Synthesis, molecular structure, spectroscopic investigations and computational studies of (E)-1-(4-(4-(diethylamino)-2-hydroxybenzylideneamino)phenyl)ethanone

Article abstract of DOI:10.1007/s11224-015-0571-2

Abstract The Schiff base compound (E)-1-(4-(4-(diethylamino)-2-hydroxybenzylideneamino)phenyl)ethanone has been synthesized and characterized by IR, UV-Vis, and ¹H and ¹³C NMR techniques. These properties of title compound were also

Full text of DOI:10.1007/s11224-015-0571-2

Struct Chem
DOI 10.1007/s11224-015-0571-2
ORIGINAL RESEARCH
Synthesis, molecular structure, spectroscopic investigations
and computational studies of (E)-1-(4-(4-(diethylamino)-2-
hydroxybenzylideneamino)phenyl)ethanone
•
Ayoub Kanaani Davood Ajloo Hasan Ghasemian
•
•
•
Hamzeh Kiyani Mohamad Vakili
•
Asiyeh Mosallanezhad
Received: 18 December 2014 / Accepted: 30 January 2015
Ó Springer Science+Business Media New York 2015
Abstract The Schiff base compound (E)-1-(4-(4-(di-
ethylamino)-2-hydroxybenzylideneamino)phenyl)ethanone
has been synthesized and characterized by IR, UV–Vis, and
1H and 13C NMR techniques. These properties of title
compound were also investigated from calculative point of
view. UV–Vis spectra of the title compound were recorded
in different organic solvents to investigate the dependence
of tautomerism on solvent types. Calculated results reveal
that its enol form is more stable than its keto form. A
detailed analysis of the nature of the hydrogen bonding,
using topological parameters, evaluated at bond critical
points.
Introduction
N-salicylidene anilines (anils) are particularly eye-catching
since they are synthesized by the condensation of the
corresponding aldehydes and amines and exhibit a strong
intramolecular H-bonding between the H-atom of the hy-
droxy group and the N-atom of the imine moiety. Par-
ticularly, ortho-hydroxy Schiff base derivatives are the
most commonly studied class of Schiff bases because of
their interesting photochromic and thermochromic features
in the solid state [1]. These features are caused by an in-
tramolecular proton transfer associated with a change in
p-electron configuration from the hydroxyl O atom to the
imine N atom occurring under the influence of light for
photochromic and temperature for thermochromic Schiff
bases, and the potential energy profile of this transfer
shapes the photochromic and thermochromic features of
the compound [2]. Schiff bases have the wide range of
applications spanning the industrial [3, 4], pharmaceutical
[5, 6], biological [7, 8], and chemical fields [9–11]. For
instance, they are industrially used as dyes and pigments in
textile [12] in addition to their application in pharmacology
for the synthesis of antibiotics, antiallergic and antitumor
substances [13, 14]. Photochromic compounds are impor-
tant because of their use as optical switches and optical
memories, variable electrical current, ion transport through
membranes [15].
Keywords Schiff base ꢀ Spectroscopy ꢀ Intramolecular
proton transfer ꢀ DFT
Electronic supplementary material The online version of this
article (doi:10.1007/s11224-015-0571-2) contains supplementary
material, which is available to authorized users.
A. Kanaani ꢀ D. Ajloo (&) ꢀ H. Ghasemian ꢀ H. Kiyani (&) ꢀ
A. Mosallanezhad
School of Chemistry, Damghan University,
36715-364 Damghan, Iran
e-mail: ajloo@du.ac.ir
H. Kiyani
e-mail: hkiyani@du.ac.ir
In conjunction with the development of technology,
among the computational methods calculating the elec-
tronic structure of molecular systems, DFT has been a
favorite one due to its great accuracy in reproducing the
experimental values of in molecule geometry, vibrational
frequencies, atomic charges, dipole moment, etc. [16]. In
recent years, besides the experimental studies, an in-
crease is seen in quantum chemical computational
D. Ajloo
School of Chemistry, College of Science, University of Tehran,
Tehran, Iran
M. Vakili
Department of Chemistry, Ferdowsi University of Mashhad,
91775-1436 Mashhad, Iran
123

Struct Chem
studies with DFT on tautomerism and intramolecular
proton transfer process in ortho-hydroxy Schiff base
compounds [17, 18].
reference electrodes at an ambient temperatures [19]. Prior
to the measurements, the solution was purged with argon to
remove residual oxygen.
A new (E)-1-(4-(4-(diethylamino)-2-hydroxybenzylide-
neamino)phenyl)ethanone (DHBE) compound was syn-
thesized, and its spectroscopic properties were studied both
experimental and theoretical insight. NBO analyses were
performed to provide valuable information about various
intermolecular interactions. Thus, in the present work, the
molecular structure, EHOMO (the highest occupied mole-
cular orbital energy), ELUMO (the lowest unoccupied
molecular orbital energy), LUMO–HOMO energy gap
(DE), global hardness (g), softness (S), electronegativity
(v), dipole moment (l), polarizabilities (\a[), the aniso-
tropy of the polarizabilities (\Da[), and the first-order
hyperpolarizabilities (\b[), Fukui functions, molecular
electrostatic potential maps (MEP) and thermodynamic
parameters (molecular energy (E), heat capacity (C0p,m),
entropy (S0m) and enthalpy (H0m)) are calculated and dis-
cussed. Also, intramolecular proton transfer process of
DHBE was investigated for ground state in gas phase.
Synthesis
In this study, we report the synthesis of a new Schiff base,
(E)-1-(4-(4-(diethylamino)-2-hydroxybenzylideneamino)
phenyl)ethanone (Scheme 1). A solution of 4-(diethyl-
amino)salicylaldehyde (1 mmol, 0.193 g) dissolved in
ethanol (10 mL) was added to a solution of 4-aminoace-
tophenone (1 mmol, 0.135 g) in ethanol (10 mL). The
resulting yellow solution was stirred at room temperature
for 3 h. After completion of the reaction (monitored by
TLC analysis), the reaction mixture was allowed to room
temperature to afford the fine crystalline powder of
N-salicylidene aniline derivative. The product was filtered
off, washed with ethanol (5 mL) and dried under vacuum.
1H NMR (400 MHz, CDCl3) (d/ppm): 13.46 (s, 1H, OH),
8.75 (s, 1H, CH = C), 7.98 (d, J = 8.4 Hz, 2H, ArH), 7.40
(d, J = 8.4 Hz, 2H, ArH), 7.35 (d, J = 8.8 Hz, 1H, ArH),
6.34 (dd, J = 2.0, 8.8 Hz, 1H, ArH), 6.08 (d, J = 2.0 Hz,
1H, ArH), 3.36-3.42 (m, 4H, CH2), 2.57 (s, 3H, COCH3),
1.12 (t, 6.8, 7.2 Hz, 6H, CH3); 13C NMR (100 MHz,
CDCl3) d: 197.2, 164.2, 163.0, 152.9, 152.5, 135.1, 134.1,
130.3, 121.3, 109.1, 104.7, 97.2, 44.4, 27.1, 13.0.
Experimental
Materials and measurements
All reagents and solvents for synthesis and analysis were
commercially available and used as received without fur-
ther purifications. The mid-IR spectrum was obtained in the
4,000–400 cm-1 region with spectral resolution of 2 cm-1
by averaging the results of 16 scans Perkin-Elmer RXI
Fourier Transform spectrophotometer using KBr pellet
technique (solid phase). The ultraviolet absorption spectra
were examined in the range of 250–600 nm using Perkin-
Elmer lambda 25 recording spectrophotometer. The NMR
spectra were recorded at the ambient temperatures on a
Brucker AVANCE DRX 400 MHz using DMSO as solvent.
All chemical shifts are reported in d units down field from
TMS. Cyclic voltammetry measurements were performed
by AUTOLAB PGSTAT20 potentiostat–galvanostat
(EcoChemie, Netherlands). The electrochemical properties
of title compound (c = 2910-3 M) was investigated by
cyclic voltammetry with DMSO as the solvent in the
presence of 0.1 MBu4NBF4 as the supporting electrolyte
using Pt working and counter electrodes and Ag/AgCl as the
Computational details
In the present work, the density functional method (DFT)
has been employed using Becke’s three parameter hybrid
exchange functional [20] with the Lee–Yang–Parr corre-
lation functional [21, 22] combined with standard
6-311??G(d,p) basis set and GAUSSIAN 03W program
package without any constraint on the geometry [23].
The prediction of vibrational wave numbers and ther-
modynamical parameters were done at the DFT (B3LYP)
level, as it has been well recognized as an efficient theo-
retical chemistry tool for studying vibrational properties of
variety of molecules. Positive values of all the calculated
vibrational wave numbers confirmed the geometries to be
located at true local minima on the potential energy sur-
face. In this investigation, we observed that the calculated
frequencies were slightly greater than the fundamental
frequencies. These discrepancies are corrected either by
O
O
N
CHO
OH
EtOH, RT
N
+
H2N
N
OH
Scheme 1 Synthesis of (E)-1-(4-(4-(diethylamino)-2-hydroxybenzylideneamino)phenyl)-ethanone (DHBE)
123

Struct Chem
computing anharmonic corrections explicitly [24] or by
introducing a scale factor. In the present study, a selective
scaling factor of 0.9961 is used for the wave numbers less
than 1,700 cm-1 and 0.9556 for greater than 1,700 cm-1 at
6-311??G(d,p) and 0.9963 are used for the wave numbers
less than 1,700 cm-1 and 0.9959 for greater than 1,700
cm-1 at 6-311??G(2d,p) [25]. The vibrational wave
number assignments were carried out by combining the
results of the GaussView 4.1.2 program [26] and VEDA4
program [27]. Detailed interpretations of the vibrational
spectrum of our compound have been made based on the
calculated potential energy distribution (PED).
A relaxed potential energy surface (PES) scan was
performed based on the optimized geometry of the OH
tautomeric form by varying the redundant internal coordi-
˚
nate (O1–H1 bond distance) from 0.9 to 1.7 A with 17 steps
˚
of 0.05 A in order to describe the potential energy barrier
belonging to the intramolecular proton transfer and to ob-
serve the effects of transfer on the molecular geometry. In
the scan process, all the remaining internal coordinates
were fully optimized. With this kind of calculation, it is
possible to observe step by step the changes in the mole-
cular geometry.
The nuclear magnetic resonance (NMR) chemical shift
calculations were performed using gauge-included atomic
orbital (GIAO) method [28] at B3LYP/6-311??G(2d,p)
Results and discussion
1
level, and the H and 13C chemical shifts were referenced
Molecular geometry optimization
to the corresponding values for TMS, which were calcu-
lated at the same levels of theory. The absorption spectra of
the tautomers were calculated using time-dependent den-
sity functional theory (TD-DFT) method, started from the
solution-phase optimized geometries.
o-hydroxy Schiff bases show prototropic tautomerism via
intramolecular proton transfer between the phenolic oxy-
gen and imino nitrogen atoms. The process of proton
transfer ends up with two tautomeric forms known as enol
and keto structures. These are illustrated for the title
compound in Fig. 1. The optimized molecular structure of
the title compound with numbering scheme for the atoms is
presented in Fig. 2. The selected structural parameters of
DHBE are calculated by B3LYP level with 6-311??
G(2d,p) basis set and presented in Table 1. The optimized
structure can only be compared with other similar systems
for which the crystal structures have been solved [31, 33].
As can be seen from their values in Table 1, the C10=N11
double, C3–C10 single and C4–O28 ingle bonds point out
Molecular electrostatic potential (MEP) surface is plot-
ted over the optimized geometry to elucidate the reactivity
of DHBE molecule. The HOMO and LUMO were calcu-
lated by B3LYP/6-311??G(2d,p) method. AIM 2000
software [29] was applied to obtain electron density at the
hydrogen bond critical points according to Bader’s atoms
in molecules (AIM) theory [30] at the B3LYP/6-
311??G(d,p) and B3LYP/6-311??G(2d,p) levels. Lor-
entzian function has been utilized for deconvolution of IR
spectrum using the Genplot package.
O
N
N
O
N
N
O
H
H
O
Keto form
Enol form
Fig. 1 Enol and keto tautomeric forms of title compound
Fig. 2 Theoretical optimized
geometric structure with atoms
numbering of DHBE
123

Struct Chem
Exp.c
Table 1 Optimized geometrical parameters of DHBE at B3LYP/6-311??G(2d,p) level
Parametersa
Cal.
keto
Exp.b
Exp.c
Parametersa
Cal.
keto
Exp.b
enol
enol
Bond lengths
C1–C2
Bond lengths
N11–C12
1.356
1.449
1.425
1.472
1.381
1.265
1.422
1.390
1.374
1.338
1.373
1.424
1.406
1.422
1.431
1.342
1.387
1.408
1.375
1.295
1.367
1.368
1.392
1.3978
1.412
1.418
1.393
1.389
1.382
1.383
1.392
1.390
0.96
C1–C6
1.420
1.410
1.415
1.430
1.354
1.380
1.408
1.369
1.294
1.420
1.404
1.412
1.438
1.358
1.383
1.408
1.371
1.289
C12–C13
1.400
1.404
1.386
1.379
1.398
1.401
0.994
2.629
1.735
1.4024
1.4039
1.3868
1.3807
1.3986
1.4019
1.00
C2–C3
C12–C14
C3–C4
C13–C15
C3–C10
C4–O28
C4–C5
C14–C17
C15–C19
C17–C19
C5–C6
RO–H
0.950
C6–N30
ROꢀꢀꢀN
RHꢀꢀꢀN
Bond angles
A(10,11,12)
A(11,12,14)
A(10,11,12)
2.616
1.70
2.578
1.692
2.607
1.744
C
10–N11
Bond angles
A(3,4,28)
120.8
121.0
120.1
120.3
128.3
121.3
121.7
120.3
A(3,10,11)
122.3
122.1
147.49
122.9
118.2
149.3
121.5
118.6
153.6
122.1
118.2
148.0
117.6
128.3
118.2
121.3
117.5
121.7
117.7
120.3
A(5,4,28)
A(28,29,11)
Dihedral angles
D(3,10,11,12)
Dihedral angles
D(10,3,4,28)
-179.5
1.5
-176.6
36.5
178.4
-2.4
178.0
-179.3
33.2
-0.2
179.2
179.7
1.8
-179.3
173.5
-0.4
D(10,11,12,13)
D(2,3,4,28)
179.5
D(10,11,12,14)
-178.6
-145.9
-149.1
D(31,30,6,1)
-178.3
a
For atom numbering from Fig. 2
b
c
Ref. [19]
Ref. [20]
that the compound adopts the OH tautomeric form rather
than the NH form in the solid state.
assisted hydrogen bond (RAHB) model [40]. The calcu-
˚
lated OꢀꢀꢀN distance (2.616 A) for the title compound is
˚
The theoretical values for C10=N11 (1.295 A) and C12–
˚
significantly shorter than 2.656 A which was reported for
˚
N11 (1.398 A) distances indicate the double and single
O–HꢀꢀꢀN in the class of RAHB [40]. The dihedral angles
between the rings are 36.5° for gas phase optimized OH
form and 1.5° for gas phase optimized NH form according
to the DFT calculations. The differences, which observed
between the geometries of counterparts, are caused by
underestimating the intermolecular interactions. According
to the value of dihedral angle, the title compound displays
photochromic features as mentioned in introduction.
bond character of these bonds, respectively. The bond an-
gle C3–C10–N11 is 122.9° which is consistent with the sp2
hybrid character of C10 atom, while the bond angle C10–
N11–C12 is 121.3° which is consistent with the sp2 hybrid
character of N11 atom [33–35]. Ortho position to the imine
group of Schiff base occupied with the OH is interesting
due to the existence of O–HꢀꢀꢀN hydrogen bond and pos-
sibility of tautomerism between enol-imine and keto-amine
form in 2-hydroxy Schiff base [36, 37]. In the structure of
Schiff base DHBE, there is an intramolecular O28–H29
ꢀꢀꢀN11 hydrogen bond (Fig. 2) as in the Schiff bases derived
from salicylaldehyde that always form the O–HꢀꢀꢀN type of
hydrogen bonding, regardless of the nature of the N sub-
stituent [38, 39]. It is known that there is a strong corre-
lation between the strength of the H-bond and the
delocalization of the system of conjugated double bonds,
and the effect is qualitatively interpreted by resonance-
In order to evaluate the strength of this hydrogen bond,
the PES of the molecule was explored by scanning the tor-
sional angle (H29–O28–C4–C3) at the B3LYP/6-
31G(d,p)level. As can be seen from Fig. S1, the resulting
potential energy profile shows one global minimum DHBE,
two global maxima and two local minima. The energies of
the local minima and the global maxima are 75.8 and
59.3 kJ mol-1 higher than DHBE, respectively. The large
barrier-height for rotating about (H29–O28–C4–C3) torsional
angle implies a strong hydrogen bonding in this system. The
123

Struct Chem
where n is the number of bonds in ring, a normalization
˚
constant is equal to 257.7, and Ropt is equal to 1.388 A for
C–C bonds. For the purely aromatic compounds, HOMA
index is equal to 1, but for non-aromatic compounds it is
equal to 0. The HOMA indexes in the range of 0.900–0.990
or 0.500–0.800 show that the rings are aromatic or the non-
aromatic, respectively [42]. In the current study, the cal-
culated HOMA index for C2/C3 ring is 0.902. This result
shows that C2/C3 ring in the title compound has aromatic
character. The change of HOMA index in terms of scan
coordinate is shown in Fig. S2. As expected, the aro-
maticity level of C2/C3 ring decreases with the scan coor-
Fig. 3 Relative energy profile during the proton transfer process
˚
dinate from 0.9 to 1.7 A.
Vibrational analysis
flexibility of the molecule for conversion to different con-
formers was determined by scanning the torsional angles
(N11–C10–C3–C2), (C15–C19–C22–O27) and (C10–N11–C12–
C13) as shown in Fig. S1.
The title compound consists of 45 atoms, which have 129
normal modes. Those normal modes of DHBE have been
assigned according to the detailed motion of the individual
atoms. To the best of our knowledge, there is no detailed
quantum chemical study for the molecular structure and
vibrational spectra of title compound. For visual compar-
ison, the observed and calculated FT–IR spectra of DHBE at
DFT–B3LYP method using 6-311??G(2d,p) basis set are
shown in Fig. 4. The observed IR bands and calculated wave
numbers (scaled) and assignments are given in Table 2. For
clear observation of these bands, the use of band deconvo-
lution techniques in the IR spectrum could be used. A de-
convoluted IR spectrum of DHBE was depicted in Fig. S3. It
is well known that the DFT and similar methods underes-
timate interactions like intermolecular hydrogen bonds in
gaseous phase (in vacuom). The calculated results by fre-
quency analysis for C=N, O–H and C–O stretching shows
significant deviations from experimental values due to in-
tramolecular hydrogen bond between N and O.
The intramolecular proton transfer was investigated in
the gas phase for the title compound by performing a PES
scan process at the B3LYP/6-311??G(d,p) level in order
to determine its effects on the molecular geometry. The
process was started from optimized enol geometry by
selecting O–H bond as redundant internal coordinate. The
graph of the relative energy versus the O–H bond distance
is given in Fig. 3. The energy values were calculated
relative to the energy of stable enol form. Figure 3 shows
two minima representing the stable forms. In the figure,
the keto form corresponds to a local minimum, while the
global minimum represents the stable enol form. The
potential energy needed for the transition from enol form
to keto form was calculated as 5.89 kcal mol-1
.
The effects of the intramolecular proton transfer on the
molecular geometry can be seen better via examining the
changes in HOMA index of C2/C3 ring and indicative
bond lengths for every step in the scan process. Fig. S2
reflects that the changes occurred in the lengths of
C10=N11 double, C4–O28 and C3-C10 single bonds during
Oxygen–hydrogen vibrations
The O–H stretching vibration is very sensitive to inter- and
intra-molecular hydrogen bonds and lays in the region
2,000–3,000 cm-1 in FT-IR spectrum. It gives rise to the
three vibrations as stretching, in-plane bending and out-of-
plane bending vibrations. In 3,000–1,800 cm-1 region, the
absorption band was attributed to the m(O–H) stretching
vibration which broaden owing to the formation of strong
intramolecular hydrogen bonding O–Hꢀ ꢀN in the structure.
Generally, the O–H in-plane bending and out-of-plane
bending vibrations of phenols lie in the region
1,400–1,300 cm-1 and 517–710 cm-1, respectively [43].
The remarkable absorption band in the experimental
spectrum was in 3,000–1,800 cm-1 regions and can be
attributed to the O–H stretching. It is well known that
the intramolecular and intermolecular hydrogen bond
˚
the transfer process. Bond lengths of C10=N11(1.297 A),
˚
˚
C3–C10(1.432 A) and C4–O28(1.339 A) belonging to be
stable OH tautomer were found as 1.343, 1.382 and 1.260
˚
A, where the stable NH tautomer was observed. The
figure clearly indicates that the intramolecular proton
transfer affects the double and single characters of these
indicative bonds.
One another way to confirm that the title compound
exists in enol form is to calculate the harmonic oscillator
model of aromaticity (HOMA) index by using the fol-
lowing equation for the rings [41]:
"
#
n
X
ꢀ
ꢁ
1
2
HOMA ¼ 1 ꢁ
ai Ri ꢁ Ropt
ð1Þ
n
i¼1
123

Struct Chem
have the same amplitudes while it vibrates. Normally,
carbonyl group vibrations occur in the region
1,780–1,680 cm-1 [45]. In the present study, the C=O
stretching vibration was assigned at 1,676 cm-1 in FT-IR
spectrum with very strong intensity. The dominant in-plane
C=O-bending vibration in the case of DHBE was calcu-
lated at 614 cm-1 in complete conformity with Rastogi
et al. [46]. The band observed for title compound at
590 cm-1 in the IR spectrum, 605 cm-1 (DFT) was as-
signed as C=O in-plane bending vibration mode.
(a)
Carbon–nitrogen vibrations
(b)
The C=N stretching mode was observed in the region
1,625 cm-1 [33]. The characteristic band in the FT-IR
spectrum of title compound is the appearance of the strong
band at 1,627 cm-1, attributed to the C=N stretching vibra-
tion frequency. This mode was calculated to be 1,608 cm-1
.
The C–N stretching modes are difficult, due to possible
mixing of vibrations in the 1,600–1,200 cm-1 region [47]. In
DHBE, one strong weak FT-IR band at 1,427 cm-1 was
assigned to C–N stretching vibration. The C–N in-plane
bending vibration is usually occurred at 440 cm-1 [48]. In
DHBE, a medium FT-IR band at 453 cm-1 was assigned to
C–N in-plane bending vibrations.
400
800 1200 1600 2000 2400 2800 3200 3600 4000
Wavenumber (cm-1)
Fig. 4 Comparison of observed and calculated IR spectra of DHBE
a observed; b calculated with B3LYP/6-31??G(2d,p)
Phenyl ring vibration
The phenyl ring spectral region chiefly involves the C–H,
C–C stretching, and C–C–C as well as H–C–C– bending
vibrations. The bands due to the ring C–H stretching vi-
brations is observed as a collection of weak-to-moderate
bands in the region 3,091–3,046 cm-1. The calculated
wave number for the CH–stretching modes was found in
the range 3,211–3,187 cm-1 and was matched with the
experimental FT-IR spectra. The PED for these modes
suggested that these are pure modes. The aromatic C–H in-
plane bending modes of benzene and its derivatives are
observed in the region 1,300–1,000 cm-1 [49]. In the case
of DHBE, vibrations involving the C–H in-plane bending
were found throughout the region 1,338–1,132 cm-1. The
C–H wagging (or out of bending vibrations) mode started
appearing from 824 cm-1 and had contribution up to
590 cm-1 and were assigned well in the spectra.
formations affect the O–H stretching vibration. Due to the
formation of strong intramolecular hydrogen bond between
the O28 and N11 atoms, the experimental-based vibrational
frequency of O–H stretching was shifted and widened to
the 3,000–1,800 cm-1 range. The corresponding theore-
tical value (3,161 cm-1) is very sharp because the intra-
and inter-molecular hydrogen bonds formations have not
taken into account by the DFT calculations. The band
observed at 1,427 cm-1 was assigned to O–H in-plane
bending vibration, and the band observed at 866 cm-1 was
assigned to O–H out-of-plane bending vibration for the title
compound.
Carbon–oxygen vibrations
The C–O stretching vibration in phenols appears as a
strong band in 1,300–1,100 cm-1 frequency ranges [43,
44]. According to our deconvolution results, the IR spec-
trum of DHBE indicates the presence of a medium FT-IR
band observed the C–O stretching vibrations at 1,246 cm-1
(see Fig. S4) and at 1,253 cm-1 (B3LYP). The C=O
stretching frequency of molecule strongly absorbs in the
region 1,850–1,600 cm-1. The absorptions are sensitive for
both carbon and oxygen atoms of the carbonyl group. Both
The ring stretching vibrations in each compound readily
assigned in the range 1,590–1,000 cm-1 [50]. In DHBE,
the FT-IR bands at 1,627, 1,571 and 1,356 cm-1 are as-
signed to ring stretching vibrations. All the ring stretching
modes are expected to appear in the expected range. It
shows good agreement between theoretical and ex-
perimental C–C stretching vibrations. The C–C–C bending
vibrations always occur below 600 cm-1 [51]. Three weak
FT-IR bands at 728 and 685 cm-1 are assigned to C–C–C
123

Struct Chem
Table 2 Experimental [FT-IR wave numbers (in cm-1)] and theoretical [scaled wave numbers (in cm-1)] of DHBE at B3LYP/6-311??G(d,p)
and B3LYP/6-311??G(2d,p) level of theory
B3LYP/6-311??G(d,p)
B3LYP/6-311??G(2d,p)
No.
Freq
I.IR
AR
100
Freq
I.IR
AR
IR(Neat)
Vibrational assignments (PED)
m129
m125
m122
m120
m119
m116
m112
m110
m109
3083
3,057
3,034
3,002
2,977
2,957
2,908
2,899
2,899
12
3,211
3,178
3,161
3,127
3,100
3,081
3,031
3,022
3,021
14
146
3,091(w)
3,046(vw)
2,000–3,000(vbr)
2,970(m)
2,932(m)
2,910(m)
2,886(m)
2,724(vw)
2,700(w)
1,932(w)
1,896(w)
1,752(vw)
1,676(65)
1,627(81)
1,571(84,br)
1,521(34)
1,509(34)
1,479(37,sh)
1,427(55,br)
1,381(15,sh)
1,356(61)
1,338(31)
1,308(13,sh)
1,266(29)
1,257(40)
1,246(35)
1,232(40)
1,200(46)
1,170(45,sh)
1,132(48)
1,117(30)
1,072(41)
1,040(w,sh)
1,009(22)
955(34)
msCHI(98)
552
8
231
36
7
290
20
113
164
175
36
msCHII(99)
mOH(58), maCHII(40)
maCH3(86)
20
66
52
74
26
58
177
34
65
taCH3(amin)(54), taCH2(32)
taCH3(amin)(85)
198
205
131
315
49
199
219
328
133
78
tsCH2(97)
31
mC10–H45(47), msCH3(amin)(37)
mC10–H45(92)
56
Overtone/combination
Overtone/combination
Overtone/combination
mC=O(86)
m106
m103
m100
m98
m97
m92
m89
m82
m80
m79
m76
m74
m73
m72
m71
m69
m67
m66
m65
m62
m61
m58
m54
m51
m49
m46
m43
m42
m39
m38
m37
m35
m33
m30
1,659
1,544
1,479
1,456
1,442
1,420
1,390
1,323
1,314
1,280
1,257
1,222
1,214
1,202
1,174
1,139
1,105
1,086
1,063
1,034
997
275
1,449
643
15
32
113
152
203
74
41
42
425
259
28
208
278
306
7
416
9,625
927
9
1,722
1,608
1,543
1,520
1,504
1,481
1,449
1,381
1,366
1,336
1,314
1,275
1,268
1,253
1,223
1,188
1,155
1,133
1,110
1,079
1,043
1,000
953
258
1,398
622
14
387
9,024
951
21
mC=N(16), mPhII(14), mPhII(12)
mPhI(16), dsCH2(16), mC6–N30(10)
daCH3(amin)(30), dsCH2(29)
dsCH2(33), daCH3(amin)(27)
daCH3(amin)(16)
203
754
234
123
642
49
36
264
756
202
101
592
58
106
139
169
56
dOH(15), mC6–N30(10)
dsCH3(76)
mPhII(41)
52
dCHI(34), sCH2(22), mC–O(12)
sCH2(27)
7
24
5
249
376
44
316
320
29
166
466
36
maC19–C22–CH3(29)
dCHI(39)
mC–O(23)
1,014
1,571
114
8
185
309
347
7
909
1,727
133
5
msC–C=N–C(19), maC38–N30–C31(13)
dCHII(53)
qCH2(11), mPhI(10)
dCHII(65), mPhII(14)
qCH3(amin)(25), maC31–N30–C38(21)
qCH3(amin)(22), mC–CH3(amin)(22)
qCH3(66), cC=O(25)
cC10H45(63), cCHII(10)
mC22–CH3(60)
23
3
1
23
1
12
3
13
1
0
1
0
959
4
4
31
204
123
8
914
102
18
43
17
11
8
128
8
105
17
869
908
898(9,br)
866(22)
D(13), mC–CH3(amin)(12)
cOH(45)
825
9
868
19
11
799
83
831
10
78
824(65)
cCHII(48)
755
2
788
13
3
789(32)
cCHI(31)
752
2
784
11
1
759(9,br)
728(w)
cCHI(23), qCH2(11), qCH3(amin)(13)
dCCCII(17), dCCCI(11)
dCCCI(16)
696
3
15
730
6
67
664
33
6
4
693
34
4
685(25)
633
2
662
7
2
655(13)
cphI(51), C(29)
580
39
7
14
605
37
14
590(45)
dC=O(26), mC22–CH3(12)
D(12), dphI(11)
563
3
589
8
3
554(8,sh)
510(13)
496
4
35
518
5
36
cphII(16)
123

Struct Chem
Table 2 continued
B3LYP/6-311??G(d,p)
B3LYP/6-311??G(2d,p)
Freq I.IR AR
No.
Freq
I.IR
AR
IR(Neat)
Vibrational assignments (PED)
m29
m26
479
426
3
9
5
1
501
445
3
8
5
1
480(w)
453(13)
dPhII(22)
dC22–CH3(18), D(13), dC34–C31–N30(11)
in-plane bending vibrations of DHBE. The bands that are
assigned to CCC out-of-plane bending vibrations are ob-
served at 655 and 510 cm-1 in DHBE.
because they appear at very low frequency. The band at
145 cm-1 (B3LYP) is assigned as the twisting mode sCH3.
The calculated values of m (C–CH3) were 953 and
908 cm-1. The experimental observed values in the FT-IR
spectrum at 955 and 898 cm-1 confirm the assignment on a
comparison with the calculated values.
Methylene group vibrations
For the assignments of CH2 group frequencies, basically
six fundamentals can be associated with each CH2 group,
which was expected to be depolarized [52]. The asym-
metrical CH2 stretching vibrations are generally observed
above 3,000 cm-1, while the symmetric stretch will appear
between 3,000 and 2,900 cm-1 region [53]. In this study,
the asymmetric and symmetric stretching vibrations are
observed at 2,932 and 2,886 cm-1, respectively, in FT-IR.
For n-alkyl benzenes, the assignments of the C–C stretch-
ing mode at about 1,464 and 1,290 cm-1 are quite prob-
lematic, since these bands are frequently masked by the
CH2 scissoring and wagging vibrations, respectively
[54, 55]. For DHBE, the CH2 scissoring mode has been
assigned at 1,521 and 1,509 cm-1 in FT-IR. The band at
1,170 cm-1 in FT-IR was assigned to CH2 rocking in-plane
vibration. The CH2 twisting out of plane bending vibrations
was observed at 1,338 and 1,308 cm-1 in FT-IR spectrum.
It can be seen from Fig. S4 (which shows the theoretical
FT-IR spectra along with the experimental spectra for
DHBE) that there is an excellent correlation between the
theoretical and experimental FT-IR spectra. As can be seen
from Fig. S4, experimental fundamentals have a good
correlation with B3LYP. The correlation graph follows the
linear equation, y = 73.967 ? 0.9235x; where ‘y’ is the
calculated wave number, ‘x’ is the experimental wave
number (cm-1). The value of correlation coefficient
(R2 = 0.9965) shows that there is good agreement between
experimental and calculated results.
NBO analysis
The natural bond orbital (NBO) calculations were per-
formed using NBO 3.1 program [59] as implemented in the
Gaussian03 package at the DFT/B3LYP level to under-
stand various second-order interactions between the filled
orbitals of one subsystem and vacant orbitals of another
subsystem. Delocalization of electron density between
occupied Lewis-type (bond or lone pair) NBO orbital and
formally unoccupied (anti-bond or Rydberg) non-Lewis
NBO orbital corresponds to a stabilizing donor–acceptor
interaction. NBO analysis has been performed on the
molecule at the DFT (B3LYP)/6-311??G(2d,p) level to
elucidate the intra-molecular, rehybridization and delocal-
ization of electron density within the molecule. The inter-
actions 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 E(2) associated with the delocalization
i ? j is determined as
Methyl group vibrations
The CH stretching in CH3 occurs at lower frequencies than
those of the aromatic ring (3,000–2,800 cm-1) [56]. In the
present work, CH3 asymmetric stretching is found at 2,970,
2,931 and 2,910 cm-1 in FT-IR spectrum. In many mole-
cules, the symmetric deformation appears with an intensity
varying from medium to strong and expected in the range
1,380 25 cm-1 [57]. According to our deconvolution
results, the IR spectrum of DHBE indicated that the pres-
ence of one band observed the dsCH3 frequencies at
1,381 cm-1 (see Fig. S4) and at 1381 cm-1 (B3LYP). For
the title compound, the scissoring modes of the CH3 group
are calculated to be 1,520, 1,504, 1,481 cm-1 (B3LYP) and
1,521, 1,509, 1,479 cm-1 (IR). The rocking vibrations
of CH3 group are generally observed in the region
1,070–1,010 cm-1 [58]. The band at 1,117, 1,072 and
1,040 cm-1 in the IR spectrum and at 1,110, 1,079 and
1,043 cm-1 (B3LYP) is assigned as qCH3 mode for the
DHBE. The twisting modes were not observed in the FT-IR
2
ð
Ej Ei
Þ
Fij
2
q
E ¼ DEij ¼
ð2Þ
i
2
ð
ꢁ
Þ
where qi is the donor orbital occupancy, Ei and Ej are
diagonal elements and Fij is the off-diagonal NBO Fock
matrix element. In NBO analysis, large E2 value shows the
123

Struct Chem
Table 3 Second-order perturbation theory analysis of the Fock matrix in NBO basis and intramolecular hydrogen bond lengths in different
solvents
E2(kcal mol-1
)
NꢀꢀꢀH (A)
NꢀꢀꢀO (A)
˚
O–H (A)
˚
˚
Solvent
Donor
Acceptor
Gas phase
Hexane
CH2Cl2
EtOH
LP(1)N11
LP(1)N11
LP(1)N11
LP(1)N11
LP(1)N11
BD*(1)O28–H29
BD*(1)O28–H29
BD*(1)O28–H29
BD*(1)O28–H29
BD*(1)O28–H29
20.45
21.34
22.99
23.35
23.41
0.9956
0.9974
1.0002
1.0008
1.0010
1.7350
1.7264
1.7091
1.7058
1.7052
2.6344
2.6293
2.61834
2.6165
2.6079
CH3CN
In the 13C NMR spectrum of the title compound
recorded in DMSO (Fig. 6), the imino carbon (C10) peak
was observed at 163.015 ppm, and the phenolic carbon
(C4) peak appeared at 164.180 ppm. The 13C NMR spec-
trum of the title compound shows peaks at 197.22 ppm
(C22), 152.904 ppm (C12) and 152.537 ppm (C6). The C3,
C5, C1, C2 and C19 carbons of aromatic ring are at 109.102,
97.169, 104.714, 135.123 134.092 ppm, respectively. The
C13, C14 and C15, C17 carbons of aromatic ring are at
121.331 and 130.257 ppm, respectively. The CH2(C31) and
CH3(C34) peaks of ethyl group are seen at 44.444 and
13.002 ppm, respectively (Fig. 6). The results agree well
with the reported values [31, 44]. The computed 13C and
1H NMR chemical shifts at the B3LYP/6-311??G(2d,p)
level of theory along with experimental data are given in
Table 4. As can be seen, the results obtained by using all
DFT methods are in reasonable agreement with ex-
perimental values.
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 NBO Table 3.
NBO analysis of the title compound was performed by
applying same level of theory in the enol form in different
solvents and gas phase. The interactions between donor N11
lone pair and acceptor O28–H29 bond for the title compound in
various solvents and gas phase are shown in Table 3. NBO
analysis for the title compound shows that there is a strong
interaction nN11 ? r*O28–H29. This interaction increases
with the increase in polarity of the solvent, and as a result,
O28–H29 bond weakens and lengthens. The delocalization
energy of the title compound increases with the increase in
polarity of the solvent. The increasing of delocalization en-
ergyof the title compoundindicates thatitismore stable in the
polar solvent. In addition, NꢀꢀꢀO distance shortens with the
increase in polarity of the solvent. The increase in nN11
?
r*O28–H29 delocalization with the increase in polarity of the
solvent strengthens the intramolecular hydrogen bond and
weakens and elongates the O–H sigma bond.
Molecular electrostatic potential (MEP) surface
In order to investigate the chemical reactivity of the
molecule, molecular electrostatic potential (MEP) surface
is plotted over the optimized electronic structure of DHBE
using density functional B3LYP level with 6-311??
G(2d,p) basis set. MEP is related to the electronic density
and is a very useful descriptor in understanding sites for
electrophilic and nucleophilic reactions as well as hydro-
gen bonding interactions [61]. Figure 7 shows the com-
putationally observed MEP surface map in association with
the fitting point charges to the electrostatic potential V(r)
for title compound. MEP values were calculated as de-
scribed previously, using the equation [62].
NMR spectral studies
The 1H NMR spectrum of the title compound was recorded
in DMSO (Fig. 5). Normally, the proton chemical shift of
organic molecules varies greatly with the electronic envi-
ronment of the proton. Hydrogen attached or nearby elec-
tron-withdrawing atom or group can decrease the shielding
and move the resonance of attached proton toward a higher
frequency, whereas electron-donating atom or group in-
creases the shielding and moves the resonance toward
lower frequency [60]. The resonance of hydroxyl proton is
at 12.46 ppm which is typical for intramolecular hydrogen
bonding (O–HꢀꢀꢀN) proton. The resonance of imino proton
is at 8.75 ppm. The absorption of ring protons is in the
range of 6–8 ppm, which corresponds to aromatic charac-
Z
pð~rÞdr0
X
ZA
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
vðrÞ ¼
ꢁ
ð3Þ
0
ꢂ
~
R ꢁ~rj
~r ꢁ~r
A
!
where pðrÞ is the electron density function of the molecule,
!
1
ter. In H NMR spectrum of the title compound, the ab-
ZA is the charge of nucleus A located at R , and r’ is the
sorption peaks of aromatic ring protons are between 6.07
and 7.99 ppm (Fig. 5). These results are in accordance with
the literature values [31, 44]. This result reveals that the
title compound adopts enol form in solution.
dummy integration variable. The negative (red) regions of
MEP were related to electrophilic reactivity and the posi-
tive (blue) regions to nucleophilic reactivity. These sites
give information about the region where the compound can
123

Struct Chem
1
Fig. 5 Experimental H NMR
spectra of DHBE
Fig. 6 Experimental 13C NMR
spectra of DHBE
have intermolecular interaction. In Fig. 7, this molecule
has several possible sites for the electrophilic attacks over
the oxygen atoms: O27 and O28. The maximum negative
electrostatic potential value for these electrophilic sites
calculated at B3LYP/6-311??G(2d,p) is about -22.041
and -22.036 a.u. The fitting point charges to those
electrostatic potentials are -0.238(O27) and -0.3(O28).
Also a maximum positive region is localized on the hy-
drogen atoms, indicating a possible site for nucleophilic
attack. The MEP map shows that the negative potential
sites are on electronegative atoms as well as the positive
potential sites are around the hydrogen atoms. However, a
123

Struct Chem
Table 4 Experimental and theoretical, 1H and 13C NMR isotropic
chemical shifts (with respect to TMS) of DHBE with DFT (B3LYP
6-311??G(2d,p)) method
transfer (ICT) from the end-capping electron-donor groups
to the efficient electron-acceptor groups through p-conju-
gated path. Therefore, an ED transfer occurs from the more
aromatic part of the p-conjugated system in the electron-
donor side to its electron-withdrawing part. HOMO and
HOMO–1 is second highest and lowest unoccupied mole-
cular orbitals LUMO and LUMO ? 1 as shown in Fig. 8.
The energy gap of HOMO–LUMO explains the eventual
charge-transfer interaction within the molecule, and the
frontier orbital gap in case of DHBE is found to be 3.5108 eV
obtained at TD-DFT method using 6-311??G(2d,p) basis
set. This large energy gap implies that the structure of the title
Schiff base ligand is very stable [65].
Assignment
B3LYP Exp.
Assignment B3LYP Exp.
H35,36,37,42,43,44
H24,25,26
H32,33,39,40
H9
1.97
2.67
3.67
6.44
6.51
7.53
7.63
8.44
8.69
12.86
1.12 C34,41
16.27
30.50
13.00
2.54 C23
3.39 C31,38
6.08 C5
6.34 C1
7.35 C3
7.40 C13,14
7.98 C15,17
8.75 C19
12.46 C2
C6
27.07
44.44
53.01
102.04
109.79
116.23
123.42
135.31
140.24
142.20
159.67
164.68
169.67
172.66
207.00
97.17
H7
104.71
109.10
121.33
130.26
134.09
135.12
152.54
152.90
163.02
164.18
197.22
H8
H16,18
H20,21
H45
In addition, the first 10 spin-allowed singlet–singlet
excitations for both enol and keto forms were calculated by
TD-DFT approach. TD-DFT calculations were started from
optimized geometry using the same level of theory and
performed for gas phase to calculate excitation energies.
For both enol and keto forms of the title compound,
wavelength (k), oscillator strength (f) and major contribu-
tions of calculated transitions are given in Table 5. The
absorption peaking at 384–417 nm arises excitation from
HOMO to LUMO transition in solution for enol form.
The UV–Vis spectra of the title compound in various
organic solvents (hexane, dichloromethane, ethanol and
acetonitrile) were recorded within 250–600 nm range
(Fig. 9). The characteristic UV–Vis absorption bands of the
molecule in hexane, dichloromethane, ethanol and ace-
tonitrile are comparatively given in Table 5. The absorp-
tion bands at 384(in hexane), 401 (in dichloromethane),
417 (in ethanol) and 417 nm (in acetonitrile) are attributed
p ? p*. However, new absorption band peaking at
443 nm was observed in the spectrum of the title com-
pound in EtOH (Fig. 9), which was not present in the case
of other solvents. Referring to the computational and
experimental studies, new absorption bands above 400 nm
can be attributed to the keto form of o-hydroxy Schiff bases
[31–33]. It can be said that the absorption band peaking at
H29
C12
C10
C4
C22
maximum positive region is localized on the C10-H45 bond,
indicating a possible site for nucleophilic attack.
The MEP is best suited for identifying sites for intra-
and inter-molecular interactions [63]. For the MEP surface
in the studied molecule, the weak negative regions asso-
ciated with the N11 atom and also the weak positive region
by the nearby H29 atom are indicative of intramolecular
(N11ꢀꢀꢀH29–O28) hydrogen bonding.
UV–Vis spectra analysis
The energy gap between HOMO and LUMO is a critical
parameter in determining molecular electrical transport
properties [64]. The conjugated molecules are characterized
by a highest occupied molecular orbital–lowest unoccupied
molecular orbital (HOMO–LUMO) separation, which is the
result of a significant degree of intra-molecular charge
Fig. 7 Molecular electrostatic
potential map (MEP) of DHBE.
(For interpretation of the
references to color in this figure,
the reader is referred to the web
version of the article)
123

Struct Chem
Fig. 8 Atomic orbital
compositions of the frontier
molecular orbital for DHBE
ELUMO+1= –1.0773 ev
ELUMO= –2.4892 ev
ΔE=3.5104 ev
ΔE=5.3271 ev
EHOMO= –5.9996 ev
EHOMO-1= –6.4044 ev
Table 5 Wavelength, oscillator strength, major contributions of calculated transitions in gas phase and various solvents for keto and enol forms
Exp.
Calculated
Enol form
Calculated
Keto form
k (nm) k (nm)
f
Major contribution
k (nm)
f
Major contribution
Gas phase
Hexane
CH2Cl2
EtOH
–
–
383
308
1.068 H ? L(99 %)
394
309
444
412
1.284 H-1 ? L(91 %)
0.181 H-2 ? L(53 %), H ? L ? 1(38 %)
0.029 H-1 ? L ? 1(82 %)
0.014 H ? L ? 1(91 %)
384
273
401
311
1.194 H ? L(99 %)
1.446 H-1 ? L(96 %)
0.241 H-2 ? L ? 1(46 %), H ? L ? 1(47 %) 309
0.037 H-1 ? L ? 1(84 %)
0.021 H ? L ? 1(95 %)
444
401
278
411
314
1.147 H ? L(99 %)
416
313
435
415
311
432
414
311
432
1.473 H ? L(93 %)
0.325 H-2 ? L(37 %), H ? L ? 1(58 %)
0.011 H-1 ? L ? 1(77 %), H ? L ? 1(15 %)
0.010 H-1 ? L(93 %)
417
280
443
419
296
411
314
1.114 H ? L(99 %)
1.456 H ? L(93 %)
0.343 H-2 ? L(35 %), H ? L ? 1(59 %)
0.047 H-1 ? L ? 1(34 %), H ? L ? 1(28 %)
0.009 H-1 ? L(93 %)
CH3CN
411
315
1.105 H ? L(99 %)
1.450 H ? L(92 %)
0.347 H-2 ? L(35 %), H ? L ? 1(59 %)
0.043 H-1 ? L ? 1(75 %), H ? L ? 1(22 %)
0.009 H-1 ? L(92 %)
123

Struct Chem
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
Electrochemical properties
Hexane
CH2Cl2
CH3Cl
EtOH
CH3CN
The IP is defined as the minimum energy necessary to bring
an electron from the material into a vacuum. In other words,
ionization potentials (IPs) are the energy difference between
neutral molecules and the corresponding cationic systems.
The electron affinity (EA) is defined as the first unoccupied
energy level that injected electrons coming from a vacuum
into the material would occupy. In other words, EA is the
energy difference between neutral molecules and the corre-
sponding anionic systems. IP and EA are usually used to
assess the energy barrier for the injection of holes and elec-
trons [66]. Obviously, lower reorganization energy is nec-
essary to achieve a high charge-transfer rate.
300
400
500
600
Wavelength (nm)
Fig. 9 UV–Vis absorption spectra of DHBE in different solvents
Enol form has an IP of 6.9457 eV (Table 6), which is
bigger than that of keto form (6.1925 eV), indicating the
hole-transporting ability of keto better than that of enol. On
the other hand, the electron-transporting ability of keto an
EA of 1.9495 eV should be better than that of enol with an
EA of 0.8143 eV.
384–417 nm arises from enol form and the absorption
band peaking at 443 nm arises from keto form in the
solution.
The title compound exists in enol form in the solid state,
while both enol and keto forms are shown in EtOH. The
keto form is important in the solution and stabilized by the
polar solvents through solute and solvent interactions. The
N,N-diethylamino group is an electron-donating group. The
zwitter ionic form arises before the formation of keto form.
The electron-donating N,N-diethylamino group stabilizes
zwitter ionic form and eases the formation of keto form with
resonance. However, not only the electron-donating group
but also the solvent is effective in the formation of keto
form. If the formation of keto form depended on the elec-
tron-donating group, the keto form would have observed in
all solvents. In addition, the formation of keto form cannot
be related to the polarity of solvent. Such a relation would
require the formation of keto form in acetonitrile unlike
observed results. Therefore, the proton transfer is affected
by H-donor–acceptor property of solvent instead of solvent
polarity. EtOH is a polar and protic solvent. This property
causes both enol and keto forms to be stable in solvent. The
hydrogen bond formation between the compound and sol-
vent plays an important role in the stabilization of the keto
form.
Cyclic voltammogram of supporting electrolyte is also
shown in Fig. 10. The oxidation and reduction peaks associ-
ated with the HOMO and LUMO levels, respectively. In the
part of the paper which deals with experimental results, one
should discuss EA and IP values rather than HOMO and
LUMO levels since the molecular orbital energies are not
observables but originate from quantum chemical ap-
proximations. Using cyclicvoltammetry, the IPwasestimated
fromtheonsetofthefirstoxidationpeak, whereasEA fromthe
onset of the first reduction peak. The oxidation and reduction
peaks associated with the HOMO and LUMO levels, re-
spectively. The HOMO energy level, EH, was estimated from
bellow equation [67]: EHOMO = Eox ? 4.4 V. The LUMO
energy level, EL, was obtained by adding the energy of the
HOMO–LUMO gap, DEHL, to EH value, while the energy gap
DEHL was determined from the difference between oxidation
andreductionpotentials. ItisgenerallyindicativeofaHOMO/
LUMO absorption transition to bear a significant charge-
transfer character. The higher HOMO/LUMO energy levels
than those corresponding estimations from the experimental
data may be related to various effects from conformation and
solvents, which have not been taken into account here.
Table 6 Electrochemical properties of the title compound
Comp
EHOMO/EaLUMO
IPa
EAa
IP/EAa
Eoxonsetb (V)
1.049
EHOMO/EcLUMO
Enol
Keto
a
-5.5600/-2.0892
-5.6261/-2.3594
6.9457
6.1925
0.8143
1.9495
6.9457/0.8143
6.1925/1.9495
5.449/1.938
DFT/B3LYP calculated values
b
c
Oxidation potential in DMSO (2 9 10-3 mol L-1) containing 0.1 mol L-1 Bu4NBF4 with a scan rate of 100 mV s-1
EHOMO was calculated by Eox ? 4.4 V, and ELUMO = EHOMO - DEHL [55]
123

Struct Chem
350
300
250
200
150
100
50
0
C
p,m
0
S
m
0
H
m
E
Fig. 10 Cyclic voltammogram of 2 9 10-3 M title compound. Scan
0
rate 100 mV s-1, electrolyte 0.1 M Bu4NBF4 in DMSO
0
100
200
300
400
500
600
700
800
900
Temperature (K)
Nonlinear optical properties
Fig. 11 Correlation graph of thermodynamic properties and tem-
peratures by B3LYP/6-311??G(2d,p) for DHBE molecule
NLO is at the forefront of current research because of its
importance in providing the key functions of frequency
shifting, optical modulation, optical switching, optical
logic, and optical memory for the emerging technologies in
areas such as telecommunications, signal processing, and
optical connectors [68]. Organic molecules that exhibit
extended p conjugation, in particular, show enhanced
second-order NLO properties [69]. The total static dipole
moment (l), the linear polarizability (a), anisotropy po-
larizability(Da) and the first hyperpolarizability (b) using
the x, y, z components are defined as [40]:
than that of the standard NLO material urea (0.13 9
10-30esu) [70]. These results indicate that title compound is
a good candidate of nonlinear optical material.
Thermodynamic functions
The standard thermodynamic functions, namely the heat
capacity (C0p,m), entropy (Sm0 ), enthalpy (H0m) and molecular
energy (E) were calculated at B3LYP/6-311??G(2d,p)
level for varying temperatures from 100 to 700 K. The
results obtained on the basis of vibrational analysis are
shown in Table S2. The results reveal that an increase in
temperature causes an increase in heat capacities, en-
tropies, enthalpies and molecular energy due to increasing
intensities of molecular vibrations [71].
1
2
ꢃ
ꢄ
l ¼ l2x þ l2y þ l2z
ð4Þ
ð5Þ
ꢀ
ꢁ
1
a
¼
axx þ ayy þ azz
tot
3
h
ꢀ
ꢁ
ꢀ
ꢁ
1
2
2
2
pffiffi
Da ¼
axx ꢁ ayy þ ayy ꢁ azz þðazz ꢁ axxÞ þ6 ax2z
2
The corresponding quadratic equations obtained by
B3LYP/6-311??G(2d,p)are as follows, and the related
figure was shown in Fig. 11.
i
1
2
þ6 a2xy þ6 a2yz
ð6Þ
ð7Þ
h
ꢀ
ꢁ
ꢀ
ꢁ
2
2
For DHBE by B3LYP/6-311??G(2d,p),
ꢀ
hbi ¼ bxxx þ byyy þ bzzz þ byyy þ byzz þ byxx
ꢁ
Cp0;m ¼ :4424 þ 0:2997T ꢁ 1 ꢂ 10ꢁ4T2
R2 ¼ 0:9991
i
1
2
ꢀ
ꢁ
2
ꢀ
ꢁ
ꢁ
þ bzzz þ bzxx þ bzyy
S0m ¼ 63:343 þ 0:2968T ꢁ 5 ꢂ 10ꢁ5T2 R2 ¼ 1
ꢀ
Hm0 ¼ 1:8223 þ 0:0829T ꢁ 2 ꢂ 10ꢁ4T2 R2 ¼ 1
It is well known that the higher values of dipole mo-
ment, molecular polarizability and hyperpolarizability are
important for more active NLO properties. The numerical
values of above-mentioned parameters were listed in Table
S1. The calculated dipole moment is equal to 8.276 and
8.240 Debye (D) in DHBE which is nearer to the value for
urea (l = 1.3732 D). The calculated polarizability aij
have nonzero and zero values and are dominated by the
diagonal components. Total polarizability (atot) calculated
as -20.257 9 10-24 and -20.211 9 10-24esu for title
molecule. The calculated first hyperpolarizability values
(\b[) of the title compound are 44.404 9 10-30 and
43.950 9 10-30esu, which comparable with the reported
values of similar derivatives [31, 32] and which are greater
ꢀ
ꢁ
E ¼ 234:84 þ 0:011T ꢁ 1 ꢂ 10ꢁ5T2 R2 ¼ 0:9999
ð8Þ
They can be used to compute the other thermodynamic
energies according to relationship of thermodynamic
functions and estimate directions of chemical reactions
according to the second law of thermodynamics in ther-
mochemical field. Notice that all thermodynamic calcula-
tions were done in gas phase, and they could not be used in
solution.
The values of some thermodynamic parameters (such
as zero-point vibrational energy (ZPVE), thermal energy,
specific heat capacity, rotational constants, rotational
123

Struct Chem
Fig. 12 Atomic charge
distribution of Enol and Keto
forms (Color figure online)
Table 7 Calculated energy values of DHBE by B3LYP/6-311??G(2d,p) basis set
Gas (NH)
Gas (OH)
Hexane (OH)
Dichloromethane (OH)
Ethanol (OH)
Acetonitrile (OH)
Etotal (hartree)
-997.52473
-5.621
-5.715
-0.087
-0.047
-5.534
2.854
-997.53046
-5.600
-6.727
-2.489
-0.389
-3.111
4.045
-997.53535
-5.655
-6.424
-2.511
-1.121
-3.144
4.083
-997.54259
-5.715
-6.492
-2.541
-1.196
-3.174
4.128
-997.54460
-5.785
-6.519
-2.582
-1.221
-3.203
4.184
-997.54467
-5.833
-6.519
-2.604
-1.221
-3.229
4.219
EHOMO (eV)
EHOMO–1 (eV)
ELUMO (eV)
ELUMO?1 (eV)
EHOMO–LUMO gap (eV)
Chemical potential (l)
Global hardness (g)
Global softness (S)
Electronegativity (v)
Electrophilicity indices (x)
2.767
1.555
1.572
1.587
1.602
1.615
0.361
0.643
0.636
0.630
0.624
0.619
-2.854
1.472
-4.045
5.259
-4.083
5.302
-4.128
5.369
-4.184
5.464
-4.219
5.511
temperature and entropy) of title compound are listed in
Table S3. The variation in ZPVE seems to be significant.
The ZPVE is higher by the B3LYP/6-311??G(2d,p) level
than by the B3LYP/6-311??G(d,p) level.
C4, C6 and C12), the carbonyl carbon C22 and bridging C10
atom bear positively charges, while the remaining carbon
atoms of the phenyl rings bear negative charges.
Charge distribution
Reactive descriptors of DHBE
The natural atomic charge has an important role in the
application of quantum mechanical calculation for the
molecular system. The natural atomic charge of enol and
keto forms calculated by B3LYP/6-311??G(2d,p) method
is shown in Fig. 12. The charge distributions over the
atoms suggest the formation of donor and acceptor pairs
involving the charge transfer in the molecule. The charge
distribution of DHBE shows that the carbon atom attached
with hydrogen atoms is negative, whereas the remaining
carbon atoms are positively charged. The oxygen and ni-
trogen atoms have more negative charges, whereas all the
hydrogen atoms have positive charges. Resulting in the
positive charges on the C4, C6, C10, C12, C22, H29, H24, H25,
H26 and H21 shows the direction of delocalization. The
oxygen and nitrogen atoms in the molecule bear negative
charges; the phenyl ring carbon atoms with substituent (i.e.,
Global reactivity parameters
The NH and OH tautomers of the title compound are given
in Fig. 1. To investigate the tautomeric stability, opti-
mization calculations at B3LYP/6-311??G(2d,p) level
were performed for the NH and OH forms of the title
compound. The energies of frontier molecular orbitals
(EHOMO, ELUMO), energy band gap (EHOMO- ELUMO),
electronic chemical potential (l), electronegativity (v),
global hardness (g), global softness (S) and electrophilicity
indices (x) [72] of DHBE have been listed in Table 7. On
the basis of EHOMO and ELUMO, these are calculated by
using the below equations.
1
l ¼ ðEHOMO þ ELUMO
Þ
ð9Þ
2
123

Struct Chem
1
For nucleophilic attack fkþ ¼ qkðN þ 1Þ ꢁ qkðNÞ
ð14Þ
ð15Þ
v ¼ ꢁl ¼ ꢁ ðEHOMO þ ELUMO
Þ
ð10Þ
ð11Þ
ð12Þ
2
For electrophilic attack fkꢁ ¼ qkðNÞ ꢁ qkðN ꢁ 1Þ
1
g ¼ ðEHOMO ꢁ ELUMO
Þ
1
2
For free radical attack fk0 ¼
½
kðN þ 1Þ ꢁ kðN ꢁ 1Þꢃ
q
q
2
1
S ¼
ð16Þ
2g
The condensed-to-atom quantity, xak corresponding to
local electrophilicity index, x(r), was obtained as described
previously [21]
l2
x ¼
2g
ð13Þ
The chemical hardness is quite useful to explain the
chemical stability. The molecules having a large HOMO–
LUMO energy gap will be more stable and less reactive
than soft molecules having small HOMO–LUMO energy
gap [73]. From Table 7, the total energy of the OH form is
lower than the NH form, while chemical hardness of the
OH form is greater than the NH one, which indicates that
the OH form of the title compound is more stable than its
NH form in the gas phase. In additional, in order to eval-
uate the solvent effect to the herein above-mentioned
properties of the title compound, we carried out calcula-
tions in four kinds of solvent (hexane, dichloromethane,
ethanol and acetonitrile) with the B3LYP/6-311??G(2d,p)
level using the PCM model, and the results are given in
Table 7. From Table 7, we can conclude that the total
molecular energies obtained by PCM method decrease with
the increasing polarity of the solvent, while the hardness
will increase with the increase in the polarity of the solvent.
The energy gap (DE) between the highest occupied mole-
cular orbital (HOMO) and the lowest lying unoccupied
molecular orbital (LUMO) increase in enol form when an
increase occurs in the polarity of the solvent. According to
these results, the stability of the title compound increases in
going from the gas phase to the solution phase.
xak ¼ xfka
ð17Þ
where a = ?, - and 0 refer to nucleophilic, electrophilic
and free radical reactions, respectively. Fukui functions,
local softness and local electrophilicity indices for selected
atomic sites in DHBE have been listed in Table S4. The
reactivity orders for the nucleophilic attack; the reactivity
of C4 in the substitution was found to have a loss in DHB
Eat 6-311??G(d,p) level. The nucleophilic reactivity
order was C4 [ C23 at 6-311??G(d,p) basis set on
DHBE. Note it was observed a major reactivity for
this kind of attack in comparison with the electrophilic
attack. On the other hand, the reactivity order for the
electrophilic case was N30 [ C3 [ N11 [ C1 [ C19
[
C5 [ C27 [ C13 [ C14 [ O28 at 6-311??G(d,p) basis sets
on DHBE. If one compares the three kinds of attacks, it is
possible to observe that the electrophilic attack shows a
more reactivity in comparison with the free radical and
nucleophilic case.
Topological parameters
One of the most useful implements to characterize atomic
and molecular interactions, particularly hydrogen bonding,
is the topological analysis using ‘atoms in molecules’
(AIM) theory [42]. According to AIM theory, any chemical
bond including hydrogen bonding is characterized by the
existence of bond critical points (BCPs). After the bond
critical points have been localized, several properties can
be calculated at their position in space. Among these, qBCP
or the charge density at the bond critical point is of chief
importance. Laplacian of the charge density at the bond
The usefulness of this new reactivity quantity has recently
demonstrated in understanding the toxicity of various pol-
lutants in terms of their reactivity and site selectivity [74].
The computed electrophilicity index of DHBE describes the
biological activity of drug–receptor interaction.
Local reactivity descriptors
2
The most relevant local descriptor of reactivity is the Fukui
function, the derivative of the electronic chemical potential
with respect to the external potential due to the compen-
sating nuclear charges in the system. For a system of N
electrons, independent calculations are to be made for
corresponding N ? 1, N - 1 and N are total electrons
present in anion, cation and neutral state of molecules,
respectively. Natural population analysis yields gross
charges qk (N ? 1), qk(N - 1), qk(N), and for all atoms k.
In a finite difference approximation, the condensed Fukui
functions are given by the equations:
critical point, r qBCP, and the ellipticity are the two
derived quantities. The latter provides a measure of the
magnitude to which charge is favorably accumulated in
given plane. It has been observed that for closed-shell in-
teractions, as found in ionic bonds, hydrogen bonds and
2
van der Waals molecules, r qBCP should be positive (in
the range 0.015–0.15 a.u.) and q low (0.002–0.040 a.u.).
The values mentioned here are according to Koch and
Popelier criteria [75] based on AIM theory. Molecular
graph of the dimer is shown in Fig. 13. As indicated, in
addition to usual bonds, the molecular graphs indicate a BP
123

Struct Chem
Fig. 13 Molecular graphs of
DHBE, red points indicate the
bond critical points (BCPs)
between bonded atoms
Table 8 Topological
parameters for hydrogen bonded
interactions
Parameters
O–HꢀꢀꢀN(BCP)
d,pa
2d,pb
Electron density
0.0498 a.u.
0.0495 a.u.
Laplacian of electron density
Lagrangian kinetic energy G(r)
Hamiltonian kinetic energy K(r)
Potential energy density V(r)
H-bond energy
0.0278 a.u.
0.0276 a.u.
0.0368 a.u.
0.0360 a.u.
-0.0091 a.u.
-0.0459 a.u.
14.4011 kcal mol-1
-0.0084 a.u.
-0.0445 a.u.
13.9619 kcal mol-1
a
B3LYP/6-311??G(d,p)
b
B3LYP/6-311??G(2d,p)
and a BCP between nitrogen and hydrogen, which confirms
that there is an intramolecular hydrogen bond (H-bond) in
these molecules. Interestingly, each BCP contains a wealth
of chemical information that properly describes the nature
of the corresponding chemical bond. The values of electron
than 1.0) have been stated for extraordinarily strong hy-
drogen bonding in other compounds [78].
In contrast to this largely electrostatic and rather direc-
tional interaction, evidence also suggests that a closed-shell
stabilizing interaction can occur between hydrogen atoms
that are electrically neutral, close to electrical neutrality, or
bearing identical or similar charges. The identity or simi-
larity of these charges is due to molecular symmetry or
similarity of the electronic environment, respectively, of
the two hydrogen atoms involved in this bonding. Cio-
slowski and Mixon [79] reported atomic interaction lines
connecting hydrogen atoms separated by short distances
2
density, qBCP, Laplacian of electron density, r qBCP, ki-
netic energy density, GBCP, potential energy density, VBCP
,
and electronic energy density, at the BCP are the pa-
rameters that are usually used to characterize a chemical
bond. These values for the BCP of the H-bonds in the
compound of the current work have been listed in Table 8.
The value of qBCP of this compound is slightly larger than
that of normal hydrogen bonds. This suggests that these
interactions should be stronger than normal H-bonds, in
view of the fact that there is a linear correlation between
qBCP and H-bond energy [76]. The energy of NꢀꢀꢀH–O
hydrogen bond can be calculated using the relationship
EHB = V(rBCP)/2 described by Espinosa et al. [77]. In case
of DHBE, EHB has been calculated to be 14.4011 kcal/mol
by B3LYP/6-311??G(d,p) and 13.9619 kcal/mol B3LYP/
6-311??G(2d,p) methods.
˚
(dHꢀꢀꢀH B 2.18 A) in several polycyclicaromatic hydrocar-
bons (PAHs). Cioslowski and Mixon paper is credited for
being the first to report the existence of this interaction in
angular PAHs and for obtaining functional dependencies
between dHꢀꢀꢀH and several properties determined directly at
the BCP or derived from them. Since the H–H is locally
stabilizing, and since these paths are present in equilibrium
geometries where there are no net forces on the nuclei, they
will be referred to as ‘bond paths.’
The ratio G/qBCP may be used to define the character of
the interaction, where G is kinetic energy density and is
always positive. This ratio may be larger than 1.0 for
closed shell (hydrogen bonding, ionic bonds and van der
Waals interaction) [42]. The ratio G/qBCP in the present
study is 0.739, which is close to 1.0 for the hydrogen
bonding. Similar results (with G/qBCP value slightly lower
Figure 13 shows the existence of hydrogen–hydrogen
(HꢀꢀꢀH) bonds. For the C–HꢀꢀꢀH–C contacts analyzed
here, the values of electron density for HꢀꢀꢀH links lie
within the range of 0.005 –0.015 a.u. and Laplacian are
0.004–0.014 a.u. for B3LYP/6-311??G(2d,p) calcula-
tions. The H-bond energy for title compound amounts to
0.78–2.85 kcal/mol. Hence, if one assumes that the
123

Struct Chem
10. Crouse KA, Chew K-B, Tarafder MTH, Kasbollah A, Ali AM,
Yamin BM, Fun H-K (2004) Polyhedron 23:161–168
11. Chandra S, Gupta LK (2005) Transit Met Chem 30:630–635
12. Taggi AE, Hafez AM, Wack H, Young B, Ferraris D, Lectka T
(2002) J Am Chem Soc 124:6626–6635
CHꢀꢀꢀHC interactions analyzed here may be classified as
H-bonds, they are weak H-bonds.
13. Layer RW (1963) Chem Rev 63:489–510
14. Atkinson RS, Barton D, Ollis WD (1979) Comprehensive organic
chemistry. Pergamon, Oxford
15. Du¨rr H, Bouas-Laurent H (2003) Photochromism: molecules and
systems: molecules and systems. Gulf Professional Publishing,
Houston
16. Gill PMW, Johnson BG, Pople JA, Frisch MJ (1992) Chem Phys
Lett 197:499–505
17. Chattopadhyay B, Basu S, Chakraborty P, Choudhuri SK,
Mukherjee AK, Mukherjee M (2009) J Mol Struct 932:90–96
18. Kluba M, Lipkowski P, Filarowski A (2008) Chem Phys Lett
463:426–430
19. Eschwege KGV, Swarts JC (2010) Polyhedron 29:1727–1733
20. Becke AD (1993) J Chem Phys 98:5648–5652
21. Lee C, Yang W, Parr RG (1988) Phys Rev B 37:785–789
22. Miehlich B, Savin A, Stoll H, Preuss H (1989) Chem Phys Lett
157:200–206
23. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, Montgomery Jr JA, Vreven T, Kudin KN, Burant
JC, Millam JM, Iyengar SS, Tomasi J, Barone V, Mennucci B,
Cossi M, Scalmani G, Rega N, Petersson GA, Nakatsuji H, Hada
M, Ehara M, Toyota K, Fukuda R, Hasegawa J, Ishida M,
Nakajima T, Honda Y, Kitao O, Nakai H, Klene M, Li X, Knox
JE, Hratchian HP, Cross JB, Adamo C, Jaramillo J, Gomperts R,
Stratmann RE, Yazyev O, Austin AJ, Cammi R, Pomelli C,
Ochterski JW, Ayala PY, Morokuma K, Voth GA, Salvador P,
Dannenberg JJ, Zakrzewski VG, Dapprich S, Daniels AD, Strain
MC, Farkas O, Malick DK, Rabuck AD, Raghavachari K,
Foresman JB, Ortiz JV, Cui Q, Baboul AG, Clifford S, Cio-
slowski J, Stefanov BB, Liu G, Liashenko A, Piskorz P, Ko-
maromi I, Martin RL, Fox DJ, Keith T, Al-Laham MA, Peng CY,
Nanayakkara A, Challacombe M, Gill PMW, Johnson B, Chen
W, Wong MW, Gonzalez C, Pople JA (2004) Gaussian 03, Re-
vision C.02. Gaussian, Wallingford
Conclusions
In this study, we have synthesized a new Schiff base
compound, (E)-1-(4-(4-(diethylamino)-2-hydroxybenzyli-
deneamino)phenyl)ethanone, and characterized by spec-
troscopic and structural techniques as well as the
theoretical methods. FT-IR, NMR and UV–Vis methods
confirm the OH form of the title compound. The PES
scanned process in gas phase shows that the potential
barrier is 5.89 kcal mol-1 to transition from the OH
tautomeric form to the NH tautomeric form. This
intramolecular proton transfer affects the molecular
geometry by changing the aromaticity of C2/C3 ring and
lengths of the indicative bonds. UV–Vis spectra of the title
compound were recorded in different organic solvents in
order to investigate the dependence of tautomerism on
solvent types. The results show that the title compound
exists in both keto and enol forms in EtOH, while it has
enol form in hexane, CH2Cl2 and CH3CN. The computa-
tional studies on the nonlinear optical properties of the title
compound show that the title compound can be used as a
good nonlinear optical material. The HOMO–LUMO en-
ergy gap and implications of the electronic properties are
discussed. In addition, thermodynamic properties were
obtained in the range of 100–800 K. Fukui functions, local
softness and electrophilicity indices for atomic sites in
DHBE have been calculated.
We hope the results of this study will help researchers to
design and synthesis new materials.
24. Scott AP, Radom L (1996) J Phys Chem 3654:16502–16513
25. Karabacak M, Cinar M, Kurt M (2009) Spectrochim Acta A
74:1197–1203
26. Millam J, Al-Nielsen A, Al-Holder A., Al-Hiscocks J (2004)
Gaussview 4.1.2. Gaussian, Inc. Wallingford, CT
Acknowledgments Authors are grateful to the Damghan University
for financial support.
´
27. Jamroz H (2013) Spectrochim Acta A 114:220–230
28. Wolinski K, Hinton JF, Pulay P (1990) J Am Chem Soc
112:8251–8260
29. Biegler Konig FW, Schonbohm J, Bayles D (2001) J Comput
Chem 22:545–559
30. Bader RFW (1990) Atoms in molecules. Wiley Online Library
References
˘
31. Albayrak C¸ , Kas¸tas¸ G, Odabas¸oglu M, Frank R (2011) Spec-
trochim Acta A 81:72–78
1. Cohen MD, Schmidt GMJ, Flavian S (1964) J Chem Soc
2041–2051
32. Albayrak C¸ , Frank R (2010) J Mol Struct 984:214–220
33. Khalaji AD, Grivani G, Seyyedi M, Fejfarova K, Dusek M (2013)
Polyhedron 49:19–23
2. Koll A, Janski J, Karpfen A, Wolschann P (2010) J Mol Struct
976:19–29
´
´
3. Papic S, Koprivanac N, Grabaric Z, Parac-Osterman Ð (1994)
34. Morshedi M, Amirnasr M, Slawin AMZ, Woollins JD, Khalaji
AD (2009) Polyhedron 28:167–171
35. Morshedi M, Amirnasr M, Triki S, Khalaji AD (2009) Inorg
Dyes Pigments 25:229–240
4. McAuliffe A, Parish RV, Abu-El-Wafa SM, Issa RM (1986)
Inorg Chim Acta 115:91–94
Chim Acta 362:1637–1640
¨
5. Zolezzi S, Spodine E, Decinti A (2002) Polyhedron 21:55–59
6. Ambike V, Adsule S, Ahmed F, Wang Z, Afrasiabi Z, Sinn E,
Sarkar F, Padhye S (2007) J Inorg Biochem 101:1517–1524
7. Jones RD, Summerville DA, Basolo F (1979) Chem Rev
79:139–179
¨
¨
36. Unver H, Yildiz M, Du¨lger B, Ozgen O, Kendi E, Durlu TN
(2005) J Mol Struct 737:159–164
37. Unver H, Yildiz M, Ozay H, Durlu TN (2009) Spectrochim Acta
A 74:1095–1099
38. Elmali A, Elerman Y (1998) J Mol Struct 442:31–37
39. Elmali A, Elerman Y (1998) J Mol Struct 443:123–130
8. Foundation H (1981) J Am Chem Soc 2:4073–4081
9. Ismail TMA (2005) J Coord Chem 58:141–151
123

Struct Chem
40. Gilli G, Bellucci F, Ferretti V, Bertolasi V (1989) J Am Chem
Soc 111:1023–1028
59. Glendening ED, Reed AE, Carpenter JE, Weinhold F (1988)
NBO, version 3.1. There is No Corresp. Rec. This Ref
´
41. Krygowski TM, Cyranski MK (2001) Chem Rev 101:1385–1419
60. Subramanian N, Sundaraganesan N, Jayabharathi
Spectrochim Acta A 76:259–269
61. Scrocco E, Tomasi J (1978) Adv Quantum Chem 11:115–193
62. Politzer P, Murray JS (2002) Theor Chem Acc 108:134–142
63. Politzer P, Concha MC, Murray JS (2000) Int J Quantum Chem
80:184–192
J (2010)
42. Filarowski A, Kochel A, Kluba M, Kamounah FS (2008) J Phys
Org Chem 21:939–944
43. Subramanian MK, Anbarasan PM, Manimegalai S (2009) J Ra-
man Spectrosc 40:1657–1663
44. Silverstein R, Webster F (2006) Spectrometric identification of
organic compounds. Wiley, NY
64. Fukui K (1982) Science 218:747–754
45. Mohan J (2001) Organic spectroscopy, principle and applications.
New Age International (P) Limited Publishers, New Delhi
46. Rastogi VK, Palafox MA, Lang K, Singhal SK, Soni RK, Sharma
R (2006) Indian J Pure Appl Phys 44:653–660
47. Woolley MS, Otero JC, Marcos JI, Lo I (1998) J Mol Struct
470:241–246
65. Tezer M, Kanbul S (2009) Procedia Soc Behav Sci 1:390–394
66. Li X, Liu X, Wu Z, Zhang H (2008) J Phys Chem A
112:11190–11197
67. Wang HY, Chen LF, Zhu XL, Wang C, Wan Y, Wu H (2014)
Spectrochim Acta A 121:35–39
68. Bernstein J, Davis RE, Shimoni L, Chang N (1995) Angew
Chemie Int Ed Engl 34:1555–1573
69. Bondi A (1964) J Phys Chem 68:441–451
48. Krishnakuma Y, Xavier RJ (2003) Indian J Pure Appl Phys
41:597–601
49. Arjunan V, Sakiladevi S, Rani T, Mythili CV, Mohan S (2012)
Spectrochim Acta A 88:220–231
70. Adant C, De Chimie S, De Recherche C, York N (1995) Int J
Quantum Chem 507:497–507
50. Parimala K, Balachandran
81:711–723
51. Gunasekaran S, Sailatha E (2009) Indian J Pure Appl Phys
47:259–264
52. Okamoto H, Inaba R, Yoshihara K, Tasumi M (1993) Chem Phys
Lett 202:161–166
53. Paulraj EI, Muthu S (2013) Spectrochim Acta A 106:310–320
54. Wiberg KB, Shrake A (1973) Spectrochim Acta A 29:583–594
55. Sundaraganesan N, Anand B, Meganathan C, Joshua BD, Saleem
H (2008) Spectrochim Acta A 69:198–204
V
(2011) Spectrochim Acta
A
71. Alcolea Palafox M (2000) Int J Quantum Chem 77:661–684
72. Padmanabhan J, Subramanian R, Subramanian V, Chattaraj PK
(2007) J Phys Chem A 111:1358–1361
¨
¨
˙
73. Ozbek N, Kavak G, Ozcan Y, Ide S, Karacan N (2009) J Mol
Struct 919:154–159
74. Subramanian V, Chattaraj PK (2003) Internet Electron J Mol Des
2:798–813
75. Koch U, Popelier PLA (1995) J Phys Chem 99:9747–9754
76. Pakiari AH, Eskandari K (2006) J Mol Struct (Theochem)
759:51–60
56. Dollish FR, Fateley WG, Bentley FF (1974) Characteristic
Raman frequencies of organic compounds. Wiley Interscience,
New York
57. Silverstein RM, Bassler GC, Morrill TC (1981) Spectroscopic
identification of organic compounds, 4th edn. Wiley, New York
58. Pasterny K (2002) J Mol Struct 616:17–32
77. Espinosa E, Molins E, Lecomte C (1998) Chem Phys Lett
285:170–173
78. Hibbs DE, Overgaard J, Piltz RO (2003) Org Biomol Chem
1:1191–1198
79. Cioslowski J, Mixon ST (1992) Can J Chem 70:443–449
123