Synthesis and spectroscopic characterization on 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid: A DFT approach

Article abstract of DOI:10.1016/j.saa.2015.07.058

Abstract A complete structural and vibrational analysis of the 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid (TPBA), was carried out by ab initio calculations, at the density functional theory (DFT) method. Molecular geometry, vibrational wavenumbers a

Full text of DOI:10.1016/j.saa.2015.07.058

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and spectroscopic characterization on 4-(2,5-di-2-thienyl-
1H-pyrrol-1-yl) benzoic acid: A DFT approach
M. Kurt a, E. Babur Sas a, M. Can b, S. Okur c, S. Icli d, S. Demic c, M. Karabacak e, T. Jayavarthanan f,
N. Sundaraganesan g,
⇑
a Department of Physics, Ahi Evran University, Kırsehir, Turkey
b Department of Engineering Sciences, Faculty of Engineering, Izmir Katip Celebi University, Cigli, 35620 Izmir, Turkey
c Izmir Katip Celebi University, Material Science and Engineering, Cigli, Izmir, Turkey
d Ege University, Solar Energy Institute, 35040 Bornova, Izmir, Turkey
e Department of Mechatronics Engineering, H.F.T. Technology Faculty, Celal Bayar University, Turgutlu, Manisa, Turkey
f Department of Physics (Science and Humanities), Sri Manakula Vinayagar Engg. College, Madagadipet, Puducherry 605107, India
g Department of Physics (Engg.), Annamalai University, Annamalai Nagar 608 002, Tamil Nadu, India
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
ꢀ
The FT-IR spectra of
NH
2
O
O
N
S
4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)
benzoic acid were recorded.
The vibrational frequencies were
calculated by DFT method and
compared.
S
p-tolunesulfonic acid
Toluene
S
S
Reflux
CN
ꢀ
NC
ꢀ
ꢀ
NMR and MEP analysis were also
carried out.
UV–Vis spectra were recorded and
compared with calculated ones.
N
S
S
COOH
a r t i c l e i n f o
a b s t r a c t
Article history:
A complete structural and vibrational analysis of the 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid
(TPBA), was carried out by ab initio calculations, at the density functional theory (DFT) method.
Molecular geometry, vibrational wavenumbers and gauge including atomic orbital (GIAO) 13C NMR
and 1H NMR chemical shift values of (TPBA), in the ground state have been calculated by using ab initio
density functional theory (DFT/B3LYP) method with 6-311G(d,p) as basis set for the first time.
Comparison of the observed fundamental vibrational modes of (TPBA) and calculated results by
DFT/B3LYP method indicates that B3LYP level of theory giving yield good results for quantum chemical
studies. Vibrational wavenumbers obtained by the DFT/B3LYP method are in good agreement with the
experimental data. The study was complemented with a natural bond orbital (NBO) analysis, to evaluate
the significance of hyperconjugative interactions and electrostatic effects on such molecular structure. By
using TD-DFT method, electronic absorption spectra of the title compound have been predicted and a
good agreement with the TD-DFT method and the experimental one is determined. In addition, the
molecular electrostatic potential (MEP), frontier molecular orbitals analysis and thermodynamic proper-
ties of TPBA were investigated using theoretical calculations.
Received 1 December 2014
Received in revised form 8 July 2015
Accepted 9 July 2015
Available online 10 July 2015
Keywords:
DFT
TPBA
Vibrational assignments
NBO
NMR
Thermodynamic properties
Ó 2015 Elsevier B.V. All rights reserved.
⇑
Corresponding author.
E-mail address: sundaraganesan_n@yahoo.com (N. Sundaraganesan).
http://dx.doi.org/10.1016/j.saa.2015.07.058
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
9
1. Introduction
NH
2
O
O
N
S
S
p-tolunesulfonic acid
Toluene
S
S
The chemical properties of compounds containing aromatic car-
boxyl have been extensively investigated in the past decades.
Pyrroles are components of more complex macrocycles, including
the porphyrins of heme, the chlorins, bacteriochlorins, chlorophyll,
porphyrinogens [1]. Pyrrole is a 5-membered aromatic heterocycle,
like furan and thiophene. Unlike furan and thiophene, it has a dipole
in which the positive end lies on the side of the heteroatom, with a
dipole moment of 1.58 D [2]. Synthesized electroactive processable
polymeric materials with a linear combination of thiophenes as the
external units and N-substituted pyrrole as the central unit
(2,5-di(2-thienyl)-1H-pyrrole derivatives) have attracted interest.
Kim et al. [3] have been studied the synthesis, electrochemical,
and spectroelectrochemical properties of conductive poly-[2,5-d
i-(2-thienyl)-1H-pyrrole-1-(p-benzoic acid)]. They investigated
their study that the 2,5-di(2-thienyl)-1H-pyrrole derivative, [(2,5-
di-(2-thienyl)-1H-pyrrole)-1-(p-benzoic acid)] (DPB) was chosen
as a model compound. Because, in that particular system, the car-
boxylic acid group of benzoic acid is one of the most useful units
to further incorporate functional groups into the polymer backbone.
New type 2,5-di(2-thienyl)pyrrole derivative namely 4-amino-
N-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzamide have been
synthesized via reaction of 1,4-di(2-thienyl)-1,4-butanedione and
p-aminobenzoyl hydrazide by Soyleyici et al. [4].
The calculations based on DFT method have been used in many
areas [5–8]; the results are also in good agreement with the exper-
imental results in calculating vibrational wavenumbers. In this
study, we first synthesized 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)
benzoic acid then the geometrical parameters, fundamental fre-
quencies, electronic transitions, thermodynamic properties and
GIAO 1H and 13C NMR chemical shifts of the TPBA molecule in
the ground state have been calculated by using the DFT method
with 6-311G(d,p) as basis set. In these DFT studies, the geometric
structures of the TPBA molecule, i.e. bond lengths, bond angles,
and torsion angles, have been calculated. We need experimental
results to confirm the calculations; however, such experimental
data are scarce. The crystal structure for the title molecule is not
available; hence it is compared with the available experimental
counterparts. Whereas, the comparison of the experimental and
theoretical spectra reveals that very useful in making correct
Reflux
CN
NC
N
S
S
COOH
Fig. 1. Synthesis scheme of 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)benzoic acid (TPBA).
TLC, it was set to cooling to room temperature, extracted with chlo-
roform (3 ꢁ 25 mL) and water (3 ꢁ 25 mL). Then, the organic phase
was dried over magnesium sulfate, and evaporated by rotary evap-
orator. The crude product was purified by column chromatography
(dichloromethane) on silica gel to afford light brown colored pro-
duct (72% yield). 1H NMR (CDCl3): 7.67 (d, 2H), 7.36 (d, 2H), 7.13
(d, 2H), 6.86 (t, 2H), 6.53 (s, 4H).
Synthesis of 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)benzoic acid
(3): In a round bottomed flask an aqueous solution of potassium
hydroxide (5 equiv., 2 N) was added to 2 (1 equiv.) dissolved com-
pletely in methanol and tetrahydrofuran (1:1) at 0 °C. Then, the
solution was refluxed under argon atmosphere overnight with stir-
ring. The reaction mixture was subjected to vacuum and crude pro-
duct with ethyl acetate, the aqueous phase was acidified with 1 N
HCl acid and subsequently extracted with ethyl acetate
(3 ꢁ 25 ml). The combined organic layers were dried with sodium
sulfate. Removal of the solvent provided the crude product of 3,
which was then used without further purification. 1H NMR
(DMSO): 8.02 (d, 2H), 7.46 (d, 2H), 7.30 (d, 2H), 6.88 (t, 2H), 6.65
(d, 2H), 6.57 (s, 2H); Synthesis scheme of 4-(2,5-di-2-thienyl-1H-
pyrrol-1-yl)benzoic acid has been shown in Fig. 1.
assignments
and
understanding
the
basic
chemical
3. Experimental details
shift-molecular structure relationship. And so, these calculations
are valuable for providing insight into molecular analysis.
The compound TPBA in solid form were prepared using a KBr
disc technique. The infrared spectrum of the compound was
recorded in the range of 4000–600 cmꢂ1 on a Perkin–Elmer FT-IR
system spectrum BX spectrometer. The spectrum was recorded at
room temperature, with a scanning speed of 10 cmꢂ1 minꢂ1 and
the spectral resolution of 4.0 cmꢂ1. The ultraviolet absorption spec-
tra of sample solved in DMSO was examined between 200 nm and
500 nm with resolution of 1 nm by Analytic JENA S 600 UV–Vis
recording spectrometer. The sample spectrum was taken inside a
quartz tupe with DMSO. NMR experiment was performed in
Bruker DPX-400 at 300 K. Chemical shifts were reported in ppm
relative to tetramethylsilane (TMS) for 1H NMR spectrum in
DMSO. NMR spectrum was obtained at the base frequency of
400 MHz for 1H nuclei. The experimental HOMO–LUMO values
for TPBA were calculated from cyclic voltammetry.
2. Synthesis
Synthesis of 1,4-dithiophene-2-yl-butane-1,4-dione (1). A solu-
tion of thiophene (9.61 mL, 0.12 mol) and AlCl3 (16 g, 0.12 mol) in
dry CH2Cl2 (50 mL) was added dropwise to a suspension of succinyl
chloride (5.5 mL, 0.05 mol) in dry CH2Cl2 (50 mL) at 0 °C. The mix-
ture was stirred for at 18–20 °C 4 h and poured into a mixture of
100 g ice and 10 mL hydrochloric acid and stirred for 1 h and the
resulting dark green organic phase was washed with concentrated
NaHCO3 (3 ꢁ 25 mL), and dried over Na2SO4. After the solvent was
evaporated, a blue–green solid remained and was suspended in
ethanol. Column chromatography (SiO2, CH2Cl2) and recrystalliza-
tion from ethanol produced 8.98 g (68%) of it in a white solid. 1H
NMR: (400 MHz; CDCl3): 7.80 (dd, 2H), 7.63 (dd, 2H), 7.13 (dd,
2H), 3.38 (s, 4H).
4. Computational details
Synthesisof 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)benzonitrile (2):
4-Aminobenzonitrile (0.26 g, 2.2 mmol), 1,4-dithiophene-2-yl-buta
ne-1,4-dione (1) (0.5 g, 2 mmol), and p-toluenesulfonic acid (6.8 mg,
0.4 mmol) in 30 ml dry toluene were heated under reflux in a Dean–
Stark apparatus. After checking the completion of the reaction by
The entire calculations were performed at Density functional
theoretical (DFT) level with 6-311G(d,p) as basis set using
Gaussian 03W [9] program package, invoking gradient geometry
optimization [10]. Initial geometry generated from the standard
geometrical parameters was minimized without any constraint on

10
M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
the potential energy surface at HF level adopting the standard
B3LYP/6-31G(d,p) basis set then re-optimized again at DFT level
using the same basis set for better description. All the optimized
structures were confirmed to be minimum energy conformations.
Harmonic vibrational wavenumbers were calculated using analytic
second derivatives to confirm the convergence to minima on the
potential surface and to evaluate the zero-point vibrational energies
(ZPVE). At the optimized structure of the TPBA, no imaginary fre-
quencies were obtained, proving that a true minimum on the poten-
tial energy surface was found. By the use of potential energy
distribution (PED) using VEDA 4 program [11] along with available
related molecules, the vibrational frequency assignments were
made with a high degree of accuracy. The natural bond orbital
(NBO) calculations were performed using NBO 3.1 program [12] as
implemented in the Gaussian 03W [9] package at the DFT/B3LYP
level in order to understand various second order interactions
between the filled orbitals of one subsystem and vacant orbitals of
another subsystem, which is a measure of the intermolecular delo-
calization or hyperconjugation. The 1H NMR isotropic shielding
were calculated with the GIAO method [13,14] using the optimized
parameters obtained from B3LYP/6-311G(d,p) method. The B3LYP
method allows calculating the shielding constants with accuracy
and the GIAO method is one of the most common approaches for
calculating nuclear magnetic shielding tensors. The effect of solvent
on the theoretical NMR parameters was included using the default
model IEF–PCM provided by Gaussian 03W. The isotropic shielding
values were used to calculate the isotropic chemical shifts d with
respect to tetramethylsilane (TMS).
Fig. 2. Theoretical optimized geometric structure of the TPBA.
DFT/B3LYP method with the 6-311G(d,p) as basis set are presented
in Tables SI-1 and SI-2 (Supplementary information). The TPBA
molecule consists of two thiophene ring and benzoic acid structure
substituted with pyrrole ring. The DFT calculation predicts the tilt-
ing around 41° between the thiophene rings and pyrrole ring. On
the other hand, the benzoic acid exhibits the tilting around 62°
with pyrrole ring. This shows the non-planarity of the entire mole-
cule and also the individual planarity of the each rings.
5. Prediction of Raman intensities
The title molecule is considered to possess C1 point group sym-
metry. The global minimum energy of TPBA was calculated at
-1733.7013 Hartree. The CAS bond lengths in the thiophene rings
are calculated at B3LYP/6-311G(d,p) level are 1.754 and 1.732 Å,
respectively, which are smaller than the bond length of the single
CAS bond (1.82 Å). The bonds, which act a bridge role between the
thiophene rings and pyrrole ring are induced the CAS bond dis-
tances to the elongation of 1.754 Å whereas another values are cal-
culated at 1.732 Å. The reported CAS bond distances values 1.759,
1.746 Å [18] 1.739 Å [19,20] 1.751 Å [21] are in agreement with
calculated values. In the case of CAN bonds, The C1AN5 and
C4AN5 bond distances are all calculated at 1.396 Å whereas the
C25AN5 bond distance has been calculated at 1.428 Å at
B3LYP/6-311G(d,p) level of theory which are shorter than that of
normal CAN bond (1.47 Å) and longer than that of C@N bond
(1.33 Å) [22]. But the second one is much closer to that of CAN
bond distance [22].
The CAC bond length in benzene ring is between 1.388 and
1.399 Å at B3LYP/6-311G(d,p) level, which is much shorter than
the typical CAC single bond (1.54 Å) and longer than the C@C dou-
ble bond (1.34 Å) [23]. All the internal CACAC bond angles in the
benzene ring have been calculated around ꢃ120° whereas in the
thiophene ring which are calculated at around ꢃ113°. The
CASAC bond angles are calculated at 91.8° which are in good
agreement with the literature value of 92.1° [18]. It can be con-
cluded from the calculated values, the geometrical parameters
are slightly overestimated from the experimental values those
are taken to be compared, due to the fact that the experimental
results belong to the solid phase and theoretical calculations
belong to isolated molecule in gas phase.
The theoretical Raman intensity (IR), which simulates the mea-
sured Raman spectrum, can be calculated using RAINT program
[15]. The Raman activities (Si) calculated by Gaussian 03 program
[9] have been converted to relative Raman intensities (IR). The the-
oretical Raman intensity (IR), which simulates the measured
Raman spectrum, is given by the equation [15,16]:
IRi ¼ Cðm0
ꢂ
mi
Þ
4mꢂi 1Bꢂi 1Si
ð1Þ
where ‘Bi’ is a temperature factor which accounts for the intensity
contribution of excited vibrational states, and is represented by
the Boltzmann distribution:
ꢀ
ꢁ
h
kT
t
ic
Bi ¼ 1 ꢂ exp ꢂ
ð2Þ
In Eq. (1) ‘
work, we have used the excitation frequency
which corresponds to the wavelength of 1064 nm of a Nd:YAG
laser), ‘
i’ is the frequency of normal mode (cmꢂ1), while ‘Si’ is
m
0’ is the frequency of the laser excitation line (in this
m
0 = 9398.5 cmꢂ1
,
m
the Raman scattering activity of the normal mode Qi. IiR is given
in arbitrary units (C is a constant equal 10ꢂ12). In Eq. (2) h, k, c,
and T are Planck and Boltzmann constants, speed of light and tem-
perature in Kelvin, respectively. Thus, the presented theoretical
Raman intensities have been computed assuming ‘Bi’ equal to 1.
The simulated spectra were plotted using a Lorentzian band shape
with a half-width at half-height (HWHH) of 3 cmꢂ1
.
6. Results and discussion
6.1. Molecular geometry
The optimized molecular structures obtained from GaussView
program [17] are shown in Fig. 2. The most relevant structural
parameters, bond lengths, bond angles and dihedral angles for
TPBA have been employed without symmetry constraint by
6.2. Vibrational assignments
Vibrational spectral assignments have been performed based on
the recorded FT-IR spectra and the theoretically predicted

M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
11
Table 1
Comparison of the calculated and experimental vibrational spectra and proposal assignments of TPBA.
No.
Exp. wavenumber
FT-IR
Theoretical wavenumber
Assignments (PED)
a
a
a
Scaled
IIR
SRa
IRa
1
2
3
4
5
6
7
8
9
10
11
12
13
3650
3647
3144
3139
3138
3130
3112
3111
3108
3102
3094
3093
3091
3089
106.78
0.34
0.56
0.56
5.66
2.25
2.41
0.78
1.98
9.10
11.44
1.77
1.35
197.57
155.40
255.24
265.11
69.06
3.01
2.89
3.67
3.71
0.20
0.19
0.18
0.35
0.23
0.40
0.40
0.13
0.06
t
t
t
t
t
t
t
t
t
t
t
t
t
OH(100)
CH(97)
CH(97)
CH(98)
CH(98)
CH(99)
CH(99)
CH(99)
CH(99)
CH(96)
CH(98)
CH(98)
CH(97)
64.57
60.81
115.62
75.74
130.27
131.13
41.56
3070
2984
2851
2671
2549
1674
1610
1576
20.84
Overtone + combination
Overtone + combination
Overtone + combination
Overtone + combination
t
t
t
t
t
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
1744
1594
1567
1555
1538
1493
1490
1459
1421
1410
1395
1380
1332
1331
1327
1301
1294
1290
1272
1234
1225
1197
1172
1172
1149
1096
1081
1072
1070
1057
1040
1032
1030
1012
998
968
956
887
885
884
869
854
840
826
819
818
815
812
771
770
763
351.28
90.21
9.62
8.72
0.62
28.04
9.11
0.02
20.53
11.03
27.53
86.21
3.52
182.11
39.75
5.47
3.51
4.40
1.09
0.31
125.72
269.34
29.22
23.22
2631.04
15.08
1.68
3024.43
0.87
44.02
4.65
33.53
9.49
64.50
96.61
0.58
44.76
0.16
1.68
102.80
15.40
16.01
1.51
29.05
64.20
1.79
6.02
19.63
6.65
5.30
3.31
3.81
157.81
32.40
3.66
0.27
0.31
27.40
2.99
5.13
5.05
0.11
6.73
5.63
4.08
76.00
1.19
1.47
3.73
0.42
0.34
CO(83)
CC(67), dCCH(16)
CC(71)
CC(72)
CC(73)
1518
38.86
0.24
0.03
49.03
0.02
0.76
0.08
0.60
0.18
1.22
1.84
0.01
0.89
0.00
0.03
2.21
0.33
0.36
0.03
0.68
1.55
0.05
0.16
0.53
0.18
0.15
0.09
0.11
4.50
0.95
0.11
0.01
0.01
0.98
0.11
0.18
0.19
0.00
0.26
0.22
0.16
3.05
0.05
0.47
0.05
1.89
0.00
0.29
1.10
0.09
0.30
0.36
dCCH(50),
t
CC(33)
t
t
t
t
t
t
CC(59), dCCH(22)
CC(63)
CC(79)
CC(69)
1431
1355
1286
CC(35), dCCH(31)
CN(27),
t
CC(24)
CC(22)
dOH[dCOH(32)], CO(22),
CC(18), dCCH(11)
CN(26)
dCCH(27),
t
t
tCC(20)
t
t
t
CN(26),
CC(34),
t
t
CC(42), dCCH(19)
dCCH(51),
dCCH(33),
tCC(41), tCN(18)
dCCH(46)
dCCH(46),
dCCH(52),
dCCH(59),
dCCH(53),
dCCH(52),
dCCH(32)
dCCH(44), dCHS(14),
dCCH(24), CC(19)
t
t
dCCH(35),
dCCH(55),
t
t
t
CC(24)
CC(25), tCN(14)
1222
1199
1164
1164
1129
1101
7.59
4.88
t
t
t
t
t
CC(26)
CC(24)
CC(28)
CC(19)
CC(23)
31.11
138.06
163.63
3.29
20.63
28.11
123.88
7.32
0.77
4.28
8.24
5.09
6.47
0.13
0.10
10.13
1.71
4.81
1.26
23.42
0.15
1.09
tCC(10)
t
CC(21), dCCH(18), dCHS(15)
CC(47), dCCH(25)
1043
1019
950
t
t
CC(32)
CC(26)
CC(33)
dCCC(37), dCCH(21), tCC(14)
c
c
dCCN(20), dCCC(17)
c
c
CH[
CH[
s
s
CCCH(38)]
CCCH(39)]
CH[
CH[
s
s
CCCH(11),
CCCH(10),
s
s
CHCH(60)],
CHCH(53)]
s
CSCH(11)
CCCO(11)
863
dCCC(28), dCCH(10)
c
c
c
t
t
c
CH[
CH[
CH[
s
s
s
CCCH(48),
CCCH(33),
CCCH(79),
sCNCH(20)],
sCNCH(13)]
sCNCH(18)]
s
840
834
49.55
23.27
8.56
15.66
47.50
25.58
34.09
6.20
CS(37), dCCS(14), dCCC(11)
CS(40), dCCS(14), dCCC(11)
CH[s
CCCH(43),
s
CSCH(18),
CCHS(19), CCHH(17)
CCCH(15), COOH(12)
sHCCH(17)]
11.56
1.11
43.03
0.04
6.09
22.75
1.80
sCCCH(44),
s
s
s
s
782
764
sCCCO(27),
t
c
t
t
CC(39), dCCC(10)
CH[ CCCH(61), CNCH(20)]
s
s
720
717
700
675
CS(59), dCCC(21)
CS(64), dCCC(21)
0.36
53.37
62.74
62.24
sCCCC(28),
s
CCCH(21),
s
CCCO(12)
695
5.75
6.67
c
CH[s
CCCH(46),
sCSCH(38)]
674
dCCH(46), cCH[sCSCH(38)]
(continued on next page)

12
M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
Table 1 (continued)
No.
Exp. wavenumber
FT-IR
Theoretical wavenumber
Assignments (PED)
a
a
a
Scaled
IIR
SRa
IRa
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
667
663
643
634
619
617
596
575
568
551
511
497
491
474
455
409
404
377
372
324
288
258
216
207
185
156
121
115
91
19.90
6.55
0.35
0.75
0.77
0.49
0.05
1.88
0.15
0.11
2.10
0.43
0.10
0.13
0.25
0.58
0.17
0.72
0.28
0.49
0.13
0.44
0.83
0.41
0.39
1.53
0.39
0.26
s
CCCN(26),
dCOO(16)
CCCN(12)
sCCHN(14)
27.28
7.01
3.00
2.31
7.04
7.42
41.85
0.09
19.91
4.83
2.82
1.59
17.39
11.00
1.34
1.01
3.84
6.99
0.58
2.27
0.71
0.13
0.26
1.29
0.51
1.11
0.14
0.62
0.44
0.74
0.76
0.15
0.26
0.59
0.10
13.68
13.55
8.50
0.78
31.17
2.44
1.65
30.81
6.09
1.25
1.65
3.02
6.60
1.78
6.50
2.48
3.87
1.05
2.78
4.37
1.85
1.26
4.70
1.02
0.50
14.44
0.59
2.02
9.98
2.62
16.92
0.40
1.86
6.37
5.04
s
dCCS(16),
dCCC(33)
dCCS(29),
t
CS(15), dCCC(15)
t
CS(18)
c
c
OH[s
CCOH(29)],
t
s
CS(13), dCCN(10)
COOH(13)
CCCH(16)],
CCCC(13)
CC(11)
CCCS(23), dCCO(18)
OH[s
CCOH(28)],
s
s
CCCC(64),
CCCS(15),
c
CH[
C
sCCCS(22)
s
dCCO(12),
t
s
s
s
CCCS(18)
CCCS(10)
dCCO(15)
CCCC(64),
CC(24), dCCS(20), dCCC(16)
s
t
cCH[sCCCH(23)]
dCCC(19)
dCCN(23)
s
CCCS(22),
dCCN(17),
dCCC(23), dCCS(18),
CC(27), dCCS(15),
s
CCCC(16)
CCCC(16),
CCCN(13)
CN(11), CS(11), dCCN(10)
s
sCCCN(11), sCCCO(11)
s
t
t
t
dCCC(11)
dCCC(49), dCCO(16)
s
s
CCCC(21), dCCN(16)
CCCN(14), dCCS(14), dCCC(12),
CCCC(14), dCCN(11)
CCCN(22), dCCN(10)
CCCN(27)
CCCO(26), dCCC(17),
11.86
0.54
2.76
16.35
6.52
100.00
2.60
17.90
82.95
74.87
sCCCC(11), sCCSN(13)
dCCC(14),
s
s
s
s
s
s
s
s
s
CCCC(23),
CCCO(48), s
s
83
66
42
40
33
28
26
s
CCCC(17), dCCN(13)
CCCN(33),
CCCN(30),
CCCN(61)
CCCN(47),
CCNC(18)
s
s
CCCO(19), sCCCS(10)
CCSN(24)
CCSN(19), sCCCS(16)
s
a
IIR, infrared intensity; SRa, Raman activity; IRa, Raman intensity; t, stretching; d, in plane bending; c, out of plane bending; s, torsion.
wavenumbers of TPBA. The recorded FT-IR and calculated vibra-
tional wavenumber along with their relative intensities and prob-
able assignments of TPBA are given in Table 1. The experimental
FT-IR and calculated Infrared and Raman spectra of the title mole-
cule depicted as Fig. 3. Any discrepancy noted between the
observed and the calculated frequencies may be due to the two
facts: one is that the experimental results belong to solid phase
and theoretical calculations belong to gaseous phase; the another
one is that the calculations have been actually done on a single
molecule contrary to the experimental values recorded in the pres-
ence of intermolecular interactions. It is customary to scale down
the calculated harmonic frequencies in order to improve the agree-
ment with the experiment. Vibrational frequencies calculated at
B3LYP/6-311G(d,p) level of theory were scaled by 0.967 to correct
the theoretical error in this work.
Vibrational analysis of COOH group is made on the basis of C@O
group and OH group. The most characteristic feature of the car-
boxylic group is a single band observed usually in the region
1740–1660 cmꢂ1 [25]. In solid state most of the carboxylic acids
exist in dimeric form because of the inter-molecular hydrogen
bonding between two COOH groups. In such a case C@O stretching
vibrations are expected, one in-phase (symmetric stretching vibra-
tion) is Raman active and other one out-of-phase (anti-symmetric
stretching vibration) is IR active. Similarly in the present study also
a very strong band observed in FT-IR at 1674 cmꢂ1 is assigned C@O
stretching vibration. But the theoretically computed value at
1744 cmꢂ1 shows deviation of about 70 cmꢂ1 when compared with
their experimental counterpart and this deviation may be due to
the presence intermolecular interaction. The carboxylic acid defor-
mation vibrations are expected in a wide range of 1450–1150 cmꢂ1
depending on whether the acid is monomeric or dimeric. In the
present study the frequency observed at 1355 cmꢂ1 in FT-IR spec-
tra is assigned for deformation vibration. The theoretically com-
puted values at 1331 cmꢂ1 show good agreement with the
experimental observations.
6.2.1. COOH group vibrations
The OAH group gives rise to the three vibrations viz., stretching,
in-plane bending and out-of-plane bending vibrations. The OAH
group vibrations are likely to be the most sensitive to the environ-
ment, so they show pronounced shifts in the spectra of the
hydrogen-bonded species. In the case of unsubstituted phenol it
has been shown that the frequency of OAH stretching vibration
in the gas phase is 3657 cmꢂ1 [24]. In the present study the broad
bands observed in FT-IR spectrum at 3650 cmꢂ1 is assigned to OAH
stretching vibrations. The theoretical values at 3647 cmꢂ1 in B3LYP
method gives good agreement with the experimental wavenum-
ber. The PED corresponding to this vibration is a pure stretching
mode and it is exactly contributing to 100%.
6.2.2. CAH vibrations
The existence of one or more aromatic rings in a structure is
readily determined from the CAH and C@CAC ring related vibra-
tions. The CAH stretching occurs above 3000 cmꢂ1 and is typically
exhibited as a multiplicity of weak to moderate bands compared
with the aliphatic CAH stretch [26]. In this region the bands are
not affected appreciably by the nature of substituent. From
Table 1 the observed FT-IR spectral wavenumbers are assigned to

M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
13
the CAH stretching modes of aromatic group of TPBA. The medium
band in FT-IR at 3070 cmꢂ1 is assigned to CAH stretching vibra-
tions. The theoretically computed wavenumbers (mode Nos. 2–
13) by B3LYP/6-311G(d,p) level of theory predicted at 3144,
3139, 3138, 3130, 3112, 3111, 3108, 3102, 3094, 3093 and
3091 cmꢂ1 fall within the recorded spectral range. As expected
these modes are pure stretching modes as it is evident from the
Table 1.
The observed CAH in-plane bending vibrations are assigned at
1222, 1199, 1164, 1164, 1129 and 1101 cmꢂ1 in FT-IR spectra.
The wavenumbers are predicted at 1272, 1225, 1197, 1172, 1172,
1149, 1096, 1081, 1072, 1070, 1032 and 1030 cmꢂ1 (mode
Nos.31, 32 and 34–42, 45 and 46) for the same vibrations which
also correlated with the experimental values. Furthermore, the
band is observed at 950 cmꢂ1 in FT-IR spectrum for out of plane
bending vibrations. The calculated wavenumber values at 968,
956, 885, 884, 854, 840, 826 and 815 cmꢂ1 for the
out-plane-bending vibrations are found to be exactly correlated
with their experimental counterpart.
6.2.3. CAS and CAN vibrations
In the case of thiophene two CAS stretching vibrations are
attributed, one is fell in higher wavenumber and another one is
in lower wavenumber. The CAS stretching wavenumbers are
observed by Kwiatkowski et al. and Bak et al. [27,28] at 840 and
754 cmꢂ1 whereas Kupka et al. [29] have been predicted theoreti-
cally at 842 and 750 cmꢂ1 by DFT method. Notwithstanding the
fact, in our present study, the ring connected CAS bond stretching
vibrations predicted in lower wavenumber at 720 and 717 cmꢂ1
whereas the another CAS bond stretching vibrations attributes in
higher wavenumber at 819 and 818 cmꢂ1. The PED contributes
around 60% in the lower wavenumber region whereas in the higher
wavenumber region this contribution falls around 40% shown in
the Table 1. The CS in-plane-bending vibrations are predicted at
634 and 617 cmꢂ1 by B3LYP method. The deformation vibrations
are also predicted in the lower wavenumber region at 497, 491,
474 and 324 cmꢂ1 respectively. The other essential characteristic
vibrations of the title compound is CAN stretching vibrations,
which are predicted at 1380, 1327 and 1301 cmꢂ1 in
B3LYP/6-311G(d,p) level of theory. There are no bands observed
in the experimental spectrum. The deformation vibrational
wavenumbers of CAN group are observed at 840 and 834 cmꢂ1
in FT-IR spectrum. The theoretically predicted CAN deformation
vibrational wavenumbers are calculated at 887, 854, 840 and
826 cmꢂ1 in B3LYP level. The PED column shows these modes are
a mixed one with minor contributions.
6.2.4. CAC vibrations
The ring stretching vibrations are very much important in the
spectrum of benzene, pyridine and their derivatives are highly
characteristic of the aromatic ring itself. CAC ring stretching vibra-
tions occur in the region 1430–1625 cmꢂ1. In general, the bands
are of variable intensity and are observed at 1625–1590, 1575–
1590, 1470–1540, 1430–1465 and 1280–1380 cmꢂ1 from the
wavenumber ranges given by Varsanyi [30] for the five bands in
the region. In the present study, the CAC stretching vibrations
are found at 1610, 1576, 1518 cmꢂ1 in IR spectra for Benzene ring.
The computed wavenumbers at 1594, 1567, 1555, 1538 and
1395 cmꢂ1 by DFT method assigned CAC stretching vibrations for
the Benzene ring. The band observed at 1431 cmꢂ1 in IR spectra
identified as CAC stretching vibrations for the pyrrole ring. These
vibrations also computed at 1490, 1410 and 1380 cmꢂ1 by DFT
method for pyrrole ring. The band observed at 1043 cmꢂ1 in IR
spectra identified as CAC stretching vibrations for the thiophene
ring. These vibrations also calculated at 1459, 1421, 1301, 1294,
1057 and 1040 cmꢂ1 by DFT method for thiophene ring. The
Fig. 3. The experimental FT-IR and calculated infrared and Raman spectra of the
TPBA.
wavenumber 1234 cmꢂ1 has also been assigned for CAC stretching
vibrations which calculated by B3LYP/6-311G(d,p) level of theory.
The CACAC in-plane-bending bands always occur between the
value 1000–600 cmꢂ1 [31]. The band observed at 863 cmꢂ1 in
FT-IR spectrum is assigned to CACAC deformations of phenyl ring.
The computed wavenumbers at 998, 869, 619, 377, 207, 185 and
115 cmꢂ1 by DFT method have been assigned CACAC in plane
bending vibrations. The PED contribution for this mode is a mixed

14
M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
mode as it is evident from Table 1. The calculated wavenumber at
700, 568, 409, 156 and 91 cmꢂ1 are assigned as CACACAC tor-
sional vibrations for the title molecule.
141.62 ppm in 13C NMR spectrum for the title molecule, since
those carbon atoms which belong to benzene ring. The calculated
values for benzene ring carbon atoms also fall within the expected
range of 131.32–149.97 ppm. The exception in the case of aromatic
ring carbon chemical shift is observed which are 125.22 and
141.62 ppm due to the substitution of carboxylic acid group and
pyrrole nitrogen respectively. The chemical shift values in the pyr-
role ring connected carbon atoms of the thiophene ring are
observed 144.52 and 144.38 ppm whereas the calculated one is
at 133.68 ppm which gives good agreement with the experimental
chemical shift values. The signals of the aromatic proton were
observed at 7.43–8.02 ppm which shows good agreement with
theoretical value of 7.27–8.24 ppm. The adjacent proton chemical
shift values H6 and H7 in pyrrole ring are calculated at 6.57 and
6.57 ppm which are exactly correlated with the experimental val-
ues those are also observed at 6.57 ppm of each. This shows that
the correlation between theory and experiment for the title com-
pound is good. For 1H and 13C chemical shifts, the calculated values
are also agreement with the experimental values.
6.3. 13C and 1H NMR spectral analysis
Application of the gauge-including atomic orbital (GIAO) [32]
approach to molecular system was significantly improved by an
efficient application of the method to the ab initio SCF calculations,
using technique borrowed from analytic derivative methodologies.
GIAO procedure is somewhat superior since it exhibits a faster con-
vergence of the calculated properties upon extension of the basis
set used. Taking into account the computational cost and the effec-
tiveness of calculation, the GIAO method seems to be preferable
from many aspects at the present state of this subject. On the other
hand, the density functional methodologies offer an effective alter-
native to the conventional correlated methods, due to their signif-
icantly lower computational cost. The 1H and 13C chemical shifts
are measured in DMSO solvent and are calculated in different sol-
vents as depicted in Table 2. The isotropic chemical shifts are fre-
quently used as an aid in identification of reactive organic as
well as ionic species. It is recognized that accurate predictions of
molecular geometries are essential for reliable calculations of mag-
netic properties. At first the full geometry optimization of TPBA
was performed by using B3LYP/6-311G(d,p) level of theory. Then,
GIAO 1H and 13C chemical shift calculations of the TPBA has been
made by same method. The 1H and 13C NMR spectra of TPBA mea-
sured in DMSO solvent are shown in Table SI-3.
6.4. NBO analysis
By the application of the second-order donor–acceptor NBO
energetic analysis, insight in the most important delocalization
schemes was obtained. NBO analysis gives information about intra
and intermolecular bonding and interactions among bonds, and
also provides a convenient basis for investigating the interactions
in both filled and virtual orbital spaces along with charge transfer
and conjugative interactions in molecular system. The second
order Fock matrix was carried out to evaluate the donor–acceptor
interactions in the NBO analysis [35]. The change in electron den-
The result in Table 3 shows that the range of 13C NMR chemical
shift of typical organic molecule usually is >100 ppm [33,34] the
accuracy ensures reliable interpretation of spectroscopic parame-
ters. The signals for aromatic carbons were observed at 125.22–
sity (ED) in the (r⁄ p⁄) antibonding orbitals and E(2) energies have
,
been calculated by natural bond orbital (NBO) analysis [36] using
DFT method to give clear evidence of stabilization originating from
various molecular interactions. NBO analysis has been performed
on TPBA using NBO 3.1 program as implemented in the Gaussian
03 W package at the DFT-B3LYP/6-311G(d,p) level of theory in
order to elucidate intramolecular hydrogen bonding, intramolecu-
lar charge transfer (ICT) interactions and delocalization of
Table 2
Experimental and calculated chemical shifts (ppm) of TPBA.
Atom
Calculated
Ethanol
Exp.
Water
Gas
DMSO
DMSO
C34
C25
C8
C19
C29
C4
168.65
149.97
144.54
144.40
135.81
135.17
135.12
135.05
134.16
134.14
132.58
132.54
131.31
130.24
130.19
129.60
129.55
116.06
116.03
168.72
149.97
144.51
144.37
135.78
135.18
135.14
135.08
134.19
134.15
132.65
132.62
131.33
130.27
130.22
129.64
129.59
116.00
115.98
166.98
149.93
144.98
144.90
136.20
134.89
134.77
134.49
133.52
133.83
131.53
131.40
131.18
129.50
129.47
128.88
128.84
116.94
116.90
168.70
149.97
144.52
144.38
135.79
135.18
135.14
135.07
134.18
134.15
132.63
132.60
131.32
130.26
130.21
129.63
129.58
116.02
116.00
166.73
141.62
133.68
133.68
130.36
131.60
131.60
130.36
130.36
130.36
129.60
129.60
125.22
127.23
127.23
124.75
124.75
110.10
110.10
p-electrons of the flavone ring. The hyperconjugative interaction
energy was deduced from the second-order perturbation approach
[37]. The interaction result is a loss of occupancy from the localized
NBO of the idealized Lewis structure into an empty non-Lewis orbi-
tal. For each donor (i) and acceptor (j), the stabilization energy E(2)
associated with the delocalization i ? j is estimated as
C1
C27
C26
C24
C11
C16
C28
C17
C10
C9
2
Fði; jÞ
Eð2Þ ¼ Eij ¼ q
D
i ej
ꢂ
ei
Some electron donor orbital, acceptor orbital and the interact-
ing stabilization energy resulted from the second-order-
micro-disturbance theory, where qi is the donor orbital occupancy,
ei and ej are diagonal elements and F(i,j) is the off diagonal NBO
Fock matrix element reported [38,39]. The larger the E(2) value,
the more intensive is the interaction between electron donors
and electron acceptors, i.e. the more donating tendency from elec-
tron donors to electron acceptors and the greater the extent of con-
jugation of the whole system.
In the present study, the intramolecular hyperconjugative inter-
actions are formed by the orbital overlap between bonding (CAC),
(CAN) and anti-bonding (CAC), (CAN) and (CAO) orbital which
results in intramolecular charge transfer (ICT) causing stabilization
of the molecular system. These interactions are observed as an
increase in electron density (ED) in (CAC), (CAN) and (CAO) anti-
bonding orbital that weakens the respective bonds shown in the
Table SI-4. A strong intramolecular hyperconjugative interaction
C18
C2
C3
H33
H32
H30
H31
H21
H15
H22
H14
H6
8.24
8.20
7.29
7.26
7.18
7.18
6.74
6.74
6.57
6.57
6.10
5.85
5.83
8.24
8.20
7.29
7.27
7.19
7.19
6.75
6.75
6.57
6.57
6.13
5.85
5.83
8.26
8.08
7.19
7.13
6.94
6.95
6.58
6.58
6.50
6.50
5.47
5.72
5.70
8.24
8.20
7.29
7.27
7.19
7.19
6.75
6.75
6.57
6.57
6.12
5.85
5.83
8.02
8.00
7.46
7.43
7.30
7.29
6.87
6.87
6.57
6.57
–
H7
H37
H13
H23
6.65
6.65

M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
15
Table 3
The experimental and computed (TD-/B3LYP/6-311(d,p)) absorption wavelength k (nm), excitation energies E (eV), absorbance and oscillator strengths (f) of TPBA.
DMSO
Water
Gas
Ethanol
Experimental
k (nm)
E (eV)
f
k (nm)
E (eV)
f
k (nm)
E (eV)
f
k (nm)
E (eV)
f
k (nm)
E
(eV)
344.63 (62 ? 63)
3.5976 0.0000 409.97
(91 ? 92)
4.4017 0.0730 329.69
(91 ? 93)
4.7959 0.1744 310.97
(91 ? 94)
(91 ? 95)
3.0242 0.0271 422.00
(91 ? 92)
3.7607 0.6886 325.22
(91 ? 93)
3.9870 0.0010 321.11
(91 ? 94)
2.9380 0.0156 410.68
(91 ? 92)
3.8123 0.5913 330.15
(91 ? 93)
3.8612 0.0011 311.47
(91 ? 94)
(91 ? 95)
3.0190 0.0274 340.68 3.643
3.7554 0.6954 269.92 4.598
3.9806 0.0011 203.54 6.098
281.67 (60 ? 63)
(61 ? 63)
258.52 (59 ? 63)
(60 ? 63)
(61 ? 64)
of
p-electrons with the greater energy contributions from
C1AC2 ? C3AC4 (18.75 kJ molꢂ1), C18AC19 (10.18 kJ molꢂ1);
C3AC4 ? C1AC2 (18.77 kJ molꢂ1), C18AC19 (10.04 kJ molꢂ1 for
the pyrrole ring, C8AC9 ? C10AC11 (16.04 kJ molꢂ1), C3AC4
(9.10 kJ molꢂ1); C10AC11 ? C8AC9 (14.71 kJ molꢂ1); C16AC17 ?
C18AC19 (14.68 kJ molꢂ1); C18AC19 ? C1AC2 (9.19 kJ molꢂ1),
C16AC17 (16.07 kJ molꢂ1) for thiophene rings of the molecule,
while
C24AC29 ? C25AC26
(22.95 kJ molꢂ1),
C27AC28
(19.33 kJ molꢂ1); C25AC26 ? C24AC29 (17.92 kJ molꢂ1), C27AC28
(22.85 kJ molꢂ1); C27AC28 ? C24AC29 (20.82 kJ molꢂ1), C25AC26
(19.73 kJ molꢂ1), C34AO35 (21.28 kJ molꢂ1); for the benzene ring
of the molecule.
6.5. Electronic properties
6.5.1. Absorption spectra
TD-DFT/B3LYP/6-311G(d,p) calculations have been performed to
determine the low-lying excited states of TPBA On the basis of fully
optimized ground-state structure. The calculated result involving
the vertical excitation energies, oscillation strength (f) and wave-
length are carried out and compared with measured experimental
wavelength listed in Table 3. Typically, according to Frank–Condon
principle, the maximum absorption peak kmax corresponds in an
UV–Vis spectrum to vertical excitation. TD-DFT/B3LYP/6-
311G(d,p) level of theory predict one intense electronic transition
for DMSO at 4.4017 eV (281.67 nm) with oscillator strength
f = 0.073 is in good agreement with the measured experimental data
DMSO (exp = 269.92 nm) shown in Fig. 4. All the structures allow
strong
p
–
p⁄ and
r
–
r⁄ transition in the UV–Vis region with high
extinction co-efficients. The
p
–
p⁄ transitions are expected to occur
relatively at lower wavelength, due to the consequence of the
extended aromaticity of the benzene ring. Natural bond orbital anal-
ysis also indicates that molecular orbitals are mainly compared of
atomic orbital so above electronic transitions are mainly derived
from the contribution of
p⁄ bands.
p
p
–
Fig. 4. The experimental (DMSO) and theoretical (gas, water, DMSO and ethanol)
UV–Vis spectra of the TPBA.
6.5.2. Frontier molecular orbital analysis
The electronic absorption corresponds to the transition from
the ground to the first excited state and is mainly described by
one electron excitation from the highest occupied molecular orbi-
tal (HOMO) to the lowest unoccupied molecular orbital (LUMO).
The HOMO represents the ability to donate an electron, LUMO as
an electron acceptor represents the ability to obtain an electron.
Both HOMO and LUMO are the main orbitals that take part in
chemical stability [40]. The energy values of LUMO and HOMO
and their energy gap reflect the chemical activity of the molecule.
The decrease in the HOMO and LUMO energy explains the
Intramolecular charge transfer (ICT) interaction taking place
within the molecule which is responsible for the activity of the
molecule. The HOMO–LUMO energy separation has served as a
simple measure of kinetic stability. A molecule with a small or
no HOMO–LUMO gap is a chemically reactive [41–43]. Pearson
showed that the HOMO–LUMO gap represents the chemical
hardness of the molecule [44,45]. The HOMO–LUMO energy gap
of TPBA was calculated at the B3LYP/6-311G(d,p) level and their
values shown below reveals that the energy gap reflect the chem-
ical activity of the molecule. The HOMO is located over the thio-
phene and pyrrole rings of the molecule, the HOMO ? LUMO
transition implies an electron density transfer to benzoic acid from
thiophene and pyrrole rings. Moreover, these orbital significantly
overlap in their position for TPBA. The atomic orbital compositions
of the frontier molecular orbital are sketched in Table SI-5. The cal-
culated energy values in different solvent are shown in Table SI-6.
HOMO energy = ꢂ5.40 eV.
LUMO energy = ꢂ1.87 eV.
HOMO–LUMO energy gap = 3.53 eV.

16
M. Kurt et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 8–17
Table 4
negative charges of O atom, C34 accommodate positive charge and
become more acidic. Other C atoms are negative. Moreover,
Mulliken atomic charges also show that all the hydrogen atoms
have a net positive charge but H37 atoms accommodate more pos-
itive atomic charges 0.257, than the other hydrogen atoms and is
acidic. This is due to the presence of electronegative oxygen atoms
(O35 and O36). The negative values of atomic charges of C atom in
the aromatic ring lead to a redistribution of electron density.
Thermodynamic properties at different temperatures at the B3LYP/6-311G(d,p) level
for TPBA.
T (K)
C (cal molꢂ1 Kꢂ1
)
S (cal molꢂ1 Kꢂ1
)
H (kcal molꢂ1
)
100
150
200
250
298.15
300
350
400
450
500
550
600
650
700
31.326
41.424
53.163
65.812
78.004
97.595
112.957
127.019
140.677
153.663
154.162
167.477
180.558
193.333
205.749
217.772
229.387
240.591
251.391
2.219
4.130
6.588
9.660
13.219
13.368
17.695
22.599
28.027
33.923
40.233
46.910
53.911
61.200
78.464
90.484
6.8. Thermodynamical properties
101.520
111.439
120.250
128.038
134.920
141.019
146.447
On the basis of Vibrational analysis, the statistical thermo
chemical analysis of TPBA is carried out by B3LYP/6-311G(d,p)
level of theory considering the molecule to be at room temperature
of 298.15 K and 1 atm pressure. The thermodynamic functions, like
heat capacity (C), enthalpy changes (H) and entropy (S), rotational
constants and zero point vibrational energy (ZPVE) of the molecule
by DFT method for the title molecule were obtained from the the-
oretical harmonic frequencies and listed in Table SI-9. It can be
observed that these thermodynamic functions such as heat capac-
ity (C), enthalpy changes (H) and entropy (S), are increasing with
temperature ranging from 100 to 700 K due to the fact that the
molecular vibrational intensities increase with temperature which
are shown in Table 4. The correlation equations between heat
capacity, enthalpy changes, entropy and temperatures were fitted
by correlation coefficients. The corresponding correlation graphics
are shown in Fig. 5. All the thermodynamic data give helpful infor-
mation for the further study on the title molecule.
7. Conclusion
The spectroscopic techniques such as FT-IR, NMR and UV–visi-
ble supported by the recent development of computational tool
such as DFT method allow the structural analysis of our title mole-
cule to be conducted in a seamless way. In the present study, the
experimental approach to molecular properties has been shown
by some examples of FT-IR, NMR and UV–visible spectroscopy.
The theoretical support has been addressed by example of
DFT/B3LYP/6-311G(d,p) calculations, and the peculiarities and lim-
itations of the theoretical approach to the analysis have been con-
sidered. The good agreement between the experimental results
and calculated frequencies indicate that the density functional
methods provide valuable information for understanding the
vibrational spectra of the TPBA molecule. NBO analysis gives the
information about intermolecular and intra molecular charge
transfer within the molecule. The UV–visible spectrum was also
recorded and the energies of frontier MO’s and the kmax of the com-
pound were also determined from TD-DFT method. The relative
stabilities, HOMO–LUMO energy gap and implications of the elec-
tronic properties are examined and discussed. The observed and
the predicted isotropic chemical shifts are found to be in good
agreement. Thermodynamic properties in the range from 100 to
700 K are obtained. The gradients of heat capacity, entropy and
enthalpy with temperature are always positive.
Fig. 5. The correlation graphic of heat capacity, entropy, enthalpy and temperature
for TPBA molecule.
6.6. Molecular electrostatic potential (MEP) analysis
The molecular electrostatic potential (MEP) is related to the
electronic density and is a very useful descriptor for determining
sites for electrophilic attack and nucleophilic reactions as well as
hydrogen-bonding interactions [46,47]. The molecular electrostatic
potential, V(r), at a given point r(x, y, z) in the vicinity of a molecule,
is defined in terms of the interaction energy between the electrical
charge generated from the molecule electrons and nuclei and a pos-
itive test charge (a proton) located at r. To predict reactive sites for
electrophilic and nucleophilic attack for the title molecule, MEP was
calculated at the B3LYP/6-311G(d,p) optimized geometry. The neg-
ative (red) regions of MEP were related to electrophilic reactivity
and the positive (white) regions to nucleophilic reactivity shown
along with contour map in Table SI-7. The negative regions are
mainly localized on the electronegative atoms. A maximum posi-
tive region is localized on the carboxylic acid group of the molecule
indicating a possible site for nucleophilic attack. The electrophilic
and nucleophilic sites give information about the region from
where the compound can have non-covalent interactions.
Appendix A. Supplementary data
6.7. Mulliken atomic charge
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.07.058.
The Mulliken atomic charges of TPBA molecule calculated by
DFT method at 6-311G(d,p) basic set in gaseous phase are given
in Table SI-8. The charge distribution on the molecule has an
important role in the application of quantum mechanical calcula-
tions for the molecular system. The charges at the sites of the C
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