Synthesis, characterization, anti-diabetic potential and DFT studies of 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde oxime

Article abstract of DOI:10.1016/j.saa.2018.07.009

A new compound named 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde oxime (7-Oxime) was synthesized and characterized by FT-IR, FT-Raman, ¹H NMR and ¹³C NMR techniques. The conformer possibilities were studied to find the most stable conformer and its molecular geometry. Then, the dimer form of the most stable monomer was built and optimized. Density functional theory (DFT) B3LYP method with 6-311++G(d,p) basis set was applied to analyze the molecular electrostatic potential (MEP), HOMO and LUMO orbitals, the vibrational wavenumbers, the infrared intensities, the Raman scattering activities and several thermodynamic properties (at different temperatures). The stability of the molecule derived from hyperconjugative interactions and charge delocalization has been analyzed by using natural bond orbital (NBO) analysis. In order to find the possible inhibitory activity of 7-Oxime, an accurate molecular blind docking simulation was performed. The results indicated that the mentioned compound has a good binding affinity to interact with the active sites of human α-glucosidase and α-amylase. For the first time, our computational finding suggests that this compound has a potential to be used as a supplementary agent in the pre-management of diabetes mellitus.

Full text of DOI:10.1016/j.saa.2018.07.009

Accepted Manuscript
Synthesis, characterization, anti-diabetic potential and DFT
studies
of
7-hydroxy-4-methyl-2-oxo-2H-
chromene-8-carbaldehyde oxime
Seyed Mohammad Bagher Hosseini Ghazvini, Parvin Safari,
Akbar Mobinikhaledi, Hassan Moghanian, Hassan Rasouli
PII:
S1386-1425(18)30662-0
doi:10.1016/j.saa.2018.07.009
SAA 16278
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 24 November 2017
Revised date:
Accepted
date:
30 June 2018
5
July 2018
Please cite this article as: Seyed Mohammad Bagher Hosseini Ghazvini, Parvin Safari,
Akbar Mobinikhaledi, Hassan Moghanian, Hassan Rasouli , Synthesis, characterization,
anti-diabetic potential and DFT studies of 7-hydroxy-4-methyl-2-oxo-2H-
chromene-8-carbaldehyde oxime. Saa (2018), doi:10.1016/j.saa.2018.07.009
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ACCEPTED MANUSCRIPT
Synthesis, characterization, anti-diabetic potential and DFT studies of 7-hydroxy-4-methyl-
2
-oxo-2H-chromene-8-carbaldehyde oxime
a
ϯ
aϯ
a
b
Seyed Mohammad Bagher Hosseini Ghazvini * , Parvin Safari , Akbar Mobinikhaledi , Hassan Moghanian ,
Hassan Rasoulic
a
Department of Chemistry, Faculty of Science, Arak University, Arak, Iran
Department of Chemistry, Dezful Branch, Islamic Azad University, Dezful, Iran
Medical Biology Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran
b
c
*
Correspondence: Smbhgh@yahoo.com
Abstract
A new compound named 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde oxime (7-
Oxime) was synthesized and characterized by FT-IR, FT-Raman, H-NMR and 13C-NMR
techniques. The conformer possibilities were studied to find the most stable conformer and its
molecular geometry. Then, the dimer form of the most stable monomer was built and optimized.
Density functional theory (DFT) B3LYP method with 6-311++G(d,p) basis set was applied to
analyze the molecular electrostatic potential (MEP), HOMO and LUMO orbitals, the vibrational
wavenumbers, the infrared intensities, the Raman scattering activities and several thermodynamic
properties (at different temperatures). The stability of the molecule derived from hyperconjugative
interactions and charge delocalization has been analyzed by using natural bond orbital (NBO)
analysis. In order to find the possible inhibitory activity of 7-Oxime, an accurate molecular blind
docking was performed. The results indicated that the mentioned compound has a good binding
affinity to interact with the active sites of human α-glucosidase and α-amylase. For the first time,
our computational finding suggests that this compound can have potential to be used as a
supplementary agent in the pre-management of diabetes mellitus.
1
Keywords
7
-Oxime; Vibrational spectra; NMR spectra; FMO; Molecular docking; diabetes mellitus
1

ACCEPTED MANUSCRIPT
1
. Introduction
Nowadays, the biological and pharmacological properties of coumarin and its derivatives have
received many attentions from pharmaceutical and food industries [1]. These natural secondary
metabolites exhibit a wide range of biological activities including anticancer and anti-diabetic
effects [2-4]. These compounds are widely used as fragrance, pharmaceuticals, agrochemicals,
laser dyes, optical brighteners and fluorescent markers [5, 6]. Among coumarins,
hydroxycoumarins are one of the most important classes of plant-derived secondary metabolites
with significant antioxidant activities and extensive applications [7]. These compounds have
originated from many different classes of plant sources. As can be seen in Fig. 1, the structure of
these compounds includes molten benzene and α-pyrone rings [7] (Fig. 1).
Fig. 1. The chemical structures of coumarin (Left) and 4-hydroxycoumarin (Right)
Many studies have indicated that computer-based drug design strategies have a central role in the
development of new drugs [8, 9]. Among computational techniques, Density functional theory
(DFT) is a promising method for the evaluation of vibrational modes, bonding and structural
properties of organic molecules [10-12]. Besides, these computational approaches have been used
to investigate the vibrational spectra and the other electronic features of coumarins and its
derivatives [13].
Therefore, the aim of the current study was to investigate the structural, electronic and
spectroscopic properties of a new compound named 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-
carbaldehyde oxime (7-Oxime) through experimental (FT Raman, FT-IR and NMR) and
computational DFT-based methods. Indeed, the anti-diabetic potential of this compound was
investigated via molecular docking simulation.
2
2
2
. Methods
.1. Experimental Section
.1.1. Synthesis of 7-Oxime
2

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As can be seen in Fig. 2, 7-Oxime was synthesized according to the following steps.
Fig. 2. Synthesis of 7-Oxime.
A. Synthesis of 8-formyl-7-hydroxy-4-methylcoumarin
,
The method reported previously (with some slight modifications) [14, 15] was used for the
synthesis of 8-Formyl-7-hydroxy-4-methylcoumarin . First, p-Toluenesulfonic acid (p-TSA, 0.36
g, 2.0 mmol) was added to a mixture of resorcinol (4.4 g, 40 mmol) and ethyl acetoacetate (5.2 g,
4
0 mmol) and the mixture was irradiated using the microwave oven for 30 s at 450 W power. Then,
the mixture was cooled to room temperature and a mixture of ethanol: water (1:1) was added to it.
The mixture was stirred for 5 min and the solid was separated by filtering and dried to give 7-
hydroxy-4-methylcoumarin (yield 95%; mp: 184–186 °C).
In the second step, 7-hydroxy-4-methylcoumarin (5 g, 28.4 mmol) and hexamine (5.6 g, 40
mmol) were added to glacial acetic acid (90 ml) and the mixture was heated for 4 h. Next, hexamine
(5.6 g, 40 mmol) was added to the mixture and heated for another 4 h. After the reaction was
completed (monitored by TLC), hydrochloric acid (20%, 70 ml) was added and the mixture was
heated for 40 min. Then, the mixture was cooled and extracted with ether (50 ml) twice. The
combined organic layer was concentrated under the reduced pressure to give the crude product.
Then, the crude product was re-crystallized from ethanol to obtain pure 8-formyl-7-hydroxy-4-
methylcoumarin (yield 18%; mp: 145–146 °C).
B. Synthesis of 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde oxime
7
-hydroxy-4-methylcoumarin (2 mmol), hydroxylamine hydrochloride (6 mmol) and sodium
acetate (6 mmol) were dissolved in ethanol (95%, 10 ml) and the solution was refluxed for 6 h.
Then, the solution was cooled down to room temperature. The white product was filtered off and
washed with cold ethanol (yield 89%; mp: 190-192 °C). The spectral data of this compound has
been represented below.
3

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-1
FT-IR (in KBr pellet) υmax (cm ): 3297 (OH of oxime group), 3084, 1692 (C=O of lactone), 1616
1
(
C=N of oxime group), 1393, 1366, 1080 (C-O-C of pyrone), 993; H NMR (400 MHz, DMSO-
d
6
): δ = 11.946 (s, 1H, OH of oxime group), 11.164 (s, 1H, OH, phenolic), 8.531 (s, 1H, CH of
oxime group), 7.660 (d, J = 8.8 Hz, 1H, CH of ring 2), 6.934 (d, J = 8.8 Hz, 1H, CH of ring 2),
1
3
6
1
1
.227 (s, 1H, CH, vinyl of ring 1), 2.510 (s, 3H, CH
3
); C NMR (100 MHz, DMSO-d ): δ =
6
59.703 (C-OH of ring 2), 159.208 (C-H of oxime group), 153.657 (C=O of lactone), 151.772,
44.023, 127.227, 112.810, 112.065, 110.728, 104.942, 18.271 (CH )
3
2
.1.2. The measurement of FT-IR and FT-Raman spectra
A Unicom Galaxy Series FT-IR 5000 spectrophotometer was used to record the FT-IR spectra of
-1
-1
the samples in the range of 400-4000 cm . The spectra were recorded with a resolution of 1 cm
and the signals were the results of 15 scans (averagely). A Bruker RFS 100/S FT-Raman was used
for recording FT-Raman spectrum of the sample by using 1064 nm line of Nd:YAG laser as
-1
excitation wavelength in the region of 800-4000 cm . The detector was a liquid nitrogen cooled
-1
Ge detector. Five hundred scans were collected at 4 cm resolution by using a laser power of 100
mW.
2
.1.3. The measurement of NMR spectra
1
13
The H and C NMR spectra were collected in DMSO-d with TMS as an internal standard on a
6
Brucker Avance spectrometer operating at 400 and 100 MHz for proton-1 and carbon-13 atoms,
respectively.
2
.2. Computational methods
The computational calculations were performed at DFT level with the Becke’s three-parameter
hybrid functional (B3) [16] for the exchange part and the Lee-Yang-Parr (LYP) correlation
function [17]. Gaussian 03 suite of quantum chemical codes [18] was used for this purpose without
any constraint in the geometry with split-valence triple-zeta basis set along with diffuse and
polarization function (6-311++G(d,p)).
First, the structure of 7-Oxime was constructed using GaussView program [19]. Next, the sixteen
possible conformations of the mentioned compound, their corresponding energies and harmonic
vibrational frequencies were calculated by B3LYP method with 6-311++G(d,p) basis set in DMSO
4

ACCEPTED MANUSCRIPT
and the vacuum. The most stable conformer was detected based on E = E Mean - E
N
formula. As
shown in Fig. 4, the dimer form was made of two units of the most stable conformer of the
monomer (A2). The absence of imaginary frequency verified that the optimized geometry of the
dimer and monomer form was true minima on the potential energy surface at B3LYP method with
6
-311++G(d,p) level of theory by assuming C
2
and C point group symmetry for the dimer and
s
monomer form, respectively. Computational analysis was performed to calculate the optimized
geometrical parameters, energy, fundamental vibrational frequencies, IR intensity, Raman activity,
FMOs analysis, NBO analysis, NMR analysis, dipole moments and other thermodynamical
parameters.
It is essential to scale down the calculated harmonic frequencies to improve the agreement
between the calculated and the experimental values. Hence, the calculated vibrational frequencies
-1
-1
above 1700 cm were scaled by 0.958 while those calculated below 1700 cm were scaled by
.983 by B3LYP method [20]. Furthermore, the theoretical vibrational spectra of the title
compound were interpreted by means of potential energy distribution (PED) via VEDA program
21]. GaussView program [19] was also utilized to get visual animation and to verify the normal
modes assignment. In addition, the Raman activities (S ) calculated by Gaussian 03 program [18]
was converted to relative Raman intensities (I ) by using Eq. 1. This formula has been derived from
0
[
푖
푖
the intensity theory of Raman scattering [22, 23]:
4
푓( − ) 푆
0
ꢁ
ꢁ
퐼ꢀ = ꢁ[1−exp
, Eq. (1)
(−((ℎ푐 )⁄(푘푇)))]
ꢁ
-1
Where 
0
was the laser exciting wavenumber in cm ,  was the vibrational wavenumber of the
푖
normal mode and h, c, ꢂ and f universal constants were suitably chosen as common normalization
factor for the intensity of all peaks.
The NBO analyses were performed via NBO 5.0 tool [24] implemented in the Gaussian 03 [18]
program at B3LYP/6-311++G(d,p) level. The molecular electrostatic potential (MEP) was
measured to study the reactive sites of the monomer form, to explain the possible reactivity sites
1
3
for building the dimer form and to correct chemical model in NMR analysis. Afterward, the C
1
and H NMR isotropic shifts were calculated by GIAO method [11, 25] using the optimized
geometry of the dimer and monomer form in both DMSO and the vacuum.
5

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2
.2.1. Molecular docking
Today, molecular docking plays a central role in drug discovery [26-28]. This method can show
an accurate view about ligand-protein interactions [29, 30]. In fact, this method has been
considered as one of the an interesting methods for structural studies despite the fact that it is a
primitive approach for finding the interaction between proteins and ligands [31, 32]. So, molecular
docking simulation (fully blind docking) was performed to investigate the possible inhibitory
property of 7-Oxime against enzyme involved in type 2 diabetes mellitus. The 3D crystallographic
structure of human lysosomal α-glucosidase (PDB ID: 5NN8 [33]) and human α-amylase (PDB
ID: 1HNY[34]) were downloaded from the Protein Databank RCSB PDB and then used as
favorable receptors to perform molecular docking. AutoDock 4.2.6 [35] software was used for
+
molecular docking, and LigPlot [6] and PyMOL (https://pymol.org/ ) tools were used to visualize
the results. The DruLio tool [36, 37] was used for Drug-likeness and ADMET prediction.
3
3
. Results and discussion
.1. Conformational stability
The possible conformers of 7-Oxime were derived from the orientation of the hydroxyl and oxime
groups in the eighth and the ninth position, respectively. Fig. 3 shows the possible sixteen
conformers for the mentioned compound. In order to find the most energetically stable
configuration of 7-Oxime, all of the possible conformers were optimized at B3LYP/6-
3
11++G(d,p) level in the vacuum and DMSO.
6

ACCEPTED MANUSCRIPT
Fig. 3. Different conformer possibilities of 7-Oxime
The results indicated that the oxime group adopted "E" configuration in A1, A2 and B1, B2
conformers when the dihedral angle of C
between the conformers A1 and A2 as well as B1 and B2 was the dihedral angle of C14=N15-O16
25 in the oxime group. The dihedral angle of C14=N15-O16-H25 was adopted 0° for A1, B1 and
80° for A2, B2 conformers. In addition, the dihedral angle of C -C -O13-H23 was 0° and the
9
-C
8
-O13-H23 was equal with 0°. The only difference
-
H
1
9
8
7

ACCEPTED MANUSCRIPT
configuration was "Z" for C1, C2 and D1, D2 conformers. The dihedral angle of the oxime group
in C1, D1 and C2, D2 conformers was 0° and 180°, respectively. Also, the dihedral angle of C
9
-
C
8
-O13-H23 was 180° in E1, E2, F1, F2, G1, G2, H1 and H2. However, the configuration of the
oxime group in E1, E2, F1, F2 conformers was "Z" while G1, G2, H1, H2 conformers had "E"
configuration. Besides, the dihedral angles of the oxime group for E1, F1, G1, H1 and E2, F2, G2,
H2 conformers were obtained to be 0° and 180°, respectively.
All sixteen possible conformers were optimized in the vacuum and DMSO. As detailed in Table
1
, B1, B2, D1, D2, E1, E2, H2 conformers (in both DMSO and the vacuum) and H1 (in the
vacuum) have imaginary wavenumbers. According to our results, the conformer was more stable
when the configuration of the oxime group was E and the dihedral angle of C -C -O13-H23 was
9
8
equal with 0°. The order of conformer stability was A2> A1> C1> C2 and A2> A1> G2> C2 in
the vacuum and DMSO, respectively. In both DMSO and the vacuum, the favored conformer A2
with dihedral angle of C14=N15-O16-H25 (180°) in the oxime group. The energy differences between
-1
the most stable (A2) and the second stable (A1) conformer were -4.177 and -3.171 kcal mol in
the vacuum and DMSO, respectively. The mean deviation of energy differences between the
conformer possibilities has been shown in Fig. S.1.
Table 1. Calculated total energies (퐸⁡푡표푡) and relative ∆퐸 (kcal/mol) energies of the conformer possibilities studied
푎
by B3LYP methods with 6-311++G(d,p) basis set
Conformer
possibilities
Gas
DMSO
∆퐸푎
b
퐸⁡푡표푡
∆퐸푎
9.668
Nimag c
퐸⁡푡표푡
Nimag c
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
A1
A2
B1
B2
C1
C2
D1
D2
E1
E2
F1
-489718.900
0
0
-489736.249
-489739.420
-489727.108
-489730.873
-489734.972
-489734.972
5.318
8.489
-3.823
-0.058
4.041
4.042
0
0
-489723.017 13.785
-489701.486 -7.746
-
1
-1
1: [-210.21 cm ]
1: [-152.57 cm ]
2: [-174.68, -21.32 cm ]
2: [-157.02, -24.09 cm ]
-
1
-1
-489709.452
-489717.636
-489717.636
0.220
8.404
8.404
0
0
0
0
-
1
-1
-489702.453 -6.778
-489700.756 -8.476
-489703.628 -5.604
-489702.801 -6.431
-489705.693 -3.539
1: [-184.23 cm ]
1: [-203.03 cm ]
1: [-77.32 cm ]
1: [-106.37 cm ]
-489720.864 -10.067
2: [-159.98, -50.21 cm ]
-
1
-1
-489721.732
-489725.321
-489726.160
-489729.343
-489733.943
-489732.107
-489735.414
-489731.443
-489734.973
-9.199
-5.610
-4.770
-1.588
3.012
1.176
4.483
0.512
4.042
1: [-138.78 cm ]
1: [-72.56 cm ]
1: [-98.73 cm ]
-
1
-1
-
1
-1
0
1
2
3
4
5
6
0
0
0
0
0
0
0
0
0
F2
-489709.947
-489706.898 -2.334
-489711.761 2.530
-489704.639 -4.593
-489711.008 1.776
0.715
G1
G2
H1
H2
-
1
1: [-33.22 cm ]
1: [-25.40 cm ]
-
1
-1
1: [-31.98 cm ]
a
b
c

E = E Mean – E
N
See conformer possibilities for the title compound in Fig. 3.
-1
The number of imaginary wavenumbers (cm ).
8

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In the most stable conformer (i.e. A2), the hydroxyl group was planar with the ring and the oxime
moiety probably due to the strong conjugation, resonance, and hydrogen-bonding interactions.
3
.2. Molecular geometry
Fig. 4 illustrates the optimized molecular structure of 7-Oxime with the C
of the monomer and C point group symmetry of the dimer form. In this molecule, the coumarin
ring was substituted with the following groups: methyl at C , hydroxyl at C and oxime at C . The
S
point group symmetry
2
4
8
9
optimized values of the bond lengths and bond angles have been detailed in Table 2. To confirm
the chemical structure of 7-Oxime, it was compared with the crystalline structure of its analogous
compound
(8-[(Hydrazinylidene)methyl]-4-methyl-2-oxo-2H-chromen-7-yl
4-
methylbenzenesulfonate) [38]. The results showed that the bond lengths and bond angles of 7-
Oxime (i.e. the most stable conformer) were larger than the observed queries in the experimental
assays. It can be explained by the fact that the calculations belonged to the isolated molecule in
the vacuum while the experimental results belonged to the molecule in solid state and the values
of the bond lengths and bond angles depended on the interaction between molecules in the crystal
lattice [13].
Fig. 4. Molecular structure of 7-Oxime along with numbering of atoms (both monomer and dimer forms)
7
-Oxime was a cyclic and aromatic compound due to the continuous delocalization of electrons in
the coumarin ring. The dihedral angles of C -C = 180° and C -C = 180° confirmed
4
5
-C10-C
9
6
5
-C10-O
1
that 7-Oxime was planar (Table 2). It has eleven C-C, seven C-H, four C-O, one C-N, one N-O
9

ACCEPTED MANUSCRIPT
and two O-H bonds and the length of C-C bonds in the coumarin ring was not the same due to the
electron donating of hydroxyl group, electron withdrawing of the oxime group and the inductive–
mesmeric interactions with the methyl group which consequently led to the contraction of some
C-C bonds and the expansion of the others.
The experimental values of these C-C bond lengths fell in the range of 1.342–1.497 Å while
those obtained by computational method fell in the range of 1.3575–1.5036 Å. The DFT
calculations showed that the bond length of C
presence of double bond character. Also, C
.4563 Å by experimental and DFT methods, respectively. This bond was the largest C-C bond in
the coumarin ring of our compound.
3
-C
4
was shortened and it was 1.3575 Å, proving the
9
-C14 bond length was obtained to be 1.461 Å and
1
In addition, the interaction between the hydroxyl and the oxime groups in 7-Oxime compound
can affect the regular hexagonal structure. The calculated bond angles represented in Table 2 were
good evidence for this effect. For example, C
21.635 Å and 117.524 Å, respectively. In addition, a significant deviation from trigonality was
observed in the bond angle of C -C -O11 (127.364 Å according to B3LYP and 126.59 Å according
to the experimental results) due to the electronic repulsion between O11 and O atoms.
Also, the corresponding dihedral angles N15-C14-C -C = 0° and H23-O13-C -C = 0° confirmed
7
-C
6
-C
5
and C10-C
5
-C
6
angles were obtained to be
1
3
2
1
9
8
8
9
that the hydrogen atom of the hydroxyl group and the nitrogen atom of the oxime group were
exactly in the same plane with the aromatic ring.
There is an intramolecular hydrogen bond between the proton of the hydroxyl group and the
nitrogen of the oxime group. The length of this hydrogen bond (H23…N15) was equal with 1.76985
Å.
To confirm the computational results, the linear regression analysis was applied between the
theoretical (at B3LYP/6-311++G(d,p) level in the vacuum) and experimental bond lengths as well
as theoretical (at B3LYP/6-311++G(d,p) level in the vacuum) and experimental bond angles. The
2
linear correlation coefficients (R ) values, obtained by B3LYP/6-311++G(d,p) level, were 0.9741
(for the bond lengths) and 0.8805 (for the bond angles), respectively.
To investigate the influence of the intermolecular interactions, the geometry was also optimized
for the dimer form of 7-Oxime. The distances between O16-H25….O36 and O41-H50….O11 were
1
.878 and 1.878 Å, respectively. These relatively short distances were probably due to the strong
intermolecular interactions. Also, the distances between O16….O36 and O11….O41 were 2.821 and
10

ACCEPTED MANUSCRIPT
2
2
.821 Å, respectively. As a result, the investigation showed that R value of the dimer form was
better than that of the monomer form.
Table 2. The optimized parameters calculated for 7-Oxime
Bond
lengths (ꢀ)
Bond
a
a
Monomer
Dimer
Experimental
Monomer
Dimer
Experimental
angles (◦)
A(2,1,10)
A(1,2,3)
A(1,2,11)
A(3,2,11)
A(2,3,4)
A(2,3,17)
A(4,3,17)
A(3,4,5)
A(3,4,12)
A(5,4,12)
A(4,5,6)
A(4,5,10)
A(6,5,10)
A(5,6,7)
A(5,6,21)
A(7,6,21)
A(6,7,8)
A(6,7,22)
A(8,7,22)
A(7,8,9)
A(7,8,13)
A(9,8,13)
A(8,9,10)
A(8,9,14)
A(10,9,14)
A(1,10,5)
A(1,10,9)
R(1,2)
R(1,10)
R(2,3)
R(2,11)
R(3,4)
R(3,17)
R(4,5)
R(4,12)
R(5,6)
R(5,10)
R(6,7)
R(6,21)
R(7,8)
R(7,22)
R(8,9)
R(8,13)
R(9,10)
R(9,14)
R(12,18)
R(12,19)
R(12,20)
R(13,23)
R(14,15)
R(14,24)
R(15,16)
R(16,25)
1.406
1.358
1.447
1.202
1.357
1.082
1.450
1.504
1.410
1.403
1.378
1.083
1.404
1.082
1.414
1.340
1.410
1.456
1.094
1.090
1.094
0.985
1.283
1.087
1.396
0.964
1.383
1.362
1.440
1.217
1.362
1.082
1.446
1.503
1.412
1.403
1.378
1.083
1.407
1.083
1.413
1.337
1.405
1.459
1.094
1.090
1.094
0.990
1.283
1.088
1.381
0.981
1.378 (18)
1.374 (18)
1.442 (2)
1.203 (2)
1.342 (2)
0.930
1.453 (2)
1.497 (2)
1.395 (2)
1.394 (2)
1.376 (2)
0.930
122.940
115.540
117.090
127.360
122.960
115.180
121.870
119.130
120.750
120.120
124.300
118.180
117.520
121.630
119.350
119.030
120.200
121.550
118.240
120.390
117.570
122.040
117.770
122.520
119.710
121.250
116.260
123.152
116.318
116.614
127.067
122.252
115.780
121.952
119.279
120.555
120.164
124.868
118.011
117.117
121.359
119.516
119.121
120.518
121.398
118.079
120.244
117.913
121.843
117.384
122.588
120.027
120.827
115.856
121.770 (12)
117.100 (14)
116.300 (15)
126.590 (15)
122.850 (14)
118.600
118.600
118.530 (14)
121.580 (15)
119.840 (15)
123.600 (14)
118.630 (14)
117.710 (14)
120.700 (15)
119.700
1.382 (2)
0.930
1.397 (2)
1.412 (18)
1.409 (2)
1.461 (2)
0.960
0.960
0.960
-
119.700
119.700 (15)
120.200
120.200
123.110 (14)
117.970 (13)
118.910 (13)
114.760 (13)
125.940 (13)
119.300 (13)
120.980 (13)
115.200 (13)
1.273 (19)
0.930
-
-
Dihedral angle (Å)
A(5,10,9)
122.480
123.311
123.800 (14)
Monomer
180.000
180.000
0.000
Dimer
A(4,12,18)
A(4,12,19)
A(4,12,20)
A(18,12,19)
A(18,12,20)
111.020
110.880
111.020
108.260
107.260
110.908
110.949
110.961
108.346
107.260
109.500
109.500
109.500
109.500
109.500
C
C
N
6
9
-C
-C10-C
15-C14-C
23-O13-C
5
-C10-O
-C
-C
-C
1
178.659
179.692
11.827
2.858
5
4
9
8
H
8
9
0.000
A(19,12,20)
108.260
108.282
109.500
Intramolecular H bond lengths and angles:
Monomer
A(8,13,23)
A(9,14,15)
A(9,14,24)
A(15,14,24)
A(14,15,16)
A(15,16,25)
108.940
120.510
118.980
120.510
112.290
103.850
108.726
120.108
119.241
120.650
112.742
105.258
-
Dimer
1.771
144.685
100.983
122.140 (14)
118.900
118.900
-
-
R(15,23)
1.770
A(13,23,15)
A(23,15,14)
144.400
101.580
Comparison of bond lengths:
Comparison of bond angles:
Dimer
Monomer
Dimer
Monomer
R
exp. = 1.3934 RB3LYP - 0.5559
R
exp = 1.4081 RB3LYP - 0.5742
A
exp. = 0.936 AB3LYP + 7.5593
Aexp = 0.9411 AB3LYP + 6.9390
R² = 0.8879, RMSD = 1.5715
2
2
R = 0.9741, RMSD = 0.0821
R² = 0.9773, RMSD = 0.0822
R = 0.8805, RMSD = 1.6251
a
Taken from Ref [38].
3
.3. Vibrational frequencies
7
-Oxime consisted of 25 atoms so it has 69 normal vibrational modes. Also, the molecule structure
point group symmetry.
of the title compound has C
s
It should be noted that the calculations were performed for a free molecule in the vacuum while
the experiments were done in the solid phase. Thus, the observed differences between the
11

ACCEPTED MANUSCRIPT
calculated frequencies and the experimental assay could be due to a crystal field effect arising from
the intermolecular interactions [13]. So, the calculated harmonic frequencies were scaled by
introducing scaling factors to improve the agreement between the calculated and the experimental
results [20].
The experimental assignments of the FT-IR and FT-Raman spectra for several vibrations, un-
scaled and scaled vibrational frequencies, Infrared intensity, Raman activity and Raman intensities
of 7-Oxime by using B3LYP method with 6-311++G(d,p) basis set has been detailed in Table 3.
-
Table 3. Experimental and calculated (unscaled and scaled) B3LYP/6-311G++(d,p) level vibrational frequencies (cm
1
)
and their assignments to the title molecule
Exp. frequencies B3LYP/6-311++G(d,p)
No.
Characterization of normal modes with PED (%)
IR
Ra
FT-IR
FT-Raman
Unscaled
Scaled
I
S
I
1
2
3297 (s)
-
-
-
3827
3367
3666
3226
169.2
318.3
210.5
71.3
53.0
28.0
υ OH Oxime (100)
υ OH Phenol (99)
12

ACCEPTED MANUSCRIPT
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
6
6
6
6
3084 (w)
-
-
-
2998 (w)
-
-
1692 (vs)
1616 (m)
-
1588 (s)
-
-
1470 (m)
-
-
-
1393 (m)
-
1366 (m)
-
1302 (m)
-
1275 (s)
1225 (m)
1190 (s)
-
-
3071 (vw)
-
-
3017 (vw)
2979 (vw)
-
-
1690 (s)
1625 (m)
-
1594 (vs)
-
1499 (w)
1462 (m)
3207
3205
3190
3154
3122
3080
3030
1806
1679
1665
1626
1616
1519
1492
1484
1478
1454
1418
1409
1398
1363
1321
1293
1266
1246
1209
1164
1143
1088
1058
1031
1005
994
963
948
871
843
831
804
763
744
734
708
706
649
606
574
543
513
3072
3071
3056
3022
2991
2950
2903
1731
1650
1636
1598
1588
1493
1466
1459
1453
1429
1394
1385
1374
1340
1298
1271
1244
1225
1189
1144
1123
1070
1040
1014
988
977
947
932
856
828
817
791
750
731
721
696
694
638
596
565
533
3.1
0.6
2.2
4.9
16.9
8.4
190.0
126.9
54.7
32.3
81.8
69.8
217.9
153.0
142.4
213.5
245.2
137.1
37.7
19.8
9.2
56.4
42.1
27.7
118.3
33.7
171.8
33.9
35.5
1.3
13.6
15.7
94.3
24.1
19.4
0.5
4.4
13.4
3.3
0.4
9.3
0.9
8.4
0.2
4.1
9.2
0.3
0.8
8.6
0.4
0.1
2.1
0.8
16.9
1.7
1.0
6.9
11.5
9.0
1.5
0.2
87.1
58.3
25.5
15.6
40.7
36.1
118.3
281.5
301.3
459.0
550.7
311.3
95.7
52.0
24.4
150.2
115.4
79.4
342.5
99.0
525.9
109.4
118.7
4.6
48.2
58.4
373.9
98.5
85.5
2.1
21.1
66.5
16.9
2.0
50.6
5.9
54.5
1.4
28.6
69.2
2.4
6.0
71.6
3.7
0.8
22.4
9.3
206.3
22.6
13.9
110.9
195.6
164.3
31.3
4.0
υ
s
CH R2 (99)
υ CH R1 (99)
as CH R2 (99)
υ CH Oxime (100)
υ
υ
υ
υ
as CH
as HCH Methyl (100)
CH (99)
3
(99)
10.0
746.8
54.8
88.7
364.8
46.3
42.0
5.6
10.8
44.0
9.7
51.1
168.4
11.5
18.0
175.9
64.2
1.9
66.2
28.2
42.8
0.6
91.7
1.9
107.4
110.3
10.8
0.3
40.6
36.1
58.7
9.1
s
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
υ C=O lactone (83)
υ CN Oxime (68)
υ CC (64)
υ CC (51)
υ CC (53)
δ CCH Scissoring R2 (32)+ υ CC (19) + υ O1-C2 lactone (10)
δ
δ
as CH
as CH
3
deformation (82)
deformation (98)
-
-
3
υ CC (30)+ δ C-OH Phenol (16)
δ HCN Oxime Scissoring (67)+ υ CC (10)
1410 (vw)
1389 (m)
-
1369 (s)
1337 (m)
1286 (m)
1253 (vw)
1231 (vw)
1192 (vw)
1178 (vs)
1139 (vw)
δ
s
CH
υ CC (15) + δ
δ C-OH Phenol (32) + υ CC (14)
υ C10-O lactone (58)
3
deformation, umbrella (70)
s
3
CH deformation, umbrella (14)
1
υ C-O Phenol (51) + δ C-OH Phenol Rocking (11)
δ HON Oxime (72) + υ CN Oxime (12)
δ HCC R2 (40)
δ HCC R1 (37) + υ C-O Phenol (13)
δ HCC R2 (38) + υ CC Oxime (13) + υ CC (11)
υ C10-O
υ CC R1(44)
2
-C lactone (62)
1
lactone (23) + δ HCC R2 (29)
-
1080 (m)
-
1022 (m)
993 (m)
1082 (vw)
1030 (vw)
997 (vw)
-
υ
as
C10-O
1
δ CH
δ CH
3
Rocking (84)
3
Rocking (57) + υ N-O Oxime (21)
υ N-O Oxime (58) + δ CH
τ HCNO Oxime (87)
τ HCCH R2 (90)
υ CC R1, R2 (41) + δ CCN Oxime Rocking (10)
γ lactone (88)
υ O
τ HCC-O Phenol R2 (92)
υ C10-O lactone (50)
δ CCC R1, R2 deformation ring (55)
3
Rocking (14)
-
-
947 (w)
-
851 (m)
-
-
-
-
737 (m)
-
-
-
951 (vw)
-
857 (vw)
-
807 (vw)
-
764 (w)
-
705 (w)
-
-
-
603 (m)
572 (m)
544 (vs)
521 (s)
508 (s)
452 (s)
419 (s)
-
384 (s)
-
311 (s)
-
1 2
-C lactone (44) + γ HCC R2 (14)
0.7
1
38.3
15.7
112.9
9.9
0.0
3.9
15.2
0.8
4.7
14.9
2.7
9.6
3.0
12.1
3.5
111.9
1.2
0.6
2.7
1.4
1.8
0.2
τ
τ
υ
s
CC-OH Phenol (78) + τ OCOC (12)
as CC-OH Phenol (79)
10-O -C lactone (11) + γ HCC R2 (48)
s
C
1
2
γ lactone deformation, umbrella (78)
τ OC-CC Phenol-Oxime (81)
-
602 (w)
-
-
-
δ CC-C Scissoring R1-CH3 (74)
τ CC-C10O1 Oxime-lactone (77)
γ CCH R2 (21) + δ CCC R1 deformation ring (45)
δ CCO Phenol Scissoring (64)
τ CCCC R1, R2 (84)
δ C -C O lactone (72)
3 2 1
δ CC-O Phenol Scissoring (55)
δ C-CN Oxime (70)
504
503
444
427
405
375
351
343
291
278
250
216
200
156
149
130
-
511
452
434
412
381
357
349
296
283
255
220
203
159
152
133
119
451 (w)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
τ
τ
s
HONC Oxime (86)
as CC-CC Oxime (82)
3.1
4.9
0.2
0.3
1.2
0.6
0.4
1.6
4.0
0.4
0.3
0.0
72.8
150.5
6.4
γ CCC R2, R1 (33) + υ C-C Oxime (24)
δ C-CN Oxime Rocking (62)
τ CCCC R2, R1 (77)
δ C-CN Oxime Rocking (62)
2 1 5
τ C O -C10C lactone (81)
-
241 (s)
-
191 (vs)
-
12.5
58.2
33.2
32.8
149.7
468.5
63.1
53.2
14.2
τ CH
τ CH
3
(88)
(84)
0.0
5.0
2.7
0.3
0.0
3.5
3
-
τ C-C-CN Phenol-Oxime (78)
δ CC-C Oxime Rocking (77)
τ OC-C-C Phenol-Oxime (74)
τ C O -C10C lactone (80)
2 1 9
τ CCC-C R1-Methyl (83)
132 (m)
-
-
-
117
95
54
96
55
Freq Theo = 1.0578 Freq Exp - 65.632
R² = 0.9931
RMSD=81.80261
a
b
c
d
s: strong; vs: very strong; m: medium; w: weak; vw: very weak.
I : Infrared intensity; S: Raman activity; I : Raman intensity.
υ: stretching; δ: in-plane bending; γ: out-of-plane bending; τ: torsion; s: symmetry; as: asymmetry; R1: lactone ring; R2: aromatic ring.
The linear regression between theoretical and experimental frequencies was shown by the formula “Freq Theo = 1.0578 Freq Exp
5.632” (R² = 0.9931 and RMSD=81.80261) which Freq Theo, Freq Exp, R and RMSD are theoretical frequencies, experimental
IR
Ra
-
2
6
frequencies, correlation coefficient and Root Mean Square Deviation, respectively.
13

ACCEPTED MANUSCRIPT
The observed and calculated frequencies of the FT-IR and FT-Raman spectra have been shown
in Fig. 5. In addition, the specific assignment of each frequency was performed via potential energy
distribution (PED) by using VEDA program [21]. Also, the normal mode animations were built
by GaussView program [19] to support the accuracy of vibrational assignments.
Fig. 5. The comparison of experimental and calculated FT-IR and FT-Raman spectra of 7-oxime
3
.3.1. O-H vibrations
All three vibrations related to OH groups (stretching, in-plane and out-of-plane bending vibrations)
are IR-active while only in-plane and out-of-plane bending modes are Raman-active. These
vibrations are the most sensitive ones to the environment and their peaks significantly shift toward
the lower frequencies upon the formation of hydrogen bonds. In fact, the strength of the hydrogen
bond determines the exact positions of O-H peaks. The stretching vibrations of the free hydroxyl
14

ACCEPTED MANUSCRIPT
group, without any hydrogen bond, usually create a strong peak in the region of 3584-3700 cm-1
-1
while these peaks appear with higher intensity and broadness in the region of 3000-3550 cm upon
the formation of intermolecular and intramolecular hydrogen bonds [39].
As shown in the FT-IR spectrum of 7-Oxime, the stretching vibrations of the phenolic OH group
-1
caused a broad absorption band between 2600 and 3400 cm [40]. The possible reason for the
broadness of this peak is the presence of strong intramolecular hydrogen bonds between the
hydrogen of the phenolic OH group (O13-H23) and the nitrogen atom of the oxime group. The
computed wavenumber related to the stretching vibrations of this mode was obtained 3226 cm-1
(mode No. 2) by B3LYP/6-311++G(d,p) method with PED contribution of 99%.
-1
Also, a relatively strong band was observed at 3297 cm which can be assigned to the O-H
stretching vibrations of the oxime group while the computed value of this O-H stretching
-1
frequency was 3666 cm (mode No. 1) with PED contribution of 100%. The possible reason for
-1
the deviation of 300 cm is due to the presence of strong intermolecular hydrogen bonds [41]. The
appearance of the red shift in the O-H stretching vibration of the oxime and phenolic group (at the
dimer form) clearly been shown in Fig. 5. This hypothesis was proved by some MEP calculations
which were applied to find the possible sites of intermolecular hydrogen bond. In addition, NBO
analysis confirmed the presence of some strong hydrogen bonds between the monomers in the
dimer form.
-1
The in-plane bending vibrations of O-H generally appeared in the region of 1150-1250 cm .
Unlike the stretching and out-of-plane bending deformation frequencies, the position of these
vibrations were not affected by the formation of hydrogen bonds [42]. Normally, the O-H in-plane
bending vibrations appear in the same region with C-H in-plane bending vibrations and C-C
-1
stretching vibrations. Herein, the medium band observed at 1366 cm in the FT-IR spectrum and
-1
the strong band observed at 1369 cm in the FT-Raman spectrum were related to the in-plane
bending vibrations of the phenolic O-H groups. Also, in the FT-Raman spectrum, the very weak
-1
band appeared at 1253 cm was assigned to the O-H in-plane bending vibrations of the oxime
group. Moreover, there was a good agreement between the experimental and the computational
-1
-1
data as the computed wavenumbers were obtained at 1374 cm (mode No. 22) and 1271 cm
mode No. 25) with PED contribution of 32% and 72 % (by B3LYP/6-311++G(d,p) method) for
(
the phenolic OH in-plane bending vibrations and the O-H in-plane bending vibrations of the oxime
group, respectively.
15

ACCEPTED MANUSCRIPT
The out-of-plane bending vibrations of O-H usually appear as a broad band in the region of 517–
-1
7
10 cm , in both intermolecular and intramolecular association [43]. In fact, the strength of the
hydrogen bond is the determining factor for the position of this band. In other words, the band
shifts toward higher wavenumbers by increasing the strength of the hydrogen bond. According to
our experimental data, the phenolic O-H out-of-plane bending vibrations created the weak bands
-1
-1
at 705 cm and 737 cm in the FT-Raman and FT-IR spectra, respectively. The corresponding
computed wavenumbers were calculated by B3LYP/6-311++G(d,p) method and obtained to be
-1
-1
7
21 cm (mode No. 44) and 731 cm (mode No. 43) with PED contribution of 79% and 78%,
respectively. The generated results indicated a good correlation between the experimental and the
computational data.
However, the O-H out-of plane bending vibrations of the oxime group appeared below 500 cm-
1
due to the formation of intermolecular and intramolecular hydrogen bonds. Also, the strong band
-1
observed at 384 cm (in the FT-Raman spectrum) was related to the O-H out-of-plane bending
-1
vibrations. Finally, the corresponding computed wavenumber was 375 cm (mode No. 56) with
PED contribution of 86%; and confirmed the agreement between the experimental and the
theoretical data.
3
.3.2. C-H and CH vibrations
3
In 7-Oxime, there are three C-H bonds related to the aromatic structure and one C-H bond related
to the oxime group so we can expect four C-H stretching, C-H in-plane and C-H out-of plane
bending vibrations corresponding to C
3
-H17, C
6
-H21, C -H22 (aromatic rings) and C14-H24 (oxime
7
group). The characteristic region for the aromatic C-H stretching vibrations is between 3000-3100
-1
cm [44-46] and the nature of the substituents only slightly affect the position of these peaks.
-1
The weak band appeared at 3084 cm in the FT-IR spectrum of our compound was assigned to
the aromatic C-H stretching vibrations. Also, the other very weak bands observed at 3071 and
-1
3
017 cm in the FT-Raman spectrum were related to the stretching vibrations of aromatic C-H as
well as C-H of the oxime moiety, respectively. The calculated frequencies for these vibrations
-1
were obtained 3072, 3071, 3056 (aromatic groups) and 3022 cm (oxime group) (mode Nos. 3-6)
by B3LYP/6-311++G(d,p) method.
The results of the PED column displayed that these modes were pure stretching modes and their
contribution was 99%, respectively. Our results for these analysis is fully in accordance with the
16

ACCEPTED MANUSCRIPT
previous reports [13, 47]. The results showed that the C-H stretching vibrations were not affected
by the substitution and also all of the mentioned vibrations were observed in the expected range.
The in-plane and out-of-plane bending vibrations of aromatic C-H group generally create peaks
-1
-1
in the range of 1050-1400 cm and 675-1000 cm , respectively [45, 46]. In our molecule, the
-1
bands recorded at 1275 (strong), 1225 (medium) and 1190 (strong) cm in the FT-IR spectrum;
plus the bands appeared at 1499 (weak), 1231 (very weak), 1192 (very weak), 1178 (very strong)
-1
and 1139 (very weak) cm in the FT-Raman spectrum belonged to the aromatic C-H in-plane
bending vibrations of the title compound. The corresponding computed frequencies were 1493,
-1
1
244, 1225, 1189 and 1144 cm (mode Nos. 15, 26-29) and the PED corresponding to these modes
-1
was a mixed mode of 29-40%. Also, the very weak band observed at 1410 cm in the FT-Raman
spectrum was related to the in-plane bending vibrations of the C-H group of the oxime moiety
-1
while the calculated frequency of this vibration was seen at 1429 cm (mode No.19), with PED
contribution of 67%.
-1
Also, the weak band at 947 cm in the FT-IR spectrum and the very weak bands at 951 and 807
-1
cm in the FT-Raman spectrum were related to the out-of-plane bending vibrations of the aromatic
C-H groups. Consequently, the computed frequencies for these modes were 947 and 817 cm-1
(mode Nos. 36 and 40) with PED contributions of 90% and 92%, respectively, and these results
showed a good agreement with the experimental data. The out-of-plane bending vibrations related
to the C-H of the oxime group could not be recognized in the experimental FT-IR and FT-Raman
spectra. However, their computed frequencies are detailed in Table 3.
In order to evaluate the peaks related to the vibrations of CH
are nine fundamental vibrations associated to each CH group: three stretching modes, three
bending modes, two rocking modes and a single torsional mode [48]. Aromatic C-H stretching
3
group, we should know that there
3
-1
vibrations appear in the range of 3000-3100 cm while C-H asymmetric and symmetric stretching
-
1
modes of CH
6].
The asymmetric stretching frequencies of the CH
3
group normally appear in lower frequencies (at the region of 2850-3000 cm ) [45,
4
-1
3
group were recorded at 2998 cm (as a weak
-1
band) in the FT-IR spectrum and 2979 cm (as a very weak band) in the FT-Raman spectrum. The
-1
calculated frequency of this mode was 2991 cm (mode No. 7) with PED contribution of 99%. In
addition, the symmetric stretching vibrations of this group were not detectable in the experimental
17

ACCEPTED MANUSCRIPT
FT-IR and FT-Raman spectra. However, the calculated frequency related to this mode was 2950
-1
cm (mode No. 8) with PED contribution of 100% (Table 3).
The asymmetric and symmetric bending vibrations of the CH
3
groups normally appear in the
-1
range of 1410-1465 and 1370-1390 cm , respectively [46, 49, 50]. In the spectra of the title
-1
-1
compound, the medium bands appeared at 1470 cm (in the FT-IR spectrum) and 1462 cm (in
the FT-Raman spectrum) were related to the CH asymmetric bending (deformation) vibrations.
The computed frequency for this mode was calculated to be equal with 1466 cm (mode No. 16)
3
-
1
with PED contribution of 82%. Also, the CH
3
symmetric bending (deformation, umbrella)
-1
-1
vibrations created the medium bands at 1393 cm in the FT-IR spectrum and 1389 cm in the FT-
-1
Raman spectrum. The calculated frequency for this mode was 1394 cm (mode No. 20) with PED
contribution of 70%, and showed a good agreement with the experimental value.
The rocking modes of methyl groups usually create the bands in the region of 1010-1070 cm-1
-1
[
45]. Herein, the medium band at 1022 cm in the FT-IR spectrum and the very weak bands at
-
1
-1
1
030 cm and 997 cm in the FT-Raman spectrum were due to the CH
rocking vibrations were equal with 1014 and 1040 cm (mode
No. 32, 33) with PED contributions of 84% and 57%, respectively.
The torsional modes related to CH groups generally appear in low-frequency regions.
Govindarajan et al. [51] calculated the normal modes of the CH out-of-plane motions (torsional
CH modes) and they reported that these signals appeared below 250 cm . According to our
results, the CH
This value showed a good correlation with the corresponding computed wavenumber (200 cm-1
mode No. 63) with PED contribution of 88%). Our results indicated that the computational
outputs for the vibrations of the methyl group were in good agreement with experimental results.
3
rocking vibrations. The
-1
calculated frequencies for the CH
3
3
3
-1
3
-1
3
torsional modes created a very strong band at 191 cm in the FT-Raman spectrum.
(
3
.3.3. C-O and C=O (lactone) vibrations
The stretching frequencies of carbonyl groups have been extensively studied by infrared
spectroscopy because almost all peaks related to these groups are very intense and narrow, and
-1
they appeared in the range of 1600-1800 cm [46]. Coumarin derivatives have two characteristic
18

ACCEPTED MANUSCRIPT
bands arising from C=O and C-O (lactone) stretching vibrations [52]. The positions of these bands
are very clear and sensitive to the infrared environment [52]. The stretching vibrations of C=O
groups in the coumarin ring occur at higher frequencies than that of normal C=O groups.
In our molecule, the stretching vibrations corresponding to the carbonyl group in the coumarin
-1
were observed as a very strong band at 1692 cm in the FT-IR spectrum and a strong band at 1690
-1
cm in the FT-Raman spectrum. The calculated C=O stretching frequency was appeared at 1731
-1
-1
cm (mode No. 10) with PED contribution of 83%. The deviation (about 40 cm ) observed
between the experimental and the computational results were probably caused by the
intermolecular hydrogen bonds. This assumption was confirmed by using the results of NBO
analysis in the dimer form.
In addition, the out-of-plane bending mode of the C=O group was appeared as a medium band
-1
-1
at 851 cm in the FT-IR spectrum and a very weak band at 857 cm in the FT-Raman spectrum.
-1
The calculated wavenumber related to this mode was 856 cm (mode No. 38) with PED
contribution of 88%. This confirmed the link between experimental and theatrical calculations.
The peaks related to C-O stretching vibrations usually appear in the range of 1050-1400 cm-1
[
51-52]. The C10-O
1
(in the lactone group) stretching vibrations appeared the medium band at 1337
-1
-1
cm in the FT-Raman spectrum. The calculated frequency for this mode (appeared at 1340 cm
(mode No. 23) with PED contribution of 58%) was in good agreement with the experimental data.
Also, the asymmetric stretching vibrations of C10-O
1
-C
2
(in the lactone group) appeared the
-1
-1
medium band at 1080 cm in the FT-IR spectrum and the very weak band at 1082 cm in the FT-
Raman spectrum. The corresponding calculated wavenumber for this mode created a band at 1070
-1
cm (mode No. 31) with PED contribution of 62% which was in good agreement with the
experimental data.
3
.3.4. C=N and N-O vibrations
The bands related to the C=N stretching vibrations of oxime groups usually appear in the range of
-1
-1
1
610-1690 cm [40, 53]. In the previous studies [54], the peak observed at 1625 cm in the FT-
IR spectrum was assigned to the C=N stretching vibrations of an oxime moiety. Herein, the
-1
-1
medium bands at 1616 cm in the FT-IR spectrum and 1625 cm in the FT-Raman spectrum were
ascribed to the C=N stretching vibrations of the oxime group (C14=N15). According to our results,
-1
the frequency of this vibrational mode was 1650 cm (mode No. 11) with PED contribution of
19

ACCEPTED MANUSCRIPT
6
8%. Also, the C=N in-plane bending vibrations of the oxime group led to a strong band at 241
-1
cm in the FT-Raman spectrum and it showed a good agreement with the corresponding computed
-1
frequency ( 250 cm (mode No. 61) with PED contribution of 62%).
The characteristic frequencies of the N-O group of oxime moieties are not usually affected by
substituents. In general, the stretching vibrations of N-O in oxime groups which are bonded to
–
1
aromatic compounds cause an absorption band at 960 cm [55]. Herein, the N15-O16 stretching
-1
vibrations were observed as a medium band at 993 cm in the FT-IR spectrum. The computed
-1
frequency related to this mode was 988 cm (mode No. 34) with PED contribution of 58% and it
was in good agreement with the experimental results. Consequently, the results that we reported
for the vibrations of C=N and N-O groups of our compound were in a good agreement with the
spectral data reported for the oxime derivatives in the literature [56-58].
3
.3.5. Ring vibrations
In the vibrational spectra of benzene and its derivatives, the ring stretching vibrations are very
prominent [59]. Varsanyi et al [59] reported that rings vibrations appear at five regions of 1590-
-1
1
625, 1550-1575, 1470-1540, 1430-1465 and 1280-1380 cm with different intensities.
Also, in saturated lactones, the absorption band related to the C=C adjacent to the -O- usually
-1
appears in the region of 1660-1685 cm . In fact, the form of substitutions around the rings can
determine the actual position of these modes [60].
-1
Herein, the calculated wavenumber of 1598 cm (mode No. 13) with PED contribution of 51%
was assigned to C=C stretching vibrations. These results are in good agreement with the
-1
experimental results (recorded as a strong band at 1588 cm in the FT-IR spectrum and a very
-1
strong band at 1594 cm in the FT-Raman spectrum).
-1
-1
In addition, a weak band at 764 cm and a very strong band at 544 cm in the FT-Raman
spectrum were assigned to the in-plane vibrations of CCC of the rings (deformation). The
-1
corresponding computed frequency was obtained to be 750 and 533 cm (mode No. 42, 50) for
this mode with PED contribution of 55% and 45%. A good agreement was observed between the
experimental and computational frequencies related to these vibrations. Also, the computed
-1
wavenumbers at 503 and 343 cm (mode Nos. 52, 58); with PED contributions of 84% and 33%
were related to the torsional and out-of-plane vibrations of CCCC and CCC in the rings,
-1
respectively. In the experimental FT-Raman spectrum, the strong bands at 508 and 311 cm were
20

ACCEPTED MANUSCRIPT
assigned to these frequencies, respectively. Fig. S.2 depicts the relationship between the
experimental and computed (by DFT/B3LYP/6-311++G(d,p)) frequencies of these vibrations. The
2
quality of the correlation in frequencies is judged by the correlation coefficient (R =0.9931) and
the Root Mean Square Deviation (RMSD=81.80261). Besides, there is a linear regression as Freq
Theo = 1.0578 Freq Exp - 65.632 between the experimental and the calculated frequencies of these
vibrations.
3
.4. NMR spectral analysis
1
The GIAO method [11, 25] was applied to calculate H NMR chemical shifts of the title compound.
X
The isotropic shielding values (σ) were used to calculate the isotropic chemical shifts δ (δ = σ
TMS
X
-
σ ) with respect to tetramethylsilane (TMS) as a reference molecule considered at the same
theoretical level (DFT/B3LYP/6-311++G(d,p)). The solvent effect of DMSO on the spectra was
modeled using the conductor-like polarizable continuum model (CPCM) with dielectric constant
ε = 46.68 on the fully optimized geometry [61-64]. Fig. 4 shows the numbering system used for
1
13
NMR calculations of the monomer and dimer form. Also, the experimental H and C NMR
spectra have been shown in Figs. 6 and 7, respectively.
21

ACCEPTED MANUSCRIPT
1
Fig. 6. H NMR spectrum of 7-Oxime
22

ACCEPTED MANUSCRIPT
13
Fig. 7. C NMR spectrum of 7-Oxime
1
13
The calculated values for H, C NMR chemical shifts (for the monomer and dimer forms) were
obtained in DMSO and the vacuum. In addition, the corresponding experimental spectra were
obtained in DMSO. Both of the obtained experimental (δ Exp) and the calculated (δ Calc) values
have been summarized in Table 4.
23

ACCEPTED MANUSCRIPT
Table 4. Calculated (δ Theo) (calculated by B3LYP method with 6-311++G(d,p) basis set) and experimental (δ Exp
)
1
13
H and C NMR chemical shifts for the monomer and dimer form of the title molecule
Monomer
Gas
Dimer
Gas
Atom
Exp.
a
a
a
a
Δδ
DMSO
6.315
2.620
2.181
2.620
7.827
7.132
11.035
9.335
7.132
Δδ
Δδ
DMSO
6.570
2.656
2.248
2.656
8.060
7.563
10.994
9.833
10.994
Δδ
H(17)
H(18)
H(19)
H(20)
H(21)
H(22)
H(23)
H(24)
H(25)
δ
δ
δ
δ
6.227
2.510
2.510
2.510
7.660
6.934
11.164
8.531
11.946
6.102
2.427
1.997
2.427
7.427
6.938
10.687
9.406
6.347
0.126
0.083
0.513
0.083
0.233
-0.004
0.477
-0.874
5.600
-0.088
-0.110
0.329
-0.110
-0.167
-0.198
0.129
-0.804
4.814
RMSD = 1.906
RMSD = 1.635
RMSD = 0.614
RMSD = 0.616
6.016
2.440
1.999
2.440
7.409
7.027
11.345
9.874
10.867
0.211
0.070
0.511
0.070
0.251
-0.093
-0.181
-1.343
1.079
MAD = 0.888
MAD = 0.750
MAD = 0.423
MAD = 0.483
-0.343
-0.146
0.262
-0.146
-0.400
-0.629
0.170
-1.302
0.952
2
Theo = 0.737δExp + 1.054
R = 0.729
Monomer (Gas phase)
Monomer (DMSO)
Dimer (Gas phase)
Dimer (DMSO)
2
Theo = 0.772δExp + 1.098
Theo = 1.001δExp - 0.076
Theo = 0.970δExp + 0.371
R = 0.785
2
R = 0.969
2
R = 0.970
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(12)
C(14)
153.657
110.728
151.772
112.065
127.227
112.810
159.703
104.942
144.023
18.271
162.904
116.801
158.901
117.339
133.058
117.892
170.916
109.721
162.603
21.8773
155.647
-9.247
-6.073
-7.129
-5.274
-5.831
-5.082
-11.213
-4.779
-18.580
-3.606
3.561
168.526
-14.869
-5.150
-14.301
-7.215
-9.065
-6.622
-11.506
-5.210
-18.068
-4.305
3.739
RMSD = 8.423
167.591
113.904
163.349
117.522
130.797
119.320
171.757
113.020
160.138
20.756
-13.934
-3.176
-11.577
-5.457
-3.570
-6.510
-12.054
-8.078
-16.115
-2.485
3.284
MAD = 7.307
171.320
-17.663
-3.420
-17.569
-8.006
-8.427
-8.395
-11.900
-7.312
-16.570
-3.210
0.205
115.878
166.073
119.280
136.292
119.432
171.209
110.152
162.091
22.5758
155.469
114.148
169.341
120.071
135.654
121.205
171.603
112.254
160.593
21.4811
159.003
159.208
155.924
2
δ
δ
δ
δ
Theo = 1.032δExp + 2.723
R = 0.984
R = 0.982
R = 0.984
R = 0.985
Monomer (Gas phase)
Monomer (DMSO)
Dimer (Gas phase)
Dimer (DMSO)
2
Theo = 1.048δExp + 2.419
Theo = 1.051δExp + 0.873
Theo = 1.070δExp + 0.639
RMSD = 10.219
RMSD = 9.097
RMSD = 10.946
MAD = 9.095
MAD = 7.840
MAD = 9.334
2
2
a
Δδ =  Exp -  Theo
The quality of each correlation in NMR data was interpreted by the following parameters: the
2
correlation coefficient (R ), the Root Mean Square Deviation (RMSD) and the Mean Absolute
Deviation (MAD). Eq. 2 and Eq. 3 represent the formulas of RMSD and MAD, respectively [65]:
1
푛
ꢀ
2
푅푀ꢃ퐷 =⁡√ ∑ ꢅ1(Exp⁡ ꢄ ⁡Theo) ,
Eq. (2)
Eq. (3)
푁
1
푛
푀퐴퐷 =⁡ ∑ ꢅ1|Theo⁡ ꢄ ⁡Exp| ,
ꢀ
푁
Where N is the number of experimental or calculated data, δ Exp denotes experimental chemical
shift values and δ Theo gives calculated chemical shift values.
In fact, there is a linear regression (δ Calc = B δ Exp + A) between the experimental and the
calculated values (Table 4). Based on the obtained correlations from the dimer and monomer
24

ACCEPTED MANUSCRIPT
forms, we can claim that the dimer form of this compound was more accurate than its monomer
form in both DMSO and the vacuum so it can be considered as accurate chemistry model for the
NMR analysis. Also, the provided results from MEP and NBO supported this issue. On the other
hand, MEP results confirmed that the maximum positive region was localized on H25 atom (in the
oxime group) and also the NBO results displayed the presence of some intermolecular hydrogen
bonds between each two monomers led to the formation of the dimer forms.
1
Also, the H chemical shift values (with respect to TMS) were calculated at B3LYP level and
they appeared in the range of 1.999–11.345 ppm in the vacuum and 2.248–10.994 ppm in DMSO
while the corresponding experimental shifts were observed in the range of 2.510–11.946 ppm. In
the experimental spectrum, the characteristic signal at 11.946 ppm was attributed to the proton of
hydroxyl group in the oxime moiety (H25) while the computational peaks related to this proton
appeared in the upfield region in comparison to the experimental one (this peak appeared at 7 ppm
in the computational spectrum of the monomer form and 10.30 ppm in that of the dimer form).
The observed difference is interpreted based on the reduction of H25 electron density by the
electronegative oxygen atom (O16) and the construction of intermolecular hydrogen bonds between
carbonyl group (O36) and H25 in the dimer form. In addition, the experimental signal related to the
proton of the other hydroxyl group (H23) was appeared at 11.164 ppm and its poor electron density
may be due to the presence of the electronegative oxygen atom (O13) and the intramolecular
hydrogen bond between the nitrogen atom (N15) of the oxime group and this proton.
1
In the experimental H NMR spectrum, the iminic proton of the oxime group (H24) appeared as
a downfield signal at 8.531 ppm. Also, the aromatic and vinyl protons of the heterocyclic ring
appeared at 7.660 (doublet, assigned to H21), 6.934 (doublet, assigned to H22) and 6.227 (singlet,
assigned to H17). In addition, the singlet signal appeared at 2.510 ppm corresponded to the protons
of the methyl group.
1
3
The experimental C chemical shifts of the compound occurred in the range of 18.271–159.703
1
3
ppm while the calculated C chemical shift values appeared in the ranges of 21.481-171.603 and
71.757-20.756 ppm in DMSO and the vacuum, respectively. The signals related to the aromatic
carbons are usually appeared in the range of 100-200 ppm [66]. The aromatic carbon bonded to
the hydroxyl group (C ) created the most downfield signal (at 159.703 ppm) probably because of
being adjacent to the electronegative oxygen atom. Also, the chemical shift of C14 (in the oxime
1
8
25

ACCEPTED MANUSCRIPT
group) was observed in downfield (159.208 ppm) due to the electronegativity of the nitrogen atom.
The signal at 153.657 ppm was assigned to the carbonyl of the pyrone ring.
Also, the signals appeared at 112.065, 127.227, 112.810, 104.942 and 144.023 ppm were
attributed to the aromatic carbons of C
observed in downfield in comparison to the other aromatic carbons which may be due to the
electronegativity of O in the pyrone ring. Besides, the peak assigned to C (110.728 ppm) appeared
in upfield in comparison to C (151.772 ppm) due to the presence of resonance between C =C
and C =O11 which made C more positive than C . In addition, the observed signal at 18.271 ppm
was related to the methyl group.
It's obvious from the correlation coefficient (R ) values that there was a good correlation between
5
, C
6
, C
7
, C and C10, respectively. The aromatic C10 was
9
1
3
4
3
4
2
4
3
2
1
13
the experimental and calculated H and C spectra (for the dimer form at B3LYP/6-311++G(d,p)
level). The obtained good correlation coefficient proved that we assigned all of the signals
2
correctly. It was obvious from the (R ) values (obtained from the correlation diagrams of the
monomer and dimer forms) that the calculated results for the dimer form (both in DMSO and the
vacuum) were closer to the experimental results than those of the monomer, proving that the
molecules existed in the dimer form. In addition, the correlation coefficient of the dimer form in
DMSO was better than that of the dimer form in the vacuum.
In Fig. 8, we have represented a histogram of the deviation and the correlation graphics for both
dimer and monomer forms of the title compound in the vacuum and DMSO.
26

ACCEPTED MANUSCRIPT
Fig. 8. (A) Correlation graphics of the experimental and calculated H and 13C NMR chemical shifts; (B) Deviation
1
1
13
of the calculated H and C NMR chemical shifts (calculated by B3LYP methods with 6-311++G(d,p) basis set) from
the experimental ones for the monomer and dimer form in vacuum and DMSO
3
.5. NBO analysis
Natural bond orbital analysis is a very powerful tool for evaluating the molecule stability
parameters including: intramolecular and intermolecular charge transfer (ICT) and delocalization
of electron density (ED). Investigation of intra- and intermolecular bonds and interactions among
bonds provide valuable reasons for studying the conjugative and hyperconjugative interactions.
Some information about electron donor orbitals, electron acceptor orbitals and the interacting
stabilization energy resulting from the second-order micro disturbance theory has been reported
previously [67, 68].
The second order Fock matrix was performed to evaluate the donor–acceptor interactions in the
NBO analysis [68, 69]. These interactions resulted in the loss of occupancy from the localized
NBO of the idealized Lewis structure to an empty non-Lewis orbital. For each donor (i) and
(2)
acceptor (j) orbital, the stabilization energy E associated with the delocalization of i→j can be
estimated by using Eq. (4).
27

ACCEPTED MANUSCRIPT
2
F(i, j)
(
2)
E  E  q
ij
i
i j
,
Eq. (4)
Where q
i
denotes the donor orbital occupancy, ε
i
and ε are diagonal elements and F(i, j) is the off
j
diagonal NBO Fock matrix element.
Delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO
orbitals and formally unoccupied (antibond or Rydberg) non-Lewis NBO orbitals lead to a
stabilizing donor–acceptor interaction. The comparison between ''filled'' (donors) Lewis-type
NBOs and ''empty'' (acceptors) non-Lewis NBOs according to second-order perturbation energy
(2)
values (E of 7-oxime) has been detailed in Table 5. In this table, only the stabilization energies
-1
of donor-acceptor interactions that were more than 4 kcal mol have been represented.
Also, the delocalization of ED between the occupied Lewis-type and unoccupied non-Lewis
NBOs leads to stabilizing donor-acceptor interactions that have a key role in the stabilization of
the entire molecular system. B3LYP/6-311++G(d,p) level (in the vacuum) can be used for
estimating the strength of these interactions using the second order perturbation theory. The large
(2)
E value in the NBO analysis confirmed the intensive interaction between electron-donors and
electron-acceptors and the greater extent of conjugation in the whole system.
The intermolecular hyperconjugative interactions are caused by overlaping the bonding orbitals
of (C-C), (C-N), (C-O), (C-H) and (O-H) and antibonding orbitals of (C-C), (C-N), (C–O) and (N-
O). These interactions result in Intramolecular Charge Transfer (ICT) which leads to the
stabilization of the whole molecular system. These interactions caused an increase in electron
density (ED) of some of the antibonding orbitals and consequently, weakened the respective bonds.
In 7-Oxime, the electron density of the two conjugated single as well as the double bond clearly
showed strong delocalization (~1.9 e).
The strong intramolecular conjugative interaction between the π electrons of C=C (of the
aromatic system) and the antibonding orbitals of C=C (of the ring), C=O (of the carbonyl group)
and C=N (of the oxime group) led to the stabilization of some parts of the ring (Table 5).
Also, the intramolecular conjugative interaction resulted from the π electrons of the C
2
-O11 and
C
14-N15 (in the oxime group) to the antibonding orbitals of C -C and C -C (in the aromatic
3
4
8
9
28

ACCEPTED MANUSCRIPT
-1
system) caused the stabilization energy to be equal with 5.10 and 6.45 kcal mol , respectively.
Besides, the stabilization energies of (9.08 and 24.62), (13.97, 21.5 and 18.06), (23.1 and 13.41)
-1
and (2081,13.19 and 26.81) kcal mol were obtained as a result of the strong intramolecular
conjugative interactions of π (C
and C -C ), π (C -C ) → π* (C -C
in the aromatic system, respectively (See Table 5).
In our molecule, the hyperconjugative interactions of σ → σ* transitions were also seen in the
various bonds. Among these interactions, σ (C -H17) → σ* (C -C ) and σ (C
3
-C
4
) → π* (C
5
-C10 and C
2
-O11), π (C
5
-C10) → π* (C
8
-C
9
, C
6
-C
7
3
4
6
7
8
9
and C -C10) and π (C
5
8
-C
9
) → π* (C14-N15, C
6
-C and C
7
5
-C10
)
3
4
5
9
-C14) → σ* (N15-O16
)
-1
showed the biggest energetic contribution of their interactions at 5.15 and 4.82 kcal mol ,
respectively.
The other important intramolecular charge transfers have been detailed in Table 5. Furtheremore,
both the hyperconjugative interactions of the σ → π* transitions from C12-H18 and C12-H20 bonds
(in the methyl group) to the antibonding orbitals of C
3
-C (in vinyl group of the pyrone ring) led
4
-1
to the stabilization energy of 4.09 kcal mol .
In addition, the other important interaction energies resulted from n → σ* transitions, defined as
intramolecular resonance, were donating electrons from the LP(1) O and LP(2) O11 atoms (of the
electron donating group in the lactone group of the pyrone ring) to the anti-bonding acceptors (σ*)
1
of C
5
-C10, C
2
-C
3
, C
2
-C
3
and O
1
-C
2
with stabilization energies of 6.14, 4.1, 15.61 and 40.25 kcal
-C )
-1
mol . Also, the charge transferred from LP(1) O13 atom of the hydroxyl group to the σ* (C
8
9
-1
created the stabilization energy of about 6.74 kcal mol .
29