Mustafa Şenyel a,
Cemal Parlak b and Esma Güneş
a
a
Department of Physics, Science Faculty, Anadolu University, Eskişehir, 26470, Turkey
b Department of Physics, Dumlupinar University, Kütahya, 43100, Turkey
INDEX
 Abstract
 Why thiophene-2-carbaldehyde and its halogeno derivatives ?
 Calculations
• Conformational analysis
• Geometrical structures
• Vibrational studies
• Electronic properties
 Results
 References
2
ABSTRACT
The effects of halogen and solvent on structural, vibrational
and electronic properties of thiophene-2-carbaldehyde (C5H4OS) and
thiophene-2-carbonyl-halogeno [C5H3XOS; X = F, Cl or Br] were
explored by DFT and TD-DFT methods.
B3LYP functional was used with 6-31++G(d,p) basis set.
Computations were focused on the two conformers of the compounds
in the gas phase and both in a non-polar and in a polar solvent.
The findings of this research work can be useful to those
systems involving changes in the conformations analogous to the
compounds studied.
3
Thiophene-2-carbaldehyde
and its halogeno derivatives
4
Why thiophene-2-carbaldehyde
and its halogeno derivatives ?
They exhibit pharmacological activity.
They have employed for the design of new
medicines and biologically active substances.
They play a role in commerce as constituents of
reactive dyes, conductive polymers, ligands for catalyst
systems, and in flavor and fragrances [1-3].
5
Calculations
 All the computations were carried out by a cluster system with a precompiled set of Gaussian 09 program, configured for parallel computing.
 All structural and spectroscopic illustrations were done with the program
GaussView 5.0.8 and GaussSum 2.2, while graphs were drawn with the
program Origin 8 [4-5].
 For the calculations, two forms of the compounds in C1 symmetry were
first optimized in the gas phase, benzene and methanol at B3LYP using
6-31++G(d,p) basis set. The polarizable continuum model (PCM) model
was used to evaluate the solvent effect.
 To determine conformational isomers, the potential energy surface (PES)
analysis was also performed by the same basis set.
6
Conformational Analysis
According to literature, conformers of thiophene-2-carbaldehyde (T2C)
is shown in figure.
It has two probable conformations with respect to rotation through the
angle Φ (S5-C3-C6-O8): trans and cis [6].
7
PES (Potential Energy Surface) Analysis
To determine conformational isomers, PES analysis was also performed by the
rotations of C2-C1-C6-O7 torsion angle, scanning from 180o to 360o, with 20o
increments.
The trans conformer was found more stable than the cis form.
8
Conformational Analysis
Free - relative energies and mole fractions of T2C and its halogeno derivatives;
Gas
Compound
Cis
Free Energy (Hartree)
T2C
Relative Stability
Mole Fractions (%)
Free Energy (Hartree)
T2C-F
Relative Stability
Mole Fractions (%)
Free Energy (Hartree)
T2C-Cl
Relative Stability
Mole Fractions (%)
Free Energy (Hartree)
T2C-Br
Relative Stability
Mole Fractions (%)
9
Benzene
Trans
Cis
Methanol
Trans
Cis
Trans
-666.386139
-666.387956
-666.389579
-666.391571
-666.393802
-666.396084
1.14
0
1.25
0
1.43
0
13
87
11
89
8
92
-765.688736
-765.688928
-765.692103
-765.692308
-765.696068
-765.696337
0.12
0
0.13
0
0.16
0
44
55
45
55
43
57
-1126.036279
-1126.037202
-1126.039334
-1126.040298
-1126.043061
-1126.044080
0.58
0
0.6
0
0.64
0
27
73
26
74
25
75
-3239.957967
-3239.959151
-3239.961026
-3239.962203
-3239.964760
-3239.965998
0.74
0
0.74
0
0.78
0
22
78
22
78
21
79
Conformational Analysis
Regarding the calculated free energies of T2C, in the gas phase, trans
conformer is more stable than cis form by 1.14 kcal/mol. According to the
calculations for mole fractions of the individual conformers, T2C prefers trans
and cis conformers with approximate probabilities of 87% and 13%, respectively.
Similarly, the calculated free energies, in benzene, show that trans
conformer is more stable than other conformer and the compound prefers trans
and cis conformers with approximate probabilities of 89% and 11%, respectively.
The calculated free energies in methanol also indicate that trans
conformer is more stable. The compound prefers these conformers with
approximate probabilities of 92% and 8%, respectively.
10
Conformational Analysis
Similarly, turning to T2C-F, T2C-Cl and T2C-Br, in the gas phase,
benzene and methanol, the trans conformer is more stable than the cis.
It is observed that all the conformers of the compounds are
stabilized as the polarity of the solvents increases. Also, the most stable
conformation of T2C and its halogeno derivatives is independent on the
medium and halogen.
11
Geometrical Structures
To clarify the vibrational frequencies, it is essential to examine the
geometry of any compound as small changes in geometry can potentially cause
substantial changes in frequencies.
12
Geometrical Structures
Compound /
Bond Length
Gas
Benzene
Methanol
Some
found
T2C
C=O
1.2136
1.2175
1.2227
C-S
1.7448
1.7462
1.7484
C=O
1.1901
1.1918
1.1945
C-S
1.7499
1.7512
1.7528
T2C-Cl
T2C-Br
significant
in
changes
the
are
geometric
parameters when the compounds
in solvated.
From
lower
to
higher
dielectric, the C=O and C-S bond
lenghts increase and there are
C=O
1.1879
1.1894
1.1916
C-S
1.7525
1.7537
1.7552
very significant changes in C=O
bond lenghts of the compounds
T2C-F
C=O
1.1884
1.1907
1.1938
C-S
1.7436
1.7448
1.7463
13
due to halogen atom.
Vibrational Studies
Theoretical vibrational frequencies for all compounds, along with corresponding
vibrational assignments and intensities are performed. The simulated vibrational spectra
are also depicted;
All the computed frequency values are obtained within the harmonic
approximation. The compounds consist of 11 atoms, with 27 normal vibrational modes,
and it belongs to the point group C1.
14
Vibrational Studies
Compound
T2C
v(C=O)
IR (cm-1)
Gas
1745
Benzene
1722
Methanol
1691
Medium
IR Intensity
(km/mol)
390
581
901
T2C-F
Gas
Benzene
Methanol
1860
1720
1689
526
568
853
T2C-Cl
Gas
Benzene
Methanol
1823
1721
1690
421
631
962
T2C-Br
Gas
Benzene
Methanol
1832
1721
1691
415
662
1009
15
The
frequencies
C=O
of
T2C
stretching
and
its
halogeno derivatives are collected
in
table
together
with
their
intensities. The relations between
the C=O vibrations/intensities and
medium/compounds are explored.
Vibrational Studies
The carbonyl vibrations of all compounds
decrease from the gas phase to methanol.
In the gas phase, frequencies
increase with halogen atom and
F-compound
has
the
highest
value.
However,
in
benzene
and
methanol, frequencies decrease
or don’t change with halogen and
F-compound has the lowest data.
16
Vibrational Studies
Intensities of C=O vibrations of all compounds
increase from the gas phase to methanol.
In
the
gas
phase,
intensities
increase with halogen atom and
F-compound has the highest value.
However, in benzene and methanol,
intensities
decrease
for
F-
compound whereas they increase
for Cl- and Br-compounds.
17
Electronic Properties
The results of the absorption wavelengths (), excitation energies (E) and
oscillator strengths (f) are collected in table together with the contributions of
these transitions.
Medium
λ (nm)
338.1
Gas
E (eV)
f
Contribution
3.66800 0.0002 H-1>L (97%), H-1>L+2 (3%)
268.7 4.613634 0.1366
H-2>L (33%), H>L (64%)
251.4 4.932537 0.1935
H-2>L (63%), H>L (33%)
332.8 3.725928 0.0002 H-1>L (97%), H-1>L+2 (3%)
Benzene
276.7 4.481233 0.2045
H-2>L (25%), H>L (73%)
258.3 4.799836 0.2395
H-2>L (72%), H>L (25%)
325.9 3.803728 0.0002 H-2>L (97%), H-2>L+2 (2%)
Methanol
279.3 4.438433 0.1757
H-1>L (30%), H>L (68%)
259.9 4.769235 0.2489
H-1>L (67%), H>L (30%)
H and L denote HOMO and LUMO, respectively.
18
Electronic Properties
UV spectra of T2C:
From the UV spectra, the absorption bands are centered at 338.1, 332.8 and
325.9 nm in the gas phase, benzene and methanol for T2C, respectively. The
area of these absorption bands decreases gradually from gas phase to the
polar solvent.
19
Electronic Properties
Energies HOMO and LUMO and values of chemical hardness, electronegativity,
chemical potential and electrophilicity index (eV) of the most stable trans
conformer of the compounds;
Compound
T2C
T2C-F
T2C-Cl
T2C-Br
HOMO–LUMO
Gap
Chemical
Hardness (h)
Electrophilicity
Index (ω)
HOMO
LUMO
Gas
-7.259
-2.325
4.934
2.467
4.792
-4.792
4.655
Benzene
-7.217
-2.331
4.885
2.442
4.774
-4.774
4.666
Methanol
-7.196
-2.369
4.827
2.413
4.783
-4.783
4.739
Gas
-7.577
-2.462
5.116
2.558
5.019
-5.019
4.925
Benzene
-7.497
-2.441
5.056
2.528
4.969
-4.969
4.884
Methanol
-7.427
-2.444
4.983
2.491
4.935
-4.935
4.888
Gas
-7.596
-2.659
4.936
2.468
5.127
-5.127
5.326
Benzene
-7.517
-2.643
4.873
2.437
5.080
-5.080
5.295
Methanol
-7.445
-2.650
4.795
2.398
5.047
-5.047
5.313
Gas
-7.599
-2.720
4.880
2.440
5.159
-5.159
5.455
Benzene
-7.525
-2.697
4.827
2.414
5.111
-5.111
5.411
Methanol
-7.457
-2.699
4.758
2.379
5.078
-5.078
5.419
20
Electronegativity(χ)
Chemical
Potential (µ)
Medium
Electronic Properties
Frontier molecular orbitals of
T2C in the gas phase;
The energy of HOMO-LUMO gap decreases
gradually from the gas phase to the polar
solvent for all compounds.
The F-compound has the largest HOMOLUMO energy gap of about 5.1 eV.
From the gas phase to the polar
solvent, the values of the chemical hardness
and electronegativity of the all compounds also
show same trends with the energy gaps.
21
Conclusions
The results can be useful for analysis of the conformers involving these
moieties. The main conclusions of this theoretical research work are as follows:
(i) The minimum energies of the optimized structures decrease with the solvent
polarity and the size of halogen.
(ii) Conformational preference is independent on the solvent and halogen effects.
(iii) The C=O vibrations of all compounds decrease from the gas phase to
methanol whereas their intensities increase.
(iv) There are also both halogen and solvent effetcs on the geometric parameters,
UV spectra (optical band gaps), HOMO-LUMO gaps (electrical gaps), the
chemical hardness and electronegativity of the all compounds.
(v) It is observed that fluorine has an atypical characteristic affecting the
vibrational frequencies and their intensities, electrical band gap, chemical
hardness and electronegativity.
22
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23
 THANKS
THANK YOU FOR
YOUR PARTICIPATION..