Synthesis, spectral analysis and quantum chemical studies on molecular geometry of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone: Experimental and theoretical approaches

Article abstract of DOI:10.1016/j.molstruc.2016.02.077

(2E,6E)-2,6-bis(2-chlorobenzylidene) cyclohexanone was synthesized and characterized by proton and carbon nuclear magnetic resonance, infrared, ultraviolet-visible, mass spectral analysis and X-ray crystallography techniques. Quantum Chemical calculations were done using Becke3-Lee-Yang-Parr with 6-31, 6-311, 6-311 + and 6-311++G (d, p) as basis sets and CAM-B3LYP with 6-31G(d,p) as the basis set. A good correlation between calculated and experimental spectroscopic data has been accomplished. Ultraviolet-Visible spectrum of the molecule was recorded in the region 200-500 nm and the electronic properties and composition were obtained using Time Dependent Density Functional Theory method. X-ray parameters (bonds, bond angles and torsion angles), Electric dipole moment, Mulliken atomic charges, polarizability and first static hyperpolarizability values have been calculated. Hyperconjugative interactions were studied with the help of natural bond orbital analysis. The thermodynamic properties of the compound were calculated at different temperatures.

Full text of DOI:10.1016/j.molstruc.2016.02.077

Accepted Manuscript
Synthesis, Spectral Analysis and Quantum Chemical Studies on Molecular Geometry
of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone: Experimental and Theoretical
Approaches
Anil Kumar Verma, Abha Bishnoi, Shaheen Fatma
PII:
S0022-2860(16)30171-5
10.1016/j.molstruc.2016.02.077
MOLSTR 22286
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 11 November 2015
Revised Date: 23 January 2016
Accepted Date: 22 February 2016
Please cite this article as: A.K. Verma, A. Bishnoi, S. Fatma, Synthesis, Spectral Analysis and Quantum
Chemical Studies on Molecular Geometry of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone:
Experimental and Theoretical Approaches, Journal of Molecular Structure (2016), doi: 10.1016/
j.molstruc.2016.02.077.
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Graphical Abstract

ACCEPTED MANUSCRIPT
Synthesis, Spectral Analysis and Quantum Chemical Studies on Molecular Geometry of
(2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone: Experimental and Theoretical
Approaches.
a
a
a
Anil Kumar Verma , Abha Bishnoi *, Shaheen Fatma
a
Department of Chemistry, University of Lucknow, Lucknow 226007, India
*Corresponding author: Dr. Abha Bishnoi, Professor, Department of Chemistry, University
of Lucknow, Lucknow-226007, India.
Email- abhabishnoi5@gmail.com, dr.abhabishnoi@gmail.com,
anilfromlucknow@gmail.com.
Phone - +91-9415028822, +91-0522-2662777, +91-9936953444.
Abstract
2E,6E)-2,6-bis(2-chlorobenzylidene) cyclohexanone was synthesized and characterized by
(
proton and carbon nuclear magnetic resonance, infrared, ultraviolet-visible, mass spectral
analysis and X-ray crystallography techniques. Quantum Chemical calculations were done
using Becke3-Lee-Yang-Parr with 6-31, 6-311, 6-311+ and 6-311++G (d, p) as basis sets and
CAM-B3LYP with 6-31G(d,p) as the basis set. A good correlation between calculated and
experimental spectroscopic data has been accomplished. Ultraviolet-Visible spectrum of the
molecule was recorded in the region 200-500 nm and the electronic properties and
composition were obtained using Time Dependent Density Functional Theory method. X-ray
parameters (bonds, bond angles and torsion angles), Electric dipole moment, Mulliken atomic
charges, polarizability and first static hyperpolarizability values have been calculated.
Hyperconjugative interactions were studied with the help of natural bond orbital analysis.
The thermodynamic properties of the compound were calculated at different temperatures.
1

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Keywords: Cyclohexanone, Density functional theory, Hyperpolarizability, Natural Bond
Orbital, Non linear optical, Molecular Electrostatic Potential.
1. Introduction
The Claisen-Schmidt reaction (cross-aldol reaction) is a condensation reaction of aldehydes
and carbonyl compounds leading to β-hydroxycarbonyl compounds and has been playing
important role in synthetic organic chemistry. Subsequent dehydration of β-hydroxycarbonyl
compounds afford α-alkylidene or α-arylidene compounds. Such an introduction of
alkylidene or arylidene moieties at the α-position of carbonyl compounds has also been a
quite useful synthetic tool in the natural product chemistry [1-6]. Although studies on the
Claisen-Schmidt reaction have been focused on α-alkylidene and α-arylidene-carbonyl
compounds, interest in α,α’-bisalkylidene and α,α’-bisarylidene-carbonyl compounds is still
increasing. Particularly, α,α’-bis(substituted benzylidene)cycloalkanones have been attracting
much attention due to not only their intriguing biological activities such as antiangiogenic,
[
7-8] quinine reductase inducer [9], cytotoxic [10,11] and cholesterol-lowering activity [12],
but also because of their large second-harmonic generation coefficient that is good enough
for nonlinear optical materials [13]. These derivatives are also the important precursors for
the synthesis of pyrimidine derivatives [14], 2,7-disubstituted tropones [15] and synthetic
intermediates to functionalize α, β-position during the total synthesis of natural products such
as cystodytins [16].
To the best of our knowledge, neither quantum chemical calculations, nor the
vibrational analysis study of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone has been
reported yet. The present paper deals with the synthesis and characterization of titled
compound with the aim to provide a complete description on the X-ray crystallography,
molecular geometry, molecular vibration, electronic features and Ultraviolet (UV)
2

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spectroscopic investigation employing the Becke3-Lee-Yang-Parr (B3LYP) and Coulomb
Attenuating Method (CAM-B3LYP) as different basis sets. Vibrational spectral analysis has
been carried out the basis of calculated potential energy distribution (PED). A comprehensive
investigation of geometrical and electronic structure in the ground state and first excited state,
dipole moment, polarizability, first static hyperpolarizability along with Molecular
electrostatic potential (MESP) surface and contour map may lead to better understanding of
structural and spectral characteristic of the title compound under investigation. Electronic
absorption spectra, Mulliken atomic charges, Global reactivity descriptors and
thermodynamic properties at different temperatures were also investigated using Density
functional theory (DFT). Nonlinear optical (NLO) study divulges the nonlinear properties of
the molecule. Stability of the title molecule arising from hyper-conjugative interactions and
charge delocalization has been investigated using natural bond orbital (NBO) analysis. The
theoretical results were found to be in coherence with the measured experimental data.
2. Materials and Method
All chemicals were purchased from Sigma-Aldrich and reagents were used without further
purification, unless otherwise specified. Infrared (IR) spectrum was recorded on Perkin-
Elmer Fourier transform infra-red spectrophotometer. Proton and Carbon Nuclear Magnetic
1
13
Resonance ( H and C-NMR) spectra were recorded on Bruker 300 MHz instrument using
Chloroform (CDCl ) as a solvent. All Chemical shifts are reported in parts per million
3
(p.p.m.) using Tetramethylsilane (TMS) as internal standard. The Positive Electron Spray
Ionization (ESI) high resolution mass spectrometry (MS) of compound was recorded on
Agilent 6520(Q-TOF) mass spectrometer. Ultraviolet spectrum was recorded 200-500 nm on
UV-visible Double-Beam Spectrophotometer (systronic-2203) instrument using chloroform
as a solvent. Melting point (m.p.) was determined in a melting point apparatus and is
uncorrected.
3

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2.1 Procedure for the Synthesis of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone
(C) and spectral recording
The synthetic route [17] for the proposed compound is illustrated in Scheme 1. A mixture of
Cyclohexanone (A) (1 mmol), 2-Chloro benzaldehyde (B) (2 mmol) and 20 mol% of NaOH
in alcohol (25 ml) was stirred for 15 min. The resulting mixture was washed with water for
several times and recrystalized from ethanol. The title compound was obtained as yellow
o
crystalline solid. Yield: 93.9%; m.p.:124 C; Retention Factor (R
f
) value: 0.338 using
Hexane: Ethyl acetate (8.0:2.0 v/v) as mobile phase; IR (KBr) νmax: 3021 (=CH stretching);
2
1
2
2
950 (Aromatic stretching of C-H); 1615 (C=O stretching); 1480 (Aromatic C=C stretching);
1
258 (C-O stretching vibration); 748 (C-Cl stretching); H NMR (CDCl
3
) : δ = 1.87 (s, 2H),
) : δ = 22.9,
1
3
.45-2.49 (s, 4H), 7.33 (s, 2H), 7.50-7.61 (m, 6H), 7.74 (s, 2H); C NMR (CDCl
3
+
8.3, 127.1, 129.5, 129.9, 130.1, 130.6, 134.9, 135.9, 140.2, 189.9; MS, m/z: M 343; Anal.
O: C, 69.98; H, 4.70; Found: C, 67.77; H, 5.16.
Calcd for C20H16Cl
2
<Scheme 1>
3. Computational methods
All the calculations of synthesized compound were carried out with help of Gaussian 09
program package [18] using hybrid functional B3LYP [19] and CAM-B3LYP [20] and 6-31,
1
13
6
-311, 6-311+ and 6-311++ G(d, p) as basis sets. The H and C-NMR chemical shifts were
calculated. B3LYP invokes Becke’s three parameter (local, non local, Hartree-Fock) hybrid
exchange functional (B3), with Lee-Yang-Parr correlation functional (LYP) [21]. UV-Vis
spectra, electronic transitions and electronic properties such as highest occupied molecular
orbital-lowest unoccupied molecular orbital (HOMO-LUMO) were computed with the help
of time-dependant DFT (TD-DFT) method with similar hybrid functional and basis set. The
molecular structures were visualized with the help of Gauss View [22]. Potential energy
4

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distribution (PED) along with internal coordinates was calculated by Gar2ped software [23].
The second-order Fock matrix was used to evaluate the donor-acceptor interactions in the
Natural Bond Order (NBO) basis [24].
4. Result and discussion
4.1 Molecular geometry
The most relevant structural parameters (bond lengths, bond angles and dihedral angles) of
title compound were determined by DFT calculations using B3LYP/CAM-B3LYP functional
6-31G(d, p) as basis sets which are given in Table S1. Geometry optimization was carried
out without any symmetry constraints. The atoms numbering of molecule used in this paper is
reported in Fig. 1. The optimized structure of title compound was compared with the
experimental structure [25]. The agreement between the optimized and experimental crystal
structure is quite good showing that the geometry optimization almost exactly reproduces the
experimental conformation. The molecular structure of title compound belongs to C1 point
group symmetry. So it can be used to calculate various molecular and spectroscopic
parameters, such as electronic properties, electric moments and vibrational wave numbers.
<Fig. 1>
1
13
4
.2 H and C NMR spectroscopy
1
13
H and CNMR chemical shifts were calculated with Gauge Independent Atomic Orbital
(GIAO) approach using DFT with B3LYP and CAM-B3LYP functional and 6-31, 6-311, 6-
1
3
11+ and 6-311++ G(d, p) as basis sets [26]. The experimental and calculated values of H
13
and C NMR chemical shifts of the title compound are given in Table 1 and Table 2
1
13
respectively. The experimental H and C NMR spectra of the title compound are given in
supplementary Fig. S1 (Supporting information) and Fig. S2 respectively. The correlation
5

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1
13
graph between the experimental and calculated chemical shifts for H and C NMR are
shown in Fig. 2 and Fig. 3 respectively.
<
<
Table 1>
Table 2>
<Fig. 2 and Fig. 3>
4.3 UV-Visible absorption spectroscopy
The UV-Visible spectrum of compound C (Fig. 4) has been studied by TD-DFT method
using B3LYP 6-31, 6-311, 6-311+ and 6-311++ G/(d, p) and CAM-B3LYP functional as 6-
31 G/(d, p) basis sets and solvent effect has been taken into consideration by implementing
Integral Equation Formalism Polarisable Continuum Model (IEFPCM). The simulated UV
data and related properties such as the vertical excitation energies, oscillator strength (f),
percentage contribution of probable transition and corresponding absorption wavelength have
been tabulated in Table 3 and compared with experimental UV data. When experimental
results compared with the quantum chemical calculations, the CAM-B3LYP method gives
better agreement. Calculations by B3LYP functional predict one intense electronic transition
at 396.54 nm with an oscillator strength ƒ = 0.0775 in chloroform which is in good agreement
with the measured experimental data (λexp. = 364 nm in chloroform) as shown in Fig. 4. This
electronic absorption corresponds to the transition from the molecular orbital HOMO (89) to
the LUMO (90) with 13.9% contribution, HOMO-2 (87) to LUMO with 33.143%
contribution and from HOMO-3 (86) to LUMO with 13.9% contribution.
In the title
*
compound these transitions appears to be due to π → π transition. Molecular orbitals of the
compound and their electronic transitions are shown in Fig. 5 which shows the distributions
and energy levels of the HOMO -3, HOMO -2, HOMO and LUMO orbitals at the B3LYP/ 6-
31G (d, p) level for the title compound. HOMO is mainly localized on the phenyl ring
6

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containing chloro group, slightly delocalized on carbon atoms of cyclohexane ring and on
oxygen atom of carbonyl group. HOMO-2 is delocalized over the cyclohexanone ring,
carbonyl group which is attached to the cyclohexane ring. HOMO-3 is localized on phenyl
ring containing chloro group. LUMO is localized on cyclohexane ring with slight
delocalization over phenyl ring, carbonyl groups attached to cyclohexane ring. The value of
the energy gap between HOMO and LUMO is 4.02 eV. The lowering of the HOMO-LUMO
band gap is essentially a consequence of the large stabilization of the LUMO due to the
strong electron-acceptor ability of the electron-acceptor group. Higher the energy of HOMO,
the easier it is for HOMO to donate electrons where as it is easier for LUMO to accept
electrons when the energy of LUMO is low. This shows the chemical reactivity of the title
compound and proves the occurrence of eventual charge transfer within the molecule.
Experimental UV-Visible spectrum of title compound is given in Supplementary Fig. S3.
<
Table 3>
<Fig. 4>
<Fig. 5>
4.4 Molecular electrostatic potential analysis
The MESP is a map of electrostatic potential over constant electron density of molecules. The
importance of MESP lies in the fact that it simultaneously displays the molecular size and
shape as well as positive, negative and neutral electrostatic potential regions in terms of the
color grading scheme which is very useful in the investigation of the most probable binding
receptor site along with the size and shape of the molecules [27,28]. To predict the reactive
sites of electrophilic and nucleophilic attack for the investigated molecules of MESP at the
B3LYP/6-31 G optimized geometry were calculated in Fig. 6. The negative (red) regions of
the MESP are relative to the electrophilic reactivity, and the positive (blue and yellow)
regions are related to nucleophilic reactivity. As seen from Figure there is one possible site on
7

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the title compounds for electrophilic attack. The negative regions are mainly localized on the
oxygen atom (Red region) of C=O group O36 is the most negative regions so, carbonyl group
is the binding site for electrophilic attack. The maximum positive regions are localized on
H23, H26, H29, H31, H32 and H33 atoms of the benzene ring, which can be considered as
possible sites for nucleophilic attack.
<Fig. 6>
4.5 Natural bond orbital analysis
NBO analysis has an appealing aspect of highlighting the individual bonds and lone-pair
energy that play a vital role in the chemical processes [29,30]. It is an important tool for
studying hybridization, co-valence, hydrogen-bonding and Van der Waals interactions. The
result of interaction is a loss of occupancy from the concentration of electron NBO of the
idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j)
the stabilization energy E(2) associated with the delocalization i → j is as follows:
(1)
In other words, NBO provides supplementary structural information. Second-order
perturbation theory analysis of the Fock matrix in NBO basis for (2E,6E)-2,6-bis(2-
chlorobenzylidene)cyclohexanone presented in supplementary Table S2. The higher E(2)
value (stabilization energy or energy of hyperconjugative interaction) points towards the
greater interaction between electron donors and electron acceptors (i.e. the more donating
tendency from electron donors to electron acceptors and the greater the extent of conjugation
in the system). Delocalization of electron density between occupied Lewis-type (bonding or
lone pair) NBO’s and unoccupied (antibonding or Rydberg) non-Lewis NBO’s correspond to
a stabilizing donor–acceptor interaction. In compound C some of the important π→π*
interactions viz π (C8-C9) → π*(C5-C7)/ π*(C10-C13)/ π*( C11-C12); π(C15-C16)→π*(C2–
8

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C14)/ π*(C17–C20)/ π*(C18–C19) are responsible for the delocalization of respective π–
electrons of phenyl ring, the molecule being stabilized by energy in the region of
2
5.29~226.15 kJ/mol. Other interactions involving the lone pair of electrons with the anti-
bonding π electrons corresponds to n (Cl37) → π*(C8-C9), n (Cl38) → π*(C15–C16) and n
2
3
3
(O31) → π*(C29–C30) stabilizing the molecule with 12.08 kJ/mol energy.
4.6 Non linear optical analysis
NLO effect is the forefront of current research because of its importance in providing the key
functions of frequency shifting, optical modulation, optical switching, optical logic and optic
memory for the emerging technologies in areas such as telecommunications, signal
processing and optical interconnections [31-33]. 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. Organic molecules able to
manipulate photonic signals efficiently are of importance in technologies such as optical
communication, optical computing, and dynamic image processing [34,35]. The first
hyperpolarizability of the title compound was calculated using B3LYP/ 6-31, 6-311, 6-311+,
6-311++G and CAM-B3LYP functional with 631-G/(d,p) basis set based on the finite field
approach. In the presence of an applied electric field, the energy of a system is a function of
electric field. The first hyperpolarizability is a third rank tensor that can be described by a 3 x
3
x 3 matrix. The 27 components of the matrix can be reduced to 10 components due to
Kleinman symmetry [36]. The complete equations for calculating the magnitude of total
dipole moment ꢀ, the average polarizability αtot and the first hyperpolarizability βtot, using the
x,y,z components is as follows:
1
2
x
2
y
2
z
2
µ = µ + µ + µ
(2)
tot
(
)
1
αtot
=
(
α xx
+
α yy
+
α zz (3)
)
3
9

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1
2
2
2
2


β
=
(
β
+
β
+
β
)
+
(
β
+
β
+
β
)
+
(
β
+
β
+
β
)
(4)
xxx
xyy
xzz
yyy
yzz
yxx
zzz
zxx
zyy




Since the value of the polarizabilities α and the hyperpolarizability of Gaussian output are
reported in a atomic mass units (a.u.), the calculated values have been converted into
−24
−30
electrostatic units (esu) (α: 1 a.u = 0.1482×10 esu; β: 1 a.u. = 0.0086393×10 esu). The
results of electronic dipole moment ꢀi, polarizability αij and first order hyperpolarizability
βijk are listed in supplementary Table S3. The calculated dipole moment as 6-31, 6-311, 6-
11+, 6-311++/G (d,p) basis set is equal to 5.5329 D, 5.1022 D, 4.8088 D and 4.8071 D
respectively for B3LYP level and 5.019 D for CAM-B3LYP level. The calculated
polarizability αtot, as 6-31, 6-311, 6-311+, 6-311++/G (d,p) basis set is equal to 38.65822
−24
−24
−24
−24
×
10 esu, 40.27641×10 esu, 43.28655×10 esu and 43.35537×10 esu respectively for
−24
B3LYP and 36.09673 ×10 esu for CAM-B3LYP level. The calculated first hyper
polarizability of the title compound as 6-31, 6-311, 6-311+, 6-311++/G (d,p) basis set is
-30
-30
-30
-30
3
.697 ×10 esu, 3.575×10 esu, 4.956×10 esu and 4.93×10 esu respectively for B3LYP
-30
level and 2.432×10 esu for CAM-B3LYP level and these values are greater (28.43, 27.5,
38.12 and 37.92 times for B3LYP level and 18.70 times for CAM-B3LYP level) than that of
-30
the standard NLO material urea (0.13 ×10 esu) [37]. We conclude that the title compound is
an attractive object for future studies of nonlinear optical properties.
4.7 Thermodynamic Properties
The values of some thermodynamic parameter of title compound, including zero-point
vibrational energy, rotational temperatures, rotational constants, energies at standard
temperature 298.15 K were obtained at the using B3LYP 6-31, 6-311, 6-311+, 6-311++G and
CAM-B3LYP functional with 631-G/(d,p) basis set (supplementary Table S4). The standard
statistical thermodynamic functions, heat capacity (CV) and entropy (S) were obtained at
various temperatures (100-500 K) for the title compound on the basis of vibrational analysis
using B3LYP and CAM-B3LYP functional with different basis sets and are listed in
1
0

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supplementary Table S5. The total energy and vibrational values are somewhat higher when
calculated in CAM-B3LYP than B3LYP. The rotational constants and rotational temperature
values are similar in all the cases. It is observed that standard statistical thermodynamic
functions increase with temperature ranging from 100 to 500 K, due to the fact that the
molecular vibrational intensities increase with temperature [38, 39]. The correlation equations
among heat capacities, entropies and temperatures were fitted by quadratic formulas and the
2
corresponding fitting factors (R ) for these thermodynamic properties are given in equation
(5-14). The corresponding fitting equations are as follows and the correlation graphics are
shown in Fig. 7.
<Fig. 7 >
−
5
2
2
CV = 4.99+ 0.253T −5.10 T
(R = 0.9996) using B3LYP 6-31G(d,p)
(5)
(6)
−
5
2
2
S = 67.725+ 0.3048T −6.10 T
(R =1)using B3LYP6-31G(d,p)
−
5
2
2
2
2
CV = 7.6073+ 0.2253T − 2.10 T
(R =0.9998)using B3LYP 6-311G(d,p) (7)
−5
2
2
S = 66.705+0.305T −6.10 T
(R = 1)using B3LYP 6-311G(d,p)
(8)
−5
2
CV = 5.1715+ 0.2536T −5.10 T
(R =0.9994)using B3LYP 6-311+G(d,p)
(9)
−5
2
2
S = 67.594+0.3061T −7.10 T
(R =1)using B3LYP 6-311+G(d,p)
(10)
(11)
−5
2
CV = 5.1538+ 0.2537T −5.10 T
(R = 0.9994)using B3LYP 6-311+G(d,p)
−
5
2
2
S = 67.486+0.3058T −6.10 T
(R =1)using B3LYP 6-311++G(d,p)
(12)
−5
2
CV = 5.487 + 0.2454T − 4.10 T
2
(
R = 0.9994) using CAM-B3LYP (13)
−5
2
2
S
= 68.176+ 0.3011
T
−6.10
T
(R =1) using CAM-B3LYP
(14)
These thermodynamic data may provide helpful information for the further study of title
compound. They can be used to compute the other thermodynamic energies according to the
relationships of thermodynamic functions and estimate directions of chemical reactions
1
1

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according to the second law of thermodynamics in thermo chemical field [40]. All
thermodynamic calculations were done in gas phase and they could not be used in solution.
4.8 Vibrational spectral analysis
Experimental FT-IR spectra of synthesized compound C has been recorded in the range of
–1
4
000-450 cm where as theoretical vibrational analysis of the compound were performed by
DFT using B3LYP and CAM-B3LYP level with 6-31G (d,p) basis set. The theoretical IR
spectrum is shown in Supplementary Fig. S4. The observed infrared and calculated wave
numbers are scaled down by a single scaling factor 0.9679 [41] by DFT using B3LYP level
with 6-31G (d,p) basis set and the assigned wavenumbers of calculated vibrational modes by
B3LYP along with their PED are given in Table 4. Experimental IR spectrum of title
compound is given in Fig. S5.
<
Table 4>
4.8.1 C=O and C-O vibrations
-1
The appearance of strong bands in the FT-IR between 1690-1800 cm [42] in aromatic
compounds shows the presence of carbonyl group and is due to the C=O stretching motion.
The wavenumber due to C=O stretch mainly depends on the bond strength which in turn
depends upon inductive, conjugative, field and steric effects. In the present study, the strong
-1
band at 1615 cm in FT-IR spectrum is assigned to C=O stretching mode. The calculated
-1
-1
C=O stretching mode at 1606.86 cm , whereas the band at 1251.41 cm is assigned to
stretching vibration of C-O which shows the good agreement with the experimental value at
-1
1
258 cm .
1
2

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4.8.2 =C–H vibrations
-1
The aromatic C–H stretching vibrations are normally found between 3100 and 3000 cm due
-1
to aromatic C–H stretching vibrations [43]. The wavenumbers calculated at 3086.48 cm is
-1
assigned to =C–H stretching vibrations. A strong band appeared at 3021 cm in FTIR
spectrum is assigned to =C–H ring stretching vibrations.
4.8.3 C=C vibration
In aromatic hydrocarbon, skeletal vibrations involving carbon-carbon stretching within ring
-1
are absorbed in the region between 1600 and 1585 cm [44]. The benzene ring possesses six
ring stretching modes, of which the four with the highest wavenumbers (occurring near 1600,
-1
1
580, 1490 and 1440 cm ) are good group vibrations. The wavenumber calculated at 1458.05
-1
cm assigned to the C=C stretching vibration in the benzene ring which show good
-1
agreement with experimental value at 1480 cm .
.8.4 C-Cl vibration
4
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 [45, 46].
Mooney [47, 48] assigned vibrations of C-Cl, Br, and I in the wavenumber range of 1129-480
-1
-1
cm . The C-Cl stretching vibrations give generally strong bands in the region 710-505 cm .
-1
For simple organic chlorine compounds, C-Cl absorptions are in the region 750-700 cm . For
-1
-1
the title compound C, the band observed at 748 cm in the IR spectrum and 734.51 cm
DFT) is assigned as the C-Cl stretching mode.
(
4
4
.9 Chemical reactivity
.9.1 Global reactivity descriptors
Global reactivity descriptors are highly successful in predicting global reactivity trends. The
energies of frontier molecular orbital (εLUMO, εHOMO), band gap (εLUMO – εHOMO ionization
)
,
1
3

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potential (IP), electron affinity (EA), electronegativity (χ), global hardness (η), chemical
potential (ꢀ), global electrophilicity index (ω), global softness (S) [49-53] and additional
electronic charge (∆Nmax) of reactant A, B and product C have been calculated using
following equations. [(15)-(22)] and listed in Table 5.
<Table 5>
IP = −ε HOMO
EA = −ε LUMO
1
(15)
(16)
χ
= −
(
εLUMO
+
εHOMO
)
(17)
(18)
2
1
η
=
(
εLUMO
−
εHOMO
)
2
1
µ
= −
χ
=
(
εLUMO
+
εHOMO
)
(19)
2
2
µ
ω =
(20)
(21)
(22)
2
η
1
S =
2η
µ
η
∆Nmax = −
According to Parr et al., electrophilicity index (ω) is a global reactivity index similar to the
chemical hardness and chemical potential. This is positive and definite quantity. This new
reactivity index measures the stabilization in energy when the system acquires an additional
electronic charge (∆N) from the environment. The direction of the charge transfer is
completely determined by the electronic chemical potential of the molecule because an
electrophile is a chemical species capable of accepting electrons from the environments.
Therefore its energy must decrease upon accepting electronic charge and its electronic
chemical potential must be negative.
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4

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Electrophilic charge transfer (ECT) [54] is defined as the difference between the
Nmax values of interacting molecules. If we consider two molecules A and B approach to
∆
each other (i) if ECT > 0, charge flow from B to A (ii) if ECT < 0, charge flow from A to B.
ECT is calculated using equation given below:
ECT =
(
∆Nmax )A
−
(
∆Nmax )B (23)
µA
η A
µB
ηB
where
(
∆Nmax )A = −
and
(
∆Nmax )B = −
(24)
For the sake of simplicity, reactants cyclohexanone and 2-chlorobenzaldehyde and
product benzylidine cyclohexanone are abbreviated as A, B & C respectively.
Ionization potential (IP), electron affinity (EA), electronegativity (χ), global hardness
(η), chemical potential (ꢀ), global electrophilicity index (ω), global softness (S)
and
additional electronic charge (∆Nmax) were calculated for reactants A and B as well as for the
product C, using the energies of frontier molecular orbitals εLUMO, εHOMO which are tabulated
in Table 5. ECT was calculated from the values of additional electron charge (∆Nmax) of
reactant A and B using the equation (23).
The calculated value of ECT > 0 (ECT = 0.690), for reactant molecules
cyclohexanone (A) (1 mmol), 2-chlorobenzaldehyde (B) indicates charge flow from B to A.
Therefore, the reactant molecules B act as global nucleophile (electron donor) and A as
global electrophile (electron acceptor). The high value of electrophilicity index (ω) = 4.456
eV for product C than from reactant (B) shows that it is strong electrophile than reactant (B).
4.9.2 Local reactivity descriptors
Fukui function (FF) is one of the widely used local density functional descriptors to model
chemical reactivity and site selectivity. Using Hirshfeld population analysis of neutral, cation
and anion state of molecule, Fukui Functions are calculated using following equations:
+
K
f = q
(
N +1
)
− q
(
N
 for nucleophilic attack (25)
)


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5

ACCEPTED MANUSCRIPT
−
K
f = q
(
N
)
− q
(
N −1
 for electrophilic attack (26)
)


1
0
fK
=
q
(
N
+
1
)
−
q
(
N
−1 for radical attack (27)

)


2
Where, N, N-1, N+1 are total electrons present in neutral, anion and cation state of molecule
respectively.
+
k
-
k
0
k
+
k
-
0
In addition local softnesses s
, s
,s
and electrophilicity indices (ω
k k
, ω , ω )
are also used to describe the reactivity of atoms in a molecule. These local reactivity
descriptors associated with a site k in a molecule are defined with the help of the
corresponding condensed to atom variants of Fukui function, using the following equations-
+
K
+
K
−
k
−
K
0
K
0
s = Sf , s = Sf , s = Sf
K
(28)
(29)
+
ωK
+
−
−
0
0
fK
=
ω
f , ωK
=
ω
f ,
ω
=
ω
K
K
K
Where +, –, 0 signs show nucleophilic, electrophilic and radical attack respectively. The
±
±
±
k k k
maximum values of all the three local reactivity descriptors (f , s , ω ) indicate that it site
is more prone site for nucleophilic or electrophilic attack than all other atomic sites in
reactants.
+
–
k
+
k
–
K
Fukui functions (fk ,
f
), local softnesses (s
,
S
) and local electrophilicity indices
+
k
–
k
(ω
, ω
) [52, 53] for selected atomic sites of molecule have been listed in supplementary
Table S6.
In product, the relative high value of local reactivity descriptors (fk ,
Table S6 at C2, C9, C16 and O36 indicate that these sites are prone to nucleophilic whereas
+
+
+
k k
s , ω ) in
-
-
-
k k
the relative high value of local reactivity descriptors (fk , s , ω ) at C1, C8 and C15 indicate
that this site is more prone to electrophilic attack. Thus synthesized molecule may be used as
intermediate for the synthesis of further new heterocyclic compounds.
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6

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5. Conclusion
In the present study, we have carried out the combined experimental and theoretical
spectroscopic analysis of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone for the first
1
13
time, using FT-IR, H, C NMR, UV-Vis techniques and DFT. In general, a good
correspondence between experimental and calculated normal modes of vibrations has been
observed. X-ray studies helped in establishing the structure with optimized geometric
parameters (bond lengths, bond angles and dihedral angles) are determined by DFT theory
and compared with the experimental data. NLO behavior of the title molecule has been
investigated by dipole moment, polarizability and first hyperpolarizability. It is concluded
that the lowest singlet excited state of the molecule is mainly derived from the
HOMO→LUMO (π → π*) electron transition. NBO results reflected the charge transfer
within the molecule. The calculated first hyper polarizability of the title compound as 6-31, 6-
-30
-30
-30
3
11, 6-311+, 6-311++/G (d,p) basis set is 3.697 ×10 esu, 3.575×10 esu, 4.956×10 esu
-30
-30
and 4.93×10 esu respectively for B3LYP level and 2.432×10 esu for CAM-B3LYP level
and these values are greater (28.43, 27.5, 38.12 and 37.92 times for B3LYP level and 18.70
-30
times for CAM-B3LYP level) than that of the standard NLO material urea (0.13 ×10 esu),
implies that the title molecule may be useful as a nonlinear optical material. The electronic
properties are also calculated and compared with the experimental UV-Vis spectrum. NBO
analysis reveals that the some important intramolecular charge transfer can induce large
nonlinearity to the title molecule and the high intramolecular hyper-conjugative interaction
around the ring can induce the large bioactivity in the compound.
Acknowledgements
The authors are grateful to the Head, Department of Chemistry, University of Lucknow,
Lucknow, for providing necessary Laboratory facilities and to the Director, Central Drug
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Research Institute (CDRI), Lucknow, India for providing spectral and elemental data.
Authors are also thankful to UGC for providing financial support.
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Legends of figure / table / scheme-
Fig. 1. Optimized geometry of the title compound using B3LYP/6-31G(d,p) level of theory.
1
Fig 2. Correlation graph between experimental and calculated H NMR chemical shift using
B3LYP (a) 6-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G
(d, p).
13
Fig 3. Correlation graph between experimental and calculated C NMR chemical shift using
B3LYP (a) 6-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G
(d, p).
Fig 4. Calculated UV-visible spectrum of compound C.
Fig. 5. Molecular orbitals (HOMO
LUMO, HOMO-2
LUMO and HOMO-3 LUMO)
of the compound at the B3LYP/6-31G(d,p) basis set.
Fig. 6. 3 D plots of the molecular electrostatic potential of title compound.
Fig 7. Correlation graphs of heat capacity calculated at various temperatures using B3LYP/6-
3
1G(d,p) (a), B3LYP/6-311G(d,p) (b), B3LYP/6-311+G(d,p) (c), B3LYP/6-311++G(d,p) (d)
and CAM-B3LYP /6-31G (d, p) (e).
Table 1. Experimental and Calculated H chemical shifts of title compound using B3LYP (a)
-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G (d, p).
1
6
13
Table 2. Experimental and Calculated C chemical shifts of title compound using B3LYP (a)
-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G (d, p).
Table 3. Experimental and theoretical absorption wavelength (nm), excitation energies E
eV) of title compound using B3LYP (a) 6-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p)
and CAM-B3LYP (e) 6-31G (d, p).
6
λ
(
2
4

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Table 4. The recorded (FT-IR) and computed vibrational wavenumbers by B3LYP/6-
31G(d,p), IR activities along with the assignments of vibrational modes of compound based
on PED results.
Table 5. Calculated εLUMO, εHOMO, energy band gap εLUMO – εHOMO, ionization potential (IP),
electron affinity (EA), electronegativity (χ), global hardness (η), chemical potential (ꢀ), global
electrophilicity index (ω), global softness (S) and additional electronic charge (∆Nmax) in eV
for reactant A, B and product C using B3LYP/6-31G(d,p).
Scheme 1. Synthesis of (2E,6E)-2,6-bis(2-chlorobenzylidene)cyclohexanone.
Fig. 1. Optimized geometry of the title compound using B3LYP/6-31G(d,p) level of theory.
2
5

ACCEPTED MANUSCRIPT
1
Fig 2. Correlation graph between experimental and calculated H NMR chemical shift using
B3LYP (a) 6-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G
(d, p).
2
6

ACCEPTED MANUSCRIPT
13
Fig 3. Correlation graph between experimental and calculated C NMR chemical shift using
B3LYP (a) 6-31G, (b) 6-311, (c) 6-311+ (d) 6-311++ /G(d, p) and CAM-B3LYP (e) 6-31G
(d, p).
2
7

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Fig 4. Calculated UV-visible spectrum of compound C.
2
8