Molecular structure, FT-IR, first order hyperpolarizability, NBO analysis, HOMO and LUMO, MEP analysis of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2- en-1-one by HF and density functional methods

Article abstract of DOI:10.1016/j.saa.2014.06.049

(E)-3-(4-Chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one is synthesized by reacting 4-fluoroacetophenone and 4-chlorobenzaldehyde in ethanol in the presence of sodium hydroxide. The structure of the compound was confirmed by IR and single crystal X-ray di

Full text of DOI:10.1016/j.saa.2014.06.049

Accepted Manuscript
Molecular structure, FT-IR, first order hyperpolarizability, NBO analysis, HO-
MO and LUMO, MEP analysis of (E)-3-(4-chlorophenyl)-1-(4-fluorophen-
yl)prop-2-en-1-one by HF and density functional methods
A. Najiya, C. Yohannan Panicker, M. Sapnakumari, B. Narayana, B.K. Sarojini,
C. Van Alsenoy
PII:
S1386-1425(14)00937-8
http://dx.doi.org/10.1016/j.saa.2014.06.049
SAA 12308
DOI:
Reference:
To appear in:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
Received Date:
Revised Date:
Accepted Date:
23 April 2014
17 May 2014
3 June 2014
Please cite this article as: A. Najiya, C. Yohannan Panicker, M. Sapnakumari, B. Narayana, B.K. Sarojini, C. Van
Alsenoy, Molecular structure, FT-IR, first order hyperpolarizability, NBO analysis, HOMO and LUMO, MEP
analysis of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one by HF and density functional methods,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.
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Molecular structure, FT-IR, first order hyperpolarizability, NBO analysis, HOMO and
LUMO, MEP analysis of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one by
HF and density functional methods
a
a*
b
b
c
A.Najiya , C.Yohannan Panicker , M. Sapnakumari , B.Narayana , B.K.Sarojini , C.Van
d
Alsenoy
a
Department of Physics, TKM College of Arts and Science, Kollam, Kerala, India.
b
Department of Studies in Chemistry, Mangalore University, Mangalagangotri,
Karnataka, India.
c
Industrial Chemistry-Division, Department of Studies in Chemistry, Mangalore
University, Mangalagangotri, Karnataka, India.
d
Department of Chemistry, University of Antwerp, B2610 Antwerp, Belgium.
Author for correspondence: email: cyphyp@rediffmail.com
Phone : +91 9895370968
Abstract
(
E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one is synthesized by reacting 4-
fluoroaacetophenone and 4-chlorobenzaldehyde in ethanol and sodium hydroxide
solution. The structure of the compound was confirmed by IR and single crystal X-ray
diffraction studies. FT-IR spectrum of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-
en-1-one was recorded and analyzed. The crystal structure is also described. The
vibrational wavenumbers were calculated using HF and DFT methods and are assigned
with the help of potential energy distribution method. The geometrical parameters of the
title compound obtained from XRD studies are in agreement with the calculated (DFT)
values. The stability of the molecule arising from hyper-conjugative interaction and
charge delocalization has been analyzed using NBO analysis. The calculated first
hyperpolarizability of the title compound is comparable with the reported values of
similar derivatives and 63.85 times that of the standard NLO material urea. The HOMO-
LUMO transition implies an electron density transfer from the chlorophenyl ring to the
fluorophenyl ring. From the MEP analysis it is evident that the negative charge covers the
C=O group and the positive region is over the phenyl rings.
Keywords: Chlorophenyl; Fluorophenyl; FT-IR; Hyperpolarizability; MEP.
1
.
Introduction
1

Chalcone (1,3-diphenyl-2-propene-1-one) and related compounds “chalconoids”
are those in which two aromatic rings are linked and conjugated together through a
reactive keto ethylenic linkage (-CO-CH=CH-), which impart an entirely delocalized π-
electron system on both benzene rings in such a way that this system has relatively low
redox potentials and has a greater probability of undergoing electron transfer reaction [1].
Chalcones with their unique chemical structure will display a wide range of
pharmacological activities depending on the nature, number and position of the
substituents on both benzene rings of the structure. Chalcones are well known
intermediates for synthesizing various heterocyclic compounds. The compounds with the
backbone of chalcones have been reported to posses various biological activities such as
antimicrobial [2], anti-inflammatory [3], analgesic [4], anti-platelet [5], anti-ulcerative
[
6], anti-malarial [7], anticancer [8], antiviral [9], antileishmanial [10], antioxidant [11],
antitubercular [12], antihypeerglycemic [13], immunomodulatory [14], inhibition of
chemical mediators release [15], inhibition of leukotriene B4 [16], inhibition of
tyrosinase [17] and inhibition of aldose reductase activities [18]. Additionally, some of
the chalcone derivatives have been found to inhibit several important enzymes in cellular
systems, such as xanthine oxidase, mammalian alpha-amylase, cyclooxygenase, 5-
lipooxygenase, while others demonstrated the ability to block voltage dependent
potassium and calcium channels [19-20]. In the present study, IR spectrum of (E)-3-(4-
chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one was reported both experimentally and
theoretically. The energies, degrees of hybridization, populations of the lone pairs of
oxygen, chlorine, fluorine, energies of their interaction with the anti-bonding orbital of
the phenyl ring and the electron density distribution and E(2) energies have been
calculated by NBO analysis using DFT method to give clear evidence of stabilization
originating from the hyper-conjugation of various intra-molecular interactions. There has
been growing interest in using organic materials for nonlinear optical devices,
functioning as second harmonic generators, frequency converters, electro-optical
modulators, etc., because of the large second order electric susceptibilities of organic
materials. Since the second order electric susceptibility is related to the first
hyperpolarizability, the search for organic chromophores with large first
hyperpolarizability is fully justified.
2

2
.
Experimental
To a mixture of 4-fluoroaacetophenone (1.38gm, 0.01mol) and 4-
chlorobenzaldehyde (1.41g, 0.01mol) in ethanol (100ml), 15 ml of 10% sodium
hydroxide solution was added and stirred at 0-5˚C for 3h. The precipitate formed was
collected by filtration and purified by re-crystallization from ethanol. Colorless blocks
were grown from toluene as solvent by the slow evaporation method. A Bruker APEX2
CCD diffractometer equipped with graphite monochromator Mo kα (λ = 0.71073Å)
radiation was used for the measurement of data. The collected data were reduced using
the SAINT program and structural refinement was carried out by full matrix least squares
2
on F (SHELXL-97) program package [21]. Molecular graphic employed includes
ORTEP 3 and Mercury. The ORTEP diagram and crystal packing are given in Figs. S1
and S2 as supporting material. In the title compound, C15H10ClFO, the fluoro substituted
benzene ring forms a dihedral angle of 44.4˚ with the chloro substituted benzene ring.
The only significant directional bonds in the crystal are weak C-H…π interactions. FT-IR
spectrum (Fig. 1) was recorded using KBr pellets on a Shimadzu-FTIR infrared
spectrometer.
3
.
Computational details
Calculations of the title compound are carried out with Gaussian09 program [22]
using the HF/6-31G(6D,7F) and B3LYP/6-31G(6D,7F) basis sets to predict the molecular
structure and vibrational wavenumbers. Molecular geometry was fully optimized by
Berny’s optimization algorithm using redundant internal coordinates. Harmonic
vibrational wavenumbers were calculated using the analytic second derivatives to
confirm the convergence to minima on the potential surface. The DFT hybrid B3LYP
functional method tends to overestimate the fundamental modes; therefore scaling factor
of 0.9613 has to be used for obtaining a considerably better agreement with experimental
data [23]. For HF method a scaling factor of 0.8929 is used [23]. Parameters
corresponding to optimized geometry (B3LYP) of the title compound with experimental
data (Fig. 2) are given in Table S1(supporting material). The absence of imaginary
wavenumbers on the calculated vibrational spectrum confirms that the structure deduced
corresponds to minimum energy. The assignments of the calculated wave numbers are
aided by the animation option of GAUSSVIEW program, which gives a visual
3

presentation of the vibrational modes [24]. The potential energy distribution (PED) is
calculated with the help of GAR2PED software package [25].
4
4
.
Results and discussion
.1. IR spectrum
The calculated (scaled wavenumbers), observed IR bands and assignments are
given in Table 1. In the following discussion, the phenyl rings attached with the chlorine
and fluorine atoms are designated as PhI and PhII respectively. The existence of one or
more aromatic rings in a structure is normally readily determined from the C=C-C ring
-
1
related modes and C-H vibrations. The C-H stretching modes occurs above 3000 cm
and is typically exhibited as a multiplicity of weak to moderate bands, compared with the
aliphatic C-H stretch [26]. For the title compound, CH stretching vibrations of the phenyl
-1
-1
rings are assigned in the range 3073-3103 cm for PhI and 3096-3110 cm for PhII
theoretically. The benzene ring possesses six ring stretching vibrations, of which the four
-1
with the highest wavenumbers (occurring near 1600, 1580, 1490 and 1440 cm ) are good
group vibrations [27]. With heavy substituents, the bands tend to shift to somewhat lower
-1
wavenumbers. In the absence of ring conjugation, the band at 1580 cm is usually
-1
-1
weaker than that at 1600 cm . In the case of C=O substitution, the band near 1490 cm
-1
can be very weak. The fifth ring stretching vibration is active near 1315 ± 65 cm , a
region that overlaps strongly with that of the CH in-plane deformation. The sixth ring
-1
stretching vibration, or the ring breathing mode, appears as a weak band near 1000 cm
in mono-, 1,3-di-, and 1,3,5-trisubstituted benzenes [27]. In the otherwise substituted
benzenes, however, this vibration is substituent sensitive and difficult to distinguish from
the ring in-plane deformation [27]. The υPh modes are expected in the region 1280-1630
-1
-1
cm for para-substituted phenyl rings [27] and the modes observed 1551, 1279 cm and
-1
1
496, 1402 cm in the IR spectrum are assigned as the phenyl ring CC stretching modes
for PhI and PhII. The DFT calculations give these modes at 1584, 1552, 1480, 1395,
-1
-1
1
276 cm for PhI and 1596, 1573, 1497, 1400, 1305 cm for PhII. The ring breathing
mode of the para-disubstituted benzenes with entirely different substituents [28] has been
-1
reported in the interval 780-880 cm . For the title compound, this is confirmed by the
-1
-1
bands in the infrared spectrum at 820, 878 cm and at 817, 874 cm theoretically, which
finds support from computational results. For para substituted benzene, the ring breathing
4

-1
-1
mode is reported at 873 cm in IR spectrum and 861 cm theoretically [29]. The in-plane
-1
CH deformation bands of the phenyl ring are expected above 1000 cm [27] and in the
-1
-1
present case , the bands at 1098 cm (IR), 1286, 1169, 1099, 1070 cm (DFT) and 1148,
-1
-1
1
007 cm (IR), 1272, 1144, 1088, 1007 cm (DFT) are assigned as the in-plane CH
deformation for PhI and PhII respectively. The CH out-of-plane deformations of the
-1
phenyl ring [27] are observed between 1000 and 700 cm . Generally, the CH out-of-
plane deformations with the highest wavenumbers have weaker intensity than those
-1
absorbing at lower wavenumbers. The bands observed at 952, 820, 806, 790 cm in IR
spectrum are assigned as the CH out-of-plane deformations of the phenyl rings. The
-1
corresponding theoretical values are 928, 923, 804, 801 cm for PhI and 954, 909, 827,
-1
-1
7
94 cm for PhII. The strong γCH occurring at 840 ±50 cm , is typical for 1,4-
-1
disubstitution, and the bands observed at 806, 820 cm in the IR spectrum is assigned to
-1
this mode. The B3LYP calculations give these modes at 804, 827 cm . The IR bands in
-1
the 1800-2900 cm region and their large broadening support the intra molecular
hydrogen bonding [30].
Fluorine atoms directly attached to the aromatic ring give rise bands [31] in the
-1
region 1100-1270 cm . Many of these compounds [31] including one fluorine atom only
-1
-1
on the ring absorb near 1230 cm . The υC-F is reported at 1157, 1233 cm (IR), 1244
-1
cm (HF) [32]. For the title compound, the DFT calculations give CF stretching mode at
-1
1
239 cm . The vibrations belonging to the bond between the ring and chlorine atoms are
worth to discuss here since mixing of vibrations is possible due to the lowering of the
molecular symmetry and the presence of heavy atoms on the periphery of the molecule
[
33]. Mooney [34, 35] assigned vibrations of C-Cl, Br, and I in the wavenumber range of
-
1
1
7
7
129-480 cm . The CCl stretching vibrations give generally strong bands in the region
-1
10-505 cm . For simple organic chlorine compounds, CCl absorptions are in the region
-
1
50-700 cm . Sundaraganesan et al.[36] reported CCl stretching at 704 (IR), 705
-1
-1
(
Raman), and 715 cm (DFT) and the deformation bands at 250 and 160 cm . The
-1
aliphatic CCl absorb [27] in the range 830–560 cm and putting more than one chlorine
atom on a carbon atom raises the CCl wavenumber. Pazdera et al. [37, 38] reported the
-1
CCl stretching mode at 890 cm . For 2-cyanophenylisocyanide dichloride, the CCl
-1
stretching mode is reported at 870 (IR), 877 (Raman), and 882 cm theoretically [39].
5

-1
-1
For the title compound, the band observed at 645 cm in the IR spectrum and 648 cm
DFT) is assigned as the CCl stretching mode. The deformation bands of CCl are also
(
identified. This is in agreement with the literature data [40, 41]. For 4-
chlorophenylboronic acid, the CCl stretching and deformation bands are reported at 571
-1
(
DFT), and at 287 and 236 cm , respectively [42].
The appearance of strong bands in the IR spectrum (less polarizability resulting
due to highly dipolar carbonyl bond) in aromatic compounds in the salient feature of the
presence of carbonyl group and are due to the C=O stretching motions. The wavenumber
of the C=O stretch due to the carbonyl group mainly depends on the bond strength, which
in turn depends upon inductive, conjugative, steric effects and lone pair of electron on
oxygen. The carbonyl stretching C=O vibration [27, 31, 43] is expected in the region
-1
-1
1
750-1680 cm and in the present case this mode appears at 1665 cm in the IR
-1
spectrum and the DFT calculation gives this mode at 1676 cm . The in-plane and out
-1
of-plane C=O deformations are expected in the regions 625 ± 70 and 540± 80 cm ,
-1
respectively [27]. The δC=O in-plane deformation band is assigned at 767 cm
-1
-1
theoretically (DFT). The band observed at 586 cm in the IR spectrum and at 581 cm
(
DFT) is assigned as γC=O mode. Cinar and Karabacak [44]reported the bands at 1697
-1
-1
-1
cm in IR, 1700 cm in Raman and 1684 cm (theoretical) as C=O stretching mode.
-1
Arjunan et al. [45] reported C=O modes at 1776, 1716, 864, 723 cm in IR spectrum for
-1
an anhydride derivative. Mariappan and Sundaraganesan [46] reported 1760 cm in the
-1
IR spectrum and 1764 cm in the Raman spectrum as C=O stretching mode for phenyl
carbonate derivative. The C=C stretching mode is expected in the region [43] 1667-1640
-1
-1
cm . According to Socrates [47] the C=C stretching mode is expected around 1600 cm
when conjugated with C=O group. For the title compound, the C=C stretching mode is
–
1
-1
assigned at 1605 cm in the IR spectrum and at 1604 cm theoretically. For a series of
-1
propenoic acid esters, Felfoldi et al. [48] reported υC=O at 1690 cm and υC=C at 1625
-1
cm . For the title compound, the CH modes associated with the anhydride group are
-1
-1
assigned at 1330 cm (in-plane bending), 858 cm (out-of-plane bending) in the IR
-1
-1
spectrum and at 3053, 3085 cm (stretching modes), 1324, 1315 cm (in-plane bending),
-1
9
99, 856 cm (out-of-plane bending) theoretically (DFT). The substitent sensitive modes
6

of the phenyl ring and other modes are also identified and assigned (Table 1). Most of the
modes are not pure but contains significant contributions from other modes also.
In order to investigate the performance of vibrational wavenumbers of the title
compound the root mean square (RMS) value between the calculated and observed
wavenumbers were calculated. The RMS values of wavenumbers were calculated using
the following expression [49].
n
1
2
exp
calc
RMS =
( i
υ
−υi
)
.
∑
n −1 i
The RMS errors of the observed IR bands are found to be 38.13 for HF and 10.62
for DFT methods. The small differences between experimental and calculated vibrational
modes are observed. This is due to the fact that experimental results belong to solid phase
and theoretical calculations belong to gaseous phase.
4
.2. NLO properties
Nonlinear optics deals with the interaction of applied electromagnetic fields in
various materials to generate new electromagnetic fields, altered in wavenumber, phase,
or other physical properties [50]. Organic molecules able to manipulate photonic signals
efficiently are of importance in technologies such as optical communication, optical
computing, and dynamic image processing [51, 52]. In this context, the dynamic first
hyperpolarizability of the title compound is also calculated in the present study. The first
hyperpolarizability (β ) of this novel molecular system is calculated using DFT method,
0
based on the finite field approach. In the presence of an applied electric field, the energy
of a system is a function of the electric field. First hyperpolarizability is a third rank
tensor that can be described by a 3×3×3 matrix. The 27 components of the 3D matrix can
be reduced to 10 components due to the Kleinman symmetry [53].The components of β
are defined as the coefficients in the Taylor series expansion of the energy in the external
electric field. When the electric field is weak and homogeneous, this expansion becomes
1
2
1
6
1
i
µ F −
i
j
α F F −
i
j
k
β F F F −
i
j
k
l
E = E −
γ ijkl F F F F + ...
0
∑
i
∑
ij
∑
ijk
∑
24
i
ij
ijk
ijkl
where E
0
is the energy of the unperturbed molecule, F
i
is the field at the origin, µ , αij, βijk
i
and γijkl are the components of dipole moment, polarizability, the first
hyperpolarizabilities, and second hyperpolarizabilities, respectively. The calculated first
7

-30
hyperpolarizability of the title compound is 8.30×10 esu, which is comparable with the
reported values of similar derivatives [49]. The calculated hyperpolarizability of the title
-30
compound is 63.85 times that of the standard NLO material urea (0.13×10 esu) [54].
We conclude that the title compound is an attractive object for future studies of nonlinear
optical properties.
4
.3. NBO analysis
The natural bond orbitals (NBO) calculations were performed using NBO 3.1
program [55] as implemented in the Gaussian09 package at the B3LYP/6-31G* level in
order to understand various second-order interactions between the filled orbitals of one
subsystem and vacant orbitals of another subsystem, which is a measure of the
intermolecular delocalization or hyper conjugation. NBO analysis provides the most
accurate possible 'natural Lewis structure' picture of 'j' because all orbital details are
mathematically chosen to include the highest possible percentage of the electron density.
A useful aspect of the NBO method is that it gives information about interactions of both
filled and virtual orbital spaces that could enhance the analysis of intra and inter
molecular interactions. The second-order Fock-matrix was carried out to evaluate the
donor-acceptor interactions in the NBO basis. The interactions result in a loss of
occupancy from the localized NBO of the idealized Lewis structure into an empty non-
Lewis orbital. For each donor (i) and acceptor (j) the stabilization energy (E2) associated
with the delocalization i → j is determined as
2
(
F )
i, j
E(2) = ∆E = qi
ij
(
E − E )
j
i
q
i
→ donor orbital occupancy, E
i
, E → diagonal elements, Fij→ the off diagonal NBO
j
Fock matrix element.
In NBO analysis large E(2) value shows the intensive interaction between electron-
donors and electron-acceptors and greater the extent of conjugation of the whole system,
the possible intensive interactions are given in Table S2 (supporting material). The
second-order perturbation theory analysis of Fock matrix in NBO basis shows strong
intra-molecular hyper-conjugative interactions of π-electrons. The intra-molecular hyper-
conjugative interactions are formed by the orbital overlap between n(Cl) and π*(C-C)
bond orbital which results in ICT causing stabilization of the system. The strong
8

intramolecular hyper-conjugative interaction of C22-C24 from Cl
1
of n3(Cl
1
)→π*(C22-C24)
which increases ED (0.38533e) that weakens the respective bonds leading to stabilization
−
1
of 12.46 kcalmol . Another intra-molecular hyper-conjugative interactions are formed
by the orbital overlap between n(O) and σ*(C-C) bond orbital which results in ICT
causing stabilization of the system. The strong intra-molecular hyper-conjugative
interaction of C13-C14 from O
that weakens the respective bonds leading to stabilization of 19.36 kcalmol . The strong
intra-molecular hyper-conjugative interaction of C -C from F of n3(F )→π*(C -C
which increases ED (0.37043e) that weakens the respective bonds leading to stabilization
2
of n2(O )→σ*(C13-C14) which increases ED (0.06394e)
3
−
1
6
8
2
2
6
8
)
−
1
of 21.05 kcalmol .
The increased electron density at the oxygen, chlorine, flourine atoms leads to the
elongation of respective bond length and a lowering of the corresponding stretching
wavenumber. The electron density (ED) is transferred from the n(Cl) to the anti-bonding
π* orbital of the C-C, n(O) to σ*(C-C), and n(F) to π*(C-C) explaining both the
elongation and the red shift [56]. The C-Cl, -C=O, -C-F stretching modes can be used as
a good probe for evaluating the bonding configuration around the corresponding atoms
and the electronic distribution of the benzene molecule. Hence the title compound is
stabilized by these orbital interactions.
The NBO analysis also describes the bonding in terms of the natural hybrid
orbital n2(Cl
character (100%) and low occupation number (1.97275a.u.) and the other n1(Cl
a lower energy orbital (-0.92528a.u.) with p-character (17.71%) and high occupation
number (1.99331a.u.).Also n2(F ), which occupy a higher energy orbital (-0.41098a.u.)
with considerable p-character (100.0%) and low occupation number (1.96810a.u.) and the
other n1(F ) occupy a lower energy orbital (-1.0287a.u.) with p-character (30.81%) and
high occupation number (1.98843a.u.). n2(O ), which occupy a higher energy orbital (-
.25097a.u.) with considerable p-character (100.0%) and low occupation number
1.88470a.u.) and the other n1(O ) occupy a lower energy orbital (-0.67888a.u.) with p-
1
), which occupy a higher energy orbital (-0.32655a.u.) with considerable p-
1
) occupy
2
2
3
0
(
3
character (41.88%) and high occupation number (1.97832a.u.). Thus, a very close to pure
p-type lone pair orbital participates in the electron donation to the π*(C-C) orbital for
9

n3(Cl
2
)→π*(C-C) and n3(F )→π*(C-C), σ*(C-C) orbital for n(O)→σ*(C-C) interactions
2
in the compound. The results are given in table S3 as supporting material.
4
.4
Frontier molecular orbitals
Frontier molecular orbital refer to the highest occupied molecular orbital
(
HOMO) and the lowest unoccupied molecular orbital (LUMO). The HOMO is
outermost higher energy orbital containing electrons so it acts as an electron donor. The
LUMO is the lowest energy orbital that has the room to accept electrons so it acts as an
electron acceptor. The frontier molecular orbitals can offer a reasonable qualitative
prediction of the excitation properties and the ability of electron transport [57, 58]. The
HOMO and LUMO are also very popular quantum chemical parameters which determine
the molecular reactivity. The energies of the HOMO and LUMO orbitals of the title
compound are calculated using DFT/B3LYP method and shown in Fig. 3. The energies
of HOMO and LUMO are negative, which indicates that the studied compound is stable
[
59]. In the title compound, the HOMO of π nature is delocalized over the phenyl ring
PhI, C=O, C=C groups and LUMO in addition to this on the PhII ring. Accordingly, the
HOMO-LUMO transition implies an electron density transfer from the phenyl ring PhI to
the PhII ring through the propane group. For understanding various aspects of
pharmacological sciences including drug design and the possible eco-toxicological
characteristics of the drug molecules, several new chemical reactivity descriptors have
been proposed. Conceptual DFT based descriptors have helped in many ways to
understand the structure of the molecules and their reactivity by calculating the chemical
potential, global hardness and electrophilicity. Using HOMO and LUMO orbital
energies, the ionization energy and electron affinity can be expressed as: I = -EHOMO, A =
-
E
LUMO, η = (-EHOMO + ELUMO)/2 and µ = (EHOMO+ELUMO)/2 [60]. Parr et al. [61] proposed
2
the global electrophilicity power of a ligand as ω = µ /2η. This index measures the
stabilization in energy when the system acquired an additional electronic charge from the
environment. Electrophilicity encompasses both the ability of an electrophile to acquire
additional electronic charge and the resistance of the system to exchange electronic
charge with the environment. It contains information about both electron transfer
(
chemical potential) and stability (hardness) and is a better descriptor of global chemical
reactivity. The hardness η and chemical potential µ are given by the following relations: η
10

=
(I-A)/2 and µ = -(I+A)/2, where I and A are the first ionization potential and electron
affinity of the chemical species [62]. For the title compound, EHOMO = -8.82 eV, ELUMO
6.23 eV, energy gap = HOMO-LUMO = 2.59 eV, Ionization potential I = 8.82 eV,
=
-
Electron affinity A = 6.23 eV, global hardness η = 1.295 eV, chemical potential µ = -
2
7
.525eV and global electrophilicity = µ /2η = 21.86 eV. It is seen that the chemical
potential of the title compound is negative and it means that the compound is stable. They
do not decompose spontaneously into the elements they are made up of. The hardness
signifies the resistance towards the deformation of electron cloud of chemical systems
under small perturbation encountered during the chemical process. The principle of
hardness works in chemistry and physics but it is not physically observable. Soft systems
are large and highly polarizable, while hard systems are relatively small and much less
polarizable.
4
.5. Molecular Electrostatic Potential (MEP)
MEP is related to the electron density and is a very useful descriptor in
understanding sites for electrophilic and nucleophilic reactions as well as hydrogen
bonding interactions [63, 64]. The electrostatic potential V(r) is also well suited for
analyzing processes based on the "recognition" of one molecule by another, as in drug-
receptor, and enzyme-substrate interactions, because it is through their potentials that the
two species first "see" each other [65,66]. To predict reactive sites of electrophilic and
nucleophilic attacks for the investigated molecule, MEP at the B3LYP level optimized
geometry was calculated. The different values of the electrostatic potential at the MEP
surface are represented by different colors: red, blue and green represent the regions of
most negative, most positive and zero electrostatic potential respectively. The negative
electrostatic potential corresponds to an attraction of the proton by the aggregate electron
density in the molecule (shades of red), while the positive electrostatic potential
corresponds to the repulsion of the proton by the atomic nuclei (shade of blue). The
negative (red and yellow) regions of MEP were related to electrophilic reactivity and the
positive (blue) regions to nucleophilic reactivity (Fig. 4). From the MEP it is evident that
the negative charge covers the C=O group and the positive region is over the phenyl
rings. The value of the electrostatic potential is largely responsible for the binding of a
11

substrate to its receptor binding sites since the receptor and the corresponding ligands
recognize each other at their molecular surface [67, 68].
4
.6. Geometrical parameters
The aromatic rings of the title compound are somewhat irregular and the spread of
the C-C bond distance is 1.3892-1.4089Å (DFT), 1.3856-1.4044Å (XRD) for ring PhI
and 1.3891-1.4061Å (DFT), 1.3790-1.4016Å (XRD) for ring PhII, which is similar to the
spread reported by Smith et al., [69]. The C-Cl bond length 1.7549Å (DFT), 1.7379 Å
(
XRD) is in agreement with the C-Cl bond length given by Mariamma et al. [70]. The C-
F bond length is reported as 1.3915Å [71], 1.3242Å [72], 1.3267 Å [32] and in the
present case as 1.3462Å (DFT) and 1.3560Å (XRD). Chlorine and fluorine are highly
electronegative and tries to obtain additional electron density. It attempts to draw it from
the neighboring atoms which moves closer together in order to share the electrons more
easily as a result. Due to this the bond angles C22-C24-C25 and C
9
-C
8
-C are found to be
6
1
21.0˚ and 122.1˚ in the present calculation, which is 120˚ for normal benzene.
According to our calculations, at C13 and C14 positions, the bond angles are C11-C13-C
4
=
=
1
1
18.6, C11-C13-C14 = 117.3, C
4
-C13-C14 = 124.0˚ and C15-C14-O = 120.9, C15-C14-C13
3
19.3, C13-C14-O
3
= 119.8˚, respectively and this shows the interaction between O
12 atom. For the title compound, the C=O bond length is 1.2300Å (DFT). 1.2279Å
XRD) and C=C bond length is 1.3483Å (DFT), 1.3380Å (XRD) which are in agreement
3
and
H
(
with the reported values [73, 74]. The discrepancies between the calculated geometrical
parameters and XRD results are due to the fact that the comparison made between the
experimental data, obtained from single crystal and calculated results are for isolated
molecule in the gaseous phase.
5
.
Conclusion
In the present study, the structural geometrical parameters, vibrational wavenumbers and
nonlinear optical properties of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one
have been studied using both the HF and DFT methods. The geometrical parameters
obtained from XRD data are in agreement with the theoretical values (DFT). The
complete vibrational assignments of wavenumbers have been made on the basis of
potential energy distribution and found to be in good agreement with experimental
values. The first order hyperpolarizability value implies that the title molecule may be
12

useful as a nonlinear optical material. Stability of the molecule arising from hyper-
conjugative interaction and charge delocalization has been analyzed using NBO analysis.
MEP, HOMO and LUMO analysis are also reported.
Acknowledgements
The authors would like to thank Dr.Hema Tresa Varghese, FMN College, Kollam,
Kerala, India and University of Antwerp for providing computational facility.
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Fig.1 FT-IR spectrum of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one
Fig.2 Optimized geometry (b3LYP) of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-
en-1-one
Fig.3 HOMO and LUMO plots of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-
one
Fig.4 MEP plot of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-1-one
17

18

19

20

21

Table 1. Vibrational assignments of (E)-3-(4-chlorophenyl)-1-(4-fluorophenyl)prop-2-en-
-one
HF/6-31G(6D,7F)
1
a
B3LYP/6-31G(6D,7F)
IR
IR
Assignments
-
υ
3
3
3
3
3
3
3
IR
I
υ
I
υ
056 3.78
054 10.40
048 1.63
045 2.36
044 3.26
041 0.74
030 11.02
3110 4.76
3107 14.59
3103 3.43
3101 4.50
3097 1.63
3096 6.35
3085 11.22
3156 υCHII(96)
-
-
-
-
-
-
υCHII(76), υCH(17)
υCHI(96)
υCHI(93)
υCHII(64), υCH(26)
υCHII(88)
υCHII(22), υCH(44),
υCHI(20)
3
3
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
022 2.81
3079 1.18
3073 5.65
3053 0.67
1676 113.61
1604 370.64
1596 84.68
1584 176.12
1573 8.03
1552 29.89
1497 29.96
1480 91.83
1400 52.98
1395 12.11
1324 144.54
1315 83.70
1305 1.00
1286 1.41
1276 88.37
1272 2.44
-
-
-
υCHI(68), υCH(21)
υCHI(98)
012 6.52
999 0.10
υCH(98)
674 197.65
621 307.98
618 215.21
609 7.02
1665 υC=O(55). υC=C(15)
1605 υC=O(12). υC=C(50)
-
-
-
υPhII(46), υPhI(12)
υPhI(41), υPhII(21)
υPhII(63), δCHI(12)
588 24.42
579 34.65
518 36.11
503 109.46
407 64.27
402 6.88
1551 υPhI(68), δCHII(16)
1496 υPhII(45), δCHI(10)
-
υPhI(42), δCHII(18)
1402 υPhII(48), υPhI(12)
υPhII(14), υPhI(43)
1330 δCH(42), υPhII(21)
-
343 3.07
336 109.39
311 5.09
-
-
-
υPhI(19), δCH(42)
υPhII(81), δCHI(10)
υPhI(27), δCHI(57)
306 140.45
241 40.64
225 87.95
1279 υPhI(48), υCC(14)
δCHII(72)
-
22

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
9
218 34.62
204 147.59
192 0.59
178 6.37
166 75.96
107 2.19
098 2.89
073 55.41
051 18.79
044 7.59
036 0.62
025 27.74
019 45.27
014 5.05
013 65.18
011 73.47
1239 104.80
1195 22.47
1191 252.74
1169 3.02
-
υCF(51), δCHII(26)
1202 υCC(35), δCH(17), υPhI(17)
-
-
υCC(44), δCHI(20)
υPhI(12), δCHI(81)
1144 118.32
1099 5.05
1148 δCHII(73)
1098 υPhI(26), δCHI(54)
1088 7.95
-
-
υPhII(24), δCHII(61)
υPhI(15), δCHI(45)
1070 89.35
1007 132.35
1007 δCHII(38), υCC(39)
999
992
990
954
928
923
909
874
22.98
32.17
43.82
0.27
-
γCH(53), τC=C(32)
δPhII(51), υPhII(21)
δPhI(62), υPhI(19)
γCHII(88)
-
989
952
-
0.63
γCHI(82), τPhI(11)
γCHI(86)
0.38
-
0.78
-
γCHII(84)
42
5.91
1.67
878
δC=C(10), δCH(12),
υPhI(41)
8
8
8
8
8
8
7
94
81
75
71
63
12
70
13.21
8.27
856
827
817
804
801
794
767
0.18
858
820
820
806
-
γCH(50), γC=O(12)
γCHII(51), γCHI(22)
δPhII(14), υPhII(40)
γCHI(66), γCHII(11)
γCHI(78)
11.88
20.18
37.82
31.70
28.66
25.07
58.67
91.91
35.07
24.88
17.06
790
-
γCHII(78)
δPhI(17), δC=O(34),
δPhII(10)
65 35.17
τC=O(14)
7
727
5.65
730
τPhII(27), τPhI(16),
7
6
36
76
0.61
6.42
686
650
0.11
3.40
-
-
τPhII(24), τPhI(45)
τPhII(42), τPhI(16),
γC=O(10)
23

6
6
6
5
5
5
44
40
39
81
34
11
3.01
648
623
622
581
513
497
4.39
0.66
2.32
42.42
9.08
12.91
645
-
δPhI(29), υCCl(35)
δPhI(75)
3.40
2.63
615
586
515
-
δPhII(72)
48.95
27.33
17.29
δPhII(32), γC=O(38)
δC=O(28), δCF(16), δCC(17)
τPhII(21), γCF(20), τPhI(15),
γCCl(11), γCC(18)
δPhI(24), γCCl(17), γCF(15),
τPhII(15), γCC(14)
δCF(15), δCCl(14), δCC(18),
δPhII(12)
5
4
01
35
4.09
7.77
485
440
3.00
7.07
482
450
4
4
3
3
28
21
87
67
0.60
407
402
396
366
0.56
409
τPhII(80)
0.08
0.08
-
-
-
τPhI(80)
15.70
11.85
16.06
15.24
δPhII(11), δCF(45)
δPhII(19), δCF(12), δPhI(11),
δCC(10)
3
3
2
2
49
14
99
49
0.90
1.72
1.25
6.50
339
315
297
254
0.23
0.99
0.11
5.35
-
-
-
-
τPhI(30), γCCl(30)
δCCl(35), δC=O(14)
γCC(30), τPhII(33)
δC=C(12), δCC(28),
δCCl(31)
81 0.38
δCC(34)
78 1.22
τC=O(12)
63 2.09
τPhII(11)
14 2.99
δCC(11)
1
180
171
158
121
0.19
0.27
1.65
1.17
-
-
-
-
δC=C(19), δPhI(16),
τPhI(26), γCCl(16),
δCC(36), δC=O(11),
τPhII(33), τC=O(16),
1
1
1
8
6
1
0
4.98
0.87
83
58
2.54
1.00
-
-
τCC(36), γCC(13), τC=C(12)
τPhI(28), τC=O(17), γCC(13)
24

4
0
0.47
41
0.11
-
δC=C(27), δC=O(15),
δCC(10)
2
8
3
0.14
0.03
22
18
0.02
0.02
-
-
τCC(50), τC=O(10)
τCC(54), τC=O(20)
1
a
υ-stretching; δ-in-plane deformation; γ-out-of-plane deformation; τ-torsion; PhI-phenyl
ring attached with chlorine; PhII-phenyl ring attached with fluorine; IRI-IR intensity;
potential energy distribution is given in brackets in the assignment column.
25

Graphical abstract
Title of the paper: Molecular structure, FT-IR, first order hyperpolarizability, NBO
analysis, HOMO and LUMO, MEP analysis of (E)-3-(4-chlorophenyl)-1-(4-
fluorophenyl)prop-2-en-1-one by HF and density functional methods
26

Highlights
*
*
*
*
IR, XRD and NBO analysis were reported.
The wavenumbers are calculated theoretically using Gaussian09 software.
The wavenumbers are assigned using PED analysis.
The geometrical parameters are in agreement with XRD data.
27