; Published on Web: March 8, 2012.
∗
Corresponding author. Email: [email protected]; Tel: +86-411-82158977.
The project was supported by the National Natural Science Foundation of China (21133005, 21073080, 21011120087, 20703022).
国家自然科学基金(21133005, 21073080, 21011120087, 20703022)资助项目
Ⓒ Editorial office of Acta Physico⁃Chimica Sinica
No.5
1
ZHANG Ming-Bo et al.: Evolution of the Molecular Face during the Reaction Process of F-+CH3Cl→CH3F+Cl-
Introduction
Bimolecular nucleophilic substitution (SN2) reactions are
one of the fundamental organic reactions, which have been
paid great attention from both theoretical and experimental
points of view.1-10 In particular, halogen exchange reactions of
CH3X+Y-→CH3Y+X- (X and Y are halogen atoms), as the simplest prototypes for SN2 reactions, have been extensively studied.11-15 Some features of this kind of reactions have been well
established. Both theoretical and experimental studies indicate
that the preferred gas-phase reaction pathway of such reaction
involves a backside attack of the halide ion, Y-, at the carbon
atom followed by the familiar“Walden inversion”of the CH3
group.16 The resulting potential energy profile can be characterized by two local-minima, formed by the association of halide
ion with the dipolar halomethane due to the strong attraction
between them and separated by a central barrier.1
Lots of computational studies have been performed on the
SN2 reactions, which have provided quantitative information
about the reaction energy potential profiles.14,17-21 Various methods including HF, MP2, QCISD, CCSD(T), and G2(+) have
been used to study the title reaction, presenting a central barrier ranging from 0 to 26 kJ·mol-1.17-21 The barrier obtained with
MP2(full)/6-31 ++ G** is 25.56 kJ·mol-1.19 Studies performed
by Gonzales et al.20 indicate that B3LYP method gave a transition structure too low in energy compared to CCSD(T) method.
By using CCSD(T) method with a basis set of aug-cc-pVQZ,
Botschwina et al.21 present a definitive theoretical study, recommending that the central barrier should be (13.8±1.3) kJ·mol-1.
Chemists are interested in not only obtaining accurate results for energetics of chemical reactions, but also exploring
other important factors during the reaction process, such as the
spatial and electron density changing features. For SN2 reactions, some progresses have already been made toward this
end.22-25 For instance, by subdividing the charge density and energy into contributions from spatially defined fragments of the
total system, Bader et al.22 presented a detailed study of the redistribution of the charge density and energy changes for the
two gas SN2 reactions. Knoerr and Eberhart23 employed several
density-based parameters to predict the reactivity of a series of
SN2 reactions, and showed that the obtained results correlated
well with those from energy-based parameters. Using an ab
initio modern valence bond calculation, Blavins and Copper24
investigated the influence of the strength of nucleophile and
the size of R group on the electronic rearrangements in a series
of SN2 identity reactions (X-+RX, X=F, Cl). Geerlings and coworkers25 interpreted the variations of the exothermicity and
the central barrier of the SN2 reactions (CH3X+Y-→CH3Y+X-)
with halogenatoms X and Y, in terms of the hard and soft acids
and bases principle (HSAB). In addition, they found that the increase in the electronegativity of Y will decrease the central
barrier, but increase the exothermicity of the reactions.
Recently, Yang et al.26-37 have developed a novel model for
describing a molecule, the molecular face theory (MFT), based
1121
on the potential acting on an electron in a molecule (PAEM).
The molecular face is an intrinsic characteristic of molecule,
which can present the molecular shape and electron density distribution at the same time. In addition, the molecular recognition and regioselectivity involved in Markovnikov reactions of
alkenes have been successfully explained in terms of MFT.36
More recently, the molecular face surface area (MFSA) and
molecular face volume (MFV) were defined and calculated by
a program of our own. It is found that the MFSA and MFV had
significant linear correlations with those of the commonly used
hard-sphere model and the electron density isosurface.37
Previous studies have shown that the essence of a SN2 reaction is the transfer of an electron from the nucleophile to the
leaving group, and thus the tendency of electron transfer is
closely related to the reactivity of a SN2 reaction.38 The goal of
this work is not to obtain quantitative information about the potential energy surface, which has been well done by others, but
to describe the spatial changing and electron transfer features
during the reaction course of F-+CH3Cl→CH3F+Cl- in a more
vivid way by applying the MFT.
2
Theoretical and computational details
2.1 Molecular face theory
We first introduce the potential acting on an electron in a
molecule, on which the definition of the molecular face (MF)
is based. For a molecule in electronic ground state, the PAEM
can be expressed as 32
ρ 2 ( r, r′)
Z
V (r) = -∑ A + 1 ∫
dr′
(1)
r
ρ(r)
| r -r′ |
A
A
where the first term on the right of Eq.(1) is the attractive potential from all nuclei, the second term is the repulsive potential created by other electrons in the system; ZA is the nuclear
charge of atom A, rA is the distance between the electron considered and the nucleus A, summation involving index A is
over all atomic nuclei; ρ(r) represents the one-electron density
of an electron appearing at position r, and ρ(r, rʹ) is the
two-electron density function, i.e. the probability of finding
one electron at r and at the same time finding another electron
at rʹ.
Considering an electron move within a molecule, its kinetic
energy varies with its position relative to other particles in the
molecule. If at a special position r, its energy is the same as the
potential acting on it, which means that its average kinetic energy is equal to zero, and then r is called a classical turning point
of the electron movement. Assuming that the potential, i.e.
PAEM, is equal to the minus value of the first vertical ionization potential of this molecule, then we have the classical turning point equation of this electron movement, V(r)=-I, where I
is the first vertical ionization potential of the molecule. The molecular intrinsic characteristic contour (MICC) can be defined
as the assembly of the classical turning points as the following
expression.26-31,34-37
G(-I)={r:V(r)=-I}
(2)
Acta Phys. ⁃Chim. Sin. 2012
1122
in which G denotes the MICC. The MICC has a clear physical
meaning as it is an iso-PAEM contour where the PAEM (or
one-electron energy) equals the minus ionization potential (-I)
of the molecule. Thus, the MICC is a characteristic boundary
of the electron movement; outside it is classical-forbidden
while inside it is classical-permitted for an electron movement.
The electron density distribution on the MICC called frontier
electron density or molecular face electron density (MFED),35-37
is also a remarkable feature of a molecule. The MFED is a direct indicator of electrophilic and nucleophilic stereo-reactivity
and molecular interactions, including hydrogen bonding.35,36
When MFED is mapped on the MICC, the MF is defined.35-37
The MF, figuratively speaking, can be viewed as an intuitive
“face”or an intrinsic characteristic“fingerprint”of a molecule, and it provides not only the spatial but also electron density distribution information of a molecule.
2.2 Computational details
In the present work, all geometrical structures considered
were optimized at the CCSD(T)/aug-cc-pVDZ level,39-41 which
has been shown to be necessary to obtain reliable results for
the reaction.42 With the same model, vertical ionization potentials of these structures were calculated, which is a prerequisite
for obtaining the MICC. The calculations mentioned above
were carried out with Gaussian 03 program.43
The PAEM and physical quantities in Eq.(1) were calculated
by the configuration interaction method with all single and double substitutions in conjunction with 6-31 + G(2d, p) basis set
using the ab initio MELD program44 and the in-house program
developed by us. By a large number of calculations, the PAEM
was obtained at each point of a grid covering the molecule,
with certain spacing between the grid points. According to Eq.
(2), the MICC was obtained by interpolation. Visualization
plots of MF were implemented by the MATLAB 7.045 and a
program of our own.
3
Results and discussion
3.1 MFs of CH3F and CH3Cl
At first, we calculated the molecular faces of CH3F and
CH3Cl, presented in Fig.1, where the MFED is denoted by the
color index on the right of the picture. So the magnitude of
MFED is represented by its darkness, that is, the darkest place
has the maximum MFED, and the brightest place has the minimum MFED. It can be seen that the MFs of CH3F and CH3Cl
Fig.1
Vol.28
are similar to each other in both shape and electron density distribution. For both of halomethanes, the electron density on the
halogen atom region is larger than that on the methyl group region. This is consistent with the fact that in a halomethane the
halogen atom can draw bonding electrons towards itself, due to
its higher electronegativity relative to methyl group. It has
been well established both theoretically and experimentally
that the backside attack of the halide ion on the halomethane is
more favorable for a SN2 reaction than that from the frontside.42
The observed stereoselectivity may partly be explained by difference in the electron density on the MF. Since the nucleophile is negatively charged, larger electron density is unfavorable for the access of the nucleophile due to electrostatic repulsion. So the attack of nucleophile on electron-deficient backside of the halomethanes is preferable to the attack on the electron-rich frontside.
3.2 Variables for depicting the variations of MF
To get a full view of the variations of the MFs during the
SN2 reaction considered, six snapshots on the C3v potential energy surface (PES) were considered. Besides the prereaction
complex c, the transition structure d, and the product complex
e, another two structures, a and b on the reactant side of the
PES and one structure f on the product side were also considered. The geometries of c, d and e were obtained by geometrical optimization at the CCSD(T)/aug-cc-pVDZ level with a
geometrical constraint of C3v symmetry. Under the same constraint, the structures of a, b and f were optimized by fixing the
bond length of r(C―F) at 0.348, 0.320, and 0.143 nm, respectively. The geometries obtained are listed in Table 1, together
with the ionization potentials and the Mulliken charges calculated with the same method. The reaction barrier we obtained
without zero-point energy correction is 8.36 kJ·mol-1, consistent with result of Angel and Ervin, 42 calculated at the same level, but lower than the value ((13.8±1.3) kJ·mol-1) of the benchmark calculation at the CCSD(T)/aug-cc-pVQZ level.21 The difference is due to relatively small basis set adopted by us, according to the work of Gonzales et al.,20 who have performed a
systematic study on the effect of basis set on the reaction barrier of the same reaction.
To display the MFs, the following visual angle is chosen: the
atoms F, C, and Cl are positioned along the C3v axis from left to
right in turn; keep one of F―C―H plane perpendicular to the
paper plane with the hydrogen atom pointing outward. To quan-
Molecular faces of (a) CH3F and (b) CH3Cl
D: electron density
No.5
1123
ZHANG Ming-Bo et al.: Evolution of the Molecular Face during the Reaction Process of F-+CH3Cl→CH3F+ClTable 1
Structure
Geometrical parameters (length in nm and angle in degree), vertical ionization potentials, Mulliken charges and
Dpb computed with CCSD(T)/aug-cc-pVDZ level
Geometrical parameters
r(F―C)
∠Cl―C―H
r(Cl―C)
r(H―C)
a
0.348
108.39
1.834
1.101
b
0.320
108.44
1.838
c
0.248
106.78
d
0.208
e
0.144
f
0.143
Mulliken charge/(a.u.)
I/(a.u.)
Dpb/(a.u.)
Cl
F
C
H
F―C
C―Cl
0.119
-0.263
-0.990
0.049
0.068
0.107
1.349
1.097
0.138
-0.279
-0.982
0.082
0.060
0.153
1.345
1.888
1.098
0.151
-0.392
-0.953
0.167
0.059
0.318
1.217
97.29
2.118
1.086
0.168
-0.691
-0.900
0.283
0.079
0.884
0.593
71.59
3.197
1.092
0.142
-0.980
-0.633
0.845
-0.077
1.774
0.229
71.45
4.197
1.087
0.136
-0.994
-0.606
0.777
-0.059
1.806
0.100
I: the first vertical ionization potential of the structure; Dpb: the depth of PAEM at the saddle point between two atoms
for structures (a-f) are listed in Table 2. Note that in the following discussion, we use F and Cl to represent fluorine and
chlorine element regardless of their true charged state for the
sake of simplicity.
For structure a, where r(C―F)=0.348 nm, the contour of F
keeps separated from that of CH3Cl, as shown in Fig.3(a). This
means that there exists a classical forbidden region for electron
movement between F and CH3Cl and electrons transfer from F
to CH3Cl is prohibited. An impressing feature of Fig.3(a) is
that the electron density on the F is evidently larger than that
on CH3Cl. D(Fout) is tens of times larger than D(Clout) as listed
in Table 1. This indicates that at this moment the extra electron
of system mainly locates on the F, which is supported by the
calculated Mulliken charge of F (-0.990 a.u.). Our calculations
show that r(Fin) is 0.016 nm longer than r(Fout), which means
that the contour of F expands towards CH3Cl and the interpolarization between F and CH3Cl has taken place.
As F approaches further to CH3Cl, forming the structure b,
where r(C―F)=0.320 nm, the MF of F begins to contact with
that of CH3Cl, as shown in Fig.3(b). It is evident that the contour of F is strongly polarized and swells towards CH3Cl. In the
structure b, the classical forbidden region between F and
CH3Cl disappears, so the electrons begin to flow between
them. This can be viewed as a starting point for the bond forming between F and CH3Cl. However, the electron density on F
region remains larger than CH3Cl, as reflected by the color of
MF. The Mulliken charge of F (-0.982 a.u.) still keeps close
to -1, which indicates that no evident electron transfer occurs
as yet.
Structure c is a prereaction complex formed between F and
Fig.2 Representative characteristic points employed to delineate
the shape and electron density evolutions of the reaction system
titatively demonstrate the changing features of molecular face,
we defined several parameters. Fig.2 is one of the C3v cut-plane
of the MFs of structure a. The C3v axis has four crossing points
with the MF of structure a, starting from left side of atom F, denoted by Fout, Fin, CF, and Clout in turn. In the case of structure f
(see Fig.3(f)), the corresponding four points are denoted by
Fout, CCl, Clin, and Clout. In the following, the distances from
these points to the corresponding nuclei and electron densities
on these points are employed to delineate the spatial and electron density variations of MF during the reaction course. For
example, the distance from the point of Fout to the fluorine nucleus is denoted by r(Fout), and the electron density on Fout is denoted by D(Fout).
3.3 Variations of MFs during the reaction course
The MFs of each structure (a-f) involved in the reaction
pathway are depicted in Fig.3(a-f), respectively. Representative charateristic distances and electron densities on the MFs
Table 2 Representative characteristic distances and electron densities on the MFs
Structure
r/nm
103D/(a.u.)
Fout
Fver
Clout
Clver
Cx
Xin
Fout
Fver
Clout
Clver
Cx
Xin
a
0.139
0.142
0.264
0.264
0.167
0.155
5.91
5.67
0.07
0.16
2.61
3.89
b
0.136
0.139
0.247
0.247
0.156
6.64
6.24
0.14
0.30
c
0.133
0.138
0.215
0.214
7.47
6.70
0.60
1.07
d
0.137
0.144
0.185
0.189
6.00
4.80
2.52
2.97
e
0.203
0.211
0.171
0.173
0.17
0.18
6.21
5.96
0.222
0.232
0.172
0.173
0.07
0.07
6.13
5.99
f
0.243
0.181
4.75
1.47
r: distance to the corresponding nucleus; Cx refers to the crossing point of MF of methyl group with the C3v axis for CH3X (X=F, Cl), Xin refers to the
crossing point of MF of X-with the C3v axis close to CH3X (X=F, Cl).
4.63
1124
Acta Phys. ⁃Chim. Sin. 2012
Vol.28
Fig.3 Variations of the MF through the reaction of F-+CH3Cl→Cl-+CH3F
CH3Cl. As shown in Fig.3(c), the contour of F has fused with
that of CH3Cl into a whole in structure c. The electron density
on the F region is still larger than that on the Cl region, as indicated by the color of MF of Fig.3(c). According to our calculations, D(Fout) is 7.473×10-3 a.u., much larger than D(Clout), being 0.594 × 10-3 a.u.. The Mulliken charges of Cl and F
are -0.392 and -0.953 a.u., respectively, which indicates that
the extra electron still locates on F atom by now.
Structure d is the transition state for the title reaction. As
shown in Fig.3(d), the electron density on the MF of F becomes evidently smaller than the previous structures, while
that of Cl becomes larger. This indicates that the extra electron
has transferred from F to Cl to a certain degree. But the color
of MF for F is still darker than that of Cl. In accord with this,
the Mulliken charge of F (-0.900 a.u.) is more negative than
that of Cl (-0.691 a.u.). Therefore, the electron transfer has only partly fulfilled at the transition state.
The most obvious changes of the MFs take places from
structure d to e, and the latter is the product complex of the reaction. The MF of e is shown in Fig.3(e). The conjoint part between F and C swells evidently with a 0.67 a.u. increasement
of r(Fver), while the region that between Cl and C shrinks inward with a 0.16 a.u. decreasement of r(Clver). At the same
time, the electron densities on the MF of F greatly decrease
dozens of times, and D(Fout) and D(Fver) decrease from 6.00 ×
10-3 and 4.80×10-3 a.u. to 0.17×10-3 and 0.18 ×10-3 a.u., respectively; while the electron densities on the MF of Cl greatly get
larger, as a result, D(Clout) and D(Clver) consumedly exceed the
corresponding D(Fout) and D(Fver). The Mulliken charge of Cl
(-0.980 a.u.) also becomes more negative than that of F
(-0.633 a.u.), which indicates that the extra electron of the system has almost totally transferred to Cl. This indicates that
there is strong bonding effect between F and C, and the bonding interaction of Cl and C gets weaker.
In structure f, the contour of Cl has separated with that of
CH3F completely as shown in Fig.3(f). Similar to the structure
a, a classical forbidden region for electron movement appears
between CH3F and Cl. There exists evident difference in the
electron densities on the MFs of CH3F and Cl. The electron
density of Cl region is much larger than that of the CH3F.
D(Fout) is 0.07 × 10-3 a.u., while D(Clout) is 6.13 × 10-3 a.u.. This
implies that the extra electron is totally localized in the region
of Cl, which is corroborated by the calculated Mulliken charge
of Cl (-0.994 a.u.).
It is also interesting to note that the volumes of F and Cl
change through the reaction process. In general, the volume of
F increases while that of Cl decreases. For instance, from structure a to f, r(Fver) increase from 0.142 to 0.232 nm; on the contrary, r(Clver) decreases from 0.264 to 0.173 nm. Essentially, the
molecular face is an iso-PAEM contour, and the variations in
atomic size reflect the changes of their electron density.
3.4 Variation of PEAM through the reaction
Essentially, chemical reaction is a process, in which electron
redistribution occurs among the reagents. So it is natural to describe a chemical reaction with the property of electrons in
molecules. Bader contributed distinctive work in this field with
atoms in molecule (AIM) theory, which has been widely used
to study bond forming/breaking with a certain extent of success.46
Bond-forming between two reagents means that they can
share their electrons with each other. That is to say, electrons
are permitted to shuttle between two atoms in case of bonding.
The PAEM is the potential felt by an electron in a molecule
and thus reflects the easiness for an electron moving from one
position to another. So the PAEM can be used as an indicator
for the bond strength between two atoms. Here, we calculated
the PAEM along the F ― C ― Cl axis for the six structures
shown in Fig.3, and the variations of the PAEM were depicted
in Fig.4. It can be seen that the PAEM at atomic nuclei is negatively infinite and rises sharply as the distance of electron to
the nucleus increases. This means that there exists a potential
well around each nucleus, which traps electrons around the vi-
No.5
ZHANG Ming-Bo et al.: Evolution of the Molecular Face during the Reaction Process of F-+CH3Cl→CH3F+Cl-
1125
Fig.4 Variations of the PAEM along the F―C―Cl axis through the reaction course
cinity of nuclei as much as possible. Our previous studies32
showed that the PAEM surface has a saddle point along a
chemical bond, and the energy gap from it to the energy level
of zero is defined as Dpb. Dpb has good linear correlations with
the force constant and bond length, and hence characterizes the
strength of chemical bond. The calculated Dpb for the structures
considered were listed in Table 1.
In structure a, F and CH3Cl are far from each other, the highest point of the PAEM between F and C atom is -0.1072 a.u.,
which is higher than the minus of the ionization potential
(-I=-0.119 a.u.). This implies that, at this moment, electrons
of each reagent are localized to itself and no exchange between
them is permitted. For structure b, the highest point of PAEM
between atoms F and C is -0.153 a.u., which is lower than the
corresponding -I (-0.138 a.u.). So from this point, electrons
are allowed to flow between two reagents and a chemical bond
begins to form between F and C. As two reagents get closer
gradually, viz. from structure c to f, the PAEM between F and
C lowers gradually, indicating that more electrons can shuttle
between two atoms and C―F bond is strengthened gradually.
In contrast, the PAEM between the leaving group Cl and C increases from -1.345 to -0.010 a.u. gradually as the reaction
proceeds, indicating that as the Cl ― C bond gets weaker and
weaker, the movement of electrons between them gets more
and more difficult and their previously shared electrons are getting localized to the region of each own. In terms of above descriptions, we can see that the PAEM can loyally reflect the
processes of bonding-forming and bond-breaking during the title reaction.
od, the shape changing and electron transfer during the reaction course of F-+ CH3Cl→Cl-+ CH3F are vividly presented. It
is found that the electron density mapped on the MFs of CH3F
and CH3Cl can soundly explain stereoselectivity for the attack
of a nucleophile. As F approaches CH3Cl, evident interpolarization effect is presented by the MFs. In addition, the variations
in electron density on the contours can well reflect the electron
transfer features, and the sizes of the nucleophile and leaving
groups are closely related to the reaction process. Investigations on the potential acting on an electron in a molecule
(PAEM) show that, as the reaction progresses, the PAEM gradually decreases between fluorine and carbon, while it gradually
increases between carbon and chlorine. This shed light on the
dynamic processes of bond-forming between F and C atoms
and bond-breaking between C and Cl atoms. The molecular
face model can loyally reflect the essential features of shape
evolution and electron transfer involved in a reaction. Both the
MF and PAEM can be utilized as a useful tool to describe the
dynamic progress of the title reaction.
References
(1)
1974, 96, 4030.
(2)
Conclusions
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