Synthesis, crystal structure and theoretical studies of a Schiff base 2-[4-hydroxy benzylidene]-amino naphthalene

Article abstract of DOI:10.1016/j.saa.2014.07.016

The molecular structure of a new Schiff base, 2-[4-hydroxy benzylidene]-amino naphthalene (HBAN) has been examined by HF and B3LYP/6-311++G(d,p) calculations. The X-ray structure was determined in order to establish the conformation of the molecule. The c

Full text of DOI:10.1016/j.saa.2014.07.016

Accepted Manuscript
Synthesis, crystal structure and theoretical studies of a Schiff base 2-[4-hydroxy
benzylidene]-amino naphthalene
C. Arunagiri, A. Subashini, M. Saranya, P. Thomas Muthiah, K. Thanigaimani,
I. Abdul Razak
PII:
S1386-1425(14)01083-X
http://dx.doi.org/10.1016/j.saa.2014.07.016
SAA 12432
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 March 2014
21 June 2014
2 July 2014
Please cite this article as: C. Arunagiri, A. Subashini, M. Saranya, P. Thomas Muthiah, K. Thanigaimani, I. Abdul
Razak, Synthesis, crystal structure and theoretical studies of a Schiff base 2-[4-hydroxy benzylidene]-amino
naphthalene, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/
10.1016/j.saa.2014.07.016
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Synthesis, crystal structure and theoretical studies of a Schiff base
2-[4-hydroxy benzylidene]-amino naphthalene
C. Arunagiri a, A. Subashini b*, M. Saranya b, P. Thomas Muthiah c,
K. Thanigaimani d, I. Abdul Razakd
a PG & Research Department of Physics, Government Arts College, Ariyalur – 621 713,
(TN) India.
b* PG & Research Department of Chemistry, Seethalakshmi Ramaswami College,
Tiruchirappalli, 620 002, (TN) India.
c School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, (TN) India.
d X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM,
Penang, Malaysia.
ABSTRACT
The molecular structure of a new Schiff base, 2-[4-hydroxy benzylidene]-amino
naphthalene (HBAN) has been examined by HF and B3LYP/ 6-311++G(d,p) calculations. The
X-ray structure was determined in order to establish the conformation of the molecule. The
compound, C17H13NO, crystallizes in the orthorhombic, P212121 space group with the cell
dimension, a = 6.2867(2), b = 10.2108(3), c = 19.2950(6) Å, α = β = γ = 90° and z = 4. The
asymmetric unit contains a molecule of a Schiff base. A strong intermolecular O–H N and a
weak C–H O hydrogen bonds stabilized the crystal structure. The vibrational spectra of HBAN
have been calculated using density functional theoretical computation and compared with the
experimental. The study is extended to the HOMO - LUMO analysis to calculate the energy gap
(ꢀ), Ionization potential (I), Electron Affinity (A), Global Hardness (η), Chemical Potential (ꢁ)
and Global Electrophilicity (w). The calculated HOMO and LUMO energy reveals that the
charge transfer occurs within the molecule.
Keywords: Schiff base; Crystal structure; FT-IR; FT-Raman spectra; Hyperpolarizability;
HOMO-LUMO energy gap
*Corresponding author’s. Tel.: +91 431-2231521.
E-mail address: asubashini2k4@yahoo.co.in (A. Subashini).
1

1. Introduction
During the last few decades, there has been a considerable interest in the chemistry of
Schiff base compounds [1]. Schiff bases exhibit unique properties which make them favourable
for an array of applications such as catalysis and medicinal chemistry [2]. Most Schiff bases have
antibacterial, anticancer, antinflammatory and antitoxic properties [3]. Moreover, Schiff bases
have the added advantage of being readily derivatized and their imino nitrogen atoms possess
high thermodynamic stability towards various metal centres. Schiff bases have been widely
explored for industrial applications also and the presence of imine group (-N=CH-) which
imparts the biological activity. The synthesis and crystal structures of related Schiff base
compounds, bis{4-[(Z)-N′-(4-hydroxybenzylidene) hydrazino]-8- (trifluoromethyl)-quinolinium}
sulfate tetra hydrate [4], (E)-1-(4-methylphenyl)ethanone [8-(trifluoromethyl) quinolin-4-yl]
hydrazone [5], 1-(4-{[8-(trifluoromethyl) quinolin-4-yl]amino} phenyl)-ethanone [6] and 2-(4-
methoxyphenyl)-6-trifluoromethyl-1H-pyrrolo[3,2-c] quinoline monohydrate [7] have been
reported. Recently, Jasinski et. al. [8] studied synthesis, crystal structures and theoretical studies
of four Schiff bases derived from 4-hydrazinyl-8- (trifluoro methyl) quinoline and FT-IR, FT-
Raman spectral and conformational studies on (E)-2-(2-hydroxybenzylidenamino)-3-(1H-indol-
3yl) propionic acid have been reported by Saleem et al [9]. Crystal structure and theoretical
studies of 2-(naphthalen-2-ylimino methyl) phenol was also reported by Arunagiri et al. [10,
11].
In continuation of our work on the synthesis of Schiff base, we report herein the crystal
structure of the title compound 2-[4-hydroxy benzylidene]-amino naphthalene (HBAN).
Literature survey reveals that to the best of our knowledge neither the complete X-ray
crystallography, IR and Raman spectra nor the force field for HBAN have been reported so for.
Therefore the present investigation was undertaken to study the vibrational spectra of the title
2

compound completely and to identify the various modes with greater wavenumber accuracy. The
ab initio and DFT calculation has been performed to support our wavenumber assignments, bond
parameters, hyperpolarizability calculation and HOMO–LUMO band gap have also been studied.
2. Experimental Details
2.1. Synthesis
The title compound was synthesized using a procedure reported in the literature [12].
Solution of 2–naphthylamine (2NA) (0.143g, 1mmol) stirred in 20ml ethanol was added
dropwise a solution of 4-hydroxybenzaldehyde (4HB) (0.122g, 1mmol) in 20ml ethanol. After
the addition was complete, the reaction mixture was heated at 323K for 2 hours with constant
stirring. The precipitate was separated by filtration, washed with diethyl ether and dried to give
brown solid which was recrystallized from (3:1) CH3CN: Ethanol (Scheme 1). The bronze
crystals are suitable for X-ray diffraction. The melting point of the Schiff base was found to be
210°C.
2.2. Instrumentation
The FT-IR spectrum of this compound was recorded in the region 4000–400 cm-1 on a
BRUKER IFS 66V spectrophotometer using the KBr pellet technique. The spectrum was
recorded at room temperature, with a scanning speed of 10 cm-1 per minute and at the spectral
resolution of 2.0 cm-1.
The FT-Raman spectrum of this compound was also recorded in the region 3500–50 cm−1
with BRUKER RFS 27 Raman module equipped with Nd:YAG laser source operating at 1064
nm line width 100 mW power. The spectra were recorded with scanning speed of 50 cm−1 min−1
of spectral width 4 cm−1. The reported wavenumbers are believed to accurate within ±1 cm−1.
3

X-ray Crystallography
A crystal with dimensions of 0.05 × 0.29 × 0.78mm3 was used for X-ray data collection.
All measurements were made on a Bruker SMART APEXII CCD area-detector diffractometer
with graphite monochromated MoKα (0.71073Å) radiation at 293(2)K, using the scan
technique. Data collection: APEX2 [13]; cell refinement: SAINT [13]; data reduction: SAINT
[13]. The programs used to solve and refine the structure were SHELXS-97 and SHELXL-97
[14]. Molecular graphics: PLATON [15]; software used to prepare material for publication:
PLATON [15]. The refinement was carried out by using the full-matrix least square on F2. All
non-hydrogen atoms were refined anisotropically. All hydrogen atoms have been geometrically
fixed and refined with isotropic thermal parameters. Crystallographic data and details of the data
collection and structure refinements are listed in Table 1.
3. Computational methods
In this study, the calculations for molecular equilibrium geometry and vibrational spectra
of HBAN were performed by means of the GAUSSIAN 09W software package [16]. The
molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands
are interpreted with the aid of structure optimizations and normal coordinate force field
calculations based on Hartree Fock (HF) and density functional theory (DFT/B3LYP) methods
combination with 6-311++G(d,p) basis set. The Cartesian representation of the theoretical force
constants has been computed at the fully optimized geometry. Transformation of force field, the
subsequent normal coordinate analysis including the least square refinement of the scale factors
and calculation of the Total Energy Distribution (TED) were done on a PC with the MOLVIB
program (version V7.0-G77) written by Sundius [17–19]. The scaled B3LYP/6-311++G(d,p)
results show the best agreement with the experimental values over the other methods. The effects
due to the substitutions of amino group and hydroxyl group were investigated. The results of the
calculations were applied to simulate spectra of the title compound, which show excellent
4

agreement with observed spectra. Besides, first hyperpolarizability, frontier molecular orbitals
(FMO) and thermodynamic properties were performed.
Raman activities were computed by numerical differentiation of dipole derivatives with
respect to the electric field, using standard Gaussian procedures (Freq = Raman) and default
options. Then, the calculated Raman activities (Si) were converted to relative Raman intensities
(Ii) using the following relationship derived from the intensity theory of Raman scattering
[20,21]:
f ν −ν 4 Si
(
)
0
i
Ii =
… (1)

hcν 




i 
νi 1−exp −


kT



where ν0 is the laser exciting wavenumber in cm−1 (in this work, ν0 = 9398.5 cm−1, which
corresponds to the wavelength of 1064 nm of the Nd:YAG laser), νi the vibrational wavenumber
of the ith normal mode (cm−1), while Si is the Raman scattering activity of the normal mode νi .
f (is a constant equal to 10−12) is a suitably chosen common normalization factor for all peak
intensities [22]. h, k, c, and T are Planck and Boltzmann constants, speed of light and
temperature in K, respectively.
4. Results and discussion
4.1. Characterization of the ligand
The Schiff base ligand was prepared by the interaction of 2–naphthylamine and
4-hydroxy benzaldehyde in acetonitrile/ethanol mixture according to Scheme 1. Some important
spectral values of this ligand are given below, the 1H NMR (DMSO δ, ppm) spectral data reveal
the appearance of the azomethine proton (–CH=N) signal at 8.60 ppm. The signals at 12.11 and
7.34 –7.39 ppm due to hydroxyl group and aromatic protons respectively. The 13C NMR
spectrum (DMSO, δ, ppm.) of the ligand showed the azomethine (-CH=N) carbon at 161.1, the
hydroxyl group attached carbon at 160.7 and all the aromatic carbons were observed at 159.6,
5

144.2, 144.1, 133.0, 131.2, 123.8, 122.7, 122.6, 119.9, 118.9, 116.5 and 115.2. UV-visible: Two
absorption bands were observed at 288 nm and 327 nm (DMF) due to π-π* transitions of the
aromatic rings and n-π* transitions of the C=N group respectively which also support the
formation of Schiff base ligand.
4.2. Geometrical parameters and first hyperpolarizability
The single crystal structure and atomic numbering chosen for HBAN compound is
demonstrated in Fig. 1 and the optimized structure of HBAN as shown in Fig.S1
(Supplementary). The optimized geometrical parameters determined with HF and B3LYP
methods at 6-311++G(d,p) basis set for molecule and the experimental data are collected in
Table 2. The geometric parameters which analyzed in this paper are of importance to have
information about the conformation of the molecule. Therefore, we mainly focused on the bond
lengths and bond angles by both methods (experimental & theoretical). By comparing the results
obtained from HF and B3LYP calculations at 6-311++G(d,p) basis set and the experimental data
in Table 2, several observations have been made.
It can be observed that the carbon–carbon bond lengths on the whole molecule is
intermediate between typical C–C single (1.54 Å) and C=C double (1.34 Å) bonds, and the
carbon–nitrogen bond lengths are also intermediate between C–N typical single (1.47 Å) and
C=N double (1.27 Å) bonds [23]. This can be explained in terms of resonance effect, involving
conjugation. The C2–N1 bond distance of HBAN is 1.414 Å (1.429(2) Å), N1=C11 is 1.286 Å
(1.288(2) Å) and O1–H18 is 0.973 Å (1.040(2) Å). The experimental N1– C2, N1=C11 and
O1–H18 bond distances are slightly longer due to hydrogen bonding. These structural parameters
obtained from B3LYP/6-311++G(d,p) are in good agreement with the X-RD values. The bond
angle C2−N1−C11 is 123.20° and 123.27° at HF and B3LYP/6-311++G(d,p) respectively, agree
well with our X-RD values.
6

Fig. 2 illustrates a representative view of HBAN crystal packing structure. The crystal
packing structure demonstrates the existence of three intermolecular hydrogen bonds:
O1—H18···N1i with bond length of 2.701(2) Å and bond angle of 173.2˚, C1—H1···O1ii with
bond length of 3.333(3) Å and bond angle of 134˚ and C13—H13···O1ii with bond length of
3.293(2) Å and bond angle of 157˚ respectively as shown in Table S1 (Supplementary). Each
Schiff base molecule interacts with other molecule through O—H···N hydrogen bond forming
one dimensional chain propagating in the b-axis direction. Further C1 and C13 atoms interact
with hydroxyl group via C—H···O hydrogen bonds forming a rings with graph set notations
R2 (6) and R2 (7) respectively.
2
2
Before calculating the hyperpolarizability of the title compound, the geometry taken from
the starting structure, based on its crystallogrphic data was optimized in the HF and B3LYP
methods. Molecular geometries were fully optimized by Berny’s optimization algorithm using
redundant internal coordinates. All optimized structures were confirmed to be minimum energy
conformations [18]. The first-order hyperpolarizabily, polarizabily and dipole moment (β0, α
and µ) of HBAN is calculated using B3LYP/6-311++G(d,p) level of theory, based on the finite-
field approach. In the presence of an applied electric field, the energy of a system is a function of
the electric field. First-order hyperpolarizability is a third rank tensor that can be described by a
3×3×3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to
Kleinman symmetry [24]. It can be given in the lower tetrahedral format. It is obvious that the
lower part of the 3 ×3 × 3 matrixes is a tetrahedral. The components of β are defined as the
coefficients in the Taylor series expansion of the energy in the external electric field. When the
external electric field is weak and homogeneous, this expansion becomes:
1
1
E = E0 −µα F − ααβF F − βαβγF F F +
… (2)
α
α
β
α β γ
2
6
7

where E0 is the energy of the unperturbed molecules, Fα is the field at the origin, and µα , ααβ,
βαβγ are the components of the dipole moment, polarizability and the first hyperpolarizabilities,
respectively. The total static dipole moment µ, the mean polarizability α0, the anisotropy of
polarizability ꢀα and the mean first hyperpolarizability β0, using the x, y, z components are
defined as
1
2
µ = µ2 + µ2 + µ2
(
… (3)
... (4)
)
x
y
x
α xx + α yy + α zz
α0 =
3
ꢀα = 21/2[(αxx −αyy)2 +(αyy−αzz)2 +(αzz−αxx)2 + 6(α2xy+α2 +α2 )]1/2
…(5)
... (6)
yz
zx
β0 = √ (βxxx + βxyy + βxzz)2 + (βyyy + βxxy + βyzz)2 +(βzzz + βxxz + βyyz)2
The α0 and β0 components of Gaussian output are reported in atomic units and therefore
the calculated values are converted into e.s.u. units (β0 : 1 a.u. = 8.3693 × 10−33 e.s.u) [25]. The
calculated dipole moment and first hyperpolarizability of the title compound is 1.1358 Debye
and 1.862 x10−30 esu, which is 0.83 and 14.36 times that of urea (µ = 1. 0.3732 Debye and β0 =
0.13 x10−30 esu) [26]. We conclude that the title compound is an attractive molecule in future for
non linear optical applications.
4.3. Vibrational assignments
The compound HBAN consists of 32 atoms and hence 90 (3N-6) (N-number of atoms)
normal modes of vibrations. The ninety normal modes of HBAN are distributed by symmetry
species as:
Γvib. = 61A' (in plane bending) + 29A"(out-of-plane bending)
The molecular conformation obtained from crystalline structure, as well as the one yielded by
geometry optimization, exhibits no special symmetries and hence the molecule belongs to Cs
point group symmetry. The fundamental vibrational wavenumbers of HBAN calculated by
8

HF and B3LYP/6-311++G(d,p) methods. The calculated wavenumbers are given in Table 3. The
resulting vibrational wavenumbers for the optimized geometries, IR intensities as well as Raman
scattering activities and experimental FT-IR, FT-Raman frequencies are also listed. A combined
experimental and theoretical spectrum of title compound has been shown in Fig. 3 and 4,
respectively. The normal modes of vibration were assigned on the basis of TED. To bring the
theoretical values closer to experimental values, we have used the different scaling factor values
for HF and B3LYP/6-311++G(d,p) methods. The results indicate that the B3LYP calculations
approximate the observed fundamental frequencies much better than the HF results. Inclusion of
electron correlation in density functional theory to a certain extent makes the frequency values
smaller in comparison with HF frequency. Also, it should be noted that the experimental results
belong to solid phase and theoretical calculations belong to gaseous phase.
4.3.1. O–H vibrations
The O–H stretching vibrations are extremely sensitive to hydrogen bonding. The non-
hydrogen bonded (or) free hydrogen group absorbs strongly in the region 3550–3700 cm–1 [27].
The weaker C–H stretching modes are generally superimposed upon the broad O–H band [28].
The free hydroxyl group absorbs strongly in the region 3700–3584 cm–1, whereas the existence
of intermolecular hydrogen bond formation can lower the O–H stretching frequency to the 3550–
3200 cm–1 region with increase in intensity and breath [29,30]. In the present investigation, the
stretching vibration of O–H group is assigned as a weak band 3494 cm–1 in FT-IR spectrum of
HBAN. The theoretically computed (scaled) frequency for O–H vibration by B3LYP/6-
311++G(d,p) method shows excellent agreement with recorded spectrum as well as the literature
data [31] and also find support from TED values.
In general, the O–H in-plane bending vibration for phenol lies in the region 1150–1250
cm–1 and it is not much affected due to hydrogen bonding unlike that to stretching and out-of-
plane bending wavenumber [32]. In this work, the O–H vibration appears as weak bond in FT-IR
9

at 1253 cm–1 (phenol). The theoretically computed wavenumber shows good agreement with
experimental observation at 1259 cm–1 by B3LYP/6-311++G(d,p) method. This assignment is
within the expected range and also in consistent with literature values [31].
The O–H out-of-plane deformation for phenol lies in the region 290–320 cm–1 for free
O–H and in the region 517–710 cm–1 for associated O–H [33]. In both intra and intermolecular
associations, the wavenumbers are at higher value than that in the free O–H. The wavenumber
increases with hydrogen bond strength because of large amount of energy required to twist the
O–H bond [34]. In accordance with above conclusion the predicted band at 699 cm–1 in FT-IR
for HBAN are assigned to C–OH mode for hydroxyl group. This vibration is in good agreement
with the literature value.
4.3.2. C–H vibrations
The C–H stretching frequencies appear in the range of 3125–3000 cm-1, which is the
characteristic region for νC-H stretching [35]. The theoretically calculated scaled down
vibrations corresponding with C–H stretch show good agreement with the experimentally
observed vibrations at 3126, 3113, 3108, 3096, 3038, 3026 and 2906 cm–1 in FT-IR and 3054
cm–1 in FT-Raman spectra for title compound. The bands are appeared with very strong
intensities. The calculated frequencies are very good agreements in B3LYP/6-311++G(d,p) basis
set for HBAN. All the above vibrations are observed in the expected range. Moreover, as
expected, all stretching vibrations are very pure modes since their TED contribution are greater
than 95%. Substitution sensitive C–H in-plane bending vibrations lie in the region 1000–1300
cm−1 [36]. In HBAN, three infrared bands at 1295, 1050 and 1005 cm−1 with medium, very
strong and very weak intensities are assigned to C–H in-plane bending vibrations. Bands
involving the out-of-plane C–H vibrations appear in the range 1000–675 cm−1 [36, 37]. The C–H
out-of-plane bending vibrations are also lie within the characteristic region. However, the change
in the frequencies of these deformations from the values in hydroxyl is almost determined
10

exclusively by the relative position of the substituents and is almost independent of their nature.
The bands at 825, 700 and 675 cm−1 are assigned to C–H out-of-plane vibrations for HBAN. If
we consider TED calculations in-plane bending vibrations and out-of-plane bending vibrations
are assigned as mixed and pure modes respectively.
4.3.3. C=N and C−N vibrations
Because of the mixing of several bands, the identification of C=N and C−N vibrations is
a very difficult task. Silverstein [30] assigned C=N and C−N stretching absorption in the region
1600–1500 and 1382–1266 cm−1. In the present work, the C=N stretching vibration band
observed at 1585/1586 cm−1 in FT-IR/FT- Raman spectra and the vibration band at 1346 cm−1 in
FT-Raman spectrum has been assigned to C−N stretching vibration for HBAN. These modes are
calculated at 1571 and 1352 cm−1 with B3LYP/ 6-311++G(d,p) basis set is in agreement with
experimental value. The TED of this mode is 15%. The TED for this mode suggests that this is a
mixed mode. The remainder of the observed and calculated wavenumbers and assignments of
present molecule are shown in Table 3.
4.3.4. C−C vibrations
The ring stretching vibrations are very much important in the spectrum of HBAN. The
bands between 1400 and 1650 cm−1 in benzene derivatives are usually assigned to C−C
stretching modes [32]. Varsanyi [33] observed six bands, 1625–1590, 1590–1575, 1540–1470,
1465–1430, 1380–1280 and 1220–1130 cm−1 in this region. For title compound, the C−C
stretching vibrations are found at 1612, 1576, 1516, 1367, 1288,1272, 1238 and 1203 cm−1 in FT
IR spectrum and 1600, 1571, 1522, 1390, 1287, 1240 and 1204 cm−1 in FT Raman spectrum for
HBAN. All bands are appeared in the expected range. Most of the bands are observed with
medium and strong intensities. The mean difference between theoretical (B3LYP/6-
311++G(d,p)) and experimental frequencies is 4 cm−1. It shows the good agreement between
11

theoretical and experimental C−C stretching vibrations. The bands are assigned to C−C in-plane
bending and out-of-plane bending vibrations are observed at 671cm−1 and 330 cm−1 in FT-IR and
FT-Raman spectra for HBAN. The bands show weak intensity in infrared and very strong
intensity in Raman.
4.3.5. C–O Vibrations
The C–O stretch lies in the spectral range 1310 – 1168 cm−1 [38] and it is very intense in
the infrared and only moderately active in Raman. In HBAN, the C–O stretching frequency is
observed at 1203 and 1204 cm−1 in FT-IR and FT-Raman spectra respectively. The fundamental
mode at 584 cm−1 in the Raman spectrum is attributed to the C–O in-plane bending of HBAN.
The C–O out-of-plane bending vibration of HBAN is observed at 221cm−1 in the Raman
spectrum as a weak band. The theoretically computed wavenumber shows good agreement with
experimental observations by B3LYP/6-311++G(d,p) method.
5. HOMO, LUMO analysis and related molecular properties
Many organic molecules, containing conjugated π electrons are characterized by large
values of molecular first-order hyperpolarizabilities by means of vibrational spectroscopy
[39,40]. The analysis of wavefunction indicates that the electron absorption corresponds to the
transition from the ground to the first excited state and is mainly described by one electron
excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied orbital
(LUMO) are very important parameters for quantum chemistry. In the present study, the band
gap energy of the one electron excitation in HBAN molecule from HOMO to LUMO is
calculated by B3LYP/6-311++G(d,p) method about − 0.11566 a.u. The HOMO and LUMO plot
of HBAN is shown in Fig.5. The HOMO−LUMO energy gap reveals that the energy gap reflects
the chemical activity of the molecule.
12

Since, DFT based chemical reactivity description provides valuable information about the
reactive sites for various types of attacks and orientation for benzidene [39], we have applied the
same concepts during the studies. Associated within the framework of Self-Consistency Function
(SCF), Molecular Orbital(MO) theory the ionization energy (I) and electron affinity (A) can be
expressed through HOMO and LUMO orbital energies as I = −EHOMO and A = −ELUMO. Pauling
introduced the concept of electro negativity as the power of an atom in a compound to attract
electrons to it. The hardness corresponds to the gap between the HOMO and LUMO orbital
energies. The larger the HOMO−LUMO energy gaps the harder the molecule [34]. The global
hardness, is η = 1/2(ELUMO − EHOMO) ≈ 1/2(I−A). The hardness has been associated with the
stability of chemical system. The electron affinity can be used in combination with ionization
energy to give electronic chemical potential, ꢁ = 1/2(EHOMO + ELUMO) ≈ −1/2(I+A). The global
electrophilicity index, w = ꢁ2/2η is also calculated [41-50]. Softness is a property of compound
that measures the extent of chemical reactivity. It is the reciprocal of hardness, is S = 1/ η and
listed in Table 4.
6. Thermodynamic properties
The thermodynamic parameters namely heat capacity, entropy, rotational constants,
vibration and vibrational zero point energies of the compound have also been computed at the
DFT-B3LYP level using 6-311++G(d,p) basis set and are presented in Table 5. The
thermodynamic data provide helpful information for the further study on the HBAN, when these
may be used as a reactant to take part in a new reaction. These standard thermodynamic
functions can be used as reference thermodynamic values to calculate the changes of entropies
(ꢀST), changes of enthalpies (ꢀHT) and changes of Gibbs free energies (ꢀGT) of the reaction.
There is no much deviation in the thermodynamic properties calculated from these methods. The
dipole moment and its principal inertial axes strongly depend upon the molecular conformation.
13

On the basis of vibrational analysis at B3LYP/6-311++G(d,p) level, statistical
thermodynamics and the standard thermodynamic functions: heat capacity (C0p,m), entropy (S0 )
m
and enthalpy (H0 ) were calculated using perl script THERMO.PL [51], for the title compound
m
were obtained from the theoretical harmonic frequencies and are listed in Table 6. The
corresponding fitting equations are as follows,
C0p,m = –13.79295 + 1.05704T – 4.44386 x 10−4 T2 (R2 = 0.99908)
S0 = – 251.19502 + 0.97237T – 1.74169 x 10−4T2 (R2 = 0.99992)
m
H0m = 10.59706 + 0.09748T + 2.86651 x 10−5 T2 (R2 = 0.99938)
From Table 6, the values of C0p,m, S0 and H0 increasing with the increasing of
m
m
temperature from 100 to 1000K, which is attributed to the enhancement of the molecular
vibrational intensities increase as the temperature increases [52]. The correlation equations
between heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic
formulas and the corresponding fitting factors (R2) for these thermodynamic properties are
0.99908, 0.99992 and 0.99938, respectively. The correlation graphs are shown in Figs. 6-8. All
thermodynamic calculations were done in gas phase only.
7. Conclusions
A new Schiff base 2-[4-hydroxy benzylidene]-amino naphthalene has been synthesized
and its structure solved by single crystal X-ray diffraction. It crystallizes in the orthorhombic
system with space group P212121. The molecules are linked by intermolecular interactions and
generate supramolecular chain along b- axis. The identification of such supramolecular patterns
will help in design and construction of preferred hydrogen bonding patterns on drug like
1
molecules. The presence of azomethine functional group was confirmed by FT-IR, Raman, H
13
and C NMR. The theoretical (B3LYP) scaled vibrational spectra shows good agreement with
the experimental data. The relative stabilities, HOMO–LUMO energy gaps and implications of
the electronic properties are examined and discussed. The optimized geometry parameters, first
14

hyperpolarizabililty, infrared intensities, Raman activities and thermodynamic parameters are
reported. Based on the above facts, it could be proposed that this novel material can be better
placed for optical applications.
Supplementary material
Crystallographic data for the structure reported in this article have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication number CCDC 938315.
Copies of the data can be obtained free of charge on application to CCDC 12 Union Road,
Cambridge CB21 EZ, UK (fax: +44 1223 336 033; e-mail: data_request@ccdc.cam.ac.uk).
Acknowledgement
The authors thank the Universiti Sains Malaysia for the use of the X-ray
diffractometer at the X-ray Crystallography Unit, School of Physics, 11800 USM, Penang,
Malaysia.
15

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19

Table 1
Crystallographic data of 2-[4-hydroxy benzylidene]-amino naphthalene.
Crystal Data
Formula
CCDC deposit No.
C17H13NO
938315
Formula Weight
Crystal System
Space group
a, b, c [Å]
247.28
Orthorhombic
P212121 (No. 19)
6.2867(2) 10.2108(3) 19.2950(6)
V [Å3]
1238.59(7)
Z
4
D(calc) [g/cm3]
µ(MoKα) [ /mm ]
F(000)
1.326
0.083
520
Crystal Size [mm]
0.05 x 0.29 x 0.78
Data Collection
Temperature (K)
Radiation [Å]
293(2)
MoKα 0.71073
2.1, 35.3
θ Min-Max [°]
Dataset
Tot., Uniq. Data, R(int)
Observed data [I > 2.0 σ(I)]
-10: 9 ; -16: 15 ; -31: 31
21345, 5300, 0.046
3909
Refinement
Nref, Npar
5300, 176
R, wR2, S
0.0538, 0.1354, 1.07
1.6(13)
-0.26,0.31
Flack x
Min. & Max. Resd. Dens. [e/Å3]
1

Table 2
Selected optimized geometrical parameters of 2-[4-hydroxy benzylidene]-amino naphthalene.
HF
B3LYP
HF
B3LYP
HF
B3LYP
Bond
lengths (Å)
Bond
Dihedral
angles (o)
XRD
XRD
XRD
angles (o)
6-311++G(d,p) 6-311++G(d,p)
6-311++G(d,p) 6-311++G(d,p)
6-311++G(d,p) 6-311++G(d,p)
C1 – C2
C1 – C10
C9– C10
C1 – H1
C2 – N1
1.364
1.417
1.412
1.071
1.414
1.385
1.421
1.436
1.083
1.414
1.378(2)
1.420(2)
1.418(2)
0.950
C2 – C1 – H1
118.82
119.58
119.58
121.03
123.27
119.57
119.00
119.00
C10 – C1 – C2 – C3
C10– C1 – C2 – N1
-2.23
1.86
-0.70(2)
C10 – C1 – H1 119.89
C10 – C1 – C2 121.28
179.61
179.63
179.74
1.67
174.73
179.88
-175.19
-2.13
-179.98(1)
-179.19(1)
179.05(1)
-0.17(2)
121.38(1) C1– C9 – C10 – C5
120.67(1) N1– C2 – C3 – C4
119.22(1) C1 – C2 – C3 – C4
C2–N1 – C11
C1 – C2 – C3
123.20
119.39
1.429(2)
C2 – C3
1.422
1.427
1.425(2)
C1 – C2 – N1
117.75
121.36
123.69(1) C1– C2 – N1 – C11
117.09(1) C3– C2 – N1 – C1
-150.24
31.67
87.92
-178.46(1)
N1–C11
1.266
1.082
1.467
1.373
0.946
1.394
1.393
1.286
1.089
1.475
1.392
0.973
1.409
1.412
1.288(2)
0.950
C3 – C2 – N1
N1–C11–H11
N1–C11–C12
122.83
121.75
122.86
118.69
114.44
132.17
120.51
116.79
112.89
122.68
-99.15
179.93
179.90
2.30(18)
C11– H11
C11– C12
C15 – O1
O1 – H18
C12 – C17
C12 – C13
117.00
125.06(1) C17– C16– C15– O1 179.94
C13– C14– C15– O1 -179.95
179.16(1)
1.457(2)
1.354(2)
1.040(2)
1.401(2)
1.400(2)
-179.58(1)
C16–C15–C14 120.61
119.60(1)
117.52(1)
109.2(1)
-
-
-
-
-
-
-
-
-
-
-
-
-
C16–C15–O1
C15–O1–H18
C14–C15–O1
117.09
115.15
122.30
-
-
-
122.87(1)
2

Table 3
Experimental and Theoretical calculated vibrational frequencies, IR intensity (KM mole−1) and Raman activity (Å4 amu−1) of 2-[4-hydroxy
benzylidene]-amino naphthalene.
Experimental
frequencies
HF/ 6-311++G(d,p)
B3LYP/ 6-311++G(d,p)
(in cm-1)
Modes of
vibration species
Cs
Sym.
TED(%) among types of internal
coordinates
Theoretical
frequencies (in cm-1)
Theoretical
frequencies (in cm-1)
FT-
Raman
IR
Raman
IR
Raman
FT-IR
intensity activity
intensity activity
Unscaled
4081
3373
3371
3354
3351
3349
3338
3324
3322
3321
3319
3314
3210
1855
1820
1791
1779
1762
Scaled
3507
Unscaled
3962
3226
3205
3187
3186
3170
3168
3163
3158
3155
3153
3148
3076
1692
1661
1640
1632
1619
Scaled
3501
1.
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
3494w
-
106.48 166.14
59.27
1.24
166.11
103.29
195.46
269.18
224.71
83.54
νO−H(100)
2.
3126w
-
3136
3121
3115
3105
3065
3042
3034
2915
2909
2907
2904
2901
1867
1855
1623
1614
1578
6.16
183.47
23.11
394.53
53.22
24.46
94.04
91.71
165.34
54.14
5.66
3129
3118
3113
3091
3059
3042
3029
2911
2907
2901
2894
2893
1876
1858
1618
1604
1571
νC−H(98)
3.
3113w
-
8.23
9.59
νC−H(98)
4.
3108w
-
30.17
25.83
22.92
36.96
3.71
9.31
νC−H(98)
5.
3096w
-
47.17
50.14
1.63
νC−H(98)
6.
-
3054w
νC−H(98)
7.
3038w
-
81.33
νC−H(98)
8.
3026w
-
9.44
101.46
44.90
νC−H(96), νC−C(02)
νC−H(96), νC−C(02)
νC−H(96), νN=C(04)
νC−H(95), νN=C(04)
νC−H(95), νN=C(02), bC−C(02)
νC−H(95), bC−C(02), νC−N(02)
bC−H(58), bC−O(12), νC−N(10)
b−CH(58), bC−O(10), νC−N(12)
νC−C(86), bC−O(02)
νC−C(86), bC−O(02), νC−N(04)
νC−C(86), bC−C(04), νC−N(02)
9.
2906w
-
3.40
18.20
10.88
3.50
10.
11.
12.
13.
14.
15.
16.
17.
18.
-
-
36.54
8.50
168.92
18.33
-
-
-
-
0.89
14.29
40.05
3.37
9.48
-
-
39.10
54.44
290.13
70.89
237.30
48.84
27.55
141.22
536.59
168.12
501.67
31.88
-
-
262.85 2819.87
66.76 1084.56
189.61 1220.76
-
-
1612ms
-
-
1600w
1586w
73.87
3.81
390.93
7.83
1585s
11.63
3

19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
1576w
-
1751
1681
1664
1630
1593
1580
1540
1509
1493
1475
1465
1398
1391
1388
1353
1349
1312
1295
1287
1284
1245
1234
1220
1209
1139
1136
1583
1572
1533
1519
1478
1457
1449
1406
1393
1379
1358
1342
1332
1322
1299
1288
1264
1253
1251
1212
1210
1209
1206
1175
1136
1128
1.62
58.44
1597
1553
1543
1510
1490
1478
1447
1411
1400
1383
1382
1343
1305
1296
1277
1243
1231
1218
1201
1191
1182
1172
1147
1129
1042
1039
1579
1566
1528
1514
1471
1452
1441
1399
1386
1372
1352
1337
1326
1318
1293
1280
1259
1248
1247
1205
1208
1206
1201
1168
1129
1113
3.31
26.12
29.80
3.94
νN=C(95), bC−C(02)
-
1571w
102.35 49.68
56.85
22.91
16.35
13.64
7.66
νC−C(86), νC−C(02), νC=N(02)
νC−C(82), bO−H(06), νC−N(02)
νC−C(82), bC−C(08), ѡC=N(02)
bC−H(58), R1trigd(13), R2trigd(05)
bC−H(58),R1 trigd(13), νC−N (05)
bC−H(58), νC=N(16), bO−H(6)
bC−H(57),R1 bend(12), ѡC−O(14)
νC−C(82), R1bend(04), tR1trigd(04)
νC−C(82), tR1 trigd(12), ѡC−O(06)
νC−N(89), R1bend(06), tR3 trigd(02)
νC−C(82),R1 bend(08), tR2 trigd(02)
νC−C(82), ѡC−O(06), tR2 trigd(02)
νC−C(81), ѡC−O(06), bC−N(05)
νC−C(81), bC−H(04), ѡC−O(08)
νC−C(81), R2 asymd(08), ѡC−O(03)
bO−H(62), ѡC−O(12), νC−C(08)
νC−C(81), bC−H(55), tR2 trigd(04)
νC−C(81), bC−H(55), tR2 trigd(06)
νC−O(79), bC−N(05), ѡC−O(12)
νC−C(76),tR2trigd(06), Butterfly(04)
νC−C(76), bC−N(03), ѡC−O(08)
ν−CC(76), bC−H(55), Butterfly(06)
bC−H(56), ѡC−O(08), ѡO−H(16)
bC−H(56), ѡO−H(12),νO−H(08)
bC−H(56), ѡO−H(06),νO−H(12)
-
1522w
23.59
5.68
2.23
81.92
6.84
11.56
0.81
9.67
4.34
2.26
5.26
5.99
15.41
239.05
12.56
161.09
96.89
422.29
338.62
42.00
14.76
10.15
3.62
1516w
-
107.24
5.51
-
1467w
1448w
-
52.70
25.29
95.01
312.78
16.54
3.20
-
1436w
19.71
6.87
-
1395w
1390w
-
2.88
1367w
-
10.27
5.40
-
1346w
-
-
22.53
6.10
23.27
1.43
-
-
-
1307w
45.50
3.62
3.95
1288w
1287vs
164.86 225.38
55.16
16.61
1.27
16.34
20.76
25.38
52.82
6.39
1272w
-
65.84
0.24
11.54
50.91
97.76
26.79
311.85
1253w
-
-
1240w
68.54
0.66
32.16
1.99
1238w
-
1203w
1204w
9.62
14.11
22.74
245.80
40.70
94.85
3.97
24.69
18.17
36.25
21.82
58.10
38.78
0.33
-
-
-
-
-
-
148.51 10.93
-
73.00
3.68
145.85
28.43
70.60
52.72
1.15
-
1162s
1123w
52.23
8.04
1107ms 1109w
0.01
1.93
4

45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′
A′′
A′′
A′
A′
A′′
A′′
A′
1028w
-
1130
1127
1116
1108
1099
1084
1048
1036
987
1029
1024
1019
1008
1001
989
972
959
919
994
895
874
859
843
822
819
784
779
776
764
715
692
658
653
636
598
0.14
0.04
1.71
2.25
3.91
28.09
6.97
4.11
7.70
2.89
1.38
4.04
7.61
0.75
11.81
42.14
0.14
5.13
47.34
1.66
4.52
2.43
8.30
0.12
4.56
2.22
4.73
1012
1010
1005
1003
985
979
970
916
912
884
859
858
848
844
805
780
773
766
734
713
685
665
650
631
599
544
1024
1013
1011
1001
993
982
966
952
910
899
888
868
853
839
819
812
779
773
771
759
706
682
652
647
631
591
0.26
0.03
1.90
0.27
0.30
1.66
0.511
0.92
0.44
4.23
2.39
56.63
2.79
2.79
0.31
16.75
57.04
2.71
0.31
2.37
2.68
2.20
8.15
2.38
12.26
6.49
1.06
bC−H(55), ѡC−O(12), νO−H(06)
bC−H(55), ѡC−O(16), νO−H(07)
bC−H(54), νO−H(18), bC=N(06)
R1 trigd(53), ѡC−O(12), νO−H(04)
R2 trigd(53), ѡC−O(12), νO−H(02)
R1 bend(52), ѡC−H(06), νC−C(06)
R3 trigd(52), ѡC−H(12), νC−C(06)
R1 symd(53), ѡC−H (08),νC−C(16)
bC=N(56), ѡC−H(12), νC−C(16),
R2 bend(46), ѡC−H (08),νN=C(05)
R2 symd(46), ѡC−H(08), νN=C(05)
R3 symd(46), ѡC−H(16), νN=C(15)
R1asymd(46), ѡC−H(08), νN=C(15),
R2asymd(46), ѡC−H(08), νN=C(10),
R3 asymd(46), ѡC−H(09), bO−H(06)
tR1 trigd(38), ѡC−H(06), bO−H(06)
tR2 trigd(38), ѡC−H(04), bO−H(06)
tR1 bend(38), ѡC−H bO−H(06)
tR3 trigd(38), ѡC−H(04), bO−H(06)
ѡC−H(46),νC−C(18), νN=C(95),
ѡO−H(46),ѡC−H(08),νC−C(06),
bC−C(46), ѡC−H(12), νC−C(06),
bC−N(65),ѡC−O(12),νO−H(10)
tR1 symd(36),bC−N(12),ѡC−O(06)
ѡC−H(36),bC−N(12),ѡC−O(02)
bC−O(36),bC−N(12),ѡC−O(06)
-
1019w
7.54
5.26
-
-
0.82
1.15
-
-
0.72
2.91
-
-
1.19
2.40
974ms
958w
-
974w
0.69
12.39
3.89
-
13.79
40.34
26.59
18.84
53.94
17.75
29.71
50.64
10.69
55.33
0.58
-
21.90
19.48
38.04
32.12
42.40
20.83
16.60
36.38
2.82
902w
893w
-
-
-
984
881w
954
862w
-
-
-
950
943
833w
-
928
812vs
882
808w
-
-
854
772w
841
30.38
2.83
769w
-
-
837
0.06
-
803
5.90
0.99
750s
699w
671w
647w
-
-
797
2.06
1.14
-
729
3.25
7.53
-
716
1.83
1.14
-
699
7.71
11.02
23.33
22.59
4.86
642w
643
9.00
623w
584w
-
-
611
8.30
589
20.60
5

71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
A′′
-
549vw
574
546
541
506
479
467
445
419
382
344
284
251
222
201
187
160
96
562
548
524
518
486
459
453
434
383
369
346
221
219
214
206
189
107
104
71
8.22
18.66
15.32
9.99
0.39
2.13
8.86
4.82
2.79
19.22
11.38
5.04
0.43
1.21
0.28
1.29
2.82
5.68
3.19
13.91
534
510
489
459
434
431
405
398
395
341
311
291
214
189
184
121
91
556
541
519
511
481
452
449
429
379
366
339
216
212
209
201
184
102
98
3.32
4.18
22.62
3.69
0.53
6.23
7.57
4.36
4.28
142.76
3.87
1.14
0.74
3.43
1.30
1.12
0.44
0.74
0.28
0.05
14.00
1.42
0.77
2.12
0.28
5.63
3.13
5.16
1.17
2.06
2.51
1.60
0.86
11.68
0.05
2.25
0.64
7.99
10.36
10.77
ѡC−H(36),bC−N(12),ѡC−O(08)
ѡC−H(36),ѡC−O(02),ѡC−N(12)
ѡC−H(36),ѡC−O(04),ѡC=N(08)
ѡC−H(32),ѡC−O(02),ѡC−N(12)
ѡC−H(34),ѡC−O(02),ѡC=N(08),
ѡC−H(34),ѡC−O(02),ѡC=N(02)
ѡC−H(34),ѡC−O(08),ѡC−N(06)
ѡC=N(36),ѡC−O(12),ѡC=N(02)
ѡC−N(36),ѡC−O(06),ѡC=N(02)
ѡC−H(26),ѡC−O(07),ѡC=N(06)
ѡC−C(26),ѡC−O(04),ѡC=N(06)
ѡC−O(26),ѡC−O(06),ѡC=N(08)
ѡC−H(26),ѡC−O(12),ѡC=N(06)
tR2 symd(26),ѡC−O(12),ѡC−N(06)
tR3 symd(46),ѡC−H(02),bC−H(08)
tR1 asymd(46), ѡC−H(02),bC−H(10)
Butterfly(36), bC−H(08),νC−H(12)
tR2 bend(46),ѡC−H(08),νC−H(02)
tR2 asymd(46),νC−H(12),bC−H(04)
tR3 asymd(46),νC−H(16),bC−H(08)
534w
-
512w
-
-
506vw
476s
-
445s
-
-
443vw
422w
-
-
-
-
-
-
-
-
-
-
-
-
-
371vw
-
330vw
165.26 2,34
221w
2.39
9.35
6.38
1.83
2.55
1.74
0.87
0.34
0.41
0.65
8.00
0.36
16.40
2.69
4.22
1.54
0.74
0.05
-
-
-
-
92w
-
-
-
53
45
40
36
64
26
62
14
53
Abbreviation: vs-very strong; ms-medium strong; s-strong; w-weak; vw-very weak; ν- stretching; b-in-plane bending; ѡ-out-of-plane bending.
6

Table 4
Calculated reactivity indices of 2-[4-hydroxybenzylidene]-amino naphthalene obtained by
B3LYP/6-311++G(d,p) method.
Molecular Energy
EHOMO (in a.u.)
Values
− 0.31241
− 0.19675
− 0.11566
−785.59058
0.31241
ELUMO (in a.u.)
Energy gap (∆) (in a.u.)
SCF energy(Hartrees)
Ionization potential (I) (in a.u.)
Electron affinity (A) (in a.u.)
Global hardness (η)(in a.u.)
Chemical potential (µ) (in a.u.)
Global Electrophilicity (ω) (in a.u.)
Softness(S) (in a.u.)
0.19675
0.05783
−0.25458
0.56036
17.29206
7

Table 5
The calculated thermodynamic parameters of 2-[4-hydroxy benzylidene]-amino naphthalene
employing B3LYP/6-311++G(d,p) method.
Thermodynamic parameters (298K)
Total energy (thermal), Etotal (kcal mol−1)
Heat capacity at const. volume, Cv (cal mol−1 K−1)
Values
168.587
59.364
Entropy, S (cal mol−1 K−1)
Vibrational energy, Evib (kcal mol−1)
Zero-point vibrational energy, E0 (kcal mol−1)
124.978
166.810
159.40184
Rotational constants (GHz)
0.74602
0.18845
0.16939
A
B
C
Rotational temperatures (Kelvin)
0.03580
0.00904
0.00813
A
B
C
8

Table 6
Thermodynamic properties at different temperatures at the B3LYP/6-311++G(d,p)
level of 2-[4-hydroxy benzylidene]-amino naphthalene.
T(K)
100
C0p,m (cal mol-1k-1)
96.45
S0 (cal mol-1k-1)
H0 (kcal mol-1)
m
m
349.91
438.72
523.02
524.61
610.41
694.03
773.75
848.86
919.29
985.28
1047.18
6.67
200
171.68
19.91
298.15
300
256.69
40.91
258.30
41.39
400
340.35
71.41
500
409.35
109.01
152.82
201.60
254.38
310.44
369.21
600
464.79
700
509.20
800
545.24
900
574.95
1000
599.78
9

Figure captions
Scheme 1: Synthesis of Schiff base HBAN.
Fig.1:
Fig.2:
An ORTEP view of the title compound HBAN.
Hydrogen bonding patterns in compound HBAN. The hydrogen bonds are
indicated by dashed lines.
Fig. 3:
Comparison of the experimental and the calculated FT-IR spectra of HBAN:
(a) observed spectra (b) and (c) present the scaled spectra by B3LYP /HF/
6-311++G(d,p), respectively.
Fig. 4:
Comparison of the experimental and the calculated FT-Raman spectra of HBAN:
(a) observed spectra (b) and (c) present the scaled spectra by B3LYP/HF/
6-311++G(d,p), respectively.
Fig.5:
Fig. 6:
Fig. 7:
Fig. 8:
The HOMO and LUMO plot of HBAN.
Correlation graph of heat capacity and temperature for HBAN molecule.
Correlation graph of entropy and temperature for HBAN molecule.
Correlation graph of enthalpy and temperature for HBAN molecule.
29