Synthesis of 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5(4H)-one and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione and solvent effects on their infrared spectra in organic solvents

Article abstract of DOI:10.1016/j.saa.2020.119424

In the present study novel 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5(4H)-one (compound (4)) and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione (compound (5)) were synthesized. These oxadiazole ring derivatives were cha

Full text of DOI:10.1016/j.saa.2020.119424

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis of 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5
(4H)-one and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-
5(4H)-thione and solvent effects on their infrared spectra in organic
solvents
a
a
b
Yesim S. Kara a, , Mustafa Ünsal , Nalan Tekin , Aslı Eßsme
⇑
a Kocaeli University, Science and Art Faculty, Department of Chemistry, Umuttepe Campus, 41001 Kocaeli, Turkey
b Kocaeli University, Department of Elementary Science Education, Umuttepe Campus, 41001 Kocaeli, Turkey
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 novel oxadiazole ring derivatives
were synthesized.
The solvent effects were studied by
Infrared spectroscopy.
The theoretical results assigned using
PED contributions.
The m(C@O), m(C@N) and m(C@S) were
correlated with the Swain, AN, KBM
and LSER.
ꢀ
The quadratic and interactive effects
of solvent parameters were also
reported.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 October 2020
Received in revised form 23 December 2020
Accepted 30 December 2020
Available online 5 January 2021
In the present study novel 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5(4H)-one (com-
pound (4)) and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione (compound (5))
were synthesized. These oxadiazole ring derivatives were characterized by IR, 1H NMR, 13C NMR and
HRMS analyses. The solvent effects on C@O, C@N and C@S stretching vibrational frequencies (
(C@N) and (C@S)) of synthesized compounds were investigated experimentally using attenuated total
reflection (ATR) infrared spectroscopy and compared with the theoretical results assigned using the
potential energy distribution (PED) contributions. Furthermore, the (C@O), (C@N) and (C@S) of com-
m(C@O),
m
m
Keywords:
Infrared spectroscopy
Solvent effects
m
m
m
pound (4) and compound (5) were correlated with empirical solvent parameters such as the solvent
acceptor numbers, the Swain equation, the Kirkwood-Bauer-Magat equation, and the linear solvation
energy relationships. Apart from the linear effects investigated in similar studies, solvent-induced vibra-
tional shifts were investigated using the quadratic equation. The prediction capabilities of empirical sol-
vent parameters were statistically compared. It was found that the linear solvation energy relationships
show better correlation than the other empirical solvent parameters. Additionally, the quadratic equation
provided more accurate predictions for the vibrational frequency locations than the Swain and the linear
solvation energy relationships equations.
Oxadiazole ring
Empirical solvent parameters
Interaction effects
Quadratic equation
Ó 2020 Elsevier B.V. All rights reserved.
⇑
Corresponding author.
E-mail address: yesimkara@kocaeli.edu.tr (Y.S. Kara).
https://doi.org/10.1016/j.saa.2020.119424
1386-1425/Ó 2020 Elsevier B.V. All rights reserved.

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
energy relationships (LSER) which includes the Kamlet-Taft’s sol-
vent parameters [24].
1. Introduction
The KBM model equation is represented in Eq. (1) [25];
Oxadiazole ring is a heterocyclic aromatic compound including
one oxygen and two nitrogen atoms in a five membered ring.
Oxadiazoles may exist in four different isomeric structures such
as 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole and 1,3,4-
oxadiazole depending on the position of the nitrogen atoms in
the ring [1]. The synthesis and biological activities of the mole-
cules containing 1,2,4-oxadiazole ring stand as a continuously
expanding area research in heterocyclic compounds which are
commonly used in both pharmaceutical and agricultural fields.
The 1,2,4-oxadiazole ring is generally present as fragments such
as aromatic, non-aromatic rings and aliphatic structures in the
structure of various drugs. Fig. 1 shows examples of drugs con-
taining the 1,2,4-oxadiazole ring [2–7]. Therefore, it is predicted
that investigating the solvent effects of heterocyclic compounds
will yield valuable results both the academic and industrial com-
munities [8].
Solvents effects are very important tools for pharmaceutical
drug design because they affect the degree of absorption, transport
and release of the drug in the organism [9]. The solvent effect can
be studied by various spectroscopy methods, such as Infrared,
NMR, Raman, Fluorescence and UV–Vis spectroscopy [10–14].
However, infrared spectroscopy is one of the oldest, well-
established and inexpensive experimental techniques to study
molecular vibrations, which are largely used to investigate solvent
effects [10]. The infrared frequency shifts obtained of solute mole-
cule in various dilute solutions show the interactions between sol-
vent and solute [15].
À
Á
m0
ꢁ
ms
D
m
Cð
e
e
ꢁ 1Þ
þ 1Þ
¼
¼
ð1Þ
m0
m0 ð2
where
e is the dielectric constant of solvent, C is a constant depen-
dent on the electrical properties and dimensions of the vibrating
s
o
solute dipole,
m
and
m
are the vibrational frequency of a solute
in the solvent and the gas phase, respectively.
The solvent acceptor number (AN) equation is given in Eq. (2)
[18],
m
¼
m0 þ KðANÞ
ð2Þ
where K is the sensitivity of vibrational frequency (
m
) to the solvent
AN and m0 is the vibrational frequency of a solute in reference
solvent.
The Swain equation is shown in Eq. (3) [16];
m
¼
m0 þ aAj þ bBj
ð3Þ
where,
m
and m0 are the vibration frequency of a solute in a solvent
and the predicated vibration frequency in reference solvent, respec-
tively. Bj and Aj are measure of the solvent hydrogen-bond acceptor
basicity and hydrogen-bond donor acidity, respectively. The coeffi-
cients of b and a describe the sensitivity of solute for a solvent to the
hydrogen-bond acceptor basicity and hydrogen-bond donor acidity,
respectively.
The model equation of LSER is represented in Eq. (4) [16,26];
Empirical solvent parameters are usually used to predict, corre-
late and characterize how solvent effects on spectral properties
and describe and quantify of specific/nonspecific interactions
between solvent and solute [16–19]. The most commonly used sol-
vent parameters (single-parameter and multi-parameters) of to
explore solvent effects on infrared spectra are the solvent acceptor
number (AN) which was proposed by Gutman [20], the Kirkwood,
Bauer and Magat (KBM) equation was presented by Kirkwood,
Bauer and Magat [21,22], the Swain equation (SE) which includes
the solvent parameters of Aj and Bj [23], and the linear solvation
m
¼
m0 þ spꢂ þ a
a
þ bb
ð4Þ
where
frequency in reference solvent and the stretching vibrational fre-
quency of solute in pure solvent, respectively. b and are a measure
of the solvent hydrogen-bond acceptor basicity and hydrogen-bond
donor acidity, respectively. * is an index of solvent dipolarity/po-
larizability. s, a and b in Eq. (4) are the regression coefficients and
provide to the sensitivities of the stretching vibrational frequency
of the organic compound to signify solvent parameters.
m0 and m are the regression value of the stretching vibrational
a
p
Fig. 1. Examples of drugs containing 1,2,4-oxadiazole ring.
2

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
During our literature review, it was seen that a number of stud-
ies were presented to develop a physically meaningful and quanti-
tatively accurate description of vibration frequency changes and
solute-solvent interactions [27,28]. To the best of our knowledge,
experimental vibrational studies of 1,2,4-oxadiazole ring in differ-
ent pure solvents has never been performed. In this study, two
novel 1,2,4-oxadiazole derivative compounds were synthesized
which were characterized by IR, 1H NMR, 13C NMR and HRMS anal-
yses. In addition, the solvent effects on C@O, C@S and C@N stretch-
600 cmꢁ1) of the solutions were recorded using a Bruker Alpha II
spectrophotometer with a resolution 2 cmꢁ1 and 64 scans by
Mercury-Cadmium-Telluride (MCT) detector. The solution FT-IR
spectra were collected using a diamond ATR (Attenuated total
reflection) at room temperature (20–23 oC). The FT-IR spectra of
pure solvents as the background spectra, solid compound (4) and
solid compound (5) were recorded under the same conditions.
The Opus 6.5 software version was used for manipulation of all
data stored on the computer.
ing vibrational frequencies (m(C@O), m(C@N) and m(C@S)) of the
oxadiazole ring derivatives was studied experimentally using
attenuated total reflection (ATR) infrared spectroscopy. The
observed spectral results of the two novel 1,2,4-oxadiazole deriva-
tive compounds have been compared with the vibration assign-
ments calculated with the help of the potential energy
3. Synthesis
4-methyl-benzaldehyde oxime (1), 4-methyl-benzimidoyl chlo-
ride (2) and 4-methyl-N-(4-ethyl-phenyl)benzamide oxime (3)
were synthesized according to the literature. The methods in liter-
ature were applied with slight modifications for the synthesis of
compound (4) and compound (5) (Scheme 1) [29].
distribution (PED). The m(C@O), m(C@N) and m(C@S) were corre-
lated with the Swain, AN, KBM and LSER solvent scales. Addition-
ally, the quadratic and interactive effects of solvent parameters
on the experimental vibrational spectra of these oxadiazole ring
derivatives were also investigated in this study.
2. Experimental procedure
3.1. Synthetic procedures
The synthesis of 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-
oxadiazol-5(4H)-one, compound (4) and 4-(4-ethyl-phenyl)-3-(4-
methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione, compound (5) is
straightforward as illustrated in Scheme 1. Melting points of com-
pound (4) and compound (5) were determined on Stuart SMP30
apparatus without a correction. The FT-IR spectra of compound
(4) and compound (5) were recorded with Bruker Alpha II spec-
trometer in the region of 4000–400 cmꢁ1. The HRMS analyses were
performed on Water SYNAPT G1 Mass Spectrometer. 1H NMR and
13C NMR spectra of compounds were recorded by Bruker Avance III
(400 MHz) NMR spectrometer. The FTIR, 13C NMR and 1H NMR
spectra for compound (4) and compound (5) were given in Supple-
mentary Material.
3.1.1. 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5
(4H)-one (Compound (4))
4-methyl-N-(4-ethyl-phenyl)benzamide oxime (3) (3.48 g, 13,6
mmol) was solved in xylene (15 mL) at room temperature with
stirring. Triethylamine (1.52 g, 15 mmol) was added to the stirred
solution and then ethyl chloroformate was added dropwise (1.47 g,
13,6 mmol) in xylene (10 mL) and the mixture was refluxed for
12 h. At the end of time, the reaction mixture was filtered whereby
a filter paper and the solution was evaporated at reduced pressure.
The crude reaction product was crystallized in ethyl acetate/petro-
leum ether (1:3) to give compound (4) (2.7 g, 72%); IR (KBr),
m
(cmꢁ1): 1771.30 (C@O), 1593.85 (C@N); mp 123.5–125.0 °C; 1H
NMR (CDCl3), d (ppm) : 7.30–7.30 (dd, aromatic, 4H), 7.19–7.16
(dd, aromatic, 4H), 2.74–2.68 (q, ACH2, 2H), 2.38 (s, ACH3, 3H),
1.29–1.25 (t, ACH3, 3H); 13C NMR (CDCl3), d (ppm) : 158.64
(C@O), 157.61 (C@N), 145.94–120.20 (aromatic C) 28.53 (ACH2),
21.55 (ACH3), 15.21 (ACH3). HRMS for C17H17N2O2 [M+H]+ calcu-
lated 281.1290. Found 281.1290.
All solvents obtained from the Merck Company used for solvent
effect studies were of spectroscopic or analytical purity and dis-
tilled prior to the experiments. For the FT-IR solution spectra, the
concentrations of compound (4) and compound (5) solutions were
the range of 0.040 and 0.060 mol/L. The FT-IR spectra (4000–
Scheme 1. Synthesis of 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazol-5(4H)-one and 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5(4H)-thione.
3

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
3.1.2. 4-(4-ethyl-phenyl)-3-(4-methyl-phenyl)-1,2,4-oxadiazole-5
(4H)-thione (Compound (5))
monomer alcohol of each unpaired electron pair in the carbonyl
group separately. It was proposed that Band I could be the effect
of hydrogen bonds and Band II could be referred to non-specific
interactions (i.e. van der Waals forces) between the investigated
molecule and alcohol solvents.
A comparison of the experimental wavenumbers along with the
computed wavenumbers using the DFT/B3LYP/6-31G(d,p) level of
theory with their potential energy distributions (PED) of the com-
pound (4) and compound (5) in the polar and non-polar solvents
Compound (4) (1.1 g, 4.33 mmol) was refluxed with P2S5
(0.466 g, 2 mmol) in xylene for 35 h. The reaction mixture was fil-
tered through a filter paper and xylene was evaporated under
reduced pressure. The crude product was purified by flash column
chromatography, using ethyl acetate-petroleum ether (1:4) as elu-
ent. The residue was crystallized from ethanol. (Rf: 0.55). The pro-
duct recrystallized from ethanol to give compound (5) (0.49 g,
Yield 40%; IR (KBr),
m
(cmꢁ1): 1590.95 (C@N), 1327.10 (C@S); mp
were also listed in Table 1. Almost all carbonyl
vibrations have a very intense and narrow peak in the range of
1800–1600 cmꢁ1 [36,37]. This experimental/theoretical
(C@O)
bands were found at lower frequencies 1779.02–
m(C@O) stretching
172–173.3 °C; 1H NMR (CDCl3), d (ppm) : 7.36–7.34 (d, aromatic,
2H), 7.25–7.16 (m, aromatic, 6H), 2.77–2.72 (q, ACH2, 2H), 2.37
(s, ACH3, 3H), 1.32–1.28 (t, ACH3, 3H); 13C NMR (CDCl3), d (ppm)
: 187.47(C@S), 158.85 (C@N), 146.72–118.81 (aromatic C) 28.56
(ACH2), 21.56 (ACH3), 14.99 (ACH3). HRMS for C17H17N2OS [M
+H]+ calculated 297.1062. Found 297.1060.
m
1782.03 cmꢁ1/1771.94–1779.27 cmꢁ1 (with 84% pure PED contri-
butions) in polar solvents such as acetonitrile, nitrobenzene, etha-
nol, n-propanol, n-butanol, dichloromethane, tetrahydrofuran and
at higher frequencies 1779.02–1785.50 cmꢁ1/1783.14–1794.09 c
mꢁ1 (with 84% pure PED contributions) in non-polar solvents such
as chloroform, diethylether, m-xylene, toluene, benzene, carbon
tetrachloride, respectively.
3.2. Computational procedures
The theoretical computations were carried out using the Gaus-
sian 09 Rev. A. 11.4 [30] program with the density functional the-
ory (B3LYP functional; Becke, 3-parameter, Lee–Yang-Parr) [31,32]
at the 6-31G(d,p) basis set. The compound (4) and compound (5)
were viewed using GaussView 5.0.8 [33]. The experimentally pre-
dicted results of the compound (4) and compound (5) in 13 differ-
ent polar or non-polar solvents have compared with the theoretical
C@O, C@N and C@S stretching vibrational frequencies, together
with the potential energy distribution (PED) contributions inter-
preted using the VEDA 4 program [34]. The computed wavenum-
bers scaled by 0.9608 were calculated by the DFT/B3LYP/6-31G
(d,p) level of theory [35].
The bands due to C@N stretching modes of 1,3,4 oxadiazole ring
are reported at 1553, 1538, 1497, 1490 cmꢁ1 (FT-IR), 1572, 1550,
1492, 1490 cmꢁ1 (DFT) by Bee et al. [38]. The calculated frequen-
cies of the
m(C@N) stretching vibrations for compound (4)/com-
pound (5) are identified at 1571.55–1572.42 cmꢁ1 (23–24%),
1533.75–1534.22 cmꢁ1 (34–35%)/1569.48–1570.60 cmꢁ1 (11–
14%), 1534.43–1533.24 cmꢁ1 (33–34%) in polar solvents and at
1573.36–1574.47 cmꢁ1 (24–25%), 1535.08–1536.05 cmꢁ1 (35%)/1
571.12–1572.40 cmꢁ1 (15–18%), 1533.54–1534.45 (33%) cmꢁ1 in
non-polar solvents.
The C@S group is less polar than the C@O group and the C@S
stretching vibration attached to an N atom is found over the wide
range of 1563–700 cmꢁ1 [39]. The wavenumbers computed at
1270.52–1272.70 cmꢁ1 (18–19%) and 1273.90–1276.29 cmꢁ1
(16–18%) using the DFT/B3LYP/6-31G(d,p) level of theory are
4. Results and discussion
4.1. Solvent effects on the experimental vibrational spectra of
compound (4) and compound (5)
assigned to m(C@S) stretching modes for compound (5), the
recorded wavenumber for this m(C@S) mode in the FT-IR spectrum
at 1334.14–1336.15 cmꢁ1 and 1337.17–1345.68 cmꢁ1 in polar and
non-polar solvents, respectively.
The experimental
m(C@O)/m(C@N) of compound (4) and m(C@S)/
m(C@N) of compound (5) in 13 different pure solvents and the sol-
Fig. 3. illustrates the expected interactions between the studied
vent parameters are presented in Table 1. For compound (4) and
compound (5), the experimental stretching vibrational frequencies
are determined at higher frequency in less polar or apolar solvents
whereas the vibrational frequency bands of the compounds were
observed at lower frequencies in polar solvents. Fig. 2(a) and (b)
display the experimental FT-IR spectra of compound (4) and com-
pound (5) in the solvents. Additionally, Fig. 2(a) and (b) show the
frequency shifts and changes in the IR intensity of vibration fre-
quencies of compound (4) and compound (5) from the polar sol-
vents to the apolar solvents.
1,2,4-oxadiazole derivatives and the alcohols. Since there is no a
hydrogen in the molecules studied, it is thought that the partially
positively charged carbon in the C = X (X: O, N, S) bond and using
alcohol serve as a hydrogen bond donor. Due to its molecular struc-
ture, the C@N group is sterically disabled compared to the C@O and
C@S groups, so its interaction with alcohol is limited. This result
can be seen in the correlation coefficients of Aj and
a.
The experimental the (C@O), (C@N) and (C@S) of compound
m
m
m
(4) and compound (5) were correlated with empirical solvent
parameters such as the Ans, the KBM equation, the SE, and the
LSER. The KBM, ANs, Swain and LSER equations of the solvent-
In FTIR spectra of compound (4), one C@O absorption band in
non-alcohol solvents and two C@O absorption bands in ethanol,
n-propanol and n-butanol were determined. This observation can
induced the
m(C@O), m(C@N) and m(C@S) and correlation coeffi-
cients are listed in Table 2 for compound (4) and Table 3 for com-
be explained due to the occurrence of two types m(C@O) of com-
pound (5).
pound (4) in alcohol solvents and possibility for alcohol molecules
for self-associate to form large cluster-like molecules by acting as
both a H-bond donor and a H-bond acceptor of their hydroxyl
Fig. 4(a–g) is plots of the
the (C@S)/ (C@N) of compound (5) versus
tion. The negative slopes of the plots show that the
of compound (4) and the (C@S)/ (C@N) of compound (5) are red-
m(C@O)/m(C@N) of compound (4) and
ðeꢁ1Þ
m
m
of the KBM equa-
2eþ1
m(C@O)/m(C@N)
group [25]. The H-bonds can form between m(C@O) of compound
m
m
(4) with the self-associated or free alcohol molecules. Therefore,
the electron density of C@O in compound (4) decreases and two
C@O absorption bands are observed [25]. Similar observation has
been reported in the literature [25]. In this study, it was reported
that the carbonyl group and alcohol can make hydrogen bonds in
three different ways. It was explained that the carbonyl group,
monomer alcohol and dimer (self-associated) alcohols can interact,
and the third type of hydrogen bonding can be connected with the
shifted with the increase of the solvent dielectric constant. The lin-
ear equation parameters and correlation coefficients for com-
pounds (4) and compound (5) are shown in Table 2 and Table 3,
respectively. It is found that a poor relationship exists between
the KBM parameters with the
and the (C@S)/ (C@N) of compound (5) (Table 2 and Table 3)
since the frequency shifts are not only depended on the dielectric
m(C@O)/m(C@N) of compound (4)
m
m
4

Table 1
The (C@O)/
m
m(C@N) of compound (4) and
m
(C@S)/
m
(C@N) of compound (5) in different solvents and solvent parameters.
Solvent
Compound (4)
(C@O)1
Compound (5)
Solvent Parameters
a
m
m
(C@O)2
m
(C@N)1
m
(C@N)2
m
(C@S)1
m
(C@S)2
m
(C@N)1
m
(C@N)2
e
f(
e)
AN
b
a
p*
Aj
Bj
Acetonitrile
Nitrobenzene
Ethanol
Exp.
Theo.
1779.02
1771.94 (84%)
–
–
1613.51
1571.55 (23%)
1592.52
1533.75 (35%)
1334.14
1270.52 (18%)
1310.50
1311.65
1304.55
1306.17
1307.86
1310.22
1310.83
1311.64
1313.77
1313.20
1314.18
1315.52
1316.31
1612.88
1569.48 (13%)
1601.82
1534.43 (34%)
35.94
0.479
0.478
0.470
0.464
0.458
0.420
0.407
0.361
0.340
0.239
0.240
0.229
0.226
18.9
0.40
0.19
0.66
0.86
0.54
0.52
0.47
0.82
0.55
0.58
0.24
0.37
0.86
Exp.
Theo.
1777.07
1771.99 (84%)
–
–
1612.78
1571.56 (23%)
1591.80
1533.73 (35%)
1336.22
1270.53 (18%)
1614.59
1569.49 (11%)
1602.67
1534.42 (33%)
34.78
24.55
20.45
17.51
8.93
7.58
4.89
4.20
14.8
37.1
33.7
32.2
20.4
8.0
0.30
0.75
0.90
0.84
0.10
0.55
0.10
0.47
0.12
0.11
0.10
0.10
0
0.29
0.66
0.63
0.61
0.33
0.17
0.42
0.12
0.06
0.13
0.15
0.09
0.86
0.45
0.44
0.43
0.80
0.67
0.73
0.34
0.50
0.54
0.59
0.34
Exp.
Theo.
1769.54
1772.84 (84%)
1774.52
1777.80
1785.39
1607.67
1571.65 (23%)
1586.09
1533.82 (35%)
1330.79
1270.80 (18%)
1608.76
1569.59 (11%)
1592.45
1534.23 (33%)
0.86
0.84
0.84
0.13
0
n-Propanol
n-Butanol
Exp.
Theo.
1771.72
1773.44 (84%)
1609.26
1571.33 (23%)
1587.24
1535.20 (34%)
1331.14
1271.09 (19%)
1610.51
1569.96 (13%)
1594.46
1532.99 (33%)
Exp.
Theo.
1770.96
1774.12 (84%)
1610.02
1571.80 (23%)
1589.52
1533.88 (35%)
1332.99
1271.29 (19%)
1611.49
1570.02 (13%)
1596.31
1532.99 (33%)
Dichloromethane
Tetrahydrofuran
Chloroform
Diethylether
m-Xylene
Exp.
Theo.
1777.07
1777.82 (84%)
1612.78
1572.23 (24%)
1590.35
1534.10 (35%)
1333.62
1272.31 (18%)
1613.01
1570.44 (14%)
1599.54
1533.16 (33%)
Exp.
Theo.
1782.03
1779.27 (84%)
1614.09
1572.42 (24%)
1592.10
1534.22 (35%)
1336.15
1272.70 (18%)
1614.12
1570.60 (14%)
1601.22
1533.24 (33%)
Exp.
Theo.
1779.02
1783.14 (84%)
1613.34
1573.36 (24%)
1593.15
1535.08 (35%)
1337.17
1273.90 (18%)
1615.85
1571.12 (15%)
1603.09
1533.54 (33%)
23.1
3.9
0.20
0
Exp.
Theo.
1789.01
1784.43 (84%)
1615.09
1573.52 (24%)
1595.21
1535.18 (35%)
1338.59
1274.14 (18%)
1615.14
1571.13 (15%)
1604.50
1534.12 (33%)
Exp.
Theo.
1784.52
1793.15 (84%)
1616.84
1574.39 (25%)
1596.05
1536.00 (35%)
1341.26
1276.12 (16%)
1616.90
1572.30 (17%)
1604.42
1534.33 (33%)
2.37
2.38
2.27
2.24
2.4
0
0.47
Toluene
Exp.
Theo.
1784.48
1793.01 (84%)
1614.32
1574.35 (25%)
1595.07
1535.96 (35%)
1342.83
1276.08 (16%)
1617.46
1572.27 (17%)
1605.04
1534.35 (33%)
6.8
0
0.49
0.55
0.21
Benzene
Exp.
Theo.
1783.65
1793.81 (84%)
1616.81
1574.43 (25%)
1596.05
1536.06 (35%)
1343.16
1276.22 (16%)
1617.35
1572.37 (18%)
1605.61
1534.42 (33%)
8.2
0
Carbon tetrachloride
Exp.
1785.50
1617.64
1597.71
1345.68
1618.69
1608.76
8.6
0
Theo.
1794.09 (84%)
1574.47 (25%)
1536.05 (35%)
1276.29 (16%)
1572.40 (18%)
1534.45 (33%)
The unit of the stretching vibrational frequency is cmꢁ1
.
a
f(e) = (eꢁ1)/(2e + 1).

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Fig. 2. FTIR spectra of compound (4) and compound (5) in solvents.
constant of solvent. The observation can be explained that the con-
sideration of only dielectric constants in KBM equation and the for-
mation of molecular complexes between solvents with compounds
(4) and compound (5) [40]. According to this result, in order to
were reported for the correlation of the experimental stretching
vibrational frequencies with the KBM equation [25,41].
Fig. 5(a–g) exhibits the plots of the
m(C@O)/m(C@N) of com-
pound (4) and the (C@S)/ (C@N) of compound (5) vs. the solvent
m
m
explain the shifts of the
m
(C@O)/
m
(C@N) and the
m
(C@S)/
m
(C@N)
ANs. The linear equation parameters and correlation coefficients
for compound (4) and compound (5) are shown in Table 2 and
Table 3, respectively. It is shown that there is a poor correlation
in different solvents, more effects such as hydrogen bonding, non-
specific interactions and steric effects must be considered. Thus,
KBM equation containing the single parameter is not sufficient to
between the
m(C@O)/m(C@N) of compound (4) and the m(C@S)/m
generally explain of solvent effects on the
m
(C@O)/m(C@N) of com-
(C@N) of compound (5) with the solvent ANs due to a role of sol-
pound (4) and the (C@S)/ (C@N) of compound (5). Similar results
m
m
vents. It was also found that when the solvent ANs which indicates
6

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
electrophilicity of the solvent increases, the
m(C@O)/m(C@N) of
compound (4) and the (C@S)/ (C@N) of compound (5) shifts to
m
m
lower frequencies (Table 1) and this trend verifies the presence
of some specific interaction between compound (4) and compound
(5) with polar solvents [40]. According to the results, the solvent
ANs do not play an important role in determining solvent-
induced vibrational shifts in this study and the contribution of
polarization effects must also be considered.
In the investigation of solvent-induced frequency shifts, specific
solvent effects such as H-bond and electron pair transfer are
described using Swain equations [42]. The Swain equations for
the
compound (5) were given in Table 2. The correlation of the Swain
equations for the (C@O)/ (C@N) of compound (4) and the (C@S)/
(C@N) of compound (5) are good and better than that of ANs of
the solvents due to considering both the Lewis basicity and acidity
for the solvents. The negative signs determined for the coefficients
of Aj and Bj show that the increase of hydrogen bond donor acidity
and hydrogen bond acceptor basicity of the solvent leads to red-
m(C@O)/m(C@N) of compound (4) and the m(C@S)/m(C@N) of
m
m
m
m
Fig. 3. Expected interaction between studied 1,2,4-oxadiazole derivatives and
alcohol.
shift of the
(C@N) of compound (5). However, the coefficients of Bj were deter-
mined as positive for (C@N)1 of compound (4) and (C@N)2 of
compound (5). This observation can be explained by the fact that
the increase in solvent hydrogen bond acceptor basicity in studied
this functional groups causes an increase in electron density and
the measured vibration frequencies is blue-shifted. It was observed
m(C@O)/m(C@N) of compound (4) and the m(C@S)/m
Table 2
Solvent equations for compound (4).
m
m
Stretching Vibrational
Frequency
Equation
R2
KBM Equation
m
m
m
(C@O)1
(C@N)1
(C@N)2
0.5934
0.6562
0.7161
1796:20 - 45:05 fð
1622:03 - 23:32 fð
1603:20 - 28:70 fð
lÞ
lÞ
lÞ
in Table 1 that the measured
m(C@N)1 of compound (4) and m
AN Equation
(C@N)2 of compound (5) tended to increase as the coefficients Bj
increased. As a result, it can be said that the tendency to blue shift
is not as strong as the red shift.
The C@O, C@N and C@S groups in compound (4) and compound
(5) are a hydrogen bond acceptor. The solvents tend to donate pro-
ton and form H-bond with the C@O, C@N and C@S groups in com-
pound (4) and compound (5) with the increase of solvent hydrogen
bond donor acidity. Consequently, there is a decrease in the elec-
m
m
m
(C@O)1
(C@N)1
(C@N)2
1787:70 - 0:49 AN
1617:30 - 0:23 AN
1597:00 - 0:27 AN
0.9060
0.8365
0.7967
Swain Equation
m
m
m
(C@O)1
(C@N)1
(C@N)2
1790:20 - 26:77 Aj - 3:81 Bj
1617:43 - 13:07 Aj þ 0:03 Bj
1598:14 - 14:90 Aj - 1:71 Bj
0.9128
0.8809
0.8363
LSER Equation
tron density of the C@O, C@N and C@S groups and the
(C@N) and the (C@S)/
coefficients of Aj and Bj, it was found that the red-shift of the
(C@O)/ (C@N) of compound (4) and the (C@S)/
m
(C@O)/
m
m
m
m
(C@O)1
(C@N)1
(C@N)2
1790:72 ꢁ 14:71pꢂ ꢁ 15:51
a
þ 0:85b 0.9695
1618:76 ꢁ 5:70pꢂ ꢁ 5:45
a
a
ꢁ 2:75b
ꢁ 4:23b
0.9076
0.9247
m
m
(C@N) are red-shifted. By comparing the
1600:05 ꢁ 8:78pꢂ ꢁ 5:29
m
m
m
m
(C@N) of com-
The unit of the stretching vibrational frequency is cmꢁ1
.
pound (5) band induced by hydrogen bond donor acidity is larger
than the one induced by hydrogen bond acceptor basicity of the
solvent since the coefficients of Aj are much larger than the coeffi-
cients of Bj. As a result, the stretch vibration frequencies of C@O/
C@N and C@S/C@N functional groups are more sensitive to solvent
hydrogen bond donor acidity than solvent hydrogen bond acceptor
basicity because of the unpaired electrons they have. The success
Table 3
Solvent equations for compound (5).
Stretching Vibrational
Frequency
Equation
R2
of SE applied to FT-IR spectroscopy for the
m(C@O)/m(C@N) of com-
pound (4) and the
Fig. 6.
m(C@S)/m(C@N) of compound (5) are shown in
KBM Equation
m
m
m
m
(C@S)1
(C@S)2
(C@N)1
(C@N)2
0.8727
0.6780
0.7526
0.5969
1353:20 - 43:13 fð
1321:50 - 27:67 fð
1623:50 - 24:66 fð
1614:50 - 34:93 fð
l
l
l
l
Þ
Þ
Þ
Þ
The determined LSER parameters are given in Table 2 and
Table 3 for compound (4) and compound (5), respectively. The
results obtained using LSER equation exhibit better correlations
than that of the KBM equation, ANs and SE since the LSER model
takes into account not only the specific interaction parameters
AN Equation
m
m
m
m
(C@S)1
(C@S)2
(C@N)1
(C@N)2
1342:80 - 0:33 AN
1315:70 - 0:26 AN
1617:90 - 0:21 AN
1607:40 - 0:35 AN
0.6678
0.7882
0.7251
0.7749
such as
* in order to explain the position shifts of the C@O/C@N and the
C@S/C@N bands [41,42]. The negative coefficients of * inform that
red-shifted of the (C@O)/ (C@N) and the (C@S)/ (C@N) is
induced by non-specific solvent effects. This situation may be
due to the decreasing electron density. The coefficients of * deter-
a and b but also the non-specific interaction parameter like
p
Swain Equation
p
m
m
m
m
(C@S)1
(C@S)2
(C@N)1
(C@N)2
1346:47 - 19:07 Aj - 5:76 Bj
1316:06 - 14:83 Aj - 0:34 Bj
1618:36 - 12:13 Aj - 0:41 Bj
1606:97 - 19:80 Aj þ 1:21 Bj
LSER Equation
0.7855
0.8337
0.7798
0.8203
m
m
m
m
p
mined from LSER equation which have the biggest absolute values
compared to other parameters prove that non-specific solvent
effects are dominant in the compound/solvent interactions. The
m
m
m
m
(C@S)1
(C@S)2
(C@N)1
(C@N)2
1348:65 ꢁ 13:52pꢂ ꢁ 3:56
a
ꢁ 9:03b 0.8660
1317:78 ꢁ 6:81pꢂ ꢁ 5:65
a
a
ꢁ 4:15b
0.9142
0.8965
0.9281
1620:24 ꢁ 5:89pꢂ ꢁ 3:26
ꢁ 5:23b
ꢁ 5:24b
coefficients of
the coefficients of Aj and Bj parameters in SE. This states the same
influence concerning the red-shift of the (C@O)/ (C@N) and the m
a and b are also negative similar to the results of
1609:94 ꢁ 8:50pꢂ ꢁ 8:10
a
The unit of the stretching vibrational frequency is cmꢁ1
.
m
m
7

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Fig. 4. Plots of KBM parameter vs. (a) m(C@O)1, (b) m(C@N)1, and (c) m(C@N)2 of compound (4) and vs. (d) m(C@S)1, (e) m(C@S)2, (f) m(C@N)1, and (g) m(C@N)2 of compound (5).
Fig. 5. Plots of AN parameters vs. (a)
m
(C@O)1, (b)
m
(C@N)1, and (c)
m
(C@N)2 of compound (4) and vs. (d)
m
(C@S)1, (e)
m
(C@S)2, (f)
m
(C@N)1, and (g)
m
(C@N)2 of compound (5).
(C@S)/
band donor acidity of the solvent. However, the coefficient of
slightly bigger than the coefficient of * and the coefficient of b
were determined as positive for (C@O)1 of compound (4). The
result can be explained as follows: Since the four unpaired elec-
trons on the oxygen atom of C@O group form hydrogen bonds,
its contribution to the solvent effect is more dominant than the
dipolarity/polarizability effect of the solvent.
m
(C@N) by hydrogen bond acceptor basicity and hydrogen
The coefficients of
(C@S)1 and
oxadiazole derivatives are examined, it can be easily seen that
the hydrogen bond acceptor group properties of these molecules
are dominant due to the unpaired electrons. Also, the hydrogen
bond donor group properties of molecules are very weak since they
a
are bigger than the coefficients of b except
a
is
m
m
(C@N)1 for compound (5). When the 1,2,4-
p
m
do not contain polarized H atoms. Therefore, the
compound (4) and the (C@S)/ (C@N) of compound (5) are more
m(C@O)/m(C@N) of
m
m
8

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Fig. 6. Calculated (a)
m(C@O)1 (b) m(C@N)1 (c) m(C@N)2 of compound (4) and (d) m(C@S)1, (e) m(C@S)2, (f) m(C@N)1, and (g) m(C@N)2 of compound (5) by using SE vs.
experimental values.
Fig. 7. Calculated (a) m(C@O)1 (b) m(C@N)1 (c) m(C@N)2 of compound (4) and (d) m(C@S)1, (e) m(C@S)2, (f) m(C@N)1, and (g) m(C@N)2 of compound (5) using LSER equation vs.
experimental values.
sensitive to hydrogen bond donor acidity of solvents than hydro-
gen band acceptor basicity.
compared to other solvent scales such as the KBM equation, ANs
and SE, the LSER equation provides physically meaningful and a
quantitatively accurate explanation of vibrational frequency shifts
caused by the solute and solvent interactions in both polar and
non-polar solvents. The success of LSER equation applied to FT-IR
The m(C@O)/m(C@N) of compound (4) and the m(C@S)/m(C@N) of
compound (5) achieve very good correlations with the parameters
of LSER equations. It is suggested that non-specific solvent effects
between solvents with compound (4) and compound (5) play an
spectroscopy for the
m(C@O)/m(C@N) of compound (4) and the m
important role because of the biggest coefficient value of
p
*. As
(C@S)/ (C@N) of compound (5) are show in Fig. 7.
m
9

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Table 4
Regression model results for SE.
Term
Coefficient
Standard Error
t
F
P
R2
Compound (4)
m
(C@O)1
0.9488
Constant
Aj
Bj
AjBj
1798.50
ꢁ54.30
ꢁ22.23
59.50
3.75
11.20
7.74
479.93
ꢁ4.86
ꢁ2.87
2.51
55.55
23.66
8.26
0.000
0.001
0.018
0.033
23.70
6.32
Compound (5)
m
(C@N)2
0.8887
Constant
Aj
Bj
AjBj
1616.01
ꢁ49.20
ꢁ18.43
63.50
4.27
12.70
8.81
378.45
ꢁ3.86
ꢁ2.09
2.35
23.95
14.93
4.37
0.000
0.004
0.066
0.043
27.00
5.53
The unit of the stretching vibrational frequency is cmꢁ1
.
4.2. Interactive effects of solvent parameters on the experimental
vibrational spectra of compound (4) and compound (5)
Bj (P = 0.018) on
The linear effect of Aj (P = 0.004) on
m
(C@O)1 of compound (4) are highly significant.
m(C@N)2 of compound (5)
are highly significant whereas Bj (P = 0.066) are not significant.
The Swain and LSER equations are commonly used to describe
the effects of solvent on vibrational spectra of organic molecules.
The Swain and LSER equations are multi-parameter equations and
Additionally, it was observed that interaction effect of Aj and Bj
are slightly significant for
and (C@N)2 of compound (5) (P = 0.043). According to the results,
the interaction effect of Aj and Bj are considered as slightly signif-
m(C@O)1 of compound (4) (P = 0.033)
m
include the main effects of solvent parameters such as Aj, Bj, p*, a
and b on the vibrational spectra. In this study, apart from the linear
effects investigated in similar studies, the linear, interactive and
quadratic effects of the solvent parameters were also studied. The
quadratic and interactive effects of solvent parameters were deter-
mined using multiparameter regression by MINITAB 19 (USA).
icant factor for the
pound (5).
m(C@O)1 of compound (4) and m(C@N)2 of com-
The solvent effects on the
m(C@O)/m(C@N) of compound (4) and
the (C@S)/ (C@N) of compound (5) for LSER equation were
m
m
explained by the following Eq. (8) including quadratic and interac-
The solvent effects on the
m
(C@O)/
m
(C@N) of compound (4) and
tive effects of solvent parameters:
the (C@S)/ (C@N) of compound (5) for SE were explained by the
following Eq. (5) including quadratic and interactive effects of sol-
vent parameters:
m
m
2
m
¼
m0 þ k1pꢂ þ k2d þ k3
a
þ k4b þ k11pꢂ þ k22d2 þ k33a2
þ k44b2 þ k12pꢂd þ k13pꢂ
a
þ k14pꢂb þ k23d
þ k24db
a
¼
m0 þ b1Aj þ b2Bj þ b11A2 þ b22B2 þ b12AjBj
ð5Þ
þ k34
a
b
ð8Þ
m
j
j
where the predicted frequency (
(m0), linear (k1, k2, k3, k4), quadratic (k11, k22, k33,k44) and interaction
m
) was correlated to the intercept
In Eq. (5), the predicted frequency (
m) was correlated to the
intercept (m0), linear (b1, b2), quadratic (b11, b22) and interaction
(k12, k13, k14, k23, k24, k34) coefficients. The linear, quadratic and
interaction coefficients of the respective effects were represented
by k and were determined by applying a Student’s t-test. The Mini-
tab 19 was used for graphical analysis and multi-linear regression
of the stretching vibrational frequencies. The regression coeffi-
cients, standard deviations of each coefficient, P values and t values
for all the linear, interaction and quadratic effects of the parameter
determined from analysis of the data was displayed in Table 5 for
LSER equation.
(b12) coefficients. Coefficients of the respective effects were repre-
sented by b and were determined by applying a Student’s t-test.
The Minitab 19 was used for graphical analysis and multi-linear
regression of the
m(C@O)/m(C@N) of compound (4) and the m
(C@S)/ (C@N) of compound (5). The regression coefficient, stan-
m
dard deviation of each coefficient, P values and t values for all
the linear, interaction and quadratic effects of the parameter deter-
mined from analysis of the data was displayed in Table 4 for SE.
As can be seen from Table 4, only
(C@N)2 of compound (5) respond to the quadratic and interaction
effects of solvent parameter. The coefficients of determination
(0.9488 for (C@O)1 of compound (4) and 0.8887 for (C@N)2 of
m(C@O)1 of compound (4) and
As can be seen from Table 5, the
the (C@S)1, (C@S)2 and (C@N)1 of compound (5) respond to the
quadratic and interaction effects of solvent parameter. The coeffi-
cients of determination (0.9605 for (C@N)2 of compound (4)
and 0.9501 for (C@S)1, 0.9548 for (C@S)2 and 0.9692 for (C@N)1
m(C@N)2 of compound (4) and
m
m
m
m
m
m
m
compound (5)) obtained from the model containing the linear,
quadratic and interaction effects are bigger than that of the linear
m
of compound (5)) obtained from the model containing the linear,
interaction and quadratic effects are bigger than that of the linear
model (0.9128 for
m(C@O)1 of compound (4) and 0.8203 for m
(C@N)2 of compound (5)) given in Table 2 and Table 3. Therefore,
it was found that the model including the linear, interaction and
model (0.9247 for
0.9142 for (C@S)2 and 0.8965 for
m
(C@N)2 of compound (4) and 0.8660 for (C@S)1,
(C@N)1 of compound (5)) given
m
quadratic effects is the most appropriate model for
compound (4) and (C@N)2 of compound (5) and shows a better
correlation compared to the linear model.
The regression equations for the (C@O)1 of compound (4) and
(C@N)2 of compound (5) is given in Eqs. (6) and (7), respectively:
m(C@O)1 of
in Table 2 and Table 3. Therefore, it was found that the model
including the linear, quadratic and interaction effects for LSER is
m
the most appropriate model for the
m(C@N)2 of compound (4)
m
and the (C@S)1, (C@S)2 and (C@N)1 of compound (5) and shows
m
m
m
m
a better correlation compared to the linear model for LSER.
According to the multi-linear regression analysis, reduced
mðC¼OÞ ¼ 1798:50 ꢁ 54:30Aj ꢁ 22:23Bj þ 59:50AjBj
ð6Þ
1
regression equations for the
and the (C@S)1, (C@S)2 and
in Eqs. (10)–(12):
m
(C@N)2 of compound (4) in Eq. (9)
(C@N)1 of compound (5) is given
m
m
m
mðC¼NÞ ¼ 1616:01 ꢁ 49:20Aj ꢁ 18:43Bj þ 63:50AjBj
ð7Þ
2
The smaller the value of P and larger the values of t and F indi-
cate that the model is statistically significant (with 95% confidence
level) [43]. It was found that the linear effects of Aj (P = 0.001) and
mðC¼NÞ ¼ 1599:68 ꢁ 7:08pꢂ þ 17:20
a
ꢁ 5:36b ꢁ 42:80
a
pꢂ
ð9Þ
2
10

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
Table 5
Regression model results for LSER equation.
Term
Coefficient
Standard Error
t
F
P
R2
Compound (4)
m
(C@N)2
0.9605
Constant
1599.68
ꢁ7.08
0.89
1.50
8.44
1.52
15.90
1790.07
ꢁ4.71
2.04
48.65
22.2
4.16
12.44
7.27
0.000
0.002
0.076
0.008
0.027
pꢂ
a
17.20
b
a
ꢁ5.36
ꢁ3.53
pꢂ
ꢁ42.80
ꢁ2.07
Compound (5)
m
(C@S)1
0.9504
0.9548
0.9692
Constant
pꢂ
a
b
a
1349.05
ꢁ10.77
ꢁ26.6
1.35
2.21
6.53
2.59
8.53
997.9
ꢁ4.87
ꢁ4.08
ꢁ5.36
3.69
38.31
23.73
16.61
28.75
13.61
0.000
0.001
0.004
0.001
0.006
ꢁ13.09
31.48
b
m
(C@S)2
Constant
pꢂ
a
b
a
1317.40
ꢁ5.02
0.95
1.59
8.94
1.61
16.80
1391.5
ꢁ3.15
2.02
42.27
9.95
4.08
10.97
7.19
0.000
0.013
0.078
0.011
0.028
18.06
ꢁ5.34
ꢁ3.31
pꢂ
(C@N)1
ꢁ45.20
ꢁ2.68
m
Constant
1619.08
ꢁ3.87
23.59
0.66
1.11
6.25
1.13
11.80
2449.1
ꢁ3.48
3.78
62.93
12.11
14.26
34.16
18.89
0.000
0.008
0.005
0.000
0.002
pꢂ
a
b
ꢁ6.58
ꢁ5.84
a
pꢂ
ꢁ51.10
ꢁ4.35
The unit of the stretching vibrational frequency is cmꢁ1
.
Fig. 8. 3D surface plot for a combined effect of (a)
the (C@N)1 of compound (5).
a
and
p
* for the
m
(C@O)1 of compound (4) and (b)
a
and b for the
m
(C@S)1, (c) a and p* for the m(C@O)2 and (d) a and p* for
m
11

Y.S. Kara, M. Ünsal, N. Tekin et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 251 (2021) 119424
face plots in Fig. 8. The interactive effect of
pꢂon the
(C@N)2 of compound (4) and (C@S)1, (C@S)2 and m(C@N)1 of
ab and
a
m
m
m
compound (5) was the most significant effect and the results are
different from that obtained from LSER equation including the lin-
ear effects. Therefore, the model containing the linear, interaction
and quadratic effects of the parameters could be effectively used
to investigate the solvent effects on the
m(C@O)/m(C@N) of com-
pound (4) and the (C@S)/ (C@N) of compound (5).
m
m
4.3. The validation of the model including the linear, quadratic and
interaction effects for SE and LSER
The validation of the model including the linear, interaction and
quadratic effects for SE and LSER was investigated for the related
stretching vibrational frequencies of compound (4) and compound
(5) in chlorobenzene. Fig. 9(a) and Fig. 9(b) display the experimen-
tal FT-IR spectra of compound (4) and compound (5) in chloroben-
zene. Solvent parameters and the experimental/calculated
stretching vibrational frequencies of compounds were given in
Table 6. It was found that the models including the linear, quadra-
tic and interaction effects for SE and LSER show a better correlation
compared to the linear model for SE and LSER.
5. Conclusions
The solvent effects on the
m(C@O)/m(C@N) of compound (4) and
the (C@S)/ (C@N) of compound (5) in 13 different pure solvents
m
m
are studied by FT-IR experiments and density functional theory
calculations using the potential energy distribution (PED) contri-
butions. The results of this study are;
Fig. 9. FT-IR spectra of compound (4) and compound (5) in chlorobenzene.
mðC¼SÞ ¼ 1349:05 ꢁ 10:77pꢂ ꢁ 26:60
a
ꢁ 13:90b þ 31:48
ꢁ 5:34b ꢁ 45:20
ꢁ 6:58b ꢁ 51:10
a
b
ð10Þ
ð11Þ
ð12Þ
1
i. Two novel 1,2,4-oxadiazole derivative compounds were syn-
thesized and characterized by IR, 1H NMR, 13C NMR and
HRMS analyses.
ii. The observed FT-IR spectra of compound (4) and compound
(5) are compared with their theoretical wavenumbers
(scaled).
mðC¼SÞ ¼ 1317:40 ꢁ 5:02pꢂ þ 18:06
a
a
pꢂ
2
mðC¼NÞ ¼ 1619:80 ꢁ 3:87pꢂ þ 23:59
a
a
pꢂ
1
It was found that the linear effect of
(P = 0.008) excluding (P = 0.076), and interaction effect of
pꢂ(P = 0.027) on the
(C@N)2 of compound (4) are highly signifi-
cant. Additionally, it was determined that linear effect of
(P = 0.001 for (C@S)1, P = 0.013 for (C@S)2 and P = 0.008 for
(C@N)1), b (P = 0.001 for (C@S)1, P = 0.011 for (C@S)2 and
P = 0.000 for (C@N)1) and (P = 0.004 for (C@S)1 and
P = 0.005 for (C@N)1 excluding (C@S)2 with P = 0.078) are highly
significant. Interaction effects of
pꢂ(P = 0.028) on the
(C@S)2 and
p* (P = 0.002) and b
iii. The
m(C@O)/m(C@N) of compound (4) and the m(C@S)/m
a
(C@N) of compound (5) were correlated with the Swain,
AN, KBM, and LSER solvent scales.
iv. It was found that the KBM and the solvent ANs of the sol-
vents with the stretching vibrational frequencies compound
(4) and compound (5) have poor correlations.
a
m
p*
m
m
m
m
m
m
m
a
m
v. The
m(C@O)/m(C@N) of compound (4) and the m(C@S)/m
m
(C@N) of compound (5) achieve good linear correlation with
the SE while the LSER equation shows excellent correlation
analysis results for the
and the (C@S)/ (C@N) of compound (5) in all solvents.
a
b (P = 0.006) on the
pꢂ(P = 0.02) on the
m
m
(C@S)1,
(C@N)1
a
m
a
m(C@O)/m(C@N) of compound (4)
of compound (5) are highly significant. The interactive effects of
m
m
ab and
a
pꢂfor LSER equation were represented in form of 3D sur-
Table 6
The experimental and the calculated stretching vibrational frequencies of compound (4) and compound (5) in chlorobenzene.
Compound and
functional group
The stretching vibrational frequencies of compound (4) and compound (5)
b
a
p*
Aj
Bj
Experimental SE (linear
effect)
LSER (linear SE (linear, quadratic and
LSER (linear, quadratic and
interaction effects)
effect)
interaction effects)
Chlorobenzene
Compound (4)
0.07 0.00 0.68 0.20 0.65
m
m
m
(C@O)1
(C@N)1
(C@N)2
1780.94
1612.14
1594.49
1782.37
1614.84
1594.05
1780.78
1614.69
1593.78
1780.93
1594.49
Compound (5)
m
m
m
m
(C@S)1
(C@S)2
(C@N)1
(C@N)2
1341.05
1313.94
1616.11
1602.79
1338.91
1312.87
1615.67
1603.79
1339.17
1312.86
1615.87
1603.79
1340.75
1313.61
1616.71
1602.45
The unit of the stretching vibrational frequency is cmꢁ1
.
12

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CRediT authorship contribution statement
Yesim S. Kara: Investigation, Writing - original draft, Writing -
review & editing. Mustafa Ünsal: Investigation. Nalan Tekin: Data
curation, Methodology, Writing - review & editing. Aslı Eßsme: Data
curation, Methodology, Writing - review & editing.
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
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to influence the work reported in this paper.
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Acknowledgement
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13