Vibrational frequency analysis, FT-IR, FT-Raman, ab initio, HF and DFT studies, NBO, HOMO-LUMO and electronic structure calculations on pycolinaldehyde oxime

Article abstract of DOI:10.1016/j.saa.2013.07.080

In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in the range 100-4000 cm^-1and 50-4000 cm^-1, respectively, for pycolinaldehyde oxime (PAO) (C ₆H₆N₂O) molecule. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on HF and B3LYP methods with 6-311++G(d,p) basis set. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The optimized geometric parameters are compared with experimental values of PAO. The non linear optical properties, NBO analysis, thermodynamics properties and mulliken charges of the title molecule are also calculated and interpreted. A study on the electronic properties, such as HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) are performed. The effects due to the substitutions of CHNOH ring are investigated. The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results.

Full text of DOI:10.1016/j.saa.2013.07.080

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Vibrational frequency analysis, FT-IR, FT-Raman, ab initio, HF and DFT
studies, NBO, HOMO–LUMO and electronic structure calculations on
pycolinaldehyde oxime
c
d
e
A. Suvitha a,b, , S. Periandy , S. Boomadevi , M. Govindarajan
⇑
a Periyar Maniyammai University, Vallam, Thanjavur, India
b St. Francies College, Bangalore, India
c Department of Physics, Tagore Arts College, Puducherry, India
d Department of Physics, Periyar Maniyammai University, Vallam, Thanjavur, India
e Department of Physics, MGGA College, Mahe, Puducheery, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Spectroscopic properties of
pycolinaldehyde oxime were
examined by FT-IR, FT-Raman and
NMR techniques, HF and DFT
methods.
ꢀ
ꢀ
ꢀ
NLO and NBO analysis of the molecule
were studied.
NMR chemical shift of the molecule
were studied.
HOMO and LUMO energies, Molecular
electrostatic potential distribution of
the molecule were calculated.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 May 2013
Received in revised form 7 July 2013
Accepted 21 July 2013
Available online 6 August 2013
In this work, the vibrational spectral analysis is carried out by using Raman and infrared spectroscopy in
the range 100–4000 cmꢁ1and 50–4000 cmꢁ1, respectively, for pycolinaldehyde oxime (PAO) (C6H6N2O)
molecule. The vibrational frequencies have been calculated and scaled values are compared with exper-
imental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field cal-
culations are based on HF and B3LYP methods with 6-311++G(d,p) basis set. The results of the calculation
shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p)
basis set. The optimized geometric parameters are compared with experimental values of PAO. The
non linear optical properties, NBO analysis, thermodynamics properties and mulliken charges of the title
molecule are also calculated and interpreted. A study on the electronic properties, such as HOMO and
LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. Besides, frontier molecular
orbitals (FMO), molecular electrostatic potential (MEP) are performed. The effects due to the substitu-
tions of CH@NOH ring are investigated. The 1H and 13C nuclear magnetic resonance (NMR) chemical
shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and com-
pared with experimental results.
Keywords:
HF
DFT
Pycolinaldehyde Oxime (PAO)
NBO analysis
HOMO
LUMO
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
Pyridine-2-carbaldehyde oxime has the general formula is
C6H6N2O. Usually it is a white to pale pink powder, belongs to a
⇑
Corresponding author. Tel.: +91 9632814332.
E-mail address: suvidanam@gmail.com (A. Suvitha).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.07.080

A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
217
family of compounds called oximes (Fig. 1). Molecular weight of
PAO is 122.125 (g/mol) with 1-H bond donor and 3-H bond accep-
tor. PAO is a frequently used ligand in synthesis of metal com-
plexes [1–3]. Oxime pyridines are widely used in
pharmacological and medical applications [4]. Pyridine compounds
have been used as nonlinear materials and photo chemicals widely
used as anticancer drugs, antihypertension, antifungal reagents,
pesticides, herbicides, plant growth reagents, etc. [5]. PAO has an
important role in reversing paralysis of the respiratory muscles
but due to its poor blood-brain barrier penetration, it has little ef-
fect on centrally-mediated respiratory depression [6]. Many substi-
tuted pyridines are involved in bioactivities with applications in
pharmaceutical drugs and agricultural products [7–9]. The picoline
derivatives prepared from aminopyridine derivatives have been
shown to have cholesterol lowering properties, anticancer and
anti-inflammatory agents [7]. The ring nitrogen of most pyridines
undergoes reactions such as protonation, alkylation and acylation
[8]. The harmonic frequencies of pyridine derivatives are calcu-
lated by several authors [10–12].
Spectrometer between 4000 and 100 cmꢁ1. The spectral resolution
is 2 cmꢁ1. The FT-Raman spectrum of the compound is also re-
corded in the same instrument with FRA 106 Raman module
equipped with Nd: YAG laser source operating at 1.064 lm line
widths with 200 mW powers. The spectra are recorded with scan-
ning speed of 30 cmꢁ1 minꢁ1 of spectral width 2 cmꢁ1. The fre-
quencies of all sharp bands are accurate to 1 cmꢁ1
.
Chemical composition of molecule
PAO is synthesized by reacting picolinaldehyde (2-formyl pyri-
dine) with hydroxylamine, giving pyridine-2-aldoxime [15]. From
Fig. 2, the following mechanism may also be postulated: nucleo-
philic displacement of the chloro group yields the alkylhydroxyl-
amine (I), subsequent protonation of the hydroxyl group of I to
produce II, followed by the elimination, yields the aldimine (III),
and the aldimine in the presence of excess hydroxylamine yields
the product oxime (IV) [16].
To the best of our knowledge, neither quantum chemical calcu-
lations, nor the vibrational analysis study of Pycolinaldehyde
oxime (abbreviated as PAO) has been reported yet. This inadequacy
observed in the literature encouraged us to make this theoretical
and experimental vibration spectroscopic research based on the
structure of molecule to give a correct assignment of the funda-
mental bands in experimental FT-IR and FT-Raman spectra were
found the spectrum varies significantly, which indicated the
changing of molecule structure. Therefore, a few modes with dif-
ferent system structure were set up for calculation. At present,
there are many papers about theoretical research: studies of vibra-
tion assignment on substituted pyridine because of pharmaceutical
application [13,14]. The understanding of their molecular proper-
ties as well as natures of reaction mechanism they undergo has
got great importance. Hence, the investigation on the structures
and the vibrations of pyridine and substituted pyridine are still
being carried out, increasingly.
Quantum chemical calculations
The entire quantum chemical calculations have been performed
at HF and DFT (B3LYP) methods with 6-311++G(d,p) basis set using
the Gaussian 03 program [17]. The optimized structural parame-
ters have been evaluated for the calculations of vibrational fre-
quencies by assuming Cs point group symmetry. At the
optimized geometry for the title molecule no imaginary frequency
modes were obtained, so there is a true minimum on the potential
energy surface was found. As a result, the unscaled calculated fre-
quencies, reduced masses, force constants, infrared intensities, and
Raman activities are obtained. In order to fit the theoretical wave
numbers to the experimental, the scaling factors have been intro-
duced by using a least square optimization of the computed to
the experimental data. Vibrational frequencies are scaled as
0.9067 for HF and the range of wavenumbers above 1700 cmꢁ1are
scaled as 0.958 and below 1700 cmꢁ1scaled as 0.983 for B3LYP to
account for systematic errors caused by basis set incompleteness,
neglect of electron correlation and vibrational anharmonicity
[18]. After scaled with the scaling factor, the deviation from the
experiments is less than 10 cmꢁ1with a few exceptions. Gauss view
Program has been considered to get visual animation and for the
verification of the normal modes assignment [19,20]. The elec-
tronic absorption spectra for optimized molecule calculated with
the time dependent DFT (TD–DFT) at B3LYP/6-311++G(d,p) and
HF/6-311++G(d,p) level at in gas phase. Furthermore, in order to
show nonlinear optic (NLO)activity of title molecule, the dipole
moment, linear polarizability and first hyperpolarizability were
obtained. Moreover, the changes in the thermodynamic functions
Experimental
The compound under investigation namely PAO is purchased
from M/S Aldrich Chemicals, USA with spectroscopic grade and it
is used as such without any further purification. The FT-IR spec-
trum of the compound has been recorded in Perkin-Elmer 180
Fig. 1. Sample picture of pycolinaldehyde oxime.
Fig. 2. Chemical composition of pycolinaldehyde oxime.

218
A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
(the heat capacity, entropy, and enthalpy) were investigated for
the different temperatures from the vibrational frequency calcula-
tions of title molecule.
HF/6-311 + G(d,p) methods, respectively. The CAN bond lengths
are shorter than experimental values (1.388 Å) and B3LYP values
are closer than HF values. The ring appears little distorted and an-
gles slightly out of perfect hexagonal structure. The asymmetry of
the pyridine ring is also evident from the positive deviation of
C4AC5AC6 and C2AC3AC4 angles which are calculated 119.4 Å
(B3LYP) and the C3AC2AC11 angle found to be bigger than calcu-
lation (1.1 Å). Substitution with the oxime leads to some changes
of the bond angles in the aromatic ring. The CACAH angles are al-
most same with (120.4 Å) except C3AC4AH8 and C5AC4AH8 [21].
Results and discussion
Molecular geometry
The optimized geometry of PAO which performed by HF and
B3LYP methods with atoms numbering are shown in Fig. 3. The
optimized bond lengths, and bond angles of title compound which
are calculated by using ab-initio HF and DFT(B3LYP) methods with
6-311++G(d,p) basis set are shown in Table S1. In this work, geom-
etry optimization parameters for PAO have been employed with-
out symmetry constrains. The carbon atoms are bonded to the
NLO activity
The second-order polarizability or first hyperpolarizability b, di-
pole moment
l and polarizability a is calculated using 6-
311++G(d,p) basis set on the basis of the finite-field approach.
The complete equations for calculating the magnitude of total di-
hydrogen atoms with
p and r bond in pyridine and the substitu-
tion of an oxime for hydrogen reduces the electron density at the
ring carbon atom. The ring carbon atoms in substituted pyridine
exert a larger attraction on the valence electron cloud of the hydro-
gen atom resulting in an increase in the CAH force constant and a
decrease in the corresponding bond length. The reverse holds well
on substitution with electron donating groups.
pole moment
polarizability
l
D
, the mean polarizability
ao, the anisotropy of the
a
and the mean first polarizability b, using the x,
y, z components from Gaussian 03 W output is as follows
1
2
ltot ¼ ðl2x
þ
ly2
þ
lz2
Þ
1
3
From Table S1, the CAH bond lengths are shorter than experi-
mental values (1.081 Å) for both B3LYP and HF methods. The actual
change in the CAH bond length would be influenced by the com-
bined effects of the inductive–mesmeric interaction and the elec-
tric dipole field of the polar substituent. CAC bond lengths are
calculated by HF method are little shorter than DFT/B3LYP method
compared with experimental value. Bond length of C2AC3 and
C5AC6 for HF is 1.390 Å but for DFT 1.402 Å, which is closer to
the experimental data (1.395 Å), where as the other CAC bonds
are like C3AC4, and C4AC5 ꢂ 1.396 Å in DFT/B3LYP respectively.
The average bond distances of CAC and CAH in the pyridine ring
calculated by DFT method are 1.395 and 1.070 Å, respectively.
The bond lengths of CAC bond are differing in value, which is
due to the substitutions on the benzene ring in the place of hydro-
gen atom. The optimized NAH bond length are calculated 1.000 Å
by B3LYP and 1.007 Å by HF with 6-311++G(d,p) method. By com-
paring those values with experimental value of 1.001 Å, it is ob-
served that B3LYP estimate the NAH bond length better than HF,
which underestimates this bond than experimental values. The
optimized CAN bond length by two methods are 1.344 and
1.344 Å for B3LYP/6-311 + G(d,p)and 1.331 and 1.313 Å for
atot
¼
ð
axx
þ
ayy
þ
azz
Þ
h
i
1
2
1
2
2
2
D
a
¼
ðaxx
ꢁ
ayyÞ þðayy
ꢁ
azzÞ þðazz
ꢁ
axxÞ þ6a2xz þ6ax2y þ6a2yz
pffiffiffi
2
h
i
1
2
2
2
2
hbi ¼ ðbxxx þbxyy þbxzzÞ þðbyyy þbyzz þbyxxÞ þðbzzz þbzxx þbzyy
Þ
The polarizabilities and hyper polarizability are reported in atomic
units (a.u), the calculated values have been converted into electro-
static units (esu)
(a:
1
a.u. = 0.1482 ꢃ 10ꢁ24 esu, b:
1
a.u. = 8.6393 ꢃ 10ꢁ33 esu). The hyperpolarizability b, dipole mo-
ment
l and polarizability a are presented in Table S2. The calcu-
lated value of polarizability (
a
zz) in PAO is 16.3193 ꢃ 10ꢁ24 esu,
predicts highest value compared to other polarizabilities. The mag-
nitude of the molecular hyperpolarizability b, is one of important
key factors in a NLO system. The maximum value of dipole moment
is calculated in HF/6-311++G(d,p) (0.9609). The highest and lowest
hyperpolarizablities are observed as 232.08891 ꢃ 10ꢁ33 esu and
22.4982 ꢃ 10ꢁ33 in the direction bzyy and bzxx in HF/6-311++G(d,p).
Natural bond orbital analysis
Natural bond orbital analysis is an essential tool for studying in-
tra- and intermolecular bonding and interaction among bonds, and
also provides a convenient basis for investigating charge transfer or
conjugative interaction in molecular systems. Some electron donor
orbital, acceptor orbital and the interacting stabilization energy
resulting from the second-order micro disturbance theory is re-
ported [22,23]. The larger the E(2) value, the more intensive is
the interaction between electron donors and electron acceptors,
i.e. the more donating tendency from electron donors to electron
acceptors and the greater the extent of conjugation of the whole
system. Delocalization of electron density between occupied Le-
wis-type (bond or lone pair) NBO orbitals and formally unoccupied
(antibond or Rydgberg) non-Lewis NBO orbitals correspond to a
stabilizing donor acceptor interaction. The intramolecular interac-
tion are formed by the orbital overlap between
p
r
(CAC), rꢄ(C AC),
(CAC), pꢄ(CAC) bond orbital which results intermolecular charge
transfer (ICT) causing stabilization of the system. These interac-
tions are observed as increase in electron density (ED) in CAC
anti–bonding orbital that weakens the respective bonds. These
Fig. 3. Optimized geometric structure with atoms numbering of pycolinaldehyde
oxime.
intramolecular charge transfer (r ? , p ?
rꢄ pꢄ) can induce large

A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
219
nonlinearity of the molecule. The strong intramolecular hypercon-
jugative interaction of the electron of C3AC4 distribute to
⁄C2AC3, C2AC11, C3AH7, C4AC5, C4AH8 and C5AH9 of the ring
functions are increasing with temperature ranging from 100 to
500 K due to the fact that the molecular vibrational intensities in-
crease with temperature [24]. The correlation equations between
heat capacity, entropy, enthalpy changes and temperatures were
fitted by quadratic formulas and the corresponding fitting factors
(R2) for these thermodynamic properties are 0.99234, 0.99994
and 0.99995, respectively. The corresponding fitting equations
are as follows and the correlation graphs of those shows in Fig. S1.
r
r
as evident from Table 1. On the other hand, side the
p (C3AC4) in
the ring conjugate to the anti-bonding orbital of pꢄ (N1AC2) and
(C5AC6) which leads to strong delocalization of 26.18 and
17.32 kJ/mol. The
p (C5AC6) bond is conjugated to the anti-bond-
ing orbital of pꢄ (N1AC2) and (C3AC4) contributing energy of
18.19 and 22.66 kcal/mol.
C ¼ 1:49565 þ 0:11612T ꢁ 6:8516 ꢃ 10ꢁ5T2ðR2 ¼ 0:98978Þ
S ¼ 52:06744 þ 0:11498T ꢁ 2:63874 ꢃ 10ꢁ5T2ðR2 ¼ 0:99994Þ
H ¼ 0:22509 þ 0:00336T þ 4:26517 ꢃ 10ꢁ5T2ðR2 ¼ 0:99995Þ
Thermodynamic properties
The variation in zero-point vibrational energies (ZPVEs) seems
to be significant. The ZPVE is much lower by the DFT B3LYP meth-
od than by the HF method. The biggest value of ZPVE of PAO is ob-
tained 1219.178 auk by B3LYP/6-311++G(d,p) whereas the
smallest values are 1201.839 a.u. obtained at HF/6-311++G(d,p).
Dipole moment reflects the molecular charge distribution and is gi-
ven as a vector in three dimensions. Therefore, it can be used as
descriptor to depict the charge movement across the molecule.
The dipole moment vector in a molecule depends on the centers
of positive and negative charges. Dipole moments are strictly
determined for neutral molecules. For charged systems, its value
depends on the choice of origin and molecular orientation. As a re-
sult of HF and DFT (B3LYP) calculations the highest dipole moment
was observed for HF/6-311G++(d,p) whereas the smallest one was
observed for B3LYP/6-311G(d,p) in each molecule. On the basis of
vibrational analysis, the statically thermodynamic functions: heat
capacity (C), entropy (S), and enthalpy changes (H) for the title
molecule were obtained from the theoretical harmonic frequencies
and listed in Table 2. It can be observed that these thermodynamic
All the thermodynamic data supply helpful information for the fur-
ther study on PAO. They can be used to compute the other thermo-
dynamic energies according to relationships of thermodynamic
functions and estimate directions of chemical reactions according
to the second law of thermodynamics in Thermo chemical field. No-
tice: all thermodynamic calculations were done in gas phase and
they could not be used in solution.
Mulliken atomic charges
The calculated mulliken charges values natural charges of PAO
are listed in Table 3. The results show that substitution of the
pyridine ring by oxime group leads to are distribution of electron
density. The charges changes with basis set presumably occurs
due to polarization, for example, the charge of O15 atom is
ꢁ0.2403eꢁ for B3LYP/6-311++G(d,p), ꢁ0.36176eꢁ for HF/6-
311++G(d,p) and ꢁ0.5350eꢁ for natural charge. The charge of atom
N is positive B3LYP with 6-311++G(d,p) basis set, however in both
Table 1
Second order perturbation theory analysis of Fock matrix in NBO basis for PAO.
Donor (I)
Type of band
Occupancy
Acceptor (J)
Type of band
Occupancy
E2 (kJ/mol)a
E (j)–E (i) (a.u)b
F (i, j) (a.u)c
C2AC11
r
1.974
1.974
1.974
1.974
1.974
1.981
1.981
1.981
1.981
1.981
1.981
1.979
1.979
1.979
1.979
1.979
1.979
1.665
1.665
1.980
1.980
1.980
1.980
1.980
1.980
1.986
1.986
1.986
1.986
1.986
1.622
1.622
N1AC2
N1AC6
C2AC3
C3AC4
N13AO15
N1AC2
C2AC11
C3AC4
C3AH7
C4AH8
C11AH12
C2AC3
C2AC11
C3AH7
C4AC5
C4AH8
C5AH9
N1AC2
C5AC6
C3AC4
C3AH7
C4AH8
C5AC6
C5AH9
C6AH10
N1AC6
C4AC5
C4AH8
C5AH9
C6AH10
N1AC2
C3AC4
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
pꢄ
0.019
0.508
0.033
0.016
0.014
0.019
0.035
0.016
0.016
0.013
0.010
0.033
0.035
0.016
0.015
0.013
0.013
0.439
0.299
0.016
0.016
0.013
0.299
0.013
0.022
0.508
0.015
0.013
0.013
0.022
0.439
0.302
0.83
3.45
1.00
2.38
4.59
2.09
1.04
2.89
1.14
2.26
0.91
3.15
3.11
1.32
2.44
0.90
2.34
26.18
17.32
2.59
2.75
0.93
2.11
1.02
1.93
1.16
2.22
2.50
0.94
0.86
18.19
22.66
1.16
1.17
1.19
1.20
0.93
1.24
1.09
1.28
1.16
1.17
1.15
1.26
1.09
1.16
1.28
1.17
1.17
0.27
0.28
1.27
1.15
1.17
1.26
1.17
1.16
1.24
1.27
1.16
1.17
1.16
0.26
0.27
0.028
0.057
0.031
0.048
0.058
0.045
0.030
0.054
0.032
0.046
0.029
0.056
0.052
0.035
0.050
0.029
0.047
0.077
0.063
0.051
0.050
0.029
0.046
0.031
0.042
0.034
0.047
0.048
0.030
0.028
0.062
0.072
C2AC3
C3AC4
r
r
C3AC4
C4AC5
p
pꢄ
r
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
rꢄ
pꢄ
C5AC6
r
p
pꢄ
a
b
c
E(2) means energy of hyper conjugative interactions.
Energy difference between donor and acceptor i and j NBO orbitals.
F(i, j) is the Fock matrix element between i and j NBO orbitals.

220
A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
Table 2
deficiencies. After applying the scaling factors, the theoretical calcu-
lations reproduce the experimental data well in agreement. The ob-
served and scaled theoretical frequencies, IR intensities, Raman
activities, and mode of description are listed in Table 4.
Thermodynamic functions at different temperatures at the B3LYP/6-311++G(d,p)
level for PAO.
T (K)
C (cal molꢁ1 kꢁ1
)
S (cal molꢁ1 kꢁ1
)
H (cal molꢁ1 kꢁ1
)
100
150
200
250
300
350
400
450
500
10.942
18.995
22.872
26.002
29.903
33.224
36.520
39.747
43.007
63.358
68.559
74.159
79.125
84.186
89.118
93.724
98.577
102.928
0.994
1.670
2.620
3.721
5.072
6.639
8.347
10.423
12.547
CAH vibrations
The CAH stretching frequencies appear in the range of 3100–
3000 cmꢁ1 [25]. The investigated molecule is single substituted,
therefore four aromatic CAH vibrations (C3AH7, C4AH8, C5AH9
and C6AH10) plus one (C11AH12) with pyridine substitution were
observed in vibrational spectra. From Table 5, the theoretically cal-
culated scaled down vibrations corresponding with CAH stretch
show good agreement with the experimentally observed vibrations
at 3080(m) and 3040(m) cmꢁ1 in FT-Raman and 3090(s), 3050(s)
and 3010(s) cmꢁ1 in FTIR. The bands are appeared with very strong
intensities. It clearly shows that CAH stretching vibrations are not
affected by the substitution of an oxime group. The CAH vibra-
tional frequencies are downshifted due to the inductive effect of
the aldehyde compound. The calculated frequencies are very good
agreement in B3LYP/6-311++G(d,p) basis set for PAO. All the above
vibrations are observed in the expected range. Substitution sensi-
tive CAH in-plane bending vibrations lie in the region 1000–
1300 cmꢁ1 [26]. In PAO, three infrared bands at 1200(s),
1150(vw), 1130(w), 1110(m) and 1050(m) cmꢁ1 are assigned to
CAH in-plane bending vibrations. All these bands are in the ex-
pected range. The upper limit of vibration of the compound is
shortened with literature values which may be due to the oxime
compounds. Bands involving the out-of-plane CAH vibrations ap-
pear in the range 1000–675 cmꢁ1[27]. The CAH out-of-plane bend-
ing vibrations are also lie within the characteristic region.
However, the change in the frequencies of these deformations from
the values in PAO is almost determined exclusively by the relative
position of the substituents and is almost independent of their nat-
ure. The bands at 880(m), 840(s), 780(m), 760(m) and 710(s) cmꢁ1
are assigned to CAH out-of-plane vibrations for PAO.
Table 3
Mulliken atomic charges and Natural charges of PAO.
Atoms
Mulliken charges
HF/6-311++G(d,p)
Natural charges
B3LYP/6-311++G(d,p)
B3LYP/6-311++G(d,p)
N1
C2
C3
C4
C5
C6
H7
H8
ꢁ0.0589
ꢁ0.3780
0.6202
0.0095
ꢁ0.4360
0.6415
ꢁ0.4539
0.1482
ꢁ0.2252
ꢁ0.1579
ꢁ0.2303
0.0690
0.1871
0.2110
0.2103
0.1931
0.0703
ꢁ0.8837
ꢁ0.9039
0.0367
0.2083
ꢁ0.1556
0.3463
0.2245
0.2181
0.2243
ꢁ0.2424
0.2837
0.1789
0.1856
0.1940
H9
H10
C11
H12
N13
H14
O15
ꢁ0.2785
ꢁ0.2558
0.2313
0.1859
0.2262
ꢁ0.0790
0.3660
ꢁ0.5350
ꢁ0.1140
0.3288
ꢁ0.3618
ꢁ0.1010
0.2921
ꢁ0.2404
HF and natural charge with 6-311++G(d,p) this charge is negative.
The charge of the nitrogen atom is lowest value in HF/6-
311++G(d,p) and highest value in B3LYP/6-311++G(d,p). The
charges of atom N13 are ꢁ0.1010eꢁ and ꢁ0.1139eꢁ for B3LYP
and HF methods with 6-311++G(d,p), respectively. In C2 carbon
atom, the charge distribution is higher value in HF/6-311++G(d,p)
basis set and little lower value in B3LYP/6-311++G(d,p). The results
show that substitution of the pyridine ring by a oxime group leads
to a redistribution of electron density. All the hydrogen atoms have
a net positive charge. Moreover, the H8, H9 and H10 atoms in car-
bon position to (CH@NOH) accommodate higher positive charge
than the H7 atom. Considering the all methods and basis sets used
in the atomic charge calculation, the oxygen atoms exhibit a nega-
tive charge, which are donor atoms. Hydrogen atom exhibits a po-
sitive charge, which is an acceptor atom, may suggest the presence
of both inter-molecular bonding in the gas phase.
CAC vibrations
The ring stretching vibrations are very much important in the
spectrum of toluene, benzene and their derivatives are highly char-
acteristic of the aromatic ring itself. The bands between 1400 and
1650 cmꢁ1 in benzene derivatives are usually assigned to CAC
stretching modes [28]. Varsanyi observed five bands, 1625–1590,
1590–1575, 1540–1470, and 1465–1430 and 1380–1280 cmꢁ1, in
this region [29]. For title compound, the CAC stretching vibrations
are found at 1530(vs), 1490(s) and 1430(s) cmꢁ1 in Raman and the
CAC stretching vibrations are assigned at 1510(w) and 1500(vs),
cmꢁ1 in IR. All bands are appeared in the expected range, except
first band. 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 are very less. It shows
the good agreement between theoretical and experimental CAC
stretching vibrations. The absorption bands arising from CAC in
plane bending vibrations are usually observed in the region at
675–1000 cmꢁ1[30]. The two bands (1040, 900) cmꢁ1 are in Raman
with medium and very strong intensity, and last one is lie in both
Raman and IR (1000 cmꢁ1) with medium intensity. This is in agree-
ment with the literature data. The bands are assigned to CAC out-
of-plane bending vibrations are observed at 450 and 112 cmꢁ1
these vibrations are assigned at 420(s), 390(vs) and 320 (vw) cmꢁ1-
in IR [31]. The mean difference between experimental and calcu-
lated (B3LYP/6-311++G(d,p)) values of CAC vibrations is only
Vibrational analysis
The title molecule consists of 15 atoms, which undergo 39 nor-
mal modes of vibrations. The 39 normal modes of PAO are distrib-
uted by symmetry species as:
C
vib ¼ 28A0 þ 11A00
It agrees with Cs point group symmetry, all vibrations are active
both in Raman and infrared absorption. Here A0 represents symmet-
ric planer and A00 asymmetric non planer vibrations. The detailed
vibrational assignment of the experimental wavenumbers is based
on normal mode analyses and a comparison with theoretically
scaled wavenumbers. In Figs. 4 and 5, the calculated frequencies
are usually higher than the corresponding experimental quantities,
due to the combination of electron correlation effects and basis set
1 cmꢁ1
.

A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
221
Fig. 4. Experimental and simulated Infrared spectra of pycolinaldehyde oxime.
Fig. 5. Experimental and simulated Raman spectra of pycolinaldehyde oxime.
CAN vibrations
group for PAO is identified at 940(w) cmꢁ1 in FTIR spectrum. The
symmetric in-plane bending mode of NAH group is assigned at
510(s) cmꢁ1 and out-of-plane 190(m) cmꢁ1 in both FTIR and FT-Ra-
man spectrum respectively. These values are lower than theoreti-
cal frequency region [34]. Even NAH stretch, in–plane and out-
of-plane vibrations are assigned at 3170(m), 1230(s) and 950(w)
in Raman, which is in agreement with the literature data [35].
These bands were also found well within the characteristic region
and summarized in Table 5.
Because of the mixing of several bands, the identification of
CAN vibrations is a very difficult task. Silverstein assigned CAN
stretching absorption in the region 1382–1266 cmꢁ1 [32]. In the
present work, the bands are observed at 1380(w) and
1320(vs) cmꢁ1 in FT-Raman spectrum has been assigned to CAN
stretching vibration. The modes are calculated at 1390 and
1302 cmꢁ1 in B3LYP/6-311++G(d,p) basis set which in good agree-
ment with experimental value. The remainder of the observed and
calculated wavenumbers and assignments of present molecule are
shown in Table 5.
Frontier molecular orbitals (FMOs)
The highest occupied molecular orbitals (HOMOs) and the
lowest–lying unoccupied molecular orbitals (LUMOs) are named
as frontier molecular orbitals (FMOs). The FMOs play an impor-
tant role in the optical and electric properties, as well as in quan-
tum chemistry and UV–VIS spectra [36]. The HOMO represents
the ability to donate an electron, LUMO as an electron acceptor
represents the ability to obtain an electron. The energy gap be-
tween HOMO and LUMO determines the kinetic stability, chem-
ical reactivity and optical polarizability and chemical hardness–
softness of a molecule [37]. In order to evaluate the energetic
behavior of the title compound, the HOMO–LUMO energy gap
NAO and NAH vibrations
The characteristics group frequencies of the NAO are indepen-
dent of the rest of the molecule. For the assignments of NAO group
frequencies can be associated to symmetric and antisymmetric
stretch, in-plane vibrations which scissoring and rocking. In addi-
tion to that, wagging and twisting modes would be expected to
be depolarized for out-of-plane vibrations. The NAO stretching
vibration in aromatic compounds has strong absorption at
960 cmꢁ1 [33]. Hence, the asymmetric stretching mode of NAO

222
A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
Table 4
Detailed vibrational assignments of experimental and theoretical wavenumbers of PAO.
Sl. No
Sy
Experimentala
FTIR
B3LYP/6-311++G(d,p)
Vibrational assignment
FTRaman
Scaled
IIR
SRaman
Force constants
1
2
3
4
5
6
7
8
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A0
A00
A0
A0
A00
A00
A0
A00
A00
A0
A00
A0
A00
A0
A00
A00
A0
A0
A00
A00
3170(m)
3090(s)
3201
3096
3081
3060
3042
3016
1613
1588
1575
1533
1457
1438
1390
1302
1293
1217
1157
1108
1093
1047
1001
987
967
910
886
886
809
763
760
741
624
556
508
412
389
337
191
162
18.61
3.76
7.17
12.87
7.25
21.21
72.08
46.29
13.56
35.68
9.06
37.34
216.65
0.82
0.40
1.03
2.07
89.42
12.30
8.22
0.73
5.59
2.23
9.20
8.23
4.55
88.37
1.03
2.30
19.42
4.05
1.96
18.11
4.10
12.39
2.46
12.89
23.29
6.47
295.77
33.40
69.12
217.51
81.01
133.60
55.43
454.36
8.20
235.94
4.14
37.85
3.68
62.07
3.97
77.07
26.81
17.17
2.66
17.74
0.50
53.94
0.18
0.17
0.66
10.62
3.61
10.56
0.01
0.06
4.73
2.05
2.94
7.09
6.73
6.65
6.59
6.47
6.36
5.90
7.50
7.85
2.58
2.65
2.70
2.13
1.94
2.76
2.88
0.93
1.65
1.18
1.54
0.80
4.34
0.81
0.65
0.62
2.35
0.70
2.30
0.44
0.85
1.72
0.57
1.00
0.38
0.30
0.52
0.15
0.06
0.02
(NAH)t
(CAH)
(CAH)
(CAH)
(CAH)
(CAH)
(C@N)
t
t
t
t
t
t
3080(m)
3040(m)
3050(s)
3010(s)
1590(w)
1530(vs)
(CAC)
(CAC)
(CAC)
(CAC)
(CAC)
t
t
t
t
t
9
1510(w)
1500(vs)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
1490(s)
1430(s)
1380(w)
1320(vs)
(CAN)
(CAN)
t
t
1230(s)
(NAH)d
(CAH)d
(CAH)d
(CAH)d
(CAH)d
(CAH)d
(CAC)d
(CAC)d
1200(s)
1150(vw)
1130(w)
1110(m)
1050(m)
1040(m)
1000(vw)
1000(m)
950(w)
940(w)
900(s)
880(vs)
840(s)
780(m)
760(m)
710(s)
620(vs)
560(s)
510(s)
420(s)
390(m)
320(vw)
190(m)
100(s)
(NAH)
(NAO)
(CAC)d
c
t
900(vs)
880(m)
(CAH)
(CAH)
(CAH)
(CAH)
(CAH)
c
c
c
c
c
780(s)
(CAN)d
(CAN)d
(NAO)d
560(w)
510(w)
420(vw)
0.60
1.43
6.06
5.31
0.68
0.14
(CAC)
(CAC)
(CAC)
c
c
c
190(w)
100(vs)
80(s)
(NAO)c
(CAN)
(CAN)
c
c
84
Sy: symmetry species; as: strong; vs: very strong; m: medium; w: weak; vw: very weak.
Raman scattering activity.
t
:stretching; d:in-plane bending;
c
:out-of-plane bending; IIR: IR intensity; SRaman
:
Table 5
The experimental, calculated and corrected 1H and 13C NMR isotropic chemical shifts (ppm) of PAO.
Atoms
B3LYP
Expt.a
Atoms
B3LYP
Expt.a
Calculated
Corrected
Calculated
Corrected
C2
C11
C6
C4
C3
C5
161.55
157.84
153.07
143.22
140.08
132.92
154.34
150.02
144.46
132.98
129.33
120.98
151.61
149.58
148.71
137.26
123.88
121.17
H14
H10
H12
H8
11.42
8.89
7.94
7.84
7.21
12.20
8.75
8.46
7.93
7.39
12.06
9.02
8.13
8.02
7.30
H9
was calculated at the B3LYP/6-311++G(d,p) level, which reveals
that the energy gap reflects the chemical activity of the molecule.
The energies of four important molecular orbitals of PAO in gas:
the second highest and highest occupied MO’s (HOMO and
HOMOꢁ1), the lowest and the second lowest unoccupied MO’s
(LUMO and LUMO + 1) were calculated. The calculated energy va-
lue of HOMO is ꢁ8.4510 eV and LUMO is 2.2430 eV in gaseous
phase. The value of energy separation between the HOMO and
LUMO is 10.6940 eV explains the eventual charge transfer inter-
action within the molecule, which influences the biological activ-
ity of the molecule. Consequently, the lowering of the
HOMO M LUMO band gap is essentially a consequence of the
large stabilization of the LUMO due to the strong electron–accep-
tor ability of the electron–acceptor group. Other quantum
descriptors like Electro negativity (
v), Chemical hardness (g),
Electrophilicity index ( ) and Softness (f) of PAO is 5.2548,
w
3.0631, 4.4636, and 0.1616 eV in gas respectively. The 3D plots
of the HOMO, HOMO ꢁ 1, LUMO and LUMO + 1 orbitals com-
puted at the B3LYP/6-311++G(d,p) level for PAO molecule are
illustrated in Fig. 6 (in gas). As can been seen, overlapping of
orbital loops located on the HOMO and LUMO confirms the pres-
ence a resonance–assisted hydrogen bonding. The positive phase
is red (For interpretation of the references to colour in this text,
the reader is referred to the web version of the article.) and the

A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
223
negative one is green. It is clear from the figure that, while the
HOMO is localized on the whole molecule which splitted up into
two rings, but in LUMO is localized on the pyridine ring and
substitution atom,which splitted up into four rings. The
HOMO ? LUMO transition implies an electron density transfer
to CH@NOH atom.
The molecular electrostatic potential (MEP) map is shown in the
Fig. 7. It is useful to study the electrophile attracted negative re-
gions (where the electron distribution effect is dominant). In the
majority of the MEP, while the maximum negative region which
preferred site for electrophilic attack indications as red colour,
the maximum positive region which preferred site for nucleophilic
attack symptoms as blue colour. The importance of MEP lies in the
fact that it simultaneously displays molecular size, shape as well as
positive, negative and neutral electrostatic potential regions in
terms of colour grading (Fig. 7) and is very useful in research of
molecular structure with its physiochemical property relationship.
The resulting surface simultaneously displays molecular size and
shape and electrostatic potential value.
Fig. 7. Molecular electrostatic potential of pycolinaldehyde oxime.
The different values of the electrostatic potential are repre-
sented by different colors. Potential increases in the order
red < orange < yellow < green < blue. Regions of negative are usu-
ally associated with the lone pair of electronegative atoms. As
can be seen from the MEP map of the title molecule, while regions
having the negative potential are over the electronegative atoms
(CC group, oxygen and nitrogen atoms), the regions having the po-
sitive potential are over hydrogen atoms. The O and N atoms indi-
cates the strongest repulsion with other aoms.
solution. Aromatic carbons give signals in overlapped areas of the
spectrum with chemical shift values from 100 to 150 ppm.
In our present investigation, the experimental chemical shift
values of aromatic carbons are in the range 121.17–151.61 ppm.
The N atom have more electronegative property polarizes the elec-
tron distribution in its bond to adjacent carbon atom and decreases
the chemical shifts value. The 1H and 13C NMR isotropic chemical
shifts (ppm) of PAO are shown in Fig. 8. On the basis of 13C NMR
spectra, in which the ring carbons (C2 and C11) attached to the
N atom have bigger chemical shift (161.55 and 157.84 ppm) than
the other carbon atoms because of the substitution of NHO group.
The chemical shift values of C3 and C5 (140.08 and 132.92 ppm)
are smaller than the other aromatic carbons. The experimental
chemical shift values of 149.58 ppm (B3LYP) for carbon atom
(C11) are in good agreement with the computed values
(150.02 ppm).
NMR spectra and calculations
The theoretical 1H and 13C NMR chemical shifts of C and H have
been compared with the experimental data [38] as shown in Ta-
ble 5. Chemical shifts are reported in ppm relative to TMS for 1H
and 13C NMR spectra. The atom statues were numbered according
to Fig. 3. Firstly, full geometry optimization of the PAO was per-
formed at the gradient corrected density functional level of theory
using the hybrid B3LYP method based on Becke’s three parameters
The chemical shifts obtained and calculated for the 1H atoms of
oxime groups are quite low. Because, the hydrogen atoms are at-
tached to nearby electron–withdrawing atom and group can de-
crease the shielding. Attached to ring protons are accumulated in
the range of 7.21–11.42 ppm (B3LYP), observed experimentally in
7.30–12.06 ppm. The correlations between the experimental and
calculated chemical shifts obtained by B3LYP method are shown
in Fig. 9. There is a good agreement between experimental and the-
oretical chemical shift results for the title compound. The perfor-
mances of the B3LYP method with respect to the prediction of
the chemical shifts within the molecule were quite close.
functional of DFT. Then, gauge–including atomic orbital (GIAO) 1
H
and 13C chemical shift calculations of the compound was made by
the same method using 6-311++G(d,p) basis set IEFPCM/CDCl3
Conclusion
A complete vibrational analysis of PAO are by performed HF and
DFT-B3LYP methods with 6-311++G(d,p) basis sets. The influences
of substitutions of oxime with ring are investigated and the vibra-
tional frequencies of the title compound are discussed. The ob-
served and stimulated spectra are agreed for the good frequency
fit in DFT B3LYP/6-311++G(d,p) method. The less standard devia-
tion between theoretical and experimental wave numbers is con-
firmed by the qualitative agreement between the calculated and
observed frequencies. The MEP map shows the negative potential
sites are on oxygen and nitrogen atoms as well as the positive po-
tential sites are around the hydrogen atoms. Furthermore, the ther-
modynamic properties of the compound are calculated. The
correlations between the statistical thermodynamics and tempera-
ture are also obtained. It was seen that the heat capacity, entropy
Fig. 6. HOMO and LUMO orbitals of pycolinaldehyde oxime.

224
A. Suvitha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 216–224
Fig. 8. 1H and 13C NMR isotropic chemical shifts (ppm) of pycolinaldehyde oxime.
[2] A. Kaminski, T. Kino, T. Tama, A. Yukon, K. Ueda, K. Taka chi, J. Hollinger, H.J.
Richler, J. Hausa, J. Fernandez, R. Bald, M. Macke, G.M.A. Gad, Jon. J. Appl. Phys
41 (2002). L603–L605.
[3] M. Komati, K. Takahashi, T. Doi, Y. Takimoto, Anal. Chem. 69 (1997). 2919–
2926.
[4] C.B. Millard, C.A. Broomfield, J. Neurochem., 1995 (Wiley Online Library).
[5] M.Y. Li, P.Z. Hu, W.R. Zhu, K.X. Xu, Chin. Chem. Lett. 14 (2003) 572–574.
[6] M. Jokanovic´, M. Prostran, Curr. Med. Chem. 16 (17) (2009) 217788.
[7] S.P. Jose, S. Mohan, Spectrochim. Acta 64A (2006) 240–245.
[8] K. Othmer, Encyclopedia of Chemical Technology, 4th ed., vol. 20, 1997.
[9] P. Pierrat, P.C. Gros, Y. Fort, J. Comb. Chem. 7 (2005) 879–886.
[10] K.B. Wiberg, V.A. Walters, K.N. Wong, S.D. Colson, J. Phys. Chem. 88 (1984)
6067–6075.
[11] T. Yamamoto, R. Mitsuhashi, M. Akiyama, Y. Kakiuti, J. Mol. Spectrosc. 117
(1986) 30–37.
[12] A. Destexhe, J. Smets, L. Adamowicz, G. Maes, J. Phys. Chem. 98 (1994) 1506–
1514.
[13] N. Sundaraganesan, S. Ilakiamani, H. Saleem, M. Piotr, Spectrochim. Acta Part A
61 (2005) 2995–3001.
[14] Z. Zhuang, J. Cheng, X. Wang, B. Zhao, X. Han, Y. Luo, Spectrochim. Acta Part A
67 (2007) 509–516.
[15] D. Nachmansonn, S.Ginsburg, U.S. Patent 2,816,113, 1957.
[16] E.H. Brennie Jr, Daniher, A. Francis, Ash⁄ Arthur B1 (1966).
[17] Gaussian 03, Gaussian, Inc., Pitttsburgh, PA, 2003.
[18] M. Karabacak, M. Kurt, Spectrochim. Acta A 71 (2008) 876–883.
[19] M.H. Jamroz, Vibrational Energy Distribution Analysis VEDA 4, Warsaw, 2004.
[20] R.I. Dennington, T. Keith, J. Millam, K. Eppinnett, W. Hovell, Gauss View
Version, 2003.
Fig. 9. NMR chemical shift comparison between experimental and calculated
frequencies of pycolinaldehyde oxime.
[21] C. Arunagiri, M. Arivazhagan, A. Subashini, Spectrochim. Acta A 79 (2011)
1747–1756.
[22] C. James, A. AmalRaj, R. Reghunathan, I. Hubert Joe, V.S. JayaKumar, J. Raman
Spectrosc. 37 (2006) 1381–1392.
[23] L.J. Na, C.Z. Rang, Y.S. Fang, J. Zhejiang Univ. Sci. 6B (2005) 584–589.
[24] J. Bevan Ott, J. Boerio–Goates, Calculations from Statistical Thermodynamics,
Academic Press, 2000.
[25] V. Krishnakumar, R.J. Xavier, Indian J. Pure Appl. Phys. 41 (2003) 597.
[26] G. Socrates, Infrared and Raman Characteristic Group Frequencies – Tables and
Charts, 3rd ed., Wiley, New York, 2001.
and enthalpy increase with the increasing temperature owing to
the intensities of the molecular vibrations increase with increasing
temperature. The magnetic properties of title compound are ob-
served and calculated, and chemical shifts are compared with
experimental data, showed a good agreement 1H and 13C NMR.
Furthermore, the thermodynamic and electronic absorption prop-
erties of the compounds have been calculated. Theoretical elec-
tronic absorption spectra have some blue shifts and molecular
orbital coefficients analysis suggests that electronic transitions
[27] T.F. Ardyukoiva et al., Atlas of Spectra of Aromatic and Heterocyclic
Compounds, Nauka Sib otd, Novosibirsk, 1973.
[28] G. Varsanyi, Assignments of Vibrational Spectra of 700 Benzene Derivatives,
Wiley, New York, 1974.
are assigned to p–
p⁄ type.
[29] M. Chao, E. Schempp, Acta Crystallogr. B33 (1977) 1557.
[30] S. Gunesekaran, R. Thilak Kumar, S. Ponnusamy, Spectrochim. Acta Part A 65
(2006) 1041.
Acknowledgement
[31] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric identification of
organic compounds, 3rd ed., John Wiley & Sons, New York, NY, 1974. 239.
[32] N. Prabavathi, V. Krishnakumar, Spectrochim. Acta Part A 72 (2009) 743.
[33] S. Dheivamalar, V. Krishnakumar, Spectrochim. Acta Part A 71 (2008) 465.
[34] S. Manohar, R. Nagalakshmi, V. Krishnakumar, Spectrochim. Acta Part A 71
(2008) 110.
The authors gratefully acknowledge the support of this work by
the honorable Vice Chancellor and Dean of Periyar Maniyammai
University, Vallam, Tanjavur.
Appendix A. Supplementary material
[35] M. Govindarajan, K. Ganasan, S. Periandy, M. Karabacak, S. Mohan,
Spectrochim. Acta A 77 (2010) 1005–1013.
[36] I. Fleming, Frontier Orbitals, Organic Chemical Reactions, Wiley, London, 1976.
[37] B. Kosar, C. Albayrak, Spectrochim. Acta Part A 78 (2011) 160–167.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.07.080.
[38] Spectral
Database
for
Organic
Compounds,
SDBS.
http://
riodb01.ibase.aist.go.jp/sdbs/cgibin/direct_frame_top.cgi.
References
[1] Linnell, Robert, J. Org. Chem. 25 (2) (1960) 290.