Two new benzamides: Synthesis, spectroscopic characterization, X-ray diffraction, and electronic structure analyses

Article abstract of DOI:10.1016/j.molstruc.2019.127314

This work includes the syntheses, molecular and electronic structure analyses of two novel secondary amide compounds 3-acetoxy-2-methyl-N-(2-methoxyphenyl)benzamide, 1 and 3-acetoxy-2-methyl-N-(3-methylphenyl)benzamide, 2. The title compounds were charact

Full text of DOI:10.1016/j.molstruc.2019.127314

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Two new benzamides: Synthesis, spectroscopic characterization, X-ray diffraction,
and electronic structure analyses
Başak Koşar Kırca, Şükriye Çakmak, Hasan Yakan, Mustafa Odabaşoğlu, Orhan
Büyükgüngör, Halil Kütük
PII:
S0022-2860(19)31423-1
DOI:
https://doi.org/10.1016/j.molstruc.2019.127314
MOLSTR 127314
Reference:
To appear in: Journal of Molecular Structure
Received Date: 25 July 2019
Revised Date: 16 October 2019
Accepted Date: 28 October 2019
Please cite this article as: Baş.Koş. Kırca, Şü. Çakmak, H. Yakan, M. Odabaşoğlu, O. Büyükgüngör,
H. Kütük, Two new benzamides: Synthesis, spectroscopic characterization, X-ray diffraction, and
electronic structure analyses, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/
j.molstruc.2019.127314.
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Two New Benzamides: Synthesis, Spectroscopic Characterization, X-ray
Diffraction, and Electronic Structure Analyses
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Başak Koşar Kırcaa,*, Şükriye Çakmakb,*, Hasan Yakanc, Mustafa Odabaşoğlud, Orhan
Büyükgüngöre, Halil Kütükf
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aDepartment of Mathematics and Science Education, Sinop University, Sinop, Turkey
bEnvironmental Health Programme, Sinop University, Sinop, Turkey
cDepartment of Chemistry Education, Ondokuz Mayis University, Samsun, Turkey
dChemical Technology Program, Pamukkale University, Denizli, Turkey
eDepartment of Physics, Ondokuz Mayis University, Samsun, Turkey
fDepartment of Chemistry, Ondokuz Mayis University, Samsun, Turkey
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*Corresponding Author
Şükriye Çakmak, PhD
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Fax : +90 368 287 62 69
Phone: +90 368 287 62 55
E-mail: scakmak@sinop.edu.tr
Address: Environmental Health Programme
Sinop University, Sinop, 57000, Turkey.
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24 Two New Benzamides: Synthesis, Spectroscopic Characterization, X-ray
25 Diffraction, and Electronic Structure Analyses
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Başak Koşar Kırcaa,*, Şükriye Çakmakb,*, Hasan Yakanc, Mustafa Odabaşoğlud, Orhan
Büyükgüngöre, Halil Kütükf
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aDepartment of Mathematics and Science Education, Sinop University, Sinop, Turkey
bEnvironmental Health Programme, Sinop University, Sinop, Turkey
cDepartment of Chemistry Education, Ondokuz Mayis University, Samsun, Turkey
dChemical Technology Program, Pamukkale University, Denizli, Turkey
eDepartment of Physics, Ondokuz Mayis University, Samsun, Turkey
fDepartment of Chemistry, Ondokuz Mayis University, Samsun, Turkey
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Abstract
This work includes the syntheses, molecular and electronic structure analyses of two novel
secondary amide compounds 3-acetoxy-2-methyl-N-(2-methoxyphenyl)benzamide, 1 and 3-
acetoxy-2-methyl-N-(3-methylphenyl)benzamide, 2. The title compounds were characterized
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by X-ray single crystal diffraction, FT-IR, H NMR and C NMR techniques and quantum
chemical calculations were used for the investigations on electronic structure. X-ray
diffraction analyses show that both compounds 1 and 2 crystallized in the triclinic system
with space group P-1. While the characteristic amide bands were observed in IR and NMR
spectra, crystallographic studies indicate that the supramolecular structures were stabilized by
intramolecular and intermolecular hydrogen bonds and C-H…π interactions for both
compounds. Beside the experimental studies, natural bond orbital and molecular electrostatic
potential analyses were carried out to understand the intramolecular charge transfers and
hydrogen bonding behaviors of compounds.
Keywords: Secondary amides, non-covalent interactions, spectroscopic techniques, X-ray
diffraction, electronic structure.
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1. Introduction
The amide functional group can be found extensively in nature and its great significance is
well known. The common features of all the most important biological molecules such as
peptides and proteins are that they contain amide functional groups [1-8].
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Literature review shows that the amide linkage containing compounds like benzamide
derivatives deserve special consideration as they have biological and pharmacological
activities such as antibacterials [9, 10], antimicrobial [11], antifungal [12], andanticonvulsant
[13] antiinflamatory [14], anti-HSV [15], analgesic [16], antitumor [17], and anticancer [18]
among other applications.
Medical and industrial fields make broad use compounds contain the amide functionality
[19]. Amides are also widespread in coordination chemistry because of their coordinating
ability [20]. Many complexes have been studied with amide group ligands which display
various coordinating behavior with diverse metal ions [21].
An increase has recently been seen in quantum chemical computational studies on
electronic structure of compounds. Density Functional Theory (DFT) calculations based upon
computational quantum chemistry has been shown as favorite among several computational
chemistry methods because of its great accuracy in reproducing the experimental values and
advantages in designing/characterizing new molecules [22, 23].
Based on this information, we have synthesized some new benzamides which have been
described below and investigated with experimental and theoretical methods to elucidate their
structures. Cakmak et al. [24] prepared many substituted secondary amide compounds such as
2,3-dimethoxybenzoic acid and aniline derivatives. These new compounds, which include 3-
acetoxy-2-methyl-N-(4-methoxyphenyl) benzamide, are shown to have great antioxidant
properties [25]. The ultimate goal of this article is to outline the synthesis and elucidation of
new secondary compounds within the line of our ongoing projects.
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2. Experimental procedures
2.1. Synthesis of 3-acetoxy-2-methyl-N-(2-methoxyphenyl)benzamide (1)
2-methoxyaniline (10 mmol) was dissolved in THF (5 mL), and trimethylamine (1.4 mL, 10
mmol) was added dropwise. Into this reaction, a mixture was slowly added 3-acetoxy-2-
methylbenzoyl chloride (2.34 g, 11 mmol) in THF (5 mL) at room temperature. After the
reaction mixture was stirred at room temperature for 15 hours, the resulting white salt
precipitate was filtered off and then 150 mL water was added dropwise to the filtrate. The
precipitate was filtered off and washed several times with water to remove excessive aniline
and triethylamine hydrochloride salt. The crude product was crystallized from acetonitrile:
methanol (2:1) (2.30 g, 70%; m.p. 128-130 ̊C). The synthesis reaction is given in Scheme 1.
2.2. Synthesis of 3-acetoxy-2-methyl-N-(3-methylphenyl) benzamide (2)
3-methylaniline (10 mmol) and triethylamine (10 mmol) in THF (10 mL) was added to
dropwise solution of 3-acetoxy-2-methylbenzoyl chloride (11 mmol) in THF (10 mL) at room
temperature. The reaction mixture was stirred at room temperature for 15 h; next, the resulting
white salt precipitate was filtered off, and then 100 mL water was added dropwise to the
filtrate. The precipitate was filtered off and washed several times with water to remove excess
aniline derivative and trimethylamine hydrochloride salt. The crude product was crystallized
from acetonitrile (1.87 g, 60%; m.p. 142-145 ̊C). The synthesis reaction is given in Scheme 1.
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Scheme 1. Synthesis of compunds 1 and 2.
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2.3. Instrumentation
All reagents were purchased from commercial sources (Merck, ABCR, or Sigma-Aldrich) and
used without further purification except commercial thionyl chloride. It was fractionally
distilled twice to give a colourless product of high purity, b.p. 77 °C/760 mmHg. The solvents
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107
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109
110
111
1
were of analytical grade. H and 13C NMR spectra were taken at room temperature on a
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Bruker/Ultraschilt operating at 300 MHz for H, and 75 MHz for C NMR. IR spectra were
recorded with a Bruker Vertex 80V. All melting points were measured with a Stuart SMP 30.
X-Ray diffraction data were collected with a STOE IPDS II diffractometer.
2.4. Crystal structure determination
A suitable sample of size 0.66 × 0.38 × 0.07 mm3 for 1 and 0.80 × 0.29 × 0.03 mm3 for 2 were
chosen for the single crystal X-ray study. Reflections were collected in the rotation mode (ω
scanning mode) and cell parameters were determined by using X-AREA software [24].
Absorption corrections (ꢀ1 = 0.094 mm-1 and ꢀ2 = 0.083 mm-1) were achieved by the
integration method via X-RED32 software [26]. The structures were solved by direct methods
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using SHELXT-2014/4 [27]. The refinements were carried out by full-matrix least-squares
method using SHELXL 2016 on the positional and anisotropic temperature parameters of the
non-hydrogen atoms, or equivalently corresponding to 201 crystallographic parameters for 1
and 383 for 2 [28]. All non-hydrogen atom parameters were refined anisotropically and after
checking the electron map, H atoms were positioned geometrically and refined using a riding
model. The C-H bond distances were fixed to 0.93 Å for CH and 0.96 Å for CH3 groups. The
Uiso values of H atoms were also fixed to 1.2 times Ueq value of parent atoms for CH and 1.5
times Ueq value of parent atoms for CH3 groups. Under the condition of I > 2σ(I) threshold,
the structures were refined to R = 0.0415, wR2 = 0.1023, S = 1.042 with 3114 observed
reflections for 1 and R = 0.0840, wR2 = 0.1959, S = 0.914 with 6623 observed reflections for
2. The other data collection conditions and parameters of refinement process are listed in
Table 1.
Table 1. Unit cell information, reflection data and refinement details for 1 and2.
1
2
Formula
C17H17NO4
299.31
Triclinic
P-1
C17H17NO3
283.31
Triclinic
P-1
Formula weight
Crystal system
Space group
Z
2
2
a (Å)
b(Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Radiation type
µ (mm-1)
Tmax, Tmin
Reflections read
Unique reflections
Refl. with I>2σ(I)
5.0970(14)
10.907 (2)
13.974 (3)
77.117 (16)
85.600 (2)
87.360 (2)
754.7 (3)
MoKα
0.094
0.9873, 0.9912
11543
2402
3114
7.6769 (7)
8.8152 (8)
23.386 (2)
82.708 (8)
82.947 (7)
89.993 (7)
1557.7 (3)
MoKα
0.083
0.9764, 0.9956
26056
2101
6623
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Refined parameters
θmax, θmin
h, k, l
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26.497, 2.680
-6<h<6, -13<k<13, -17<l<17
383
26.752, 1.769
-9<h<9, -11<k<10, -29<l<29
R[F2>2σ(F2)]
wR(F2)
S
0.0415
0.1023
1.0420
0.0840
0.1959
0.9140
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2.5. Supplementary data
CCDC 1472110 for 1 and CCDC 1472112 for 2 contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/structures, by emailing data_request@ccdc.cam.ac.uk, or by contacting
The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
3. Results and discussion
3.1. Crystal structures
Fig. 1 and Fig. 2 show the ORTEP-3 [29] plots and atom numbering schemes for the title
compounds 1 and 2. Hydrogens are drawn as small spheres of arbitrary radii and the other
atoms are seen as displacement ellipsoids at 30% probability level.
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Figure 1. ORTEP-3 depiction of 1 with number scheme. The dashed bonds are the
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intramolecular hydrogen bonds.
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Figure 2. ORTEP-3 depiction of 2 with number scheme. The dashed bonds indicate the
intramolecular hydrogen bonds and the hydrogen bonding in asymmetric unit. For clarity,
hydrogen atoms not involved in hydrogen bonding were omitted.
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There are two crystallographically independent molecules in the asymmetric unit of 2
(named molecule A and molecule B). Molecular geometries of 1 and 2 are not planar and the
dihedral angles between the planes P1, P2 and P3 are listed in Table 2. P1, P2 and P3 are the
planar groups which form the molecular structure (see Figure s1 at supplementary materials).
Table 2. Dihedral angles between planes P1, P2 and P3 for 1 and 2 (°).
Molecule
P1-P2
53.84
58.93
73.02
P2-P3
37.01
39.24
36.82
P1-P3
89.30
82.03
70.32
1
2A
2B
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154
The molecular conformations are also affected by intermolecular and intramolecular
hydrogen bonds, van der Waals interactions, C-H…π and π…π interactions. Both the crystal
packing of compound 1 and the crystal packing of compound 2 contain intermolecular
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hydrogen bonds, C-H…π interactions and weak van der Waals interactions in their own three-
dimensional networks.
The crystal packing of 1 appears to be stabilized by two intramolecular C-H…O bonds,
intermolecular N-H…O and C-H…O hydrogen bonds and two C-H…π interactions. While
the intramolecular C6-H6…O2 [with D…A distance: 2.9095(8) Å] and C15-H15B…O2
[3.0345 (8) Å] bonds which can be seen from Fig. 1 form two pseudo six-membered rings of
N(6) graph-set motif, the intermolecular N1-H1…O2i [3.0014 (8) Å, symmetry code: (i) 1+x,
y, z] and C17-H17A…O4ii [3.5044 (8) Å, symmetry code: (ii) -1+x, y, z] bonds form
hydrogen-bonded
motifs according to Graph-Set Notation [30]. It shows the
formation of these motifs parallel to bc-plane of the unit cell. C7-H7C…Cg(1)i [3.5743 (10)
Å, symmetry code: (i) 1+x, y, z] and C14-H14…Cg(2)ii [3.6563 (10) Å, symmetry code: (ii) -
1+x, y, z] bonded chain structure of 1 along the a-axis of the unit cellis (see Figures s2 and s3
at supplementary materials).
The crystal packing of 2 appears to be stabilized by four intramolecular C-H…O bonds, an
N-H…O hydrogen bond in asymmetric unit, an intermolecular N-H…O bond, two
intermolecular C-H…O bonds and two C-H…π interactions. The N1-H1…O4 [2.8633 (3) Å]
hydrogen bond which links two independent identical molecules in asymmetric unit,
intermolecular N2-H2A…O1iii [2.8531 (3) Å, symmetry code: (iii) x, 1+y, z], C12-
H12…O6iv [3.3874 (3) Å, symmetry code: (iv) -1+x, y, z] and C17-H17B…O3v [3.4067 (3)
Å, symmetry code: (v) 1-x, -y, 1-z] bonds can be seen (see Figure s4 at supplementary
materials). Among these bonds, C17-H17B…O3v forms a
motif. All these
intermolecular hydrogen bonds in compound 2 connect the molecules along all directions and
form a complex bonding motif. The C14-H14…Cg(3) [3.6539 (3) Å] (in asymmetric unit)
and C32-H32…Cg(1)iii [3.6759 (3) Å] interactions generate a chain motif along b-axis of the
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unit cell (see Figure s5 at supplementary materials). Very similar intermolecular interactions
can be seen from the previous paper [31].
The contact distances, angles, and the other details of intramolecular and intermolecular
hydrogen bonds are summarized in Table 3.
Table 3. Hydrogen bonding geometry for 1 and 2 (Å, °).
D-H (Å)
H…A (Å)
D…A (Å)
D-H…A(°)
D-H…A
1
C6-H6…O2
C15-H15B…O2
N1-H1…O2i
C17-H17A…O4ii
C7-H7…Cg(1)i
0.93
0.96
0.86
0.96
0.93
2.49
2.41
2.18
2.58
2.69
2.76
2.9095 (8)
3.0345 (8)
3.0014 (8)
3.5044 (8)
3.5743 (10)
3.6563 (10)
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122
159
163
154
156
C14-H14…Cg(2)ii 0.93
2
C2-H2…O1
0.93
0.96
0.93
0.96
0.86
0.86
0.93
0.96
0.93
2.59
2.37
2.56
2.59
2.05
2.06
2.48
2.54
2.79
2.94
2.9816 (3)
3.0383 (3)
2.9665 (3)
3.2071 (3)
2.8633 (3)
2.8531 (3)
3.3874 (3)
3.4067 (3)
3.6539 (3)
3.6759 (3)
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158
154
167
150
155
137
C15-H15B…O1
C19-H19…O4
C28-H28C…O4
N1-H1…O4
N2-H2A…O1iii
C12-H12…O6iv
C17-H17B…O3v
C14-H14…Cg(3)
C31-H31…Cg(4)iii 0.93
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i[1+x, y, z], ii[-1+x, y, z], iii[x,1+y,z], iv[-1+x, y, z], v[1-x, -y, 1-z].
Cg(1): ring C1/C6 of 1, Cg(2): ring C9/C14 of 1, Cg(3): ring C18/C23 of 2, Cg(4): ring C1/C6 of 2.
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Some selected bond lengths and angles are listed in Table 4. The C-N and C=O bond
lengths in the amide group of molecules fall within expected values and the good agreement
can be seen between these bond lengths and angles with the counterparts in similar amide
compounds [24, 25, 31-35].
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Table 4. Selected geometrical parameters for 1 and 2 (Å, °).
2A
1.220 (5)
1
2B
C8=O2
1.2218 (17)
1.3435 (19)
1.4165 (18)
1.504 (2)
C8=O1
C8-N1
N1-C1
C8-C9
C25=O4
C25-N2
N2-C18
C25-C26
C29-O5
O5-C23
C33=O6
-
1.224 (5)
1.337 (6)
1.446 (7)
1.500 (7)
1.407 (6)
1.360 (6)
1.188 (5)
-
C8-N1
N1-C1
C8-C9
C2-O1
1.339 (6)
1.426 (6)
1.508 (6)
1.406 (6)
1.373 (7)
1.179 (6)
-
1.3633 (18)
1.4177 (19)
1.4027 (19)
1.354 (2)
C11-O2
O2-C16
C16=O3
-
O1-C7
C11-O3
C16-O3
C16=O4
C9-C8-N1
C9-C8-O2
O2-C8-N1
C8-N1-C1
1.196 (2)
-
-
-
-
114.92 (12)
121.68 (13)
123.40 (14)
123.23 (12)
C9-C8-N1
C9-C8-O1
O1-C8-N1
C8-N1-C1
114.8 (4)
120.8 (5)
124.5 (4)
126.6 (4)
C26-C25-N2 114.8 (4)
C26-C25-O4 121.9 (4)
O4-C25-N2
123.3 (5)
C25-N2-C18 127.6 (4)
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It is well known that the aromaticity is a sign of more delocalized electron clouds, and the
delocalization of electrons gives more stability to the molecules. Beside the delocalization,
trans configuration of main groups of molecules is another factor which gives additional
stability to the molecule. In trans configuration steric interactions between the hydrogen
atoms are less effective than that of cis configuration. Molecules have two six-membered
rings which are in trans configuration with respect to amide C-N bonds. The harmonic
oscillator model of aromaticity (HOMA) index gives information about the aromaticity of
compounds and is based upon average squared deviation of bond lengths. HOMA index has
been calculated for both rings of 1 and 2 by using following equation [36, 37] because we
observed that the bond lengths in one of the rings in molecule 2B are very different from each
other.
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207
(1)
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212
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214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
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231
Where n is the number of bonds in the molecular fragments of interest (in our case n is
equal to 6 for the six-membered rings), αi normalization constant is equal to 257.7, Ri is
individual bond length and Ropt is equal to 1.388 Å for C-C bonds in an aromatic ring. For the
purely aromatic systems the HOMA index is equal to 1 and for the non-aromatic ones equal to
0. The calculated indices are found as 0.974 for C1/C6 ring (ring containing atoms C1 to C6,
hereafter abbreviated C1/C6 ring) and 0.976 for C9/C14 ring (ring containing atoms C9 to
C14) of 1, 0.727 for C1/C6 ring, 0.961 for C9/C14 ring of 2A and 0.322 for C18/C23 ring
(ring containing atoms C18 to C23), 0.937 for C26/C32 ring (ring containing atoms C26 to
C32) of 2B. There is one slight andone considerable deviation from the aromaticity for the six
membered rings in compound 2. The slight deviation belongs to C1/C6 ring of 2A but the ring
can still be defined as aromatic. On the other hand, C18/C23 ring of 2B appears to show a
somewhat reduced degree of aromaticity in the solid state. The C-H… π interaction including
the C18/C23 ring and the hyperconjugative resonance effect with the methyl group must be
responsible for the deviations.
3.2. Electronic structures
For all the DFT calculations, B3LYP hybrid exchange-correlation functional [38,39] has been
employed with 6-311+G(d,p) basis set [40] as implemented in Gaussian03 package [41].
The electron delocalization gives amides a polar character, and because of this polar
character, amides forms relatively strong hydrogen bonds involving both their C=O group and
N-H proton [42]. In this part of the study, we examine the electronic delocalization and
electrostatic potential surfaces on the basis of natural bond orbital (NBO) analyses and
molecular electrostatic potential (MEP) plots of compounds 1 and 2 with the help of density
functional theory (DFT) to investigate the above-mentioned hydrogen bondings.
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The electron delocalization can be rationalized well by the NBO analysis which gives the
stabilization energy and the redistribution of electron density in bonding and antibonding
orbitals. The NBO calculations were performed using NBO 3.1 program [43] as implemented
in the Gaussian 03W package on the optimized geometries of compounds 1 and 2. In this
method, the stabilization energy E(2) associated with the delocalization i→j for each donor (i)
and acceptor (j) is defined with the following equation:
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(2)
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241
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where qi is the donor orbital occupancy, Ei and Ej are the diagonal and Fij is the off-diagonal
elements of the Fock matrix (orbital energies) [44, 45]. The larger E(2) values indicate the
stronger interactions between electron-donors and acceptors and larger extent of conjugation
of the whole system. Table 5 summarizes the possible intensive interactions (which the
stabilization energies are larger than 15 kcal/mol) for compound 1 and 2.
Table 5. Electron delocalization and second order interaction energies for 1 and 2.
Donor (i)
Acceptor (j) E(2) (kcal/mol) Ej-Ei (a.u.)
Fij (a.u.)
1
π(C1-C6)
π(C1-C6)
π(C2-C3)
π(C2-C3)
π(C4-C5)
π(C4-C5)
π*(C2-C3)
π*(C4-C5)
π*(C1-C6)
π*(C4-C5)
π*(C1-C6)
π*(C2-C3)
π*(C10-
20.65
19.07
16.54
18.93
20.07
18.83
0.28
0.29
0.30
0.30
0.28
0.27
0.068
0.067
0.064
0.068
0.068
0.065
π(C9-C14)
C11)
20.38
0.29
0.069
π*(C12-
π(C9-C14)
π(C10-C11)
C13)
18.65
0.30
0.29
0.067
0.067
π*(C9-C14) 19.80
π*(C12-
π(C10-C11)
π(C12-C13)
C13)
20.47
0.30
0.29
0.071
0.069
π*(C9-C14) 20.62
π*(C10-
π(C12-C13)
C11)
20.69
0.29
0.069
13

n1(N1)
n1(N1)
n2(O1)
n2(O2)
n2(O2)
π*(C1-C6)
π*(C8-O2)
π*(C2-C3)
σ*(C8-C9)
σ*(C8-N1)
σ*(C16-
34.04
50.02
26.79
18.54
25.08
0.30
0.30
0.35
0.66
0.70
0.090
0.112
0.093
0.100
0.120
n2(O4)
n2(O4)
C17)
17.62
0.64
0.61
0.098
0.134
σ*(C16-O3) 36.04
2
π(C1-C2)
π(C1-C2)
π(C3-C4)
π(C3-C4)
π(C5-C6)
π(C5-C6)
π*(C3-C4)
π*(C5-C6)
π*(C1-C2)
π*(C5-C6)
π*(C1-C2)
π*(C3-C4)
π*(C11-
22.14
18.05
18.49
23.78
20.77
16.27
0.29
0.28
0.28
0.27
0.29
0.30
0.072
0.064
0.064
0.072
0.070
0.063
π(C9-C10)
C12)
π*(C13-
C14)
π*(C9-C10) 20.92
π*(C13-
21.03
21.63
0.29
0.068
π(C9-C10)
π(C11-C12)
0.30
0.30
0.070
0.071
π(C11-C12)
π(C13-C14)
C14)
19.80
0.29
0.29
0.068
0.068
π*(C9-C10) 19.50
π*(C11-
π(C13-C14)
n1(N1)
n1(N1)
n2(O1)
n2(O1)
C12)
20.28
33.16
48.24
18.56
25.39
0.28
0.30
0.31
0.66
0.70
0.068
0.090
0.111
0.100
0.121
π*(C1-C2)
π*(C8-O1)
σ*(C8-C9)
σ*(C8-N1)
σ*(C16-
C17)
n2(O3)
n2(O3)
17.60
0.64
0.61
0.098
0.132
σ*(C16-O2) 35.07
245
246
247
248
249
250
251
In Table 5, first twelve lines for both 1 and 2 are about the electron delocalization in the
phenyl rings of compounds. These are expected donor – acceptor interactions because of the
aromaticity of phenyl rings which they give additional stability to the compounds. The
stabilization energy values for these expected π(C-C) → π*(C-C) intramolecular charge
transfers are in the range of 16 kcal/mol - 20 kcal/mol. The strongest interaction for 1 is the
electron donation that forms the donor lone pair n1(N1) orbitalto the π*(C8-O2) anti-bonding
14

252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
orbital with the 50.02 kcal/mol stabilization energy which contributes to a resonance
interaction in the amide group of molecules. The other significant contibutions in second
order perturbation approach table for 1 is n2(O4) → σ*(C16-O3), n1(N1) → π*(C1-C6) and
n2(O2) → σ*(C8-N1) with the stabilization energies of 36.04, 34.04 and 25.08 kcal/mol,
respectively. The similar donor – acceptor interactions occured in compound 2 according to
the second order perturbation theory analysis of 2. Beside the π(C-C) → π*(C-C) interactions,
there are four more noteworthy donations attract the attention in Table 5. The strongest one is
the electron donation that forms the donor lone pair n1(N1) orbital to the anti-bonding π*(C8-
O1) orbital in the amide group with the 48.24 kcal/mol stabilization energy. The others are
n2(O3) → σ*(C16-O2), n1(N1) → π*(C1-C2) and n2(O1) → σ*(C8-N1) with the
stabilization energies of 35.07, 33.16 and 25.39 kcal/mol, respectively. NBO analyses of 1
and 2 reveal that the electron delocalizations in amide groups make these groups more polar,
the oxygen and NH proton becomes much better hydrogen bond acceptors and donors.
The charge density and chemical reactivity, so also the relative polarity of a molecule can
be understood well by looking at the molecular electrostatic potential (MEP) map which
represents different values of electrostatic potential with different colours [46]. MEPs are
drawn onto the constant electron density surface. On these maps, while blue colour represents
the most positive regions which have the strongest attraction, red colour is for the most
electronegative regions which indicate the strongest repulsion. The MEPs of title compounds
are presented in Figures 3 and 4 for compound 1 and 2, respectively. The colour scales on the
maps show the lower and upper limits of electrostatic potentials. The electrostatic potential is
in the range between -5.452x10-2 a.u. and 5.452x10-2 a.u. for compound 1 and in the range
between -6.527x10-2 a.u. and 6.527x10-2 a.u. for compound 2. The figures clearly show that
the MEPs of two investigated compounds are very similar. In both maps, the most positive
regions are localized on the hydrogen atoms bonded to nitrogens of amide groups. On the
15

277
278
279
280
other hand, the most negative regions are on the C=O oxygens. These results are in agreement
with the well-known fact that the negative regions of MEPs are associated with the lone
electron pairs of the electronegative atoms in general. The obtained results are also in
accordance with NBO data.
281
282
Figure 3. MEP of title compound 1.
283
284
Figure 4. MEP of title compound 2.
16

285
286
287
288
289
290
291
292
293
294
We have also calculated the NLO (non-linear optical) properties like linear polarizability
(α) and the first-order hyperpolarizability (β) values of the title compounds with the help of
DFT because of their good transfer of charges which can be seen from the NBO analyses
results. The NLO properties of a compound have an important role for design of new
materials in optical technology, for example signal processing and optical interconnection
devices. Because of their π-electron cloud movement, especially organic molecules have
larger NLO susceptibilities [47]. In order to obtain the α and β values of the compounds, the
components of linear polarizability and the first-order hyperpolarizability have been
calculated using polar=ENONLY input to Gaussian03 at the level of B3LYP/6-31+G(d,p) in
the gas phase and the components have been used in the following equations: [48]
295
(3)
(4)
296
297
298
299
300
301
302
303
304
305
306
307
The calculated α and β values are 230.762 Å3 and 3.716x10-30 cm5/esu for compound 1,
224.567 Å3 and 3.513x10-30 cm5/esu for compound 2. In order to understand whether the
compound is a good candidate for non-linear optical studies or not, we compared the linear
polarizability and the first-order hyperpolarizability values with those of urea as a common
way in literature. For urea with the same functional and basis set by DFT method, calculated α
and β values were found as 3.831 Å3 and 0.373x10-30 cm5/esu [49]. In our ongoing work,
while β of compound 1 is 9.96 times greater than that of urea, β of compound 2 is 9.41 times
greater than that of urea. These values are relatively high when compared to the literature [50,
51] and point out that both compound 1 and 2 can be good candidates for non-linear optical
materials.
17

308
309
310
311
312
313
314
315
316
317
318
319
320
321
3.3. Vibrational frequencies
In the IR spectra, characteristic amide bands were observed for the compounds (see Figure s6
at supplementary materials). The N–H stretching vibration was observed as characteristic
absorption at 3323 cm-1 for compound 1. In compound 2, the same band appeared at 3234
cm1. In compounds 1 and 2, the C=O (amide I) stretching vibrations were observed as second
characteristic absorption band at 1660 cm-1 and 1651 cm-1, respectively. For compounds 1 and
2, the C=O stretching vibration of ester carbonyl groups were observed very strong
vibrational bands at 1750 cm-1 and 1761 cm-1, respectively. The strong C=O stretching
vibration of ester carbonyl group was observed at higher wavenumber than the normal
stretching vibration of aliphatic ester (~1740 cm-1) due to resonance of the phenyl group with
oxygen. Another group wavenumber was the C-N stretching vibration with the N-H bending
vibration (amide II) resulting from Fermi resonance effect. In compounds 1 and 2, this mode
was observed at 1458 cm-1 and 1455 cm-1 in the infrared spectra, respectively. These data are
in agreement with those both previously reported for similar compounds [25, 52].
322
323
3.4. NMR spectra
1
324
325
326
327
328
329
330
331
The H NMR spectrum of compound 1 was recorded in CDCl3 [Fig. 5]. While the three
methyl protons attached to ester carbonyl was resonated at 2.38 ppm (s, 3H, -OCOCH3) as a
singlet, three protons due to methyl group at 2-position on the phenyl ring were observed at
2.35 ppm (s, 3H, ArCH3) as a singlet. The signal was observed at 3.89 ppm (s, 3H, ArOCH3)
due to the methoxy group at 2′-position of the phenyl ring. The signal of NH proton appeared
as a singlet at 8.15 ppm (s, 1H, NH-C=O) which was very characteristic for this type of amide
protons. For compound 1, the aromatic protons of the phenyl rings appeared in the region of
δ= 6.92-7.42 ppm [Fig. 5].
18

332
333
Figure 5. 1H NMR spectrum of compound 1.
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
This compound was further characterized by 13C NMR [Fig. 6]. The 13C NMR spectrum of
compound 1 showed 17 distinct resonances in agreement with the proposed structure. The
carbon atom of the ester carbonyl group appeared at 169.4 ppm, whereas the amide carbonyl
functional group was observed at 167.0 ppm. The aromatic C1 and C2′ carbons were the most
downfield in comparison with the other carbons of the aromatic rings and so these carbons
gave the signal at 149.9 ppm and 148.1 ppm respectively. This downfield shift was due to the
presence of acetoxy group at the 1-position in the aromatic ring and the methoxy group at 2′-
position of the other phenyl ring. The other carbons of the aromatic rings (C2, C3, C4, C5,
C6, C1′, C3′, C4′, C5′ and C6′) were at 127.6 ppm, 138.9 ppm, 126.9 ppm, 128.9 ppm, 124.2
ppm, 124.7 ppm, 119.8 ppm, 126.9 ppm, 124.0 ppm and 121.1 ppm, respectively. The methyl
carbon attached to ester carbonyl group (-OCOCH3) gave a signal at 20.8 ppm, while the
signal at 13.0 ppm belonged to methyl group carbon (-CH3) located at 2-position on the
phenyl ring. The methyl carbon attached to methoxy group (-OCH3) at 2′-position of the
phenyl ring gave a signal at 55.6 ppm. These values are in agreement with the values of
previously reported for similar compounds [25].
19

349
350
351
352
Figure 6. 13C NMR spectrum of compound 1.
The 1H NMR spectrum of compound 2 was recorded in CDCl3 [Fig. 7]. The methyl group
protons at the 3′- and 2-positions of phenyl rings were observed as two different singlets at
2.30 and 2.34 ppm for compound 2. The methyl proton of ester carbonyl group was observed
at 2.38 ppm. The proton of the amide group (NH-C=O) also appeared as a singlet at 7.64
ppm. Aromatic protons of phenyl ring appeared in the region of 7.10-7.50 ppm. The H2ʹ
proton showed a singlet at 7.50 ppm. The H4ʹ proton coupled to H5′ proton and gave doublet
peak at 6.99 ppm.
353
354
355
356
357
358
20

359
360
Figure 7. 1H NMR spectrum of compound 2.
361
362
363
364
365
366
367
368
369
370
371
372
373
The 13C NMR spectrum of compound 2 was recorded in CDCl3 [Fig. 8]. The chemical
structure was confirmed by the presence of 17 peaks, as expected. The 13C NMR spectrum of
compound 2 displayed a peak at 21.5 ppm, which was consistent with methyl group carbon at
3′-positionon the phenyl ring. The other two methyl carbons were attached to ester carbonyl
group (-OCOCH3) and were located at 2-positions of phenyl ring resonate at 20.8 ppm and
13.0 ppm, respectively. The carbon of ester carbonyl group appeared at 169.3 ppm, whereas
the amide carbonyl functional group was observed at 167.2 ppm. The aromatic C1 carbon
bearing the acetoxy group (-OCOCH3) and the aromatic C3′ carbon of phenyl ring was the
most deshielded carbons, and so these carbons gave the signals which were the furthest
downfield at 149.90 ppm and 139.09 ppm respectively. The rest of aromatic carbon signals
were observed between 138.7-117.0 ppm. These results are consistent with the literature
values [25].
21

374
375
Figure 8. 13C NMR spectrum of compound 2.
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
4. Conclusions
In the present work, we have described the syntheses and characterizations of two secondary
amide compounds 3-acetoxy-2-methyl-N-(2-methoxyphenyl) benzamide and 3-acetoxy-2-
1
13
methyl-N-(3-methylphenyl) benzamide by using the X-ray diffraction, IR, H NMR and C
NMR techniques experimentally and by using DFT theoretically. The results of X-ray studies
showed that the six-membered rings are in trans configuration with respect to C-N bond of
amide bridge in both molecules. The intramolecular and intermolecular hydrogen bonds and
C-H…π interactions stabilized the crystal structures of compounds 1 and 2. According to the
FT-IR and NMR results, characteristic absorption bands and NMR signals are in the expected
ranges for the amide structures. MEP and NBO studies carried out by DFT method are
qualified to explain the hydrogen bondings in compounds. Calculated linear polarizability and
first-order hyperpolarizability values of compounds indicated that they can be considered as
potential non-linear optical materials. We hope that the results of this study will be helpful for
the further studies.
Conflict of Interest: The authors declare that they have no conflict of interest.
22

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393
Acknowledgements
We would like to thank Ondokuz Mayis University (Grant No. PYO.FEN.1904.12.007) for its
financial support of this work.
394
395
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