X-ray crystallographic, spectroscopic and quantum chemical studies on ethyl 2-cyano-3-N,N-dimethyl amino acrylate

Article abstract of DOI:10.1016/j.saa.2006.11.021

Structural and spectral characteristics of ethyl 2-cyano-3-N,N-dimethyl amino acrylate have been studied by methods of X-ray crystallography, infrared spectroscopy and quantum chemistry. The compound crystallizes in monoclinic space group P2₁/n

Full text of DOI:10.1016/j.saa.2006.11.021

Spectrochimica Acta Part A 68 (2007) 237–243
X-ray crystallographic, spectroscopic and quantum chemical
studies on ethyl 2-cyano-3-N,N-dimethyl amino acrylate
a,∗
a
b
b
V.P. Gupta , Archna Sharma , Dinesh , Rajnikant
a
Spectroscopy Laboratory, Department of Physics, University of Jammu, Jammu-Tawi 180006, India
b
X-ray Crystallography Laboratory, Department of Physics, University of Jammu, Jammu-Tawi 180006, India
Received 17 July 2006; received in revised form 3 November 2006; accepted 17 November 2006
Abstract
Structural and spectral characteristics of ethyl 2-cyano-3-N,N-dimethyl amino acrylate have been studied by methods of X-ray crystallography,
˚
infrared spectroscopy and quantum chemistry. The compound crystallizes in monoclinic space group P2 /n with unit cell parameters a = 4.26(1) A,
1
◦
˚
˚
b = 11.16(1) A, c = 19.63(3) A and β = 95.5(1) . The X-ray based three-dimensional structure analysis has been carried out by direct methods and
fully refined. Density functional theory calculations for potential energy curves, optimized geometries and vibrational spectra have been carried
out using 6-31G and 6-31G** basis sets and B3LYP functionals. These suggest the possibility of existence of two structural isomers for the
molecule—a more stable s-cis and a less stable s-trans isomer, having enthalpy difference of 2.85 kcal/mol. The optimized molecular geometry is
in agreement with experimental geometry from X-ray analysis and suggests a preferential s-cis conformation for the molecule in the solid state.
Based on experimental and theoretical studies, it may be concluded that the molecule has an almost planar conformation with the cyanide group
◦
also lying in the molecular plane; the deviation from planarity does not exceed 3 . The structure is stabilized by the presence of intra-molecular
and inter-molecular interactions.
©
2007 Published by Elsevier B.V.
Keywords: X-ray crystallography; Ab initio calculations; 2-Cyanoacrylate; Conformational analysis; Physico-chemical parameters; Infrared spectra; Vibrational
analysis
1
. Introduction
-Cyanoacrylates and their derivatives have received con-
of an analogous molecule ethyl 2-cyano-3-N,N-dimethyl amino
acrylate by experimental and theoretical methods of X-ray crys-
tallography, infrared spectroscopy and quantum chemistry. A
complete analysis of the vibrational spectra using density func-
tional theory (DFT) is also being provided.
2
siderable attention recently [1–5] because of their versatile
biological activity and the possibility of application in agro-
chemistry. Some of the 2-cyanoacrylates are also known to
exhibit Hill inhibitory activity [3]. Song et al. [1] have reported
anti-cancer bioactivity in some 2-cyano-3,3-dimethyl thioacry-
lates for which they carried out detailed spectroscopic and
structural studies using methods of infrared spectroscopy, NMR
and X-ray crystallography. It is inferred that molecules like ethyl
2. Methodology
2.1. Experimental methods
The synthesis of ethyl 2-cyano-3-N,N-dimethyl amino acry-
2-cyano-3,3-dimethyl thio acrylate maintain a planar structure
late has been carried out by making an equimolar mixture
of ethylcyanoacetate and N,N-dimethyl formamide dimethy-
lacetate, which was refluxed in methanol for about 2–5 h and
cooled. The solvent was removed by rotatory evaporation. The
semi-solid mass was obtained and recrystallized from n-hexane.
Transparent needle shaped crystal (dimensions: 0.30 mm ×
due to strong hydrogen bonding. In the present communication,
we are reporting a detailed study of the three-dimensional struc-
ture, physico-chemical properties and spectral characteristics
∗
Corresponding author at: Macromolecular Laboratory, Department of
0
.15 mm × 0.10 mm) of grown material was mounted on the
Physics, University of Lucknow, Lucknow 226 007, UP, India.
Tel.: +91 522 2735874; fax: +91 522 2740840.
goniometeroftheCAD4singlecrystaldiffractometer. Thethree-
E-mail address: vpgpt1@yahoo.co.in (V.P. Gupta).
dimensional data has been collected by using Mo K␣ radiation
1
386-1425/$ – see front matter © 2007 Published by Elsevier B.V.
doi:10.1016/j.saa.2006.11.021

2
38
V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
Table 1
Crystal data and structure refinement for ethyl 2-cyano-3-N,N-dimethyl amino
acrylate
Empirical formula
Formula weight
Temperature
C8H12N2O2
168.20
293(2) K
0.71073 A˚
Wavelength
Crystal system, space group
Monoclinic, P21/n
Unit cell dimensions
a = 4.258(5) A˚ , α = 90
◦
b = 11.163(12) A˚ , β = 95.50(11)
c = 19.632(30) A˚ , γ = 90
◦
◦
928.8(21) A˚ 3
4, 1.203 Mg/m
Volume
Z, calculated density
F(0 0 0)
θ range for data collection
Limiting indices
Reflections collected/unique
Refinement method
Data/restraints/parameters
Fig. 1. Numbering scheme of atoms of ethyl 2-cyano-3-N,N-dimethyl amino
acrylate with displacement ellipsoids drawn at 50% probability level.
3
360
2.10–24.99
◦
◦
(
λ = 0.71073) in the θ range of 2.10–24.99 by using ω/2θ scan
0 ≤ h ≤ 5, 0 ≤ k ≤ 13, −23 ≤ l ≤ 23
1807/1595
mode. A total of 1747 reflections were recorded, out of which
545 were found unique (index range: 0 ≤ h ≤ 5, 0 ≤ k ≤ 13,
Full-matrix least-squares on F2
1573/0/140
1
−
23 ≤ l ≤ 23) and 889 were treated as observed [F0 > 4σ(F0)].
2
Goodness-of-fit on F
Final R indices [F0 > 4σ(F0)]
R indices (all data)
1.069
Two standard reflections (1, −2, −1) and (1, −3, 3), measured
after every 100 reflections, showed no significant variation in the
intensity data. The data were corrected for Lorentz and polar-
ization effects. Absorption and extinction corrections were not
applied.
R1 = 0.0938, wR2 = 0.2357
R1 = 0.1475, wR2 = 0.3933
0.327 and −0.318 einstein A˚
−
3
Largest diff. peak and hole
suggested by Yoshida et al. [8] using the expression:
The structure determination of the title compound has
been carried out by direct methods using SHELXS software
ν
= (1.0087 − 0.0000163νcalc.) νcalc.
obs.
[
6]. Full-matrix least-squares refinement were carried out by
All calculations were performed by using computer software
Gaussian 98W [9] and the vibrational modes were analyzed by
using the software GaussView [10].
using SHELXL software [7]. Refinement of the positional and
isotropic thermal parameters of non-hydrogen atoms led to the
reliability-factor of 0.215. Few more cycles of refinement with
anisotropic thermal parameters reduced the R-factor. The final
cycles of refinement with stereo-chemical fixation of hydro-
gen atoms converged the R-factor at 0.095. The maximum and
3. Results and discussion
minimum value for the residual electron density is 0.32 and
3.1. Structural studies
2
−
0.35, respectively. The goodness-of-fit on F was 1.0516. The
−
1
infraredspectrumofthesampleinthe4000–400 cm rangewas
recorded in the KBr pellet on FT-IR spectrophotometer Bruker
Vector 22.
The crystallographic data for ethyl 2-cyano-3-N,N-dimethyl
amino acrylate (CAAC) are summarized in Table 1. The final
fractional coordinates and equivalent isotropic displacement
parameters for non-hydrogen atoms are presented in Table 2.
Potential energy curve (Fig. 2) for internal rotation of the
molecule about C1 C2 bond, as obtained from DFT/6-31G
quantum chemical calculations, shows two energy minima at
2
.2. Computational methods
In order to verify the possibility of rotational isomerism in
ethyl 2-cyano-3-N,N-dimethyl amino acrylate (CAAC), poten-
tial energy curve for asymmetric torsion about C1 C2 bond
Table 2
Atomic coordinates and equivalent isotropic displacement parameters for non-
hydrogen atoms in ethyl 2-cyano-3-N,N-dimethyl amino acrylate
(
Fig. 1) was obtained by calculating the variation in the
total energy of the molecule with change in dihedral angle
◦
◦
ϕ(O1C1C2C3) in intervals of 20 in the range of 0–360 by
DFT/6-31G method. Geometries of the stable conformers of the
molecule were optimized by density functional theory (DFT)
using 6-31G** basis set and Becke’s three parameter (local,
non-local, Hartree–Fock) hybrid exchange functionals with
Lee–Yang–Parr correlational functional (B3LYP). The vibra-
tional spectra of the two stable conformers of CAAC were
calculated by DFT/6-31G**, using the optimized geometries
obtained by the same method and basis set. Since the DFT vibra-
tional frequencies are known to be higher than the experimental
frequencies due to neglect of anharmonicity effects, they were
scaled down by wavenumber linear scaling (WLS) procedure
Atom
x
y
z
U (equiv.)
O1
O2
N1
N2
C1
C2
C3
C4
C5
C6
C7
C8
5414(10)
5555(8)
6569(3)
7866(3)
4202(3)
6841(4)
6825(4)
6101(4)
5030(4)
4251(4)
3127(5)
6502(4)
8649(5)
9755(7)
4704(2)
3846(2)
3560(2)
2385(3)
4120(3)
3626(2)
3869(2)
2853(2)
3932(3)
2944(3)
4322(3)
3945(5)
0.084(1)
0.069(1)
0.055(1)
0.083(1)
0.058(1)
0.052(1)
0.052(1)
0.065(1)
0.074(2)
0.057(1)
0.085(2)
0.127(3)
−138(9)
1869(11)
4666(11)
2762(10)
1638(10)
−1385(11)
−910(17)
2219(10)
7399(16)
8082(29)

V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
239
Table 3
Bond lengths ( A˚ ) and bond angles ( ) of ethyl 2-cyano-3-N,N-dimethyl amino
◦
acrylate
Experimental
Calculated
s-Cis
s-Trans
1.2148
O1 C1
O2 C1
O2 C7
N1 C3
N1 C4
N1 C5
N2 C6
C1 C2
C2 C3
C2 C6
C7 C8
C3 H3
C4 H4A
C4 H4B
C4 H4C
C5 H5A
C5 H5B
C5 H5C
C7 H7A
C7 H7B
C8 H8A
C8 H8B
C8 H8C
C1 O2 C7
C3 N1 C4
C3 N1 C5
C4 N1 C5
O1 C1 O2
O1 C1 C2
O2 C1 C2
C1 C2 C3
C1 C2 C6
C3 C2 C6
N1 C3 C2
N2 C6 C2
O2 C7 C8
N1 C3 H3
C2 C3 H3
N1 C4 H4A
N1 C4 H4B
N1 C4 H4C
N1 C5 H5A
N1 C5 H5B
N1 C5 H5C
O2 C7 H7A
O2 C7 H7B
C7 C8 H8A
C7 C8 H8B
C7 C8 H8C
1.1948(63)
1.3499(56)
1.4537(69)
1.3062(56)
1.4398(62)
1.4583(74)
1.1559(70)
1.4491(62)
1.3886(62)
1.4113(66)
1.4830(109)
0.9967(507)
0.9600(64)
0.9601(72)
0.9600(65)
0.9095(849)
0.9567(793)
0.9975(794)
0.9700(89)
0.9699(97)
1.0515(653)
0.8981(719)
1.0338(1698)
114.58(37)
124.38(39)
119.86(41)
115.74(41)
121.97(43)
126.09(45)
111.94(37)
116.05(38)
119.26(40)
124.67(40)
130.73(41)
177.92(52)
107.45(52)
112.35(2.82)
116.90(2.89)
109.48(0.50)
109.48(0.50)
109.48(0.50)
111.73(5.27)
116.05(4.74)
108.88(4.64)
110.23(0.67)
110.23(0.63)
101.46(3.80)
115.54(5.11)
81.90(9.69)
1.2207
1.3486
1.4449
1.3416
1.4598
1.4589
1.1667
1.4812
1.3803
1.4212
1.5163
1.0871
1.0860
1.0964
1.0964
1.0908
1.0966
1.0966
1.0946
1.0946
1.0945
1.0935
1.0935
116.00
125.82
119.81
114.37
123.50
124.79
111.78
114.80
119.09
126.11
132.97
179.49
107.49
114.20
112.82
111.27
109.73
109.69
110.20
110.42
110.40
108.87
108.85
109.79
110.91
110.91
1.3629
1.4444
1.3448
1.4599
1.4585
1.1658
1.4792
1.3806
1.4244
1.5166
1.0843
1.0856
1.0965
1.0965
1.0968
1.0966
1.0906
1.0943
1.0942
1.0943
1.0940
1.0940
Fig. 2. Potential energy curve of ethyl 2-cyano-3-N,N-dimethyl amino acry-
late for rotation about C1 C2 bond. The abscissa is the angle of rotation
about C1 C2 bond relative to the s-cis conformer for which the dihedral angle
ϕ(O1C1C2C3) = 0 . The ordinate represents total energy relative to the s-cis
conformation.
◦
◦
◦
ϕ(O1C1C2C3) = 0 and 180 . These correspond to the s-cis and
s-trans conformations of the molecule in which the C1 O1
and C2 C3 bonds are either on the same side or on opposite
sides of the C1 C2 bond (Fig. 1). It may thus be inferred that
the molecule can exist in two rotameric conformations s-cis
and s-trans; with the former being more stable than the lat-
ter. More accurate DFT calculations using 6-31G** basis set
show after complete geometry optimization that the total ener-
gies of the s-cis and s-trans conformers are −572.03280344 and
115.31
126.12
119.75
114.12
122.88
124.27
112.83
119.79
114.74
125.47
132.65
179.49
107.49
113.18
114.17
111.36
109.73
109.58
110.47
110.41
110.32
108.93
108.92
109.81
111.04
111.02
−
572.02826294 Hartree, respectively. The s-cis conformer is,
therefore, more stable than s-trans by 2.850 kcal/mol. Further,
it is found that the s-cis conformer has to overcome a rotational
barrier of 19.496 kcal/mol to change into the s-trans conformer.
A rotational barrier of 17.638 kcal/mol has to be overcome for
the reverse process. Due to high barrier to internal rotation, the
molecule therefore prefers the lower energy s-cis conformation.
This result is confirmed by X-ray crystallographic data which
indicates the presence of only the more stable s-cis conformer in
the crystalline state. A similar observation about preference for
a s-cis conformation has been made by Song et al. [1] in some
other 2-cyanoacrylates.
The results of X-ray single crystal analysis and the optimized
geometries of the s-cis and s-trans conformers of CAAC are
given in Tables 3 and 4. Table 5 contains the optimized values of
the dihedral angles involving hydrogen atoms. It follows from
these tables that there is no significant difference in the molecu-
lar geometries of the s-cis and s-trans conformers; the maximum
◦
˚
difference in bond lengths and bond angles being 0.01 A and 5 ,
respectively. The experimental values of these parameters agree
E.s.d. values are given in parenthesis.
◦
˚
with the optimized values within 0.03 A and 2 , respectively,
for bonds between non-hydrogen atoms. The experimental val-
ues of the dihedral angles between non-hydrogen atoms agree
lar plane. Further, it is observed that significant changes occur
in the lengths of bonds C1 O1, C1 C2, C2 C3, C3 N1 and
C1 O2 with respect to their normal values as covalent single
and double bonds. This indicates delocalization of electron den-
sity along the chain N1–C3–C2–C1–O1, which is confirmed by
Mulliken population analysis given in Table 6. A similar obser-
vation has been reported by Song et al. [1] in the case of other
2-cyanoacrylates.
◦
with the optimized values for the s-cis conformer within 3 and
show that in the crystalline state the molecule exists in the s-
cis form. The optimized as well as experimental values of the
dihedral angles between non-hydrogen atoms have values close
◦
◦
to 0 or 180 and suggest an almost planar conformation of
the molecule with the cyanide group also lying in the molecu-

2
40
V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
Table 4
Table 6
Dihedralanglesfornon-hydrogenatomsinethyl2-cyano-3-N,N-dimethylamino
acrylate
Atomic population density and dipole moments of s-cis and s-trans conformers
of ethyl 2-cyano-3-N,N-dimethyl amino acrylate
Experimental
Calculated
Atom no.
s-Cis
s-Trans
s-Cis
s-Trans
Total
charge
Net atomic
charge
Total
charge
Net atomic
charge
C7 O2 C1 O1
C7 O2 C1 C2
C1 O2 C7 C8
C4 N1 C3 C2
C5 N1 C3 C2
O1 C1 C2 C3
O1 C1 C2 C6
O2 C1 C2 C3
O2 C1 C2 C6
C1 C2 C3 N1
C6 C2 C3 N1
−1.61(0.66)
178.29(0.40)
−178.27(0.55)
−0.48(0.76)
178.02(0.50)
2.17(0.71)
−176.71(0.47)
−177.73(0.38)
3.39(0.59)
0.02
−179.97
−179.82
0.12
179.89
0.00
180.00
180.00
−0.01
−180.00
0.00
0.00
180.00
179.34
0.05
179.44
179.84
−0.10
−0.15
179.90
179.88
−0.18
O1
O2
N1
N2
C1
C2
C3
C4
C5
C6
C7
C8
8.524
8.849
7.414
7.537
5.356
6.036
5.829
6.178
6.199
5.726
5.942
6.339
0.850
0.863
0.869
0.869
0.833
0.871
0.870
0.883
0.883
0.893
0.874
0.874
−0.524
−0.489
−0.414
−0.537
0.642
8.494
8.514
7.414
7.529
5.363
6.045
5.832
6.176
6.199
5.712
5.936
6.342
0.857
0.869
0.868
0.868
0.831
0.871
0.871
0.879
0.878
0.886
0.883
0.833
−0.494
−0.514
−0.414
−0.529
0.637
−0.036
−0.045
0.171
0.168
−0.178
−0.199
0.274
−0.176
−0.199
0.288
179.12(0.46)
−2.07(0.79)
0.058
0.064
−0.339
−0.342
H3
0.150
0.143
3
.2. Atomic population density, dipole moment and
H4A
H4B
H4C
H5A
H5B
H5C
H7A
H7B
H8A
H8B
H8C
0.137
0.131
0.131
0.167
0.129
0.130
0.117
0.117
0.131
0.132
0.132
0.169
0.129
0.129
0.121
0.122
hydrogen bonding
The atomic population densities for the s-cis and s-trans
conformers of CAAC based on Mulliken analysis are given
in Table 6, which also contains the calculated dipole moments
of the two conformers. It may be noted that the oxygen atoms
O1 and O2 have large net negative charge −0.524 and −0.489
and the adjoining carbon atom C1 has a large net positive
charge 0.642. Similarly, the nitrogen atoms N1 and N2 also have
large negative charge −0.414 and −0.537, respectively. Being
attached to more electronegative carbon atoms, all the hydro-
gen atoms have a net positive charge; in particular, the hydrogen
atoms H3, H4A and H5A have significantly large net positive
charge 0.150, 0.137 and 0.167. The presence of large amounts of
negative charge on O1, O2 and N2 atoms and net positive charge
0.107
0.126
0.126
0.114
0.117
0.117
Dipole moment (Debye)
4.655
8.106
on H3, H4A and H5A atoms may suggest the presence of both
inter-molecular as well as intra-molecular hydrogen bonding in
the crystalline phase.
The analysis of inter-molecular hydrogen interactions is
shown in Fig. 3. In agreement with the quantum chemical predic-
tions, the X-ray diffraction study suggests that atom O1 is related
Table 5
Dihedral angles for hydrogen atoms in ethyl 2-cyano-3-N,N-dimethyl amino
acrylate
s-Cis
58.60
s-Trans
C1 O2 C7 H7A
C1 O2 C7 H7B
C4 N1 C3 H3
C5 N1 C3 H3
C3 N1 C4 H4A
C3 N1 C4 H4B
C3 N1 C4 H4C
C5 N1 C4 H4A
C5 N1 C4 H4B
C5 N1 C4 H4C
C3 N1 C5 H5A
C3 N1 C5 H5B
C3 N1 C5 H5C
C4 N1 C5 H5A
C4 N1 C5 H5B
C4 N1 C5 H5C
C1 C2 C3 H3
C6 C2 C3 H3
O2 C7 C8 H8A
O2 C7 C8 H8B
O2 C7 C8 H8C
−59.08
57.74
−58.24
−179.89
−0.12
−180.00
−0.61
−1.26
119.40
−121.87
179.33
−60.01
58.71
−0.50
120.11
121.08
179.72
−59.67
59.13
0.21
0.95
−120.00
120.40
−179.98
59.81
119.27
121.15
−179.59
60.18
−59.40
−0.07
179.87
180.00
60.35
−59.79
0.01
−179.99
−179.89
60.27
−60.05
Fig. 3. Inter-molecular hydrogen interactions in ethyl 2-cyano-3-N,N-dimethyl
amino acrylate.
−60.35

V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
241
Table 7
Inter- and intra-molecular hydrogen bonds in ethyl 2-cyano-3-N,N-dimethyl amino acrylate
Donor
H
Donor· · ·acceptor
H· · ·acceptor
Donor H· · ·acceptor
(
a) Inter-moleculara
b
C5 H5A
C3 H3
C4 H4A
C5· · ·O1: 3.40(1) (weak)
C3· · ·O1: 3.45(1) (weak)
C4· · ·N2: 3.56(1) (weak)
H5A· · ·O1: 2.54(1) (weak)
H3· · ·O1: 2.54(5) (weak)
H4A· · ·N2: 2.62(1) (weak)
C5 H5A· · ·O1 : 160(7) (moderate)
b
C3 H3· · ·O1 : 153(4) (moderate)
c
C4 H4A· · ·N2 : 167(1) (moderate)
(
b) Intra-moleculard
s-Cis
C3 H3
C4 H4B
C3· · ·O1: 2.768
C4· · ·N2: 3.543
H3· · ·O1: 2.282
H4B· · ·N2
C3 H3· · ·O1: 104.38
C4 H4B· · ·N2: 158.27
s-Trans
C3 H3
C4 H4B
C3· · ·O2: 2.694
C4· · ·N2: 3.543
H3· · ·O2: 2.213
C3 H3· · ·O2: 104.33
C4 H4B· · ·N2: 158.27
H4B· · ·N2: 2.511
a
Based on X-ray crystallographic analysis.
b
c
d
−
x + 1, −y + 1, −z + 1.
−
x − 1/2, +y − 1/2, −z + 1/2.
Based on quantum chemical studies.
to atoms C3 and C5 through two inter-molecular hydrogen inter-
actions. Thus, O1 acts as bifurcated acceptor. There also exists
one weak C H· · ·N hydrogen inter-molecular interaction. The
details of inter-molecular and intra-molecular hydrogen interac-
tions are presented in Table 7. Using compiled data for a large
number of C H· · ·O and C H· · ·N contacts, Desiraju et al. [11]
stronger intra-molecular hydrogen bond C3 H3· · ·O2 owing to
˚
a smaller distance of 2.213 A between atoms H3 and O2.
4. Vibrational analysis
The infrared spectrum of ethyl 2-cyano-3-N,N-dimethyl
˚
−1
find significant statistical directionality even as far out as 3.0 A,
amino acrylate (CAAC) in the 4000–400 cm region in KBr
and conclude that these are to be legitimately viewed as ‘weak’
hydrogen bonds with a greater contribution to packing forces
than simple van der Waals attractions. Table 7 also reveals that
in the isolated molecule of the s-cis isomer of CAAC, there
exists the possibility of weak intra-molecular hydrogen bonding
between atoms O1 and H3 and N2 and H4B, having inter-atomic
pellet is given in Fig. 4. The fundamental frequencies of its s-
cis and s-trans conformers, as calculated by Density Functional
Theory using 6-31G** basis set and B3LYP functionals, are
given in Table 8
, which also contains the experimental infrared frequencies
and spectral assignments. The atomic numbering used in this
table is based on Fig. 1. It may be noted from Table 8 that,
with the presently used scaling factors, the observed and calcu-
˚
distances of 2.282 and 2.511 A, respectively. In the case of the
s-trans conformer, there also exists the possibility of a much
Fig. 4. Infrared spectrum of ethyl 2-cyano-3-N,N-dimethyl amino acrylate.

2
42
V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
Table 8
Experimental and calculated vibrational frequencies, intensities and assignments for s-cis and s-trans conformers of ethyl 2-cyano-3-N,N-dimethyl amino acrylate
νexpt. (cm 1)
−
s-Cis
s-Trans
Assignmentsa
S. no.
calc. (cm 1)
−
Intensity (kM/mol)
␯calc. (cm
−1
)
Intensity (kM/mol)
␯
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
24
55
62
82
94
2.30
0.15
3.27
1.51
3.21
0.02
0.00
5.09
1.76
7.94
0.08
0.36
9.00
9.11
8.32
1.80
0.05
1.34
2.52
4.77
23.43
4.30
0.09
3.87
42
53
67
82
96
0.00
0.53
0.78
0.35
1.53
0.31
0.01
5.69
2.12
2.04
0.16
9.16
1.34
13.86
1.35
2.69
0.80
1.27
4.23
4.46
21.98
5.46
0.11
10.89
O2 C7 torsion
C3 N1 torsion
N1 C4 torsion
N1 C5 torsion, C7 C8 torsion
i.p. skeletal bend
C1 C2 torsion
N1 C4 torsion, N1 C5 torsion
C6 N2 bend
o.p. skeletal bend
i.p. skeletal bend
i.p. skeletal bend
C3 N1 C5 bend
o.p. skeletal bend
C1O2C7 bend
i.p. skeletal bend
C2 C6 N2 o.p. bend
C2 C6 N2 i.p. bend
C5N1C4 i.p. bend
C1C2C6 i.p. bend
C6 N2 o.p. bend
C2C1O2 i.p. bend
O1C1O2 i.p. bend
CH2 rock
110
143
159
202
222
263
285
291
352
395
404
460
475
549
592
751
783
808
828
102
139
161
193
219
267
287
294
364
399
393
446
486
511
590
748
795
811
824
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
424(w)
484(vw)
568(w)
759(m)
813(w)
N1C3C2 bend, C2 C6 str., N1 C5
str.
2
2
2
2
2
3
3
3
3
3
5
6
7
8
9
0
1
2
3
4
850(w)
894(w)
950(w)
1025(w)
866
916
989
1037
1075
1111
1121
1130
1152
1165
10.37
0.26
2.18
889
893
962
1031
1076
1100
1120
1128
1142
1165
2.08
5.83
2.14
C1O2C7 bend
N1C4 str., C7C8 str.
C1H3 o.p. def.
9.41
0.35
C7C8 str., O2C7 str.
CH3 asym. def. (N1 C5)
CH3 asym. def. (N1 C4)
CH3 asym. def. (N1 C5)
CH3 asym. def. (C7 C8)
C2C6 str., C3N1C4 def.
CH3 asym. def. (N1 C5), CH3
asym. def. (N1 C4)
CH2 asym. def.
N1C4 str., N1C5 str., C1O2 str.
CH2 twist
C1O2 str., C1C2 str.
CH3 sym. def. (C7 C8)
C3H3 i.p. bend
20.13
358.2
0.56
13.64
54.24
1.88
18.80
333.68
0.41
11.81
89.65
1.80
1092(s)
1148(m)
35
36
37
38
39
40
41
1172
1242
1279
1293
1384
1398
1417
4.13
219.57
0.54
711.02
35.53
19.31
6.34
1174
1223
1281
1295
1387
1401
1419
3.91
230.09
0.44
484.57
23.95
3.74
1222(s)
1289(s)
1365(m)
1437(m)
10.68
CH2 sym. def., CH3 asym. def.
(
N1 C5)
4
4
4
4
4
4
2
3
4
5
6
7
1432
1446
1460
1466
1476
1484
1.80
8.38
69.88
2.62
4.88
16.98
1428
1447
1464
1466
1478
1484
94.90
24.29
33.40
5.14
5.52
16.06
C1 C2, N1 C3 str.
CH3 sym. def. (N1 C5)
CH3 sym. def. (N1 C4)
CH3 asym. def. (N1 C5)
CH3 asym. def. (C7 C8)
CH3 asym. def. (N1 C5), CH3
asym. def. (N1 C4)
CH3 asym. def. (C7 C8), CH2
asym. def.
1460
1480(b)
4
8
1487
2.57
1489
2.82
4
5
9
0
1491
1508
12.29
5.79
1492
1510
14.06
5.00
CH3 asym. def. (N1 C5)
CH3 asym. def. (C7 C8), CH2
asym. def.
5
1
1516
6.26
1517
6.44
CH3 asym. def. (N1 C5), CH3
asym. def. (N1 C4)
C2 C3 str., N1 C5 str.
C1 O1 str.
N2 C6 str.
CH3 sym. str. (N1 C6)
52
53
54
55
1622(vs)
1700(s)
2204(s)
1649
1747
2251
2907
602.94
276.74
69.50
1655
1758
2259
2906
573.95
278.82
60.50
35.81
36.09

V.P. Gupta et al. / Spectrochimica Acta Part A 68 (2007) 237–243
243
Table 8 (Continued )
νexpt. (cm 1)
−
s-Cis
s-Trans
Assignmentsa
S. no.
calc. (cm 1)
−
Intensity (kM/mol)
␯calc. (cm
−1
)
Intensity (kM/mol)
␯
56
57
58
59
60
61
62
63
64
65
66
2898(m)
2934(m)
2915
2931
2937
2957
2962
2974
2999
3008
3026
3053
3070
96.53
16.59
21.42
37.52
11.07
11.99
25.30
31.87
10.61
1.87
2914
2929
2941
2956
2960
2976
2997
3003
3021
3073
3080
93.96
16.31
19.38
35.96
12.77
4.62
26.15
41.45
11.76
3.98
CH3 sym. str. (N1 C5)
CH3 sym. str. (C7 C8)
CH2 str.
CH3 asym. str. (N1 C4)
CH3 asym. str. (N1 C5)
CH2 asym. str.
CH3 asym. str. (C7 C8)
CH3 asym. str. (C7 C8)
CH3 asym. str. (N1 C4)
C1H3 str.
2982(s)
2982(s)
3018(w)
2.96
0.25
CH3 asym. str. (N1 C5)
Abbreviations: w weak, vw very weak, m medium, s strong, vs very strong, b broad, i.p. in-plane, o.p. out-of-plane.
a
Atom numbering as per Fig. 1.
lated frequencies agree on an average within 20 cm 1 and the
observed intensities are fairly reproduced by the calculations.
Despite the fact that both in the s-cis and s-trans confor-
mations, the CAAC molecule is almost planar (deviations from
−
Acknowledgements
Grateful acknowledgement is made of the financial support
extended by Council of Scientific and Industrial Research, New
Delhi (India) to one of the authors (VPG) and by Indian Council
of Medical Research, New Delhi to another author (Rajnikant)
for this work through major research projects.
◦
planarity not exceeding 3 ), for the purpose of vibrational analy-
sis, it was taken as belonging to C1 symmetry group. In this case,
the vibrational frequencies of the heavy atom skeleton may be
broadly divided into in-plane and out-of-plane modes (Table 8),
with very small interaction between them. This results in the
appearance of a large number of calculated frequencies, both
stretch and deformation, for the three methyl groups with very
few corresponding experimental frequencies. It is also noted that
the attachment of the methyl group to a nitrogen atom, which is
more polar than a carbon atom, shifts the frequency of its sym-
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metric deformation mode by about 100 cm from 1365 cm
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ν39) in C CH3 to 1460 cm (ν44) in N CH3, i.e. to a region
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close to that for asymmetric deformation modes. The very strong
−
1
−1
absorption band at 1622 cm and a strong band at 1700 cm
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[
[
6] G.M. Sheldrick, Program for Solution of Crystal Structures, University of
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−
1
The strong band at 2204 cm may be assigned to the stretch
mode of the nitrile group. Some other prominent absorption
−
1
−1
bands in the spectrum at 1092 (s) cm , 1222 (s) cm , 1289
−1
−1
(
s) cm and 2982 (s) cm may be assigned to methyl asym-
metric deformation (ν30) and N1 C4 (ν ), C1 O2 (ν38) and
36
methyl asymmetric stretch modes, respectively. It is also found
that while the calculated frequencies of almost all the bands of
the s-cis and s-trans conformers are very close to each other,
their intensities are significantly different, particularly for bands
corresponding to the skeletal modes such as in-plane skeletal
bend (ν ), C1 O2 C7 bend (ν ), C1 O2 stretch (ν38), C1 C2
15
25
stretch (ν42) and C C stretch (ν ). Finally, a comparison of
52
the calculated vibrational frequencies and intensities of the two
stable isomers of CAAC with the corresponding experimental
values lead to the conclusion that in the solid state the molecule
is primarily in the s-cis conformation. This is in agreement with
the findings based on X-ray crystallographic studies.
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