Synthesis, spectroscopic characterization and computational studies of 2-(4-bromophenyl)-2-oxoethyl 3-methylbenzoate by density functional theory

Article abstract of DOI:10.1016/j.molstruc.2015.03.028

The title compound, 2-(4-bromophenyl)-2-oxoethyl 3-methylbenzoate, has been synthesized and characterized using experimental FTIR, ¹H and ¹³C NMR, single crystal XRD and various theoretical methods (FTIR, NMR, electronic and band gap

Full text of DOI:10.1016/j.molstruc.2015.03.028

Journal of Molecular Structure 1092 (2015) 192–201
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization and computational studies
of 2-(4-bromophenyl)-2-oxoethyl 3-methylbenzoate by density
functional theory
a
d
b,e
Diwaker a, C.S. Chidan Kumar b,c, , Ashish Kumar , Siddegowda Chandraju , Hoong-Kun Fun
,
⇑
Ching Kheng Quah b
a School of Basic Sciences, Indian Institute of Technology Mandi, Mandi, HP 175005, India
b X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia (USM), 11800 Penang, Malaysia
c Department of Engineering Chemistry, Alva’s Institute of Engineering & Technology, Mijar, Moodbidri 57422, Karnataka, India
d Department of Sugar Technology and Chemistry, Sir M. Visvesvaraya PG Center, University of Mysore, Tubinakere, Mandya 571402, India
e Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Molecular structure of title
compound is reported using DFT and
X-ray analysis.
ꢀ
NLO investigation reveals the title
compound a strong candidate for
SHG.
ꢀ
ꢀ
IR and NMR spectra are computed
using DFT approach.
Band structure and TDOS along with
PDOS are plotted.
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compound, 2-(4-bromophenyl)-2-oxoethyl 3-methylbenzoate, has been synthesized and
characterized using experimental FTIR, 1H and 13C NMR, single crystal XRD and various theoretical meth-
ods (FTIR, NMR, electronic and band gap studies). The compound crystallizes in monoclinic space group
P21/c with a = 8.176 (2) Å, b = 7.82 (2) Å, c = 2.952 (6) Å, b = 91.330 (4)° and Z = 4. The initial coordinate
geometry obtained by XRD is further used to obtain the optimized ground state geometry of the inves-
tigated compound using HF and DFT/B3LYP/6-311++G(2d,2p) level of theory. Geometrical parameters,
vibrational frequencies, (GIAO) 1H and 13C NMR chemical shifts have been calculated theoretically using
the optimized ground state geometry. Apart from this, density of states of different atoms, total density of
states and band gap studies have also been successfully studied using theoretical models.
Ó 2015 Elsevier B.V. All rights reserved.
Received 13 December 2014
Received in revised form 13 March 2015
Accepted 17 March 2015
Available online 24 March 2015
Keywords:
DFT
DOS
GIAO
XRD
FTIR
NMR
Introduction
⇑
Corresponding author at: Department of Engineering Chemistry, Alva’s Institute
of Engineering & Technology, Mijar, Moodbidri 57422, Karnataka, India. Tel.: +91
9980200463.
There have been long-standing interests in photo-releasable
protecting groups, for their applications in various multistep syn-
thesis. Keto ester is a derivative of an acid which is formed by
E-mail address: chidankumar@gmail.com (C.S. Chidan Kumar).
http://dx.doi.org/10.1016/j.molstruc.2015.03.028
0022-2860/Ó 2015 Elsevier B.V. All rights reserved.

Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
193
the reaction between an acid and a phenacyl bromide. They are
well-known as protecting groups for carboxylic acids in organic
synthesis and biochemistry [1,2]. The ease of using these photosen-
sitive blocking groups is, they can easily be cleaved under com-
pletely neutral or mild conditions [3] and therefore used for the
identification of organic acids. These derivatives have immense
applications in the field of synthetic chemistry [4] such as in the
synthesis of imidazoles and oxazoles as well as benzoxazepine
[5]. These are also useful in peptide synthesis. Keto esters, an
important class of versatile intermediates, have been reported to
show antitumor activity against Ehrlich cells and HeLa cells [6].
They also regulate the flowering times of some plants [7]. Recent
studies have revealed that they also exhibit inhibitory activity
against two isozymes of 11b-hydroxysteroid dehydrogenases
(11b-HSD1 and 11b-HSD2), which catalyze the inter-conversion
of active cortisol and inactive cortisone [8]. Many researchers have
reported the synthesis and photolysis studies of phenacyl esters.
Dicarbonyl compounds and their derivatives are also among the
most versatile and frequently employed synthons in organic syn-
thesis, especially in heterocyclic chemistry [9,10]. Hence phenacyl
benzoates attract commercial importance due to their immense
applications in various fields of chemistry. In continuation of our
work [11–13], herewith we report the synthesis of 2-(4-bro-
mophenyl)-2-oxoethyl 3-methylbenzoate, (1), which may be used
as an effective synthon in synthetic chemistry.
and weighed to get the amount of solute present in the solution.
The percentage solubility can be determined using the formula:
Solubility ðwt%Þ ¼ ðweight of the solute ꢁ 100Þ
=weight of the ðsolute þ solventÞ:
This process was repeated thrice to get the accurate results at
different temperatures in acetone and DMF and the solubility
parameters were estimated. It is known that, the compound in
which it is moderately soluble is chosen for crystal growth. The
compound is very moderately soluble and steadily increases with
both acetone and DMF. Since the slow evaporation of DMF takes
considerably long duration, acetone was used to grow the single
crystals of the title ester compound.
Crystal growth
To grow single crystals of the title ester derivative, the slow
evaporation technique at constant temperature method was
employed. A saturated solution of the compound in acetone as sol-
vent was prepared and warmed slightly to get a homogeneous
mixture. The solution was filtered to remove any impurities pre-
sent and was kept undisturbed for few days. The mouth of the bea-
ker was covered with filter paper to ensure slow evaporation. The
defect free seed crystals obtained in this way were used for grow-
ing bulk crystals. The grown crystals are shown in Fig. 1.
Crystallography
Experimental and theoretical methods
Colorless, block shaped single crystal of the analyzed compound
(C16H13BrO3), with dimensions of 0.93 mm ꢁ 0.54 mm ꢁ 0.25 mm
was selected and mounted on a Bruker APEX-II CCD diffractometer
Synthesis
The reagents and solvents for the synthesis were obtained from
the Aldrich Chemical Co., and were used without additional purifi-
cation. The title ester derivative was synthesized as per the proce-
dure reported earlier [14–16]. 2-Bromo-1-(4-bromophenyl)ethan-
1-one (0.01 mol) and m-toluic acid (0.015 mol) was dissolved in
8 ml dimethyl formamide. A slight excess of anhydrous potassium
carbonate was added to the solution with vigorous stirring. The
reaction mixture was stirred for about 2 h at room temperature.
The progress of the reaction was monitored by TLC. The formed
products was filtered and recrystallized. Crystals suitable for X-
ray diffraction studies were obtained from acetone solution by
slow evaporation technique at room temperature. Melting point
(374–376 K) was determined by Stuart Scientific (UK) apparatus.
The purity of the compound was confirmed by thin layer chro-
matography using Merck silica gel 60 F254 coated aluminum
plates.
with a fine-focus sealed tube graphite-monochromated Mo K
a
radiation (k = 0.71073 Å) at 296 K in the range of 2.5 6 h 6 23.9°.
The data were processed with SAINT and corrected for absorption
using SADABS [17]. A total of 16230 reflections were collected, of
which 4257 were independent and 2660 reflections with
I > 2r(I). The structures were solved by direct method using the
program SHELXTL [18] and were refined by full-matrix least
squares technique on F2 using anisotropic displacement parame-
ters for all non-hydrogen atoms. All the hydrogen atoms were posi-
tioned geometrically [CAH = 0.93–96 Å] and refined using riding
model with isotropic displacement parameters set to 1.2 or 1.5
Solubility study
It is well-known that, solvent and temperature plays a signifi-
cant role in growing the single crystals. The challenge is to select
a suitable solvent for the slow evaporation crystal growth tech-
nique. In order to choose the best solvent, the solubility studies
in various solvents are done and came to know that, the title com-
pound is insoluble in water, less soluble in ethanol and methanol
and moderately soluble in acetone and DMF. A known volume of
the solvent is taken in a clean beaker and heated to a specific tem-
perature. The finely powdered sample was added slowly to the sol-
vent with stirring to get a saturated solution. About 20 ml of this
saturated solution was transferred to a pre-weighed specific grav-
ity bottle and weighed again. The difference in weight of the bottle
containing the solution and the weight of the empty bottle gave
the actual weight of the solution taken. The solution from the grav-
ity bottle is transferred to a clean beaker, evaporated to dryness
Fig. 1. Crystals grown by the slow evaporation technique.

194
Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
Table 1
bonds and Brꢃ ꢃ ꢃO short contacts dominates in the crystal packing.
The C4AH4Aꢃ ꢃ ꢃO1 (Symmetry code: x, y ꢂ 1, z) hydrogen bond
connects the molecules into head-to-tail chains (Fig. 3a) propagat-
ing along the crystallographic b-axis direction. Two adjacent anti-
parallel chains are interconnected via Brꢃ ꢃ ꢃO short contacts
(3.301 Å) forming 2D supramolecular layer (Fig. 3b). Further, the
Crystal data and parameters for structure refinement of the title compound.
Crystal data
Chemical formula
Mr
C16H13BrO3
333.17
Monoclinic, P21/c
296
Crystal system, space group
Temperature (K)
a, b, c (Å)
b (°)
crystal packing is stabilized by CAH. . .p (Table 2) interactions pro-
8.176 (2), 7.82 (2), 2 .952 (6)
91.330 (4)
1468.6 (7)
4
ducing a three dimensional network involving the centroids of the
C1AC6 and C10AC15 benzene rings. The bond length and bond
angles agree with the literature values [22] and are comparable
with those reported earlier. Simulated PXRD diagram for the title
compound using plotCIF is depicted in Fig. 4. The title compound
shows different types of bond interactions i.e. CAHꢃ ꢃ ꢃO. As seen
from Table 2, atom C4 acts as a donor to the symmetry related at
x, y ꢂ 1, z [3.277 (3) Å]. Bond length and bond angle of such kind
interactions are listed in Table 2. Using the initial coordinates
obtained from the X-ray analysis, we have optimized the
ground state geometry of the title compound using B3LYP/6-
311++G(2d,2p) level of theory. The title compound possesses C1
point group, dipole moment of 2.11 Debye and ground state energy
around ꢂ3417.62 atomic units. Some of the theoretically opti-
mized parameters of the title compound which included bond
length, angles and torsion angles are compared with experimental
data and are given in Table 3. The correlation values of 0.9956
for bond lengths and 0.9928 for bond angles is obtained
respectively.
V (Å3)
Z
Radiation type
Mo K
2.80
a
l
(mmꢂ1
)
Crystal size (mm)
0.93 ꢁ 0.54 ꢁ 0.25
Data collection
Diffractometer
Absorption correction
Tmin, Tmax
No. of measured, independent and 16320, 4257, 2660
observed [I > 2 (I)] reflections
Rint
(sin h/k)max (Åꢂ1
Bruker APEX-II CCD diffractometer
Multi-scan (SADABS; Bruker, 2009)
0.181, 0.535
r
0.051
0.704
)
Refinement
R[F2 > 2 (F2)], wR(F2), S
No. of reflections
No. of parameters
H-atom treatment
r
0.045, 0.125, 1.00
4257
181
H atoms treated by a mixture of
independent and constrained
refinement
0.46, ꢂ0.58
D
qmax
,
D
qmin (e Åꢂ3
)
The optimized parameters of title compound along with their
experimental counterparts are given in Table 3.
(methyl group) times the equivalent isotropic U values of the par-
ent carbon atoms. A rotating group model was used for methyl
groups. The final full-matrix least squares refinement gave
The good correlation values obtained for both the bond length
as well as bond angles suggests that the theoretical values
obtained by DFT approach are in close agreement with their
experimental counterparts. The difference in a few compared val-
ues may be due to the fact that, the experimental values corre-
spond to solid phase, while the theoretical values corresponds to
gas phase. The existence of crystal field along with intermolecular
interactions connects the molecule together, which results in the
difference between the compared parameters [23].
R = 0.045 and wR = 0.125 (w = 1/[
r
2(Fo2) + (0.0546 P)2 + 0.3051P]
where P = (Fo2 + 2Fc2)/3, S = 1.00, (
D/r)max = 0.004, Dqmax = 0.46 e
Åꢂ3 and
D
q
min = ꢂ0.58 e Åꢂ3. A summary of crystal data and
parameters for structure refinement details are given in Table 1.
Computational details
NMR spectra
All theoretical calculations in the current work has been per-
formed by using Gaussian 09 package along with CASTEP package.
For simulation purpose the initial coordinates obtained from X-ray
analysis are used in both the packages to obtained the optimized
geometry of the title compound both at HF and DFT level of theory
using 6-311++G(2d,2p) basis set [19–21]. The Vibrational fre-
quency, chemical shifts, DOS and electronic band structures for
title compound has been calculated using optimized geometries.
NMR spectroscopy is considered to be a valuable and remark-
able tool for structural and functional characterization of mole-
cules. Theoretical GIAO 1H and 13C NMR chemical shifts of the
title compound with respect to TMS has been calculated using
HF and DFT approach at B3LYP level of theory using 6-
311++G(2d,2p) basis set. Solvents effect in the theoretical NMR
has been included using CPCM model with chloroform available
in g09 package. The experimental NMR for the title compound
has been given in Figs. 5 and 6 respectively. The experimental 1H
NMR chemical shifts of the title compound may be read as 1H
NMR (500 MHz, CDCl3): d ppm 7.972 (s, 1H, methylbenzoate),
7.962–7.946 (d, 1H, J = 7.7 Hz), 7.869–7.852 (d, 2H, J = 8.5 Hz,
Bromophenyl), 7.686–7.669 (d, 2H, J = 8.5 Hz, Bromophenyl),
7.444–7.429 (d, 1H, J = 7.7 Hz, methylbenzoate), 7.399–7.368 (t,
1H, J = 7.7 Hz, methylbenzoate) 5.537 (s, 2H, CH2), 2.443 (s, 3H,
CH3). Theoretically the present compound under investigation,
has 13 protons out of which eight protons are aromatic protons,
two are aliphatic protons and three are attached to methyl group.
Aliphatic protons shows a singlet peak at 6.01 ppm and 5.02 ppm
using HF approach while 6.61 ppm and 5.52 ppm using DFT
approach. The aromatic protons shows singlet peak in the range
of 7.7–8.7 ppm using HF and in the range of 8.0–8.5 ppm using
DFT approach. On comparison as shown in Table 4, we found that
the investigated compound gave better chemical shifts with DFT
approach than of HF approach and are near the experimental coun-
terparts. The title compound also consists of 16 carbon atoms, out
Results and discussions
Molecular geometry
The structure as analyzed from the X-ray analysis as well as
from the optimized ground state geometry of the title compound
are shown in Fig. 2. The compound with chemical formula,
C16H13BrO3, crystallizes in monoclinic system with space group
P21/c with unit cell dimensions a = 8.176 (2) Å, b = 7.82 (2) Å,
c = 2 .952 (6) Å and with the volume of 1468.6 (7) A3. The Ortep
diagram of 2-(4-bromophenyl)-2-oxoethyl 3-methylbenzoate,
with atom labeling scheme drawn at 50% probability displacement
ellipsoid is also depicted in Fig. 2. The molecular structure of the
title compound consists of a bromophenyl ring and a substituted
phenyl ring connected by a flexible C(@O)AOACAC(@O) chain.
The phenyl rings (C1AC6 and C10AC15) lie almost perpendicular
to each other, with the dihedral angle between these two aromatic
rings being 86.03 (12)°. In the structure, strong CAHꢃ ꢃ ꢃO hydrogen

Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
195
Fig. 2. (a) Displacement ellipsoids for title compound are drawn at 50% probability level. (b) Theoretical ground state structure of title compound at (B3LYP/6-311++G(2d,2p)
level of theory.
Fig. 3. Crystal packing of the title compound, showing intermolecular CAHꢃ ꢃ ꢃO hydrogen bonding interactions and Brꢃ ꢃ ꢃO short contacts as dotted lines. H atoms not involved
in hydrogen bonding are omitted for clarity.
of which 13 atoms are aromatic carbon and the remaining are ali-
phatic carbon atoms. The aromatic carbon atoms shows singlet
peak in the range of 121.72–165.20 ppm using HF approach and
in the range of 133.96–173 ppm using DFT approach. The 13C
chemical shifts of the title compound are also observed
experimentally and can be read as 13C NMR (125 MHz, CDCl3): d
ppm 191.39 (C@O), 166.17 (OAC@O), 138.32, 134.24, 133.09,
132.27, 130.49, 129.34, 129.17, 129.14, 128.40, 127.14 (Ar), 66.24
(CH2), 21.26 (CH3) The calculated chemical shifts for the title com-
pound are summarized in Tables 5 and 6 respectively in detail.

196
Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
Table 2
Table 3
Hydrogen-bond geometry (Å, °).
Randomly selected geometrical parameters for title compound in (Å, °).
DAHꢃ ꢃ ꢃA
DAH
Hꢃ ꢃ ꢃA
2.36
2.92
2.86
Dꢃ ꢃ ꢃA
3.277 (3)
3.770 (3)
3.675 (3)
DAHꢃ ꢃ ꢃA
170
153
147
Numbering
scheme (X-ray
structure)
Experimental
(X-ray)
Numbering scheme
(DFT calculated
structure)
DFT/6-
311++(2d,2p)/
B3LYP
C4AH4Aꢃ ꢃ ꢃO1i
0.93
0.93
0.93
C(13)AH(13A)ꢃ ꢃ ꢃCg(2)ii
C(15)AH(15A)ꢃ ꢃ ꢃCg(1)iii
Bond length
Br1AC3
O1AC7
O2AC9
O2AC8
O3AC9
C1AC2
C1AC6
C2AC3
C3AC4
C4AC5
1.89
1.20
1.34
1.43
1.20
1.37
1.39
1.39
1.37
1.38
1.39
1.49
1.50
1.48
1.38
1.39
1.38
1.39
1.51
1.37
1.37
1.89
1.20
1.34
1.43
1.20
1.37
1.39
Br1AC9
1.90
1.20
1.35
1.41
1.20
1.38
1.39
1.39
1.38
1.38
1.39
1.49
1.51
1.48
1.39
1.39
1.39
1.39
1.51
1.38
1.38
1.90
1.20
1.35
1.41
1.20
1.38
1.39
Symmetry codes:
O2AC15
O3AC19
O3AC16
O4AC19
C5AC7
i
x, y ꢂ 1, z.
ii
ꢂx, y + 1/2, ꢂz + 3/2.
iii
ꢂx, ꢂy + 1, ꢂz + 2.
C5AC14
C7AC9
C9AC10
C10AC12
C12AC14
C14AC15
C15AC16
C19AC20
C20AC28
C20AC21
C21AC23
C23AC24
C23AC30
C24AC26
C26AC28
Br1AC9
C5AC6
C6AC7
C7AC8
C9AC10
C10AC15
C10AC11
C11AC12
C12AC13
C12AC16
C13AC14
C14AC15
Br1AC3
O1AC7
O2AC9
O2AC8
O3AC9
C1AC2
O2AC15
O3AC19
O3AC16
O4AC19
C5AC7
C1AC6
C5AC14
Fig. 4. Simulated PXRD diagram for the title compound using plotCIF.
Bond angles
C9AO2AC8
C4AC3ABr1
C2AC3ABr1
O1AC7AC6
O1AC7AC8
O2AC8AC7
O3AC9O2
114.83
119.38
119.20
121.30
120.50
111.0
123.10
124.8
112.10
C19AO3AC18
C10AC9ABr1
C7AC9ABr1
02AC15AC14
O2AC15AC16
O3AC16AC15
O4AC19AO3
O4AC19AC20
O3AC19AC20
115.83
119.29
119.41
121.74
120.60
111.0
123.60
124.9
112.30
IR spectra
In the present work, the IR spectra of the title compound has
been computed theoretically using both HF and DFT approaches.
The compound possesses C1 point group with 93 normal modes
of vibrations and do not contain any imaginary frequency. The
computed IR spectra of the title compound is shown in Fig. 7.
O3AC9AC10
O2AC9AC10
Fig. 5. Experimental 1H NMR chemical shifts of the title compound.

Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
197
Fig. 6. Experimental 13C NMR chemical shifts of the title compound.
Table 4
1H NMR chemical shifts(ppm) relative to the TMS for the title compound using B3LYP/
6-311++G(2d,2p) level of theory.
Table 6
Assignement of selected modes of vibration for the title compound.
Atoms Aromatic/
aliphatic
HF/B3LYP/6-
311++G(2D,2P)
DFT/B3LYP/6-
311++G(2D,2P)
Experimental
S.
Modes of
Calculated
Experimental
No. vibration
HF/B3LYP/6-
311++G(2d,2p)
DFT/B3LYP/6-
311++G(2d,2p)
H6
H8
Ar CH
Ar CH
Ar CH
Ar CH
CH
8.8
7.8
8.57
8.11
8.03
8.38
6.61
5.52
8.38
8.05
7.89
8.56
2.32
2.79
2.76
7.80
7.67
7.67
7.80
5.53
5.53
7.97
7.44
7.37
7.95
2.44
2.44
2.44
1
2
3
4
5
6
7
s8
9
vCAHaromatic
3263
1096
523
3296
1085
685
2944
1068
685
H11
H13
H17
H18
H22
H25
H27
H29
H31
H32
H33
7.91
8.37
6.01
5.02
8.73
8.04
7.73
8.55
2.17
2.54
2.53
UCAHaromatic
vsCABr + UC@O
UCABr
vsC@O
vsCAO
vsCH3
vsC@Cring1
vsC@Cring2
194
197
200
CH
1824
1291
3107
1526
1637
1768
1385
3109
1623
1643
1722
1396
3089
1609
1698
Ar CH
Ar CH
Ar CH
Ar CH
CH3
CH3
CH3
Vibrational modes: v, stretching, U, Bending, abbreviations: s, symmetric. ring 1
(C5AC7AC9AC10AC12AC14), ring 2 (C20AC21AC23AC24AC26AC28).
Table 5
13C NMR chemical shifts (ppm) relative to the TMS for the title compound using
B3LYP/6-311++G(2d,2p) level of theory.
Atoms Aromatic/
aliphatic
HF/B3LYP/6-
311++G(2D,2P)
DFT/B3LYP/6-
311++G(2D,2P)
Experimental
C5
C7
C9
Ar C
Ar C
Ar C
Ar C
Ar C
Ar C
C
127.9
125.6
140.5
125.2
127.2
125.5
190.4
52.6
165.2
121.7
129.9
133.8
132.5
121.9
124.5
8.6
133.8
136.7
154.0
136.3
134.6
136.8
199.8
69.5
173.0
133.9
136.5
146.4
136.8
132.8
131.2
21.4
130.4
132.7
128.4
132.2
130.4
134.2
191.0
66.2
166.1
129.1
129.3
138.3
133.0
129.1
127.1
21.2
C10
C12
C14
C15
C16
C19
C20
C21
C23
C24
C26
C28
C30
CH
Ar C
Ar C
Ar C
Ar C
Ar C
Ar C
Ar C
CH3
Fig. 7. Simulated [HF/DFT/B3LYP/6-311++g(2d,2P) levels] FT-IR spectra of the title
compound.

198
Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
Table 7
CABr vibrations
Calculated polarisibility (a) and first hyperpolarisibility (b) using DFT/B3LYP/6-
311++G(2d,2p) level of theory in atomic units (a.u) for our title compound.
According to literature values, the bending CABr vibrations gen-
erally occurs in the range of 100–400 cmꢂ1 and CABr stretching
vibrations ranging 690–515 cmꢂ1 [26]. We have investigated such
kind of vibrations in the present compound using both HF and DFT
approach. Using HF approach we found that the bands observed at
194 cmꢂ1 are assigned to CABr bending vibrations and that at
523 cmꢂ1 are assigned to CABr stretching vibrations. The bending
mode is a pure mode while stretching mode is mixed with C@O
bending vibrations. Using DFT approach we found that the band
assigned at 685 cmꢂ1 correspond to CABr stretching modes which
is mixed with C@O bending modes of vibrations while the one
observed at 197 cmꢂ1 is a pure mode and is for CABr bending
modes of vibrations.
DFT/B3LYP/6-311++G(2d,2p)
axx
10.47
axy
ayy
axz
ayz
ꢂ0.15
ꢂ6.14
ꢂ1.93
3.04
azz
ꢂ4.32
15.16
ꢂ13.86
16.60
36.25
0.94
26.33
5.05
2.6
atot
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
btot
96.24
4.56
C@O vibrations
ꢂ7.24
122.60
C@O stretching vibrations generally occurs in the range of
1670–1820 cmꢂ1. Using HF approach the bands at 1526, 1703,
1806 and 1824 cmꢂ1 are assigned to C@O stretching vibrations.
Out of these bands, the one at 1824 cmꢂ1 is highly intense and a
pure band. The bands at 1600, 1755 and 1768 cmꢂ1 are assigned
to C@O stretching vibrations using DFT approach among which,
the band at 1768 cmꢂ1 is intense in comparison to other observed
bands.
The experimental IR spectra of the title compound is also given in
Fig. 8. The vibrational bands have been assigned using Gauss View
molecular visualization program and calculated bands with both
HF and DFT approach along with selected experimental counter-
parts are presented in Table 6.
Aromatic CAH vibrations
CAO vibrations
The bands in the region 3100–3000 cmꢂ1 are due to CH stretch-
ing vibrations in aromatic compounds [24,25]. In the title com-
pound, the bands observed in the IR spectra and with the help of
Gauss View Molecular visualization program are in the range of
3146–3185 cmꢂ1 are assigned to CH stretching vibrations of aro-
matic rings at HF level of theory. Along with this, out of plane
bending vibrations of aromatic ring is also observed at 965, 988
and 1096 cmꢂ1 respectively. Using DFT approach the bands
observed in the range 3166–3196 cmꢂ1 are assigned to CH stretch-
ing vibrations, while the bands observed at 977, 957 and
1085 cmꢂ1 respectively are assigned to the out of plane bending
vibrations of aromatic rings.
CAO stretching vibrations generally occurs in the range 1000–
1320 cmꢂ1 as reported in literature. The bands observed at 1040,
1115, 1117, 1180, 1199, 1222, 1291, 1385 cmꢂ1 respectively are
assigned to CAO stretching vibrations using HF approach. Out of
all these bands, the one observed at 1040 cmꢂ1 is a pure mode
while other modes of vibrations is mixed with C@C stretching
and bending modes of vibrations. The bands observed at 1080,
1115, 1115, 1222, 1199, 1291, 1385 cmꢂ1 respectively are
observed using DFT approach and shows a similar trend of pure
and impure modes as calculated using HF approach, while the
one observed at 1385 cmꢂ1 is an intense band.
Fig. 8. Experimental IR spectra of title compound.

Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
199
Fig. 9. Band gap, TDOS and PDOS of title compound.

200
Diwaker et al. / Journal of Molecular Structure 1092 (2015) 192–201
C@C vibrations
hyperpolarisibility values are 15.56 a.u and 59.4 a.u. respectively.
Since from the computed results, the values are 1 and 2 times that
of standard values. So we propose that the compound under
investigation is a strong potential material for NLO applications
like frequency doubling and SHG.
As per the literature reports, the available C@C stretching vibra-
tions generally occurs in the range (1400–1600) cmꢂ1. In the title
compound there are C@C stretching vibrations in two rings namely
ring 1 (C5AC7AC9AC10AC12AC14) and ring 2 (C20AC21AC23A
C24AC26AC28). The bands observed using HF approach at
1526 cmꢂ1 are due to C@C stretching vibrations of ring 1, while
the bands observed at 1554, 1565, 1637 cmꢂ1 respectively are
due to C@C stretching vibrations of ring 2. Similarly using the
DFT approach, the bands observed at 1504 and 1643 cmꢂ1 are
assigned to C@C stretching vibrations of ring 2, while the bands
observed at 1523, 1600, 1623, 1622 cmꢂ1 respectively are assigned
to C@C stretching vibrations of ring 1.
Band structure, PDOS and TDOS
Density of states (partial and total) along with band structure of
a material or a particular type of compound is useful in predicting
the physical properties such as electrical resistivity, optical absorp-
tion and to understand the solid state device physics. We have
reported the band structure, partial and total density of states
using GGA approximation with ultrasoft pseudopotentials in reci-
procal space. The computed TDOS, PDOS and band structure of
the title compound are shown in Fig. 9a–d. The computed energy
gap using GGA approximation along with PBE functional comes
out to be 2.960 eV. In the title compound, it has bromine and oxy-
gen atoms apart from carbon and hydrogen which contributes to
the density of states. The total density of states along with partial
density of states are plotted in Fig. 9b–d. Partial density of states
gives information about the contribution of individual states for
formation of band gaps. From Fig. 8b (PDOS for bromine atom) it
is found that, in the energy range ꢂ22 eV–10 eV, s-states of bro-
mine atom contributes to the band formation while near the fermi
level the contribution from p states is more. A similar trend is
observed in the energy range from 5 eV to 10 eV with negligible
contribution form the d and f states of bromine atom. In case of
oxygen atom, it has more contribution from s-states near energy
20 eV while near the fermi level p-states are dominant over all
other states with negligible contribution from d and f states of oxy-
gen atom. The total density of states for the title compound is
depicted in Fig. 9d.
CH3 vibrations
Methyl vibrations are generally occur in the range (2900–
3000) cmꢂ1. The bands observed in the range (3000–3185) cmꢂ1
using HF are assigned to different modes of methyl vibrations
which varies from stretching, bending, twisting modes of vibra-
tions. Using DFT approach the bands observed at 3109 cmꢂ1 and
3111 cmꢂ1 are assigned to stretching methyl vibrations.
Non-linear optical (NLO) effects
Type of molecules which shows asymmetric polarization
induced due to electron donor and acceptor groups in pi-electron
conjugated systems are potential candidates for electro optic and
NLO applications [27,28]. The investigated compound was sub-
jected for such kind of possible applications by theoretical
approach using Gaussian package. Our study includes the calcula-
tion of first hyperpolarisibility tensor for all 10 derivatives. First
hyperpolarisibility is a third rank tensor which is described by a
3 ꢁ 3 ꢁ 3 matrix. The 27 components of this 3D matrix can be
reduced to 10 components due to Kleinman symmetry [29]. The
output from Gaussian provides ten components of its matrix as
bxxx, bxxy, bxyy, byyy, bxxz, bxyz, byyz, bxzz, byzz, bzzz respectively. The
Conclusion
In conclusion, a novel ester compound which could be a poten-
tial synthon in synthetic chemistry has been synthesized. The
structure of the compound has been determined by both X-ray
analysis as well as DFT approach. Molecular geometry obtained
using DFT approach shows an excellent agreement with that
obtained with X-ray analysis. Various theoretical spectroscopic
characterization like NMR and IR spectroscopy for optimized
molecular structure of title compound has been done. NLO
investigation reveals title compound a strong candidate for fre-
quency doubling and SHG. Large band gap of around 2.90 eV make
title compound suitable for many solid state device applications.
TDOS and PDOS plots using GGA approximation along with PBE
functional helps us in understanding the contribution of different
states for band gap formation.
calculations of mean polarisibility (atot) and first hyperpolarisibil-
ity (btot) in atomic units has been reported in the present work.
The components of b can be calculated by using the following
equation given below.
X
ꢀ
ꢁ
1
3 i – j
bi ¼ biii
þ
biij þ bjij þ bjji
further using the x, y and z components of b, the magnitude of
first hyperpolarisibility can be calculated using the relation given
as
ꢀ
ꢁ
1=2
btot ¼ b2x þ b2x þ b2x
further the complete equation for calculating the magnitude of
Acknowledgements
btot from package output is given as
h
ꢀ
ꢁ
ꢀ
ꢁ
Diwaker would like to thank IIT Mandi for HTRA scholarship as
well as computational facilities. C.S.C.K. thanks Universiti Sains
Malaysia (USM) for a postdoctoral research fellowship (2013–
2015). C.S.C.K., C.K.Q. & H.K.F. thank to USM for RUI 2014 Grant
(No. 1001/PFIZIK/811278). The authors extend their appreciation
to The Deanship of Scientific Research at King Saud University for
the research group project no. RGP VPP-207.
2
2
btot
¼
bxxx þ bxyy þ bxzz þ byyy þ byzz þ byxx
i
1=2
ꢀ
ꢁ
2
þ bzzz þ bzxx þ bzyy
The values of polarisibility (
a
tot) and first hyperpolarisibility
(btot) calculated using DFT approach along with B3LYP functional
and 6-311++G(2d,2p) basis set for the title compound are summar-
ized in Table 7.
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for comparison purposes whose polarisibility and first
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