Dynamic 1H NMR studies of hindered internal rotations in the synthesized particular phosphorus ylide: Experimental and theoretical approaches

Article abstract of DOI:10.1016/j.saa.2015.02.084

Dynamic ¹H NMR measurements were performed within the synthesized particular phosphorus ylide involving 4-formylphenyl phenylcarbamate. Four rotational process and thereby parameters were targeted for rotation around the CC, C-C, HCNC and OCNC

Full text of DOI:10.1016/j.saa.2015.02.084

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
1
Dynamic H NMR studies of hindered internal rotations in the
synthesized particular phosphorus ylide: Experimental and theoretical
approaches
⇑
Sayyed Mostafa Habibi-Khorassani , Mehdi Shahraki, Malek Taher Maghsoodlou, Susan Erfani
Department of Chemistry, University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Two rotational isomers of the
synthesized ylide indicated
experimentally.
The barriers around the selected
bonds are obtained by the dynamic
1H NMR.
DFT and ab initio methods are
performed.
The calculated barriers confirmed the
experimental data.
20
TS
18
16
14
12
10
8
6
4
2
0
ꢀ
ꢀ
ꢀ
E-6
Z-6
180
-20
0
20
40
60
80
100
120
140
160
200
Dihedral Angle
a r t i c l e i n f o
a b s t r a c t
Dynamic 1H NMR measurements were performed within the synthesized particular phosphorus ylide
involving 4-formylphenyl phenylcarbamate. Four rotational process and thereby parameters were tar-
geted for rotation around the C@C, C-C, HCANC and OCANC bonds. The Gibbs free activation energy in
Article history:
Received 8 July 2014
Received in revised form 6 January 2015
Accepted 19 February 2015
Available online 9 March 2015
CDCl3,
D
G–exp, was found to be 64 2, 50 2, 41 2 and 63 2, respectively. These findings were compared
with related ab initio and DFT results on simulated situation. Theoretical methods tested, were comparable
to the present D 1H NMR data.
Keywords:
Ó 2015 Elsevier B.V. All rights reserved.
D
1H NMR
Rotational barrier
DFT
Ab initio
Ylide
Introduction
compounds has evoked considerable interest. Usually, the addition
of nucleophiles devoid of an acidic hydrogen atom leads to a 1:1
Multicomponent reactions (MCRs) by virtue of their conver-
gence, productivity, facile execution and generally high yields of
products have received great attention from combinatorial chem-
istry [1–5]. These reactions have gained more use in synthetic
organic chemistry [6–13]. The fascinating chemistry that stems
from the addition of nucleophiles to activated acetylenic
zwitterionic intermediate that can undergo further trans-
formations culminating in a stabilized product [14]. It is known
that groups such as triphenylphosphine, [15–17] pyridine,
[18–20] amines [21,22] and isocyanides [23] can invoke a zwit-
terions formation. Moreover, MCRs are important systems in
organic chemistry because of their application in the synthesis of
organic products [24–31], especially in the synthesis of phospho-
rus ylides and naturally occurring products with biological and
pharmacological attributes [32–34]. Some of the phosphorus ylides
exhibited the dynamic 1H NMR effect which provides good
⇑
Corresponding author. Tel./fax: +98 541 2446565.
E-mail address: smhabibi@chem.usb.ac.ir (S.M. Habibi-Khorassani).
http://dx.doi.org/10.1016/j.saa.2015.02.084
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

S.M. Habibi-Khorassani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
411
CO2Me
C
OHC
OH
C
O
C
Ph
N
PPh3 +
CO2Me
5
Et2O / n-hexane
H
Ph
H
O
N
Solvent free
r.t, 6h
4
O
N
C
C
O
Ph
+
C
r.t, 24h
P
P
O
OHC
MeO2C
h
CHO
3
CO2
Me
1
2
3
6
Fig. 1. The reaction between 4-hydroxybenzaldehyde 1 and phenylisocyanate 2 lead to carbamate 3, it was employed in the presence of triphenylphosphine 4 and dimethyl
acetylenedicarboxylate (DMAD) 5 for the synthesis of dimethyl-2-[4- formylphenyl phenylcarbamate-N-yl]-3-(triphenylphosphoranylidene) butandioate 6.
information regarding the interchangeable process of rotational
isomers, which in turn provides important kinetic data [35–42].
In the present work, reaction between 4-hydroxybenzaldehyde
structures were optimized using the ab initio and DFT methods
at the HF/6-31G (d,p) and B3LYP/6-31G (d,p) levels of theory by
the GAMESS program [43]. Then, relative energy versus dihedral
angles was plotted by scanning method at the HF/6-31G (d,p)
and B3LYP/6-31G (d,p) levels of theory, and all points in energy
profile were fully optimized.
1
and phenylisocyanate 2 leads to 4-formylphenyl phenyl-
carbamate 3 then the product is utilizes as an NH source in the pres-
ence of triphenylphosphine 4 and dimethyl acetylenedicarboxylate
(DMAD) 5 for the synthesis of dimethyl-2-[4-formylphenyl phenyl-
carbamate-N-yl]-3-(triphenylphosphoranylidene) butandioate 6 in
excellent yield (Fig. 1). The experimental data of 1H, 13C and 31P
NMR indicate two rotational isomers of ylide 6 with the major
Z-6 and minor E-6 forms. Herein, in order to further understand
the mechanism of the interchangeable process around the C@C,
CAC, HC–NC and OC–NC bonds, the rotational energy barrier
Experimental
To a magnetically stirred solution of 4-hydroxybenzaldehyde 1
(0.122 g, 1 mmol) and phenylisocyanate 2 under solvent-free con-
dition at 6 h obtained carbamate 3, then to a magnetically stirred
solution of compounds with triphenylphosphine (0.26 g, 1 mmol)
in 10 mL of dichloromethane, dimethyl acetylenedicarboxylate
(0.14 g, 1 mmol) was added drop wise over a period of 10 min at
room temperature. After approximately 24 h of stirring at room
temperature, the product was filtered and washed with cold
diethyl ether (3 Â 5 mL). Dimethyl-2-[4-formylphenyl phenyl-
(D
G–exp) obtained by the dynamic 1H NMR. The experimental data
was also compared with the theoretical rotational barrier (
calculated using the DFT and ab initio methods.
D )
G–calcd
Methods
carbamate-N-yl]-3-(triphenylphosphoranylidene) butandioate
6
Melting points and IR spectra of all compounds were measured
on an Electro thermal 9100 apparatus and a JASCO FT-IR spec-
trometer, respectively. The 1H, 13C, and 31P NMR spectra were
obtained with a Bruker DRX-500 and 400 Avance instrument using
CDCl3 and acetone-d6 as applied solvent TMS as internal standard
at (400.1, 100.6, 161.9 MHz), respectively. Elemental analyses for
C, H, and N were performed using a Heraeus CHN-O-Rapid ana-
lyzer. In addition, the mass spectra were recorded on an Agilent
Technologies 5973 mass spectrometer operating at an ionization
potential of 70 eV. Triphenylphosphine, dialkyl acetylenedicar-
boxylates and 4-formylphenyl phenylcarbamate were obtained
from Fluka and used without further purification. In order to deter-
mine theoretical hindered internal rotational in the rotational
interchangeable processes of the two Z- and E-isomers, first their
was obtained in excellent yield (Fig. 1). The mechanism of this
reaction has not been experimentally established; nevertheless
an illustrative mechanism is shown in Fig. 2.
The structure of compound 6 was deduced from elemental
analysis, IR, 1H, 31P, 13C NMR and mass spectroscopy and no other
product could be detected by NMR spectroscopy. The mass spec-
trum displayed a molecular ion peak at the appropriate m/z value.
Any initial fragmentations involve partial or complete loss of the
side chains and scission of the aromatic rings. The 1H, 13C and
31P NMR spectra of ylide 6 are consistent with the presence of
two isomers. The ylide moiety of this compound is strongly conju-
gated with the adjacent carbonyl group and the rotation around
the partial double bond in the two E-6 and Z-6 geometrical isomers
quite the reverse of rotation around the C@C bond (Fig. 3) and is
O
C
H
N
OH
O
CHO
O
N
Ph
C
C
O
Ph
NH
O
CO2Me
CHO
C
3
CHO
2
C
1
CHO
PPh3
4
+
O
CO2Me
Ph
C
5
N
O
H
PPh3
PPh3
6
CO2Me
CO2Me
CO2Me
CO2Me
Fig. 2. A plausible mechanism for the synthesized product 6.

412
S.M. Habibi-Khorassani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
CHO
CHO
CHO
CHO
O
N
O
N
O
N
O
N
O
C
MeO2C
O
MeO2C
C
O
C
MeO2C
C
MeO2C
O
MeO
O
O
MeO
O
O
H
H
H
H
PPh3
MeO
CHO
PPh3
PPh3
MeO
PPh3
Tc=233K
Tc=221 K
CHO
Z-6
Z-6
E-6
E-6
CHO
(e)
(d)
CHO
O
O
MeO2C
C
C
MeO2C
O
O
O
C
O
MeO2C
N
MeO2C
C
N
O
O
MeO
O
O
N
N
Ph
MeO
Ph
MeO
(c)
(a)
Ph
(b)
Ph
H
H
H
H
Tc=293 K
PPh3
O
Tc=293 K
PPh3
Tc=308 K
O
PPh3
MeO
PPh3
Z-6 Major
Z-6
E-6
E-6 minor
(f)
(g)
CHO
CHO
CHO
CHO
O
N
O
O
N
O
O
O
O
C
MeO2C
MeO2C
C
O
MeO2C
C
C
MeO2C
O
MeO
O
N
2
MeO
O
N
O
Ph
H
H
Ph
H
Ph
Ph
H
PPh3
MeO
PPh3
PPh3
Tc=203 K
PPh3
MeO
Tc=193 K
Z-6
E-6
Z-6
Fig. 3. Interchangeable processes of rotational isomers for the synthesized ylide 6.
E-6
slow on the NMR time scale at ambient temperature. Selected 1H,
13C and 31P NMR chemical shifts and coupling constants in the
major and minor geometrical isomers of product 6 are shown in
the below section.
Minor isomer E-6 (33%): 1H NMR (400.22 MHz, d, CDCl3): 3.13
3
and 3.92 (6H, 2s, 2 OCH3), 5.01 (1H, d, JPH = 20.0 Hz, P@CACH),
6.9–7.9 (23H, m, 3C6H5 and carbamate) 9.93 (1H, s, CHO). 13C
NMR (100.63 MHz, d, CDCl3): 48.98 and 49.55 (2s, 2 OCH3), 62.85
2
1
(d, JPC = 17.1 Hz, P@CACH), 126.52 (d, JPC = 92.2 Hz, Cipso),
3
4
127.87 (d, JPC = 12.1 Hz, Cmetha), 133.53 (d, JPC = 2.0 Hz, Cpara),
134.72 (d, JPC = 10.1 Hz, Cortho), 118.52, 125.04, 127.46, 126.12,
Dimethyl 2-[(4-formylphenyl)phenylcarbamate-N-yl]-3-
(triphenylphosphoranylidene)butandioate (6)
2
128.16, 133.27, 138.01 (7s, Carom), 152.08 (s, C,ArAO), 154.60 (s,
COcarbamat), 170.02 (d, 3JPC = 13.08 Hz, C@O), 173.84 (d,
2JPC = 14.08 Hz, PAC@C). 31P NMR (162.01 MHz, d, CDCl3): 24.78
[s, (Ph3P+-C)].
Orange powder, yeild: 0.61 g (95%), mp 127–129 °C. IR (KBr)
(
t
max, cmÀ1): 1745, 1712, 1644 (C@O).
Major isomer Z-6 (67%): 1H NMR (400.22 MHz, d, CDCl3): 2.92
3
and 3.83 (6H, 2s, 2 OCH3), 5.00 (1H, d, JPH = 20.0 Hz, P@CACH),
6.90–7.9 (23H, m, 3C6H5 and carbamate), 9.93 (1H, s, CHO). 13C
Results and discussion
1
NMR (100.63 MHz, d, CDCl3): 41.07 (d, JPC = 135.85 Hz, P@C),
52.40 and 52.71 (2s, 2 OCH3), 62.96 (P@CACH, JPC = 17.1 Hz),
125.34 (d, JPC = 91.6 Hz, Cipso), 128.67 (d, JPC = 12.1 Hz, Cmetha),
2
Dynamic effect for the E-6 and Z-6 rotational isomers as a result of
restricted rotational around the partial carbon–carbon double bond
(process a, C@C) (Fig. 3)
1
3
4
2
132.23 (d, JPC = 2.0 Hz, Cpara), 134.78 (d, JPC = 10.1 Hz, Cortho),
119.62, 125.14, 127.46, 128.14, 128.56, 131.39, 139.05 (7s, Carom),
152.65 (s, C, ArAO), 156.56 (s, C@Ocarbamat), 168.61 (d,
Two doublets (d = 5.03 and 5.04 ppm) are observed for the CH
protons of major and minor isomers of compound 6 in the 1H
NMR spectrum in CDCl3 solvent at ambient temperature which
3JPC = 13.08 Hz, C@O), 172.87 (d, JPC = 14.08 Hz, PAC@C). 31P
3
NMR (162.01 MHz, d, CDCl3): 24.78 [ s, (Ph3P+-C)].

S.M. Habibi-Khorassani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
413
Table 1
The key D 1H NMR data and related thermodynamic parameters of activation estimated for restricted rotational process and the related theoretical data around the carbon–
carbon double bond C@C.
Ea (kJ molÀ1
)
D
S– (kJ molÀ1 KÀ1
)
D
H– (kJ molÀ1
)
D
G– (kJ molÀ1
)
D
m
(Hz)
kc (sÀ1
)
Tc (K)
Exprimentali
Theoreticalj
Theoreticalk
–
–
–
64
75.00
68.93
2
48
–
–
107.56
–
–
308
308
308
72.21
64.92
À0.017
69.65
62.36
À0.021
i
j
Data obtained from the 1H NMR study.
Data obtained using ab initio method at HF/6-31G (d,p) level of theory.
Data obtained using DFT method at B3LYP/6-31G (d,p) level of theory.
k
appear as a broad doublet near 298 K. From the coalescence tem-
perature of the proton resonances of the CH group and using the
equation for the rate constant, the first-order rate constant (k)
was calculated for the bond rotation in product 6 as 107.56 sÀ1
at 308 K. For this process, activation and kinetic parameters involv-
20
18
16
14
12
10
8
TS
ing kc and
D D
G–exp and other activation parameters such as Ea, H–
and
D
S– calculated for ylide 6 are accumulated in Table 1. In order
to determine the theoretical rotational energy barrier in the rota-
tional interchangeable process (a) of the two Z- and E isomers in
the ylide 6, their structures were first optimized at the HF/6-31G
(d,p) and B3LYP/6-31G (d,p) levels of theory [44–47]. Then, the scan-
ning method was employed at the same levels with a change in dihe-
dral angle (OCCP) on the basis of 4 degrees rotation in each step. This
gave the relative energy at each point in accord with 4 degrees
rotation in a fully optimized process. Fig. 4 showed the optimized
structures corresponding to the E-6, Z-6 isomers and TS. Then, the
corresponding relative energies were plotted versus the dihedral
angle (OCCP, Fig. 5). As can be seen in Fig. 5, a transition state (TS)
has appeared at the top of this plot. Frequency calculations were
employed for all states involving TS and the first negative frequency
value (À70.93 and À71.25 Hz at HF/6-31G (d,p) and B3LYP/6-31G
(d,p) levels, respectively) could be considered as good proof in con-
firming the TS structure. With respect to the relative energies
obtained from Fig. 5, and relevant equations [35,40], values of Ea,
6
4
2
Z-6
E-6
0
-50
0
50
100
Dihedral Angle
150
200
Fig. 5. Profile of relative energy in restricted rotational process around the C@C
bond for the ylide 6 versus dihedral angel (OCCP) at the B3LYP/6-31G (d,p) level.
Dynamic effects for the rotational around the carbon–carbon single
bonds (processes b and c, H–C–C–PPh3) (Fig. 3)
Herein, when the temperature was reduced with respect to the
ambient temperature, the 1H NMR spectrum of the Z-6 isomer in
CDCl3 at +5 °C showed a resonance arising from the methoxy pro-
ton (HACACAP, 3JPH) which is broad in comparison with a
corresponding doublet that was measured at the ambient tempera-
ture. When temperature was considerably reduced, the methoxy
proton coalesces near the 296 K and a sharp signal resonance at
298 K, which is related to the rotational process around the car-
bon–carbon single bond (HACACAPPh3) in the Z-6 isomer. The
experimental data are reported in Table 2. It must be mentioned
that the methoxy protons of E-6 isomer coalescence near 291 K
and appear as a sharp signal resonance at 293 K (Fig. 3, process
b). These values are also reported in Table 2. In addition, as men-
tioned in the previous section, theoretical studies were investi-
gated on the basis of rotation around the carbon–carbon single
D
H–, G–, S– were calculated for the restricted rotational process
D D
(a) around the C@C double bond at the HF/6–31G (d,p) and B3LYP/6–
31G (d,p) levels of theory. Results are accumulated in Table 1 along
with the experimental data that has been obtained from the dynamic
1H NMR effects at the experimental temperature of 308 K. The
results indicated that there is a good agreement between the experi-
mental rotational energy barrier (
at the B3LYP/6-31G (d,p) level (
D
D
G–exp = 64 2) and those obtained
G–calcd = 68.93). It seems that the
B3LYP/6-31G (d,p) is a suitable level for the calculation of restricted
rotational process (a) around the C@C double bond in a huge mole-
cule like the ylide 6 with large atoms such as 6 oxygen, 1 nitrogen
and 1 phosphorus atoms and a large number of other atoms.
TS
Z-6
E-6
Fig. 4. Optimized structures corresponding to the E-6, Z-6 isomers and TS.

414
S.M. Habibi-Khorassani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
Table 2
The key D 1H NMR data and related thermodynamic parameters of activation estimated for rotational process and the related theoretical data around the carbon–carbon single
bond C–C.
Ea (kJ molÀ1
)
D
S– (kJ molÀ1 KÀ1
)
D
H– (kJ molÀ1
)
D
G– (kJ molÀ1
)
D
m
(Hz)
kc (sÀ1
)
Tc (K)
Exprimentali
Exprimentalj
Theoreticalk
Theoreticall
–
–
–
–
–
–
41
39
78.93
48.10
2
2
44
44
–
98.68
89.71
–
203
193
203
203
79.14
47.51
À0.005
77.46
45.82
À0.011
–
–
i
j
Data obtained from the 1H NMR study for Z-6.
Data obtained from the 1H NMR study for E-6.
Data obtained using ab initio method at HF/6-31(d,p) level of theory for Z-6.
Data obtained using DFT method at B3LYP/6-31G (d,p) level of theory for Z-6.
k
l
14
12
TS3
10
TS1
8
6
4
2
TS2
GS
0
-150
-100
-50
0
50
100
150
200
250
-2
Dihedral Angle
Fig. 6. Profile of relative energy in rotational process around the C–C bond for the Z-6 versus dihedral angel (CCCP) at the B3LYP/6-31G (d,p) level.
Table 3
The key D 1H NMR data and related thermodynamic parameters of activation estimated for rotational process and the related theoretical data around the nitrogen–carbon single
bonds HC–NC.
Ea (kJ molÀ1
)
D
S– (kJ molÀ1 KÀ1
)
D
H– (kJ molÀ1
)
D
G– (kJ molÀ1
)
D
m
(Hz)
kc (sÀ1
)
Tc (K)
Exprimentali
Exprimentalj
Theoreticalk
Theoreticall
88.79
27.30
24.04
37.98
0.140
87.77
26.47
22.10
36.04
50
47
29.62
40.76
2
2
12
16
–
26.91
35.88
–
233
221
233
233
À0.098
À0.330
À0.020
–
–
i
j
Data obtained from the 1H NMR study for Z-6.
Data obtained from the 1H NMR study for E-6.
k
l
Data obtained using ab initio method at HF/6-31 (d,p) level of theory for Z-6.
Data obtained using DFT method at B3LYP/6-31G (d,p) level of theory for Z-6.
bond in the Z-6 isomer (HACACAPPh3, process b) using the HF/6-
31G (d,p) and B3LYP/6-31G(d,p) levels of theory. Then, relative
energies were plotted against dihedral angle (CCCP, Fig. 6). As
can be seen in Fig. 6, three transition states (TS1, TS2 and TS3) with
negative frequency values had been appeared on the tops of this
single bond (HCANC) only for Z-6 isomer at the HF/6-31G (d,p)
and B3LYP/6-31G(d,p) levels of theory. Then, relative energy versus
dihedral angle (CNCC) was plotted in Fig. 7. As can be seen, three
transition states (TS1, TS2 and TS3) have appeared on this plot.
Frequency calculations were employed for all TSs and ground
states and TS structures were confirmed. Rotational energy barrier
plot. Rotational energy barriers (D
G–calcd) at TSs points exhibited that
TS3 has a higher value; hence, this process was chosen as a main
rotational barrier. All theoretical calculations are reported in
Table 2. As can be seen, the B3LYP/6-31G (d,p) is a better level than
HF/6-31G (d,p).
(D
G–calcd) for all TSs exhibited that TS2 has a higher value and hence
TS2 was chosen as a main rotational barrier. Theoretical data
G–calcd) reported in Table 3 indicate that there is a good agreement
between the experimental rotational barrier and the
G–exp
obtained data at B3LYP/6-31G (d,p) level of theory.
(D
(
D
)
Dynamic effects for the restricted rotational around the nitrogen–
carbon single bonds (processes d and e, N–C–COOCH3) (Fig. 3)
Dynamic effects for the restricted rotational around the carbon–
nitrogen single bond (processes f and g, OC–NC) (Fig. 3)
More investigations were made for the rotation around the car-
bon–nitrogen single bonds in the Z-6 and E-6 isomers and the
results are summarized in Tables 3. The same procedure was
employed as in the previous sections and theoretical study was
investigated on the basis of rotation around the carbon–nitrogen
Through investigation of the 1H NMR spectra of product 6, the
dynamic 1H NMR effect has been observed which is attributed to
restricted rotational process around the carbon–nitrogen bond
(Fig. 3, processes f and g) the experimental data are accumulated

S.M. Habibi-Khorassani et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 145 (2015) 410–416
415
TS2
TS1
TS3
GS
Dihedral Angle
Fig. 7. Profile of relative energy in rotational process around the HC–NC bond for the Z-6 versus dihedral angel (CNCC) at the B3LYP/6-31G (d,p) level.
Table 4
The key D 1H NMR data and related thermodynamic parameters of activation estimated for rotational process and the related theoretical data around the nitrogen–carbon single
bond OC–CN.
Ea (kJ molÀ1
)
D
S– (kJ molÀ1 KÀ1
)
D
H– (kJ molÀ1
)
D
G– (kJ molÀ1
)
D
m
(Hz)
kc (sÀ1
)
Tc (K)
Exprimentali
Exprimentalj
Theoreticalk
Theoreticall
51.38
54.54
29.57
37.07
0.012
0.011
58.99
62.18
27.11
34.61
63
63
40.80
49.18
2
2
24
20
–
53.82
44.85
–
296
291
296
296
À0.046
À0.049
–
–
i
j
Data obtained from the 1H NMR study for Z-6.
Data obtained from the 1H NMR study for E-6.
Data obtained using ab initio method at HF/6-31G (d,p) level of theory for Z-6.
Data obtained using DFT method at B3LYP/6-31G (d,p) level of theory for Z-6.
k
l
TS2
TS1
GS
Dihedral Angle
Fig. 8. Profile of relative energy in rotational process around the OC–NC bond for the Z-6 versus dihedral angel (CNCO) at the B3LYP/6-31G (d,p) level.
in Table 4. The same procedure was employed as previous sections.
Then, relative energy versus dihedral angle (OCNO) was plotted in
Fig. 8. As can be seen, two transition states (TS1 and TS2) have
appeared on this plot. As a result, all theoretical data with respect
to TS1 reported in Table 4. Herein, B3LYP/6-31G (d,p) was also
recognized as a suitable level.
The experimental and theoretical data, taken together, indi-
cated that the rotational energy barrier around the C@C bond is
considerably high, and observation of the two rotational isomers,
E-6 and Z-6, is impossible (seen as a single isomer) at high tem-
perature, since the rate of rotation (k = 107.56 SÀ1) around the
C@C bond is too fast on the NMR time scale. Herein, the B3LYP/
6-31G (d,p) level was recognized as a suitable level. It seems that
employment of the DFT method is more preferable than the ab ini-
tio method for a huge molecule like the ylide 6 that suffers from
crowds of atoms during the interchangeable rotational processes.
Application of a solvent in the presence of a huge molecule caused
so many complications that it became an unsuccessful perfor-
mance. In total, our attempts failed to employ solvents media.
Under this condition (huge molecules with a large number of
Conclusion
Four rotational processes around the C@C, CAC, HCANC and
OCANC bonds were investigated using dynamic 1H NMR and theo-
retical calculations at the HF/6-31G (d,p) and B3LYP/6-31G(d,p)
levels of theory.

416
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Acknowledgments
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We gratefully acknowledge financial support from the Research
Council of the University of Sistan and Baluchestan.
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.02.084.
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