Quantum mechanical study of the structure and spectroscopic, first order hyperpolarizability, Fukui function, NBO, normal coordinate analysis of Phenyl-N-(4-Methyl Phenyl) Nitrone

Article abstract of DOI:10.1016/j.saa.2013.04.007

The title compound, Phenyl-N-(4-Methyl Phenyl) Nitrone (PN4MPN) was synthesized and characterized by FT-IR, FT-Raman and ¹HNMR, ¹³CNMR spectral analysis. The molecular geometry, harmonic vibrational frequencies and bonding features of the title compound in the ground state are computed at the Hartree-Fock/6-311++G(d,p) and three parameter hybrid functional Lee-Yang-Parr/6-311++G(d,p) levels of theory. The calculated results show that the predicted geometry can well reproduce the structural parameters. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The calculated HOMO and LUMO energies confirm that charge transfer occurs within the molecule. The dipole moment (i), polarizability (a) and hyperpolarizability (b) of the investigated molecule is calculated by using HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) methods on the finite field approach. Besides, Molecular Electrostatic Potential (MEP), Natural Bond Orbital analysis (NBO) and thermodynam-ical properties are described from the computational process. The electron density-based local reactivity descriptor such as Fukui functions are calculated to explain the chemical selectivity or reactivity site in PN4MPN. Finally, the calculations are applied to simulated FT-IR and FT-Raman spectra of the title compound which show good agreement with observed spectra.

Full text of DOI:10.1016/j.saa.2013.04.007

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Quantum mechanical study of the structure and spectroscopic, first order
hyperpolarizability, Fukui function, NBO, normal coordinate analysis of
Phenyl-N-(4-Methyl Phenyl) Nitrone
N.R. Sheela a,b, S. Sampathkrishnan a, M. Thirumalai Kumar c, S. Muthu a,
⇑
a Department of Applied Physics, Sri Venkateswara College of Engineering, Sriperumbudur 602 105, India
b Research and Development Centre, Bharathiar University, Coimbatore 641 046, India
c Department of Applied Chemistry, Sri Venkateswara College of Engineering, Sriperumbudur 602 105, 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
The compound was synthesized from freshly distilled benzaldehyde (1.06 g,0.01 m) in ethanol (30 ml)
was added to 4-methyl phenyl hydroxylamine (1.85 g, 0.015 m) in ethanol (20 ml) and refluxed for
1 h. Evaporation of the solvent under reduced pressure gave
a solid which was recrystallised from ethanol yield 1.73 g (83%). The scheme of the synthesis is shown
in figure.
a-Phenyl-N-(4-Methyl Phenyl) Nitrone as
ꢀ
FT-IR and FT-Raman spectra of
Phenyl-N-(4-Methyl Phenyl) Nitrone
(PN4MPN) in the solid phase were
recorded and analyzed.
ꢀ
ꢀ
Vibrational assignments PED of
PN4MPN were calculated.
The first order hyperpolarizability
and HOMO, LUMO energy gap were
theoretically predicted.
ꢀ
The electron density-based local
reactivity descriptor such as Fukui
functions is calculated.
a r t i c l e i n f o
a b s t r a c t
Article history:
The title compound, Phenyl-N-(4-Methyl Phenyl) Nitrone (PN4MPN) was synthesized and characterized
by FT-IR, FT-Raman and 1HNMR, 13CNMR spectral analysis. The molecular geometry, harmonic vibra-
tional frequencies and bonding features of the title compound in the ground state are computed at the
Hartree–Fock/6-311++G(d,p) and three parameter hybrid functional Lee–Yang–Parr/6-311++G(d,p) levels
of theory. The calculated results show that the predicted geometry can well reproduce the structural
parameters. The assignments of the vibrational spectra have been carried out with the help of normal
co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF).
The calculated HOMO and LUMO energies confirm that charge transfer occurs within the molecule.
Received 21 January 2013
Received in revised form 20 March 2013
Accepted 1 April 2013
Available online 10 April 2013
Keywords:
FT-IR
FT-Raman
DFT
The dipole moment (l), polarizability (a) and hyperpolarizability (b) of the investigated molecule is cal-
culated by using HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) methods on the finite field approach.
Besides, Molecular Electrostatic Potential (MEP), Natural Bond Orbital analysis (NBO) and thermodynam-
ical properties are described from the computational process. The electron density-based local reactivity
descriptor such as Fukui functions are calculated to explain the chemical selectivity or reactivity site in
PN4MPN. Finally, the calculations are applied to simulated FT-IR and FT-Raman spectra of the title com-
pound which show good agreement with observed spectra.
Fukui function
NBO
Ó 2013 Published by Elsevier B.V.
Introduction
Many nitrone derivatives are found to possess pharmacological
activity [1] and form an essential part of the molecular structure of
⇑
Corresponding author. Tel.: +91 9443690138; fax: +91 4427162462.
E-mail address: muthu@svce.ac.in (S. Muthu).
1386-1425/$ - see front matter Ó 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2013.04.007

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
63
important drugs. Remarkable region, stereo, face and chemo
selectivity along with efficient incorporation of multiple stereo
centers, have made nitrone cycloaddition reactions an attractive
and key step in the synthesis of many natural products of biologi-
cal interest [2]. More recently several, nitrones including alpha-
phenyl-tert-butyl nitrone (PBN), have been shown to have potent
biological activity in many experimental animal models [3,4].
Many diseases of ageing, including stroke, cancer development,
Parkinson’s disease and Alzheimer disease are known to have
enhanced levels of free radicals and oxidative stress. Recent re-
search has shown that PBN related nitrones also have anti-cancer
activity in several experimental cancer models and have potential
as therapeutics in some cancers [5]. Also, in recent observations
nitrones have been shown to act synergistically, in combination
with anti-oxidants, in the prevention of acute acoustic noise-in-
duced hearing loss [6]. Studies on the corrosion of metals/alloys
in organic acid media using nitrones are of industrial importance
since most carboxylic acids are used as building blocks in a variety
of industrial products such as plastics, fibers, drugs and pharma-
ceuticals [7–10] literature survey reveals that to the best of our
knowledge, no ab initio Hartee–Fock (HF)/Density Functional The-
ory (DFT) frequency calculations for Phenyl-N-(4-Methyl Phenyl)
Nitrone (PN4MPN) have been reported so far. In an effort to create
new derivatives of pharmacologically-active nitrones, owing to
their wide application, in this work we report the synthesis, and
recrystallised from ethanol yield 1.73 g (83%). The scheme of the
synthesis is shown in Fig. 1.
Experimental section
The FTIR spectrum of the compound PN4MPN was recorded in
the region 4000–400 cmꢁ1 on an IFS 66V Spectrophotometer using
KBr pellet technique. The spectrum was recorded at room temper-
ature, with scanning speed of 10 cmꢁ1 minꢁ1 and the spectral
resolution of 4.0 cmꢁ1. The FT-Raman spectrum of PN4MPN was
recorded using 1064 nm line of Nd:YAG laser as excitation wave-
length in the region 4000–100 cmꢁ1 on a Thermo Electron Corpo-
ration model Nexus 670 spectrophotometer equipped with
FT-Raman module accessory. The theoretically predicted FT-IR
and Raman spectra at HF and three parameter hybrid functional
Lee–Yang–Parr (B3LYP) using 6-311++G(d,p) basis set level of cal-
culations along with experimental FT-IR and FT-Raman spectra
are shown in Figs. 2 and 3 respectively. NMR spectra are recorded
using BRUKER 500 MHz AVANCE III instruments using CDCl3 as
solvent, with TMS as an internal standard. Carbon (13C) spectrum
at 300 MHz and Proton (1H) spectrum at 500 MHz are recorded
at room temperature on the same instrument. The spectral mea-
surements are carried out at Sophisticated Analytical Instruments
Facility (SAIF), Indian Institute of Technology (IIT), Chennai.
a
detailed vibrational study on Phenyl-N-(4-Methyl Phenyl)
Nitrone (PN4MPN) using HF/6-311++G(d,p) and B3LYP/6-311++G
(d,p) levels of theory. The FT-IR, FT-Raman spectral investigations
of PN4MPN are performed using DFT and ab initio HF theory.
Vibrational spectra of the compound under investigation are ana-
lyzed on the basis of calculated potential energy distribution
(PED). The main objective of this work is to find theoretical meth-
ods that would offer a higher certainty of finding molecular struc-
ture parameters and vibrational wave numbers. Also, the electron
density-based local reactivity descriptor such as Fukui functions
are calculated employing Mulliken charges to explain the chemical
selectivity or reactivity site in PN4MPN. Various properties like
structure geometry, Non-Linear Optical (NLO) property, Natural
Bond Orbital (NBO), Highest Occupied Molecular Orbital (HOMO),
Lowest Unoccupied Molecular Orbital (LUMO) energies, Nuclear
Magnetic Resonance (NMR), and Molecular Electrostatic Potential
(MEP) analysis of the PN4MPN are performed to elucidate the
information regarding charge transfer within the molecule.
Computational details
Calculations of the title compound are carried out with Gauss-
ian 03W software program [11] using the HF/6-311++G(d,p) and
B3LYP/6-311++G(d,p) basis sets and Gaussview visualization pro-
gram [12]. To predict the molecular structure and vibrational
wavenumber, calculations are carried out using B3LYP method.
Molecular geometry was fully optimized by Berny’s optimization
algorithm using redundant internal co-ordinates. Harmonic vibra-
tional wavenumbers are calculated using analytic second deriva-
tives to confirm the convergence to minima on the potential
surface. At the optimized structure Fig. 4 of the title compound,
no imaginary wavenumber modes are obtained, proving that a true
minima on the potential surface was found. The DFT hybrid B3LYP
functional tends to overestimate the fundamental modes; there-
fore, scaling factors have to be used for obtaining a considerably
better agreement with experimental data. The observed disagree-
ment between theory and experiment could be a consequence of
the an-harmonicity and of the general tendency of the quantum
chemical methods to overestimate the force constants at the exact
equilibrium geometry. Normal co-ordinate analysis has been
performed in order to obtain the detailed interpretation of the fun-
damental modes using the MOLVIB program version 7.0 written by
Sundius [13,14]. Natural co-ordinate analysis as suggested by Pu-
lay et al. [15] have been written as input for the MOLVIB program.
The Gaussian force constants are used by the MOLVIB in the calcu-
lation of vibrational frequencies. The Raman activities (Si) calcu-
Synthesis
The compound was synthesized from freshly distilled benzalde-
hyde (1.06 g, 0.01 m) in ethanol (30 ml) was added to 4-methyl
phenyl hydroxylamine (1.85 g, 0.015 m) in ethanol (20 ml) and
refluxed for 1 h. Evaporation of the solvent under reduced pressure
gave
a-Phenyl-N-(4-Methyl Phenyl) Nitrone as a solid which was
_
O
EtOH, Δ
C
N
+
CHO
HOHN
CH3
+
1 h
H
Benzaldehyde 4-Methylphenyl hydroxylamine
CH3
α-phenyl-N-(4-methylphenyl) nitrone
Fig. 1. The scheme of the synthesis of PN4MPN.

64
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Fig. 4. Optimized molecular structure and atomic numbering of PN4MPN.
dependent density functional theory (TD-DFT) method [18–21].
Also, to investigate the stability, molecular properties such as
Highest Molecular Orbital (HOMO) and Lowest Molecular Orbital
(LUMO) energies, and the chemical hardness [22] of the title com-
pound are obtained at B3LYP/6-311++G(d,p) level in gas phase.
The calculated normal mode vibrational frequencies also provide
the thermodynamic properties through the principle of statistical
mechanics. By using Gaussview program [12] with symmetry
considerations, vibrational frequency assignments are made with
a high degree of accuracy. The NBO analysis was performed at
B3LYP/6-311++G(d,p) level by means of the NBO 3.1 program [23]
within the Gaussian 03W package. To investigate the reactive sites
of the title compound, the MEP was evaluated using B3LYP/
6-311++G(d,p) method. In addition, the linear polarizability and
first hyperpolarizability of the title compound are obtained from
molecular polarizabilities based on theoretical calculations.
Fig. 2. FT-IR spectrum of PN4MPN (experimental, HF/6-311++G(d,p) and B3LYP/6-
311++G(d,p)).
Results and discussion
Molecular geometry
The optimized structure parameters of this compound calcu-
lated by HF and DFT/B3LYP levels with the 6-311++G(d,p) basis
set are listed in Table 1. A general priority for reproducing the
experimental bond length and bond angles [24] is not present
among HF and DFT levels. All calculated geometrical parameters
obtained at the DFT level of theory are in good agreement with
the experimental structural parameters.
Since the crystal structure of this compound is not available.
The optimized structure can be only being compared with other
similar system for which the configurations have been optimized
[25]. For example the optimized bond lengths of C–C in phenyl ring
fall in the range from 1.383 to 1.393 Å for HF/6-311++G(d,p) meth-
od and 1.390–1.409 Å for B3LYP/6-31G(d,p) method, which are in
Fig. 3. FT-Raman spectrum of PN4MPN (experimental, HF/6-311++G(d,p) and
B3LYP/6-311++G(d,p)).
lated by the Gaussian 03W program and adjusted during the scal-
ing procedure with MOLVIB was converted to the relative Raman
intensities (Ii) using the following relationship derived from the ba-
sic theory of Raman scattering [16,17]
good agreement with a similar structure [25]. The optimized Cring
–
4
N bond length by two methods are 1.444 Å for HF/6-311++G(d,p)
method and 1.458 Å for B3LYP/6-311++G(d,p) method which is
slightly longer than that in compound with similar structure
[25]. These bonds play a bridge role between two phenyl groups.
Based on the above comparison, although there are some differ-
ences between theoretically calculated values and XRD data of
similar structure [25], these differences are probably due to intra-
molecular interaction in the solid state. Despite these differences,
the calculated geometrical parameters represent a good approxi-
mation, and they are the basis for the calculation of other
parameters such as polarizability, vibrational frequencies and ther-
fðmo
ꢁ
miÞ Si
Ii ¼
mi½1 ꢁ expðꢁhc
m
i=kTÞꢂ
where mi is the vibration
m
o is the exciting frequency (in cmꢁ1 units)
wavenumber of the ith normal mode; h, c and k are the universal
constants and f is the suitably chosen common scaling factor for
all the peak intensities. The simulated IR and Raman spectra have
been plotted using pure Lorentzian band shapes with full width at
half maximum (FWHM) bandwidth of 10 cmꢁ1. The calculated geo-
metrical parameters of the title compound are presented in Table 1.
The electronic absorption spectra are calculated using the time-

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
65
Table 1
Geometrical parameters optimized in PN4MPN (bond length (Å) and bond angle (°).
Parameters
Experimentala
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
Parameters
Experimentala
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
Bond length (Å)
Bond angle (°)
C(1)–N(2)
1.319
1.483
1.096
1.292
1.383
1.346
1.388
1.337
0.95
1.141
0.95
1.375
1.421
1.384
0.96
1.278
1.478
1.074
1.278
1.444
1.386
1.378
1.379
1.073
1.395
1.076
1.386
1.51
1.388
1.076
1.074
1.086
1.083
1.086
1.392
1.393
1.384
1.076
1.384
1.075
1.386
1.076
1.383
1.075
1.074
1.317
1.458
1.084
1.283
1.458
1.391
1.389
1.390
1.083
1.402
1.085
1.398
1.509
1.393
1.085
1.083
1.095
1.092
1.093
1.409
1.408
1.390
1.085
1.394
1.084
1.395
1.084
1.390
1.084
1.081
N(2)–C(1)–C(11)
N(2)–C(1)–H(17)
C(1)–N(2)–O(3)
126.45
111.4
118.71
121.17
123.45
117.38
118.63
120
120.84
119.16
119.9
119.9
121.47
119.3
119.3
118.68
120.58
121.28
120.84
119.4
119.4
119.7
120
128.9
113.0
118.1
121.9
123.9
114.2
117.9
121.1
120.9
119.2
119.4
121.4
121.2
119.2
119.6
118.2
120.4
121.4
121.1
119.9
119.0
119.3
120.5
120.2
110.8
111.2
111.0
108.0
107.6
108.1
117.4
123.6
118.9
120.7
119.6
119.7
120.0
119.8
120.3
119.7
120.2
120.1
120.4
120.1
119.5
120.3
120.2
119.5
130.0
112.0
117.9
122.4
123.4
114.2
118.5
120.4
121.0
119.1
119.5
121.4
121.2
119.2
119.5
118.2
120.7
121.1
121.3
119.6
119.2
119.1
120.2
120.7
110.9
111.5
111.4
107.6
107.3
108.1
116.4
125.7
117.9
121.3
119.1
119.6
120.1
119.7
120.2
119.3
120.4
120.3
120.8
119.9
119.3
120.6
120.2
119.1
C(1)–C(11)
C(1)–H(17)
N(2)–O(3)
N(2)–C(4)
C(4)–C(5)
C(4)–C(9)
C(5)–C(6)
C(5)–H(18)
C(6)–C(7)
C(6)–H(19)
C(7)–C(8)
C(1)–N(2)–C(4)
C(11)–C(1)–H(17)
C(1)–C(11)–C(12)
C(1)–C(11)–C(16)
O(3)–N(2)–C(4)
N(2)–C(4)–C(5)
N(2)–C(4)–C(9)
C(5)–C(4)–C(9)
C(4)–C(5)–C(6)
C(7)–C(10)
C(8)–C(9)
C(4)–C(5)–H(18)
C(4)–C(9)–C(8)
C(4)–C(9)–H(26)
C(6)–C(5)–H(18)
C(5)–C(6)–C(7)
C(5)–C(6)–H(19)
C(7)–C(6)–H(19)
C(6)–C(7)–C(8)
C(6)–C(7)–C(10)
C(8)–C(7)–C(10)
C(7)–C(8)–C(9)
C(7)–C(8)–H(20)
C(7)–C(10)–H(22)
C(7)–C(10)–H(23)
C(7)–C(10)–H(24)
C(9)–C(8)–H(20)
C(8)–C(9)–H(29)
H(22)–C(10)–H(23)
H(22)–C(10)–H(24)
H(23)–C(10)–H(24)
C(12)–C(11)–C(16)
C(11)–C(12)–C(13)
C(11)–C(12)–H(25)
C(11)–C(16)–C(15)
C(11)–C(16)–H(21)
C(13)–C(12)–H(25)
C(12)–C(13)–C(14)
C(12)–C(13)–H(26)
C(14)–C(13)–H(26)
C(13)–C(14)–C(15)
C(13)–C(14)–H(27)
C(15)–C(14)–H(27)
C(14)–C(15)–C(16)
C(14)–C(15)–H(28)
C(16)–C(15)–H(28)
C(15)–C(16)–H(21)
C(8)–H(20)
C(9)–H(29)
C(10)–H(22)
C(10)–H(23)
C(10)–H(24)
C(11)–C(12)
C(11)–C(16)
C(12)–C(13)
C(12)–H(25)
C(13)–C(14)
C(13)–H(26)
C(14)–C(15)
C(14)–H(27)
C(15)–C(16)
C(15)–H(28)
C(16)–H(21)
0.96
0.96
0.93
0.93
1.389
1.386
1.337
0.93
1.367
0.93
1.375
0.93
1.375
0.93
120
109.5
111.38
111.68
107.52
107.46
109.3
117.5
123.5
117.5
120.6
119.4
119.4
120.3
119.9
119.9
118.6
120.5
120.3
120.4
119.8
119.8
120.2
119.8
119.1
0.93
a
Ref. [25].
modynamical properties which are described in the following
sessions.
Based on above comparison, although there are some difference
between our values and literature data, the optimized structural
parameters can well reproduce with literature ones and they are
the bases for thereafter discussion.
Rahut and Pulay [26] and they are presented in Table 3. The
observed calculated frequencies calculated IR intensities, Raman
activities and normal mode descriptions characterized by PED are
depicted in Table 4.
The compound under investigation possesses C1 point group.
The assignment of the experimental frequencies are based on the
observed band frequencies in the FTIR and FT-Raman spectra of
the PN4MPN, confirmed by establishing one to one correlation
between observed and theoretically calculated frequencies. A
linearity between the experimental and calculated wave numbers,
can be estimated by plotting the calculated versus experimental
wave numbers (Fig. 5). The correlation coefficients (r) for experi-
mental and observed wavenumbers computed from B3LYP and
HF methods are found to be 0.9993 and 0.9512, respectively. It
can be noted from the ‘r’ values that the theoretical prediction
are in good agreement with the experimental wavenumbers. Also
Fig. 5 reveals the overestimation of the calculated vibrational mode
due to neglect of anharmonocity in real system.
Vibrational assignments
The title compound PN4MPN has 81 normal vibration mode and
the detailed vibrational band assignments have been made based
on normal co-ordinate vibrational analysis (NCA). Internal co-ordi-
nates have been chosen according to Pulay’s recommendation [26].
The non-redundant set of internal co-ordinates of PN4MPN has
been defined in Table 2. From these a non-redundant set of local-
symmetry co-ordinates are constructed by suitable linear combi-
nations of internal co-ordinates following the recommendation of

66
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Table 2
Definition of internal valence co-ordinate of PN4MPN.
No.
Symbol
Type
Definition
Stretching
1–12
Ri
C–C(Ring)
C4–C5, C5–C6, C6–C7, C7–C8, C8–C9, C9–C4, C11–C12, C12–C13, C13–C14, C14–C15, C15–C16,
C16–C11
13
14
Ri
Ri
Ri
Ri
Ri
Ri
Ri
C–C(Chain)
C–C(Methyl)
C–H(Ring)
C–H(Chain)
C–H(Methyl)
C–N
C11–C1
C7–C10
15–22
23
24–26
27–28
29
C5–H18, C6–H19, C8–H20, C9–H29, C12–H25, C13–H26, C14–H27, C15–H28
C1–H17
C10–H22, C10–H23, C10–H24
C1–N2, C4–N2
N2–O3
N–O
Bending
30–35
36–41
42–43
44–45
46–48
49–50
51
bi
bi
bi
bi
bi
bi
bi
bi
C–C–C(Ring-1)
C–C–C(Ring-2)
C–C–C(Chain)
C–C–C(Methyl)
N–C–C
O–N–C
N–C–H
C–C–H(Ring)
C4–C5–C6, C5–C6–C7, C6–C7–C8, C7–C8–C9, C8–C9–C4, C9–C4–C5
C11–C12–C13, C12–C13–C14, C13–C14–C15, C14–C15–C16, C15–C16–C11, C16–C11–C12
C1–C11–C16, C1–C11–C12
C8–C7–C10, C6–C7–C10
N2–C4–C9, N2–C4–C5, N2–C1–C4, O3–N2–C4, O3–N2–C1, O3–N2–C4, O3–N2–C1
O3–N2–C4, O3–N2–C1
N2–C1–H17
52–69
C4–C5–H18, C6–C5–H18, C5–C6–H19, C7–C6–H19, C7–C8–H20, C9–C8–H20, C4–C9–H29, C8–C9–
H29, C11–C12–H25, C13–C12–H25, C12–C13–H26, C14–C13–H26, C13–C14–H27, C15–C14–H27,
C14–C15–H28, C16–C15–H28, C11–C16–H21, C15–C16–H21
H22–C10–H23, H22–C10–H24, H23–C10–H24, H23–C10–H22, H24–C10–H22, H24–C10–H23
H22–C10–C7, H23–C10–C7, H24–C10–C7
70–75
76–78
79
bi
bi
bi
bi
H–C–H(Methyl)
H–C–C(Methyl)
C–C–H(Chain)
C–N–C(Bridge)
C11–C1–H17
C1–N2–C4
80
Out of plane bending
81–84
85–89
xi
xi
C–H(Ring-1)
C–H(Ring-2)
H18–C5–C4–C6, H19–C6–C5–C7, H20–C8–C9–C7, H29–C9–C8–C4
H21–C16–C15–C11, H28–C15–C14–C16, H27–C14–C15–C13, H26–C13–C12–C14, H25–C12–C13–
C11
90–91
92
93
94
95
xi
xi
xi
xi
xi
xi
C–H(Chain)
O–N–C–C
N–C–C–C
H–C–C–N
C–C–C–C(Chain)
C–C(Methyl)
H17–C1–C11–C12, H17–C1–C11–C16
O3–N2–C1–C4
N2–C4–C5–C9
H17–C1–C11–N2
O17–C12–C13–C11
C10–C7–C8–C6
96
Torsion
97–102
103–108
si
si
C–C(Ring-1)
C–C(Ring-2)
C4–C5–C6–C7, C5–C6–C7–C8, C6–C7–C8–C9, C7–C8–C9–C4, C8–C9–C4–C5, C9–C4–C5–C6
C11–C12–C13–C14, C12–C13–C14–C15, C13–C14–C15–C16, C14–C15–C16–C11, C15–C16–C11–
C12, C16–C11–C12–C13
109–114
si
tCH3
C8–C7–C10–H22, C8–C7–C10–H23, C8–C7–C10–H24, C6–C7–C10–H22, C8–C7–C10–H23, C6–C7–
C10–H24
115–116
117–118
119–122
si
si
si
tC–C(Chain)
Butterfly
tC–N
C1–C11–C12–C13, C1–C11–C16–C15
O3–N2–C1–C11, C4–N2–C1–H17
N2–C4–C9–H29, N2–C4–C5–H18, N2–C1–C11–C16, N2–C1–C11–C12
C–H vibration
54–40). The PED confirms this vibration are mixed mode as it
The hetero aromatic structure shows the presence of C–H
stretching vibrations in the region 3100–3000 cmꢁ1, which is the
characteristic region for the ready identification of C–H stretching
vibrations [27]. In this region, the bands are not affected apprecia-
bly by the nature of substituents. For our title molecule the band
corresponding to C–H stretching vibration at 3104, 3098, 3092,
3086, 3084, 3074, 3064 cmꢁ1 (mode nos. 81–74) by B3LYP/
6-311++G(d,p) method shows excellent agreement with the litera-
ture data and also with the bands observed in the recorded FTIR
spectrum at 3121, 3104, 3070, 3067, 3062 and 3054 cmꢁ1 and with
the FT-Raman bands at 3095, 3064, 3048, 2990 cmꢁ1 [28,29]. The
PED corresponding to this vibration is pure mode of contributing
to 96% as shown in Table 4.
evident from Table 4.
The C–H out-of plane bending vibrations are strongly coupled
vibrations and occur in the region 1000–750 cmꢁ1 [30]. The
aromatic C–H out-of plane bending vibrations of PN4MPN are as-
signed to the bands observed at 992, 981, 948, 878, 842, 834,
802 and 762 cmꢁ1 in FT-IR spectrum and 967, 942, 939, 926, 824
and 819 cmꢁ1 in FT-Raman spectrum, is well correlated with
B3LYP/6-311++G(d,p) method at 979–742 cmꢁ1, with appropriate
PED. In our present study all C–H symmetric bending and wagging
modes of vibration are assigned within the said region and are
presented in Table 4.
CH3 vibrations
The aromatic C–H in-plane bending modes of benzene and its
derivatives are observed in the region 1300–1000 cmꢁ1 and are
very useful for characterization purpose [30]. For our title
molecule, the C–H in plane bending vibrations appear as a weak
to medium strong bands in FT-IR spectrum at 1294, 1282, 1277,
1203, 1175, 1160, 1080, 1066, 1034 and 1029 cmꢁ1 and at 1303,
1192, 1172, 1141, 1123, 1054 and 1000 cmꢁ1 in FT-Raman spec-
trum shows good agreement with computed wavenumber by
B3LYP/6-311++G(d,p) method at 1291–1002 cmꢁ1 (mode nos.
The wavenumbers of the vibrational modes of methoxy groups
in this compound are known to be influenced by a variety of inter-
esting interactions such as electronic effects, intermolecular
hydrogen bonding in the crystalline network [31] and Fermi reso-
nance. Electronic effects such as back donation and induction,
mainly caused by the presence of oxygen atom adjacent to CH3
group, can shift the position of C–H stretching and bending modes
[32–34]. In aromatic compounds, the CH3 asymmetric stretching
vibrations are expected in the range 2925–3000 cmꢁ1 and

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
67
Table 3
Definition of local symmetry co-ordinates of PN4MPN.
No.
Symbol
Definition
Stretching
1–12
13
14
15–22
23
24
25
26
27, 28
29
m
m
m
m
m
m
m
m
m
m
C–C(Ring)
C–C(Chain)
C–CM
C–H (Ring)
C–H (Chain)
CH3ss
CH3ips
CH3ops
C–N
R1–R12
R13
R14
R15–R22
R23
p
3
[R24 ꢁ +R25 + R26]/
p
6
[2R24 ꢁ R25 ꢁ R26]/
p
[R25 ꢁ R26]/
R27, R28
R29
2
N–O
Bending
30
31
32
33
34
35
36
37
38
39
40
41
42
43–51
p
6
b trig1
b asym1
b sym1
b trig2
b asym2
b sym2
b C–C (Chain)
b C–CM
b NCC asdf
[
a
30 ꢁ
a
31 +
a
32 ꢁ
a
33 +
a
34 ꢁ
a
35]/
p
34 + 2 a35]/ 12
[ꢁ
a
30 ꢁ
a31 + 2
a
32 ꢁ
a
33 ꢁ
a
p
[a
30 ꢁ
36 ꢁ
a
31 +
a
a
33 ꢁ
38 ꢁ
a34]/
2
a
p
[a
a
37 +
a
39 +
40 ꢁ
a
41]/ 6
p
[ꢁ
a36 ꢁ
a37 + 2
a
39 ꢁ
38 ꢁ
a
40]/
39 ꢁ
a40 + 2
a
41]/ 12
p
[a
[a
[a
36 ꢁ
42 ꢁ
44 ꢁ
a
a
a
a
a
37 +
a
2
2
a
2
p
p
43]/
45]/
p
[2
[2
a
a
46 ꢁ
47 ꢁ
a48]/
6
6
p
c
NCC asdfo
47 ꢁ
46 ꢁ
a48]/
p
b ONC
[a
49 ꢁ
80 ꢁ
51
a
a
50]/
2
p
b CNC def
b NCH ipb
b CCH
[2
a
a
49 ꢁ
a
50]/
6
p
p
p
p
59]/ 2,
p
67]/ 2
[
[
[
a
a
a
52 ꢁ
a
a
a
53]/ 2, [
a
a
54 ꢁ
62 ꢁ
a
a
55]/ 2, [
63]/ 2, [
a
a
a
56 ꢁ
a
a
57]/ 2, [
a
a
58 ꢁ
66 ꢁ
a
a
p
p
p
60 ꢁ
76 ꢁ
61]/ 2, [
64 ꢁ
65]/ 2, [
p
52
53
54
55
56
57
58–61
62–66
67–68
69
70
71
72
73
74
75
76
77
b CH3Sb
b CH3ipb
77 ꢁ
a
78 ꢁ
a
72 ꢁ
73 ꢁ
a
74]/
6
p
[ꢁ
a
72 ꢁ
a
64]/
73 ꢁ
a
74]/
6
p
c
CH3opb
b CH3rok
CH3rok
b CH ipb
[a
[a
[a
[a
62 ꢁ
a
a
a
a
82,
86,
91
6
p
76 ꢁ 2
77 ꢁ
a78]/
6
p
p
c
77 ꢁ
79 ꢁ
78]/
51]/
2
2
x
x
c
CH wag
CH wag
CH
x
x
x
x
x
x
x
81,
85,
90,
92
93
94
95
x
x
x
x
x
83,
87,
x
84
x
88, x89
x
x
x
x
s
ONCC wag
NCCC wag
HCCN wag
C–C wag
trig1
p
101]/ 6
[s
96 ꢁ
s
s
97 +
98 +
s
s
98 ꢁ
99 ꢁ
s
s
99 +
101]/
s
100 ꢁ
s
p
s
asym1
[s
96 ꢁ
2
p
t sym1
t trig2
[ꢁ
s96 + 2
s
97 ꢁ
s
98 ꢁ
s
99 + 2
s
100 ꢁ
s
101]/ 12
p
[
[
s
s
102 ꢁ
s
s
103 +
104 +
s
104 ꢁ
s
s
105 +
107]/
s
106 ꢁ
s107]/
6
p
t asym2
t sym2
t C–CH3
t Butterfly
t HCCC
102 ꢁ
s105 ꢁ
2
p
78
79
80
81
[ꢁ
s102 + 2
s
103 ꢁ
109 +
108 +
s104 ꢁ
s
105 + 2
s
106 ꢁ
s
107]/ 12
p
[s
[s
[s
108 +
104 ꢁ
114 ꢁ
s
s
s
s
110 ꢁ
s111 +
s
112 +
s
s
113]/
6
p
s
109 ꢁ
s
110 +
s
111 +
112]/
6
p
115]/
2
symmetric CH3 vibrations in the range 2905–2940 cmꢁ1 [35,36].
The asymmetric stretching modes of the methyl group are calcu-
lated at 3003 and 2976 cmꢁ1 (mode nos. 71 and 70) by B3LYP/6-
311++G(d,p) method show good agreement with recorded FTIR
spectrum at 3009 and 2973 cmꢁ1 and at 2919 cmꢁ1 in FT-Raman
spectrum respectively. The PED corresponds to this vibration is al-
most 92%. The bands observed at 2918 and 2919 cmꢁ1 in FTIR and
FT-Raman spectra are respectively assigned to symmetric CH3
vibrations (mode no. 69) is well correlated with the computed
wavenumber by B3LYP method at 2925 cmꢁ1 with PED contribu-
tion of 91%.
The CH3-in-plane bending vibration are expected in the region
1400–1485 cmꢁ1 [37]. The FTIR band occurs at 1500, 1483, 1443
and 1418 cmꢁ1 and the bands appeared at 1503, 1445 and
1421 cmꢁ1 in FT-Raman spectrum are identified as CH3-in-plane-
bending vibration. Computed PED values shows that CH3-out-of-
plane bending vibration coupled with CH3-in-plane bending vibra-
tion occurred at 1418 cmꢁ1 in FTIR spectrum and the bands at 1373
and 1357 cmꢁ1 are due to CH3 symmetric vibrations. The theoret-
ical values computed by B3LYP method at 1485–1363 cmꢁ1 (mode
nos. 63–56) show a good agreement with the recorded spectral val-
ues for these mode of vibrations. As CH3 torsional modes are ex-
pected below 100 cmꢁ1 the computed wavenumber at 58, 49, 41
and 26 cmꢁ1 (mode no. 4–1) are assigned to CH3 torsional mode.
The recorded spectra do not show such kind of band in this region.
These modes are not pure but contain contributions from biphenyl
ring vibrations as evident from Table 4.
Ring vibrations
The ring carbon–carbon stretching vibrations in benzene ring
occur in the region 1430–1625 cmꢁ1. In general, the bands are of
variable intensity and are observed at 1625–1590, 1575–1590,
1470–1540, 1430–1465 and 1280–1380 cmꢁ1 from the frequency
ranges given by Varsanyi [38] for the five bands in the region. In
the present work, the frequencies computed by B3LYP/6-
311++G(d,p) at 1572–1289 cmꢁ1 (mode nos. 66–53) have been
designated to C–C stretching vibrations [39]. The recorded spec-
trum show very strong to medium intense band in FTIR spectrum

Table 4
The experimental FT-IR, FT-Raman and calculated wave numbers (cmꢁ1) atHF/B3LYP/6-311++G(d,p), IR intensities (km/mol), Raman scattering activities (Å4)/(a.m.u) and force constant (mdyn Åꢁ1), assignments and potential energy
distribution (PED) for PN4MPN.
Mode no.
Experimental wave number (cmꢁ1
)
Calculated wave number (cmꢁ1
)
PED > 10%
FT-IR
FT-Raman
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
Scaled (cmꢁ1
)
IIR
IRaman
Fce const
Scaled (cmꢁ1
)
IIR
IRaman
Fce const
a
b
a
b
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
3121(s)
3104(w)
3070(w)
3067(s)
3062(m)
–
3065
3058
3054
3049
3046
3036
3026
3025
3020
3017
2950
2927
2880
1667
1636
1625
1605
1597
1518
1499
1467
1458
1447
1409
1399
1394
1331
1312
1218
1203
1196
1183
1175
1169
1157
1111
1077
1070
1062
1056
1018
1016
1009
1002
998
0.32
2.89
2.28
1.05
17.47
11.48
7.81
1.19
10.53
1.55
14.32
13.66
24.29
52.94
3.74
0.56
0.93
1.31
27.61
2.88
7.46
3.97
7.39
2.20
7.85
8.33
5.13
11.66
14.53
6.53
5.38
8.30
8.86
2.06
5.09
8.07
20.91
100.03
7.03
13.54
2.18
2.37
0.46
0.02
0.71
0.87
0.67
0.13
1.12
1.56
0.60
0.12
5.19
1.66
0.13
1.66
0.91
0.09
2.26
5.24
1.67
0.13
0.55
0.02
1.20
0.12
0.01
0.14
0.03
5.77
0.07
0.03
1.60
3.63
0.24
7.34
7.31
7.29
7.23
7.26
7.19
7.12
7.11
7.10
7.06
6.84
6.73
6.14
18.67
10.78
9.85
11.41
9.43
4.17
3.48
1.71
1.58
3.14
3.41
1.79
2.34
1.70
1.59
2.07
3.67
2.70
1.75
1.14
1.28
2.16
2.44
2.78
1.50
1.56
1.23
1.55
1.02
2.10
0.99
0.97
3.93
1.07
0.93
1.00
0.88
2.10
3104
3098
3092
3086
3084
3074
3064
3064
3061
3057
3003
2976
2925
1591
1583
1572
1556
1534
1485
1471
1446
1440
1426
1388
1369
1363
1316
1291
1289
1286
1234
1188
1173
1167
1160
1145
1108
1097
1068
1026
1016
1002
979
1.01
9.27
13.17
7.65
43.21
7.65
12.25
12.86
9.58
14.32
3.02
7.54
12.62
43.95
15.40
37.39
14.61
3.40
100.00
0.88
0.45
1.14
1.84
1.47
0.39
3.59
10.34
1.01
0.48
3.66
0.52
39.65
2.56
1.59
7.85
0.53
1.09
7.17
0.52
0.20
6.63
6.61
6.59
6.58
6.52
6.50
6.44
6.44
6.43
6.40
6.26
6.12
5.60
9.28
8.67
10.01
7.87
9.74
3.44
2.95
1.48
1.37
2.87
3.08
1.47
2.07
1.57
1.63
4.09
5.96
6.80
2.62
1.35
1.19
1.08
0.91
2.15
1.04
1.26
1.03
1.43
1.82
3.65
0.84
0.76
0.78
0.78
0.73
0.81
1.52
0.65
t
t
t
t
t
t
t
t
t
t
C–H(98)
C–H(94)
C–H(96)
C–H(97)
C–H(95)
C–H(97)
C–H(97)
C–H(94)
C–H(95)
C–H(93)
3095(m)
0.21
0.61
4.96
3.92
6.20
0.09
3.58
4.56
1.12
5.11
4.87
9.86
2.04
0.31
7.60
1.82
55.91
9.17
0.27
3.49
2.53
4.63
0.30
0.52
5.28
0.81
1.24
0.90
1.06
100.00
1.44
15.31
9.25
3.45
0.11
0.78
3.48
3.69
3.92
1.05
1.44
0.08
0.25
0.19
0.03
0.09
1.05
5.47
6.04
6.46
3064(w)
–
3048(m)
2990(w)
–
–
–
–
–
3054(w)
3049(w)
3038(w)
3009(w)
2973(vw)
2918(w)
–
1594(w)
1573(m)
1569(m)
1549(vs)
1500(w)
1483(w)
–
CH3ips(94)
CH3ips(93)
CH3ops(91)
–
2919
1594(s)
–
–
1551(vs)
–
1503(w)
–
1445(m)
–
1421(m)
–
–
–
t
C–N(72),
tC–C(17)
bC–H(63), bC–N(12)
t
t
t
t
C–C(87)
C–C(85)
C–C(76)
C–C(67), bC–H3(22), bC–C(10)
bC–H3(35),
bC–H3(39),
t
x
c
t
t
t
t
t
bC–H(19), bR1trig(15),
C–Hb(37), C–H(21),
bC–H(34), bC–C–C(17)
C–Hb(35),
bC–H(34),
bC–H(19),
t
t
C–C(17)
C–C(35)
1443(m)
–
C–C(41), bCH3(30)
C–H(34), bCH3(31)
CH3(49), CH3(37)
C–N(26), bC–N(11), CH3sb(62)
C–C(61), HCCN(14), C–N(12)
C–C(47), bC–H(29),
C–C(60), N–O(24), bC–H(19)
C–C(34), C–Hb(25), bN–C–Casdf(11), bC–H(29)
HCCN(14)
C–C(19)
1418(m)
1373(w)
1357(vw)
1322(m)
1294(vs)
1282(m)
1277(m)
1203(m)
–
1175(m)
1160(m)
–
–
–
1080(w)
1066(m)
1034(m)
1029(w)
–
992(w)
981(vw)
–
c
0.31
0.56
1.19
1.29
x
t
1324(m)
1303(w)
–
–
t
0.78
62.92
72.06
1.45
0.53
2.59
100.13
58.64
66.87
0.42
15.41
3.40
1.15
0.20
3.29
0.06
0.02
0.39
1.03
5.12
x
–
x
t
1192(s)
–
–
1172(s)
1141(w)
1123(w)
–
1054(w)
–
–
1000(m)
–
–
967(w)
–
942(w)
939(w)
926(w)
–
tC–C(12), CH3sb(10), C–Nb(11)
x
x
HCCN(26), bR1trig(19)
HCCN(11), C–C(21),
t
t
C–N(29),
t
t
C–C(21), bC–H(19)
C–C(12), CH3sb(10), C–Nb(11)
C–Hb(35),
tC–N(40), bR2trig(26), bC–H(14)
bR1trig(34), bC–H(21),
CCCN(29), bC–H(26),
bC–H(26), CCCN(16),
t
t
t
C–C(14)
C–C(17)
C–C(16), b CH3rok(14)
0.04
3.69
0.03
12.07
0.08
0.12
0.15
0.03
x
x
cCH3rok(29), tR1trig(17), tR2trig(15), bC–H(12)
tR2trig(17),
tR2trig(57),
c
c
c
c
t
C–H(21)
C–C(21),
974
967
952
950
933
901
873
837
c
CH3rok(14)
NCC(11)
CH(27),
CH(25), tR2smt(19),
CH(23), ONCb(24), x
t
C–C(15), tR1sym(14),
C–C(12)
HCCN(12)
CH(22),
HCCNwag(12)
CCCN(17), tR1trig(13),
tC–C(18), tR1sym(12), C–Cb(10)
x
948(w)
–
–
984
981
973
956
920
873
x
0.02
tR1asym(38), tR1sym(24),
CNCdef(47), CH(22),
CH(26), bNCH(22),
C–H(27),
c
tC–N(11)
–
16.81
6.24
31.64
0.28
0.69
7.23
c
x
878(m)
842(s)
c
c
x
–

30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
09
08
07
06
05
04
03
02
01
–
824(w)
–
819(w)
–
–
–
710(w)
672(w)
–
659(m)
627(m)
587(w)
–
862
853
848
798
764
723
697
681
652
644
613
611
574
512
475
420
414
408
351
342
323
284
213
179
131
108
58
0.11
5.93
36.06
3.87
22.39
4.74
33.97
6.21
7.16
13.50
0.74
0.97
9.90
7.69
10.14
2.89
2.47
0.99
1.18
1.94
2.80
6.50
0.20
1.24
1.54
1.87
0.12
0.18
0.21
0.05
0.40
0.11
0.18
3.56
0.61
0.33
0.03
0.13
0.34
0.32
0.40
1.09
0.14
0.14
0.82
0.33
0.05
0.17
0.09
0.29
0.28
0.57
0.39
0.30
0.51
0.25
0.55
0.35
0.11
0.53
0.66
0.68
0.76
2.12
0.72
1.03
0.66
1.62
1.68
1.45
1.57
1.40
1.05
0.63
0.54
0.47
0.45
0.35
0.37
0.23
0.47
0.31
0.13
0.11
0.05
0.05
0.01
0.01
0.00
0.00
820
820
816
795
742
710
682
678
646
640
611
597
572
498
477
412
405
398
346
335
303
274
212
175
139
99
6.77
9.35
0.84
0.58
7.11
2.50
16.24
2.93
4.78
1.29
0.23
0.40
6.93
3.32
4.69
1.97
0.23
0.16
0.11
1.19
0.51
3.10
0.06
0.44
0.43
0.68
0.08
0.07
0.11
0.10
0.29
0.10
0.43
3.62
1.40
0.33
0.05
0.12
0.54
0.66
0.70
1.01
0.52
0.26
0.60
0.44
0.38
0.30
0.20
0.03
0.53
1.02
0.73
0.50
0.50
0.39
1.00
0.09
1.38
0.60
0.58
0.64
0.53
2.02
0.66
0.88
0.60
0.99
1.60
1.29
1.47
1.08
0.94
0.50
0.48
0.51
0.32
0.29
0.22
0.38
0.26
0.25
0.12
0.09
0.05
0.04
0.01
0.00
0.00
0.00
x
x
x
C–H(26), tR1trig(26),
c
CH(22), tR2trig(12)
N–C–Casdf0(13), bR2asym(11)
C–H(23), bR2sym(17)
C–H(24)
C–H(26), bR1asymd2(17)
834(w)
–
802(m)
762(m)
721(vs)
697(m)
–
655(vs)
650(m)
–
594(w)
571(vs)
502(vs)
489(vw)
C–H(43),
C–H(43),
c
c
C–H(19), c
tR1trig(35), tR2trig(25), x
c
C–Cb(36), tR2trig(26), C–CH3b(13)
tR2trig(25), C–Cb(32)
C–Cb(32), tR1trig(16), bR1asym(12)
tR1trig(16), C–Cb(19)
tR1sym(40), xC–H(24), tR1asym(21), xC–C(12)
tR2asym(45), tR2sym(23)
bR1sym(22), bR1asym(12), C–Cb(32)
bN–C–Casdf(38), bR1asyd(18), C–Cb(10)
C–C(60), tN–C(10)
C–CH3(53), bR2symd(36), C–Cb(14)
C–C(18), C–N–C def(12), CCCN(11)
tC–C(30), Rsymd1(19), tC–N(12)
C–C–Ndef(29), N–C–C asdfo(21), tC–C(17)
508(w)
–
x
t
x
424(s)
412(w)
402(w)
397(w)
355(w)
347(w)
311(w)
271(w)
229(w)
189(w)
127(m)
101(m)
–
x
–
–
–
–
–
–
–
–
–
–
–
–
–
–
c
tC–C(39), bR1symd(12), tC–N(12)
bR2asym(73), bR1sym(10)
x
bR2sym(35), C–Cb(13), bR1sym(12)
tC–C(39), butt(18), C–C–Cb(11)
bC–C–N asdfo(16), cCH3(20)
tC–C(46), tR2asym(19), tR1smt(15)
tR2asym(40), tR1sym(34)
tR2asym(41), tC–N(38), tCH3(20)
tC–N(42), tR1asy,(30), tCH3(10)
tCH3(38), tR1asym(15), tR1sym1(10)
tC–N(15)
C–N(17), bR2sym(50), bR1asym(12)
58
49
41
26
–
–
–
44
31
30
Notes: s: strong, vs: very strong, m: medium, w: weak,
t
: stretching, ops: out of plane stretching, ips: in plane stretching, t: torsion, b: in plane bending,
c
: out of plane bending, sb: symmetric bending, asyd: asymmetric
deformation, asydo: out of plane asymmetric deformation, R1: Ring1, R2: Ring2, trig: trigonal deformation, wag; wagging, butt: butterfly.
Fce Const, Force Constant.
a
Relative absorption intensities normalized with highest peak absorption equal to 100.
Relative Raman intensities normalized to 100.
b

70
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
are mixed mode as it is evident from Table 4. The remaining vibra-
3500
3000
2500
2000
1500
1000
500
tions such as in-plane and out-of plane bending of NCC asymmetric
deformation, symmetric deformation, CNC deformation, HCCN
wagging have been identified and presented in Table 4 are well
in agreement with the experimental observations.
HF
R=0.95123
13C and 1H NMR spectral analysis
The experimental and theoretical values for 1H, 13C NMR, and
calculated structural parameters of the title compound are given
in Table 5. The recorded NMR spectra of carbon (13C) and proton
(1H) using CDCl3 as a solvent are shown in Figs. 6 and 7
respectively.
The isotropic chemical shifts are frequently used as an aid in the
identification of reactive organic as well as ionic species. It is rec-
ognized that accurate predictions of molecular geometries are
essential for reliable calculations of magnetic properties. The theo-
retical 13C and 1H chemical shifts are calculated for the optimized
geometry obtained from HF/6-311++G(d,p) and B3LYP/6-
311++G(d,p) by using GIAO method implemented in the Gaussian
program [8]. The results in Table 5 shows that the range 13C
NMR chemical shift of the typical organic molecule usually >100
[42–44]. The accuracy ensures reliable interpretation of spectro-
scopic parameter. In our present study, the title molecule also falls
with the above literature data. In general, highly shielded electrons
appear downfield and vice versa. The predicted chemical shift
values by the DFT theoretical method values well coincides with
the experimental values. In this work, aromatic carbons are ob-
served from 122.14 to 129.65 ppm in 13C NMR spectrum for the
title molecule. Quaternary carbon signals appeared to be less in-
tense compared to the proton attached carbons and they resonate
at 146.84, 140.19 and 125.66 ppm as shown in Fig. 6, due to C4, C7,
and C11. The highly shielded methyl carbons signals at 21.16 ppm,
is assigned to C10 carbon and coincides well with computed chem-
ical shifts at 20.52 ppm using DFT level and appear at downfield
(lower chemical shift). The chemical shifts of H atom would be
more susceptible to intermolecular interactions as they are the
0
500
1000
1500
2000
2500
3000
3500
Experimental Frequencies (cm-1)
3500
3000
2500
2000
1500
1000
500
B3LYP
R=0.99935
500
1000 1500 2000 2500 3000 3500
Experimental Frequencies (cm-1
)
Fig. 5. Correlation graph between experimental and calculated wavenumbers at HF
and B3LYP levels.
Table 5
Experimental and theoretical chemical shifts of PN4MPN in 13C, 1H NMR spectra d
(ppm).
Atom position
Expt.
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
at 1573, 1569, 1549, 1500, 1483, 1443, 1418, 1373, 1357, 1322,
1294 and 1282 cmꢁ1 as well as in FT-Raman spectrum at 1551,
1503, 1445, 1421, 1324 and 1303 cmꢁ1 respectively are assigned
to C–C stretching vibration. The PED corresponding to all C–C
vibrations are lies between 30% and 70% as shown in Table 4. with
combination of C–H in plane bending in this region. The in-plane
deformation vibration is at higher wavenumber than the out of
plane vibrations. Shimanouchi et al. [40] gave the frequency data
for these vibrations for different benzene derivatives as a result
of normal co-ordinate analysis. The PED contribution for this mode
is a mixed mode it is evident from Table 4. The theoretically com-
puted C–C–C vibrations by B3LYP method shows good agreement
with recorded spectral data.
C1
C4
C5
C6
C7
C8
C9
130.84
146.84
129.65
130.81
140.19
129.65
129.87
21.16
125.66
128.63
129.02
132.90
122.14
121.5
8.54
8.79
7.67
7.29
7.29
3.65
2.44
2.44
2.44
143.43
148.20
135.70
133.66
146.69
130.14
130.69
19.49
137.46
19.49
137.46
134.48
133.07
136.68
7.82
7.77
7.39
6.69
6.72
2.31
1.70
2.23
3.52
132.31
147.10
130.97
131.95
143.97
129.28
126.24
20.52
132.75
129.95
130.56
129.45
125.27
127.41
8.62
8.34
7.45
7.36
7.27
3.12
2.48
2.74
2.71
C10
C11
C12
C13
C14
C15
C16
H17
H18
H19
H20
H21
H22
H23
H24
H25
H26
H27
H28
H29
C–N vibrations
Primary aromatic amine with nitrogen directly on the ring ab-
sorb strongly at 1330–1260 cmꢁ1 due to stretching of the phenyl
carbon–nitrogen bond [41]. In accordance with the above literature
data, for our title molecule, the C–N stretching vibrations are ob-
served at 1373 and 1357 cmꢁ1 in FTIR spectrum. The counterpart
vibrations in FT-Raman spectrum were not observed. The theoret-
ically predicted values by the B3LYP method also coinciding well
with the measured FTIR intensity data. The PED of these vibrations
6.9
7.44
7.39
8.61
7.42
6.88
7.01
7.12
6.18
7.32
7.83
8.24

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
71
Fig. 6. Experimental spectrum of 13C of PN4MPN.
Fig. 7. Experimental spectrum of 1H of PN4MPN.
smallest of all atoms and mostly localized on the periphery of mol-
HOMO LUMO analysis
ecules. From the recorded proton spectra Fig. 7, it is evident that
the chemical shift of aromatic protons was observed at 1.94–
8.51 ppm.
Molecular orbitals (MO’s); both the Highest Occupied Molecular
Orbital (HOMO) energy value and Lowest Unoccupied Molecular
Orbital (LUMO) and their properties such as energy are very useful
for physicists and chemists are the main orbital taking part in
chemical reaction. While the energy of the HOMO is directly re-
lated to the ionization potential, LUMO energy is directly related
to the electron affinity [45,46]. This is also used by the frontier
electron density for predicting the most reactive position in p-elec-
tron systems and also explains several types of reaction in conju-
gated system [47]. The conjugated molecules are characterized
by a small Highest Occupied Molecular Orbital–Lowest Unoccupied
Molecular Orbital (HOMO–LUMO) separation, which is the result of
a significant degree of intramolecular charge transfer from the
end-capping electron-donor groups to the efficient electron-accep-
The N atom’s high electronegative property polarizes the elec-
tron distribution in its bond to the adjacent carbon atom and
decreases the electron density at the bridge for our title molecule.
Therefore, the chemical shift value seems to be moderately high for
the title molecule under study at 130.84 and 146.84 ppm (C1,C4).
The computed and recorded 1H chemical shift values also comple-
ment with experimental finding at 8.59 ppm with computed
chemical shifts at 8.11 ppm for H29. It is evident from Table 5 the
predicted chemical shift values by the theoretical method both
DFT and RHF slightly deviates from the experimental values are
due to the theoretical calculations were carried out in the isolated
gas phase.

72
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Table 6
Calculated energy values of PN4MPN by HF/6-311++G(d,p) and B3LYP/6-311++G(d,p).
Basis set
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
SCF energy (a.u)
Dipole moment
EHOMO (ev)
ELUMO (ev)
EHOMO–LUMO gap (ev)
ꢁ667.0971
5.7289
ꢁ671.3945
4.5443
ꢁ5.8099
ꢁ1.9769
3.833
l
(Debye)
ꢁ8.3521
0.8656
9.2177
Chemical hardness (
g
)
4.6088
1.9769
Softness (S)
Chemical potential (
Electronegativity (
0.1085
0.26089
ꢁ3.8934
3.8934
l
v)
)
ꢁ3.7432
3.7432
Electrophilicity index (
x
)
1.52011
3.9547
However, the value of chemical hardness, electronegativity, chemi-
cal potential and electrophilicity index are given in Table 6.
HOMO (Ground state)
Global and local reactivity descriptors
The energy gap between HOMO and LUMO is a critical parame-
ter to determine molecular electrical transport properties. By using
HOMO and LUMO energy values for a molecule, the global chemi-
cal reactivity descriptor of molecules such as hardness, chemical
potential, softness, electronegativty and electrophilicity index as
well as local reactivity have been defined [49–53]. Pauling intro-
duced the concept of electronegativity as the power of an atom
in a molecule to attract electrons to it. Hardness (
g
), chemical po-
tential (
follows.
ꢀ
l) and electronegativity (v) and softness are defined
ꢁ
ꢀ
ꢁ
1
2
@zE
@Nz
1
2
@u
@N
g
l
v
¼
¼
VðrÞ ¼
VðrÞ
ꢀ
ꢁ
@E
@N
VðrÞ
ꢀ
ꢁ
@E
@N
LUMO (Excited state)
¼ ꢁl
¼ ꢁ
VðrÞ
Fig. 8. The atomic orbital compositions of the frontier molecular orbital for
PN4MPN.
where E and V(r) are electronic energy and external potential of an
N-electron system respectively. Softness is a property of molecule
that measures the extent of chemical reactivity. It is the reciprocal
of hardness:
tor group through p-conjugated path [48]. Surfaces for the frontier
orbitals are drawn to understand the bonding scheme of present
compound. The energy difference between HOMO and LUMO
orbital which is called as energy gap is a critical parameter in
determining molecular electrical transport properties because it
is a measure of electron conductivity, calculated 3.833 eV for title
molecule. The plots of MO’s (HOMO and LUMO) are drawn and gi-
ven in Fig. 8. All the HOMO and LUMO have nodes. The nodes in
each HOMO and LUMO are placed symmetrically. The positive
phase is red1 and the negative one is green. According to Fig. 8,
the HOMO a charge density localized over the ring of the entire
molecule, but the LUMO is characterized by a charge distribution
on all structure, except H atoms in methyl group. The observed
1
S ¼
g
Using Koopman’s theorem for closed-shell molecules,
be defined as
g, l and v can
ꢀ
ꢁ
I ꢁ A
g
l
v
¼
2
ꢀ
ꢁ
I þ A
¼ ꢁ
2
ꢀ
ꢁ
transition from HOMO to LUMO is
r ?
rꢃ. The calculated self-con-
I þ A
¼
sistent field (SCF) energy of PN4MPN is ꢁ671.3945 a.u moreover
lower in the HOMO and LUMO energy gap explains the eventual
charge transfer interactions taking place within the molecule.
2
where A and I are ionization potential and electron affinity of the
molecules respectively. The ionization energy and electron affinity
can be expressed through HOMO and LUMO orbital energies as
I = ꢁEHOMO and A = ꢁELUMO, electron affinity refers to the capability
of a ligand to accept precisely one electron from a donor.The ioniza-
tion potential calculated by HF/6-311++G(d,p) and B3LYP/6-
311++G(d,p) methods for PN4MPN is 8.3521 eV and 5.8099 eV
respectively. Considering, the chemical hardness, large HOMO–
LUMO gap means a hard molecule and small HOMO–LUMO gap
HOMOenergy ¼ ꢁ5:8099 eV
LUMOenergy ¼ ꢁ1:9769 eV
HOMO—LUMOenergy gap ¼ 3:833 eV
1
For interpretation of colour in Figs. 8 and 9, the reader is referred to the web
version of this article.

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
73
means a soft molecule. One can also relate the stability of the mol-
ecule to hardness, which means that the molecule with least
HOMO–LUMO gap means it is more reactive.
Recently, Parr et al [49] have defined a new descriptor quantify
the global electrophilic power of the molecule as electrophilicity
stabilization energy of 20.30 kJ/mol. Similarly, the case of
p
(C7–
C8) orbital to pꢃ (C4–C9) shows the highest stabilization energy of
22.59 kJ/mol. The most important interaction energy in this mole-
cule is electron donating from O3 LP(1) to the antibonding acceptor
rꢃ (C1–N2) resulting moderate stabilization energy of 4.89 kJ/mol.
The same O3 LP(2) with pꢃ (C4–C9) leads to less stabilization energy
of 1.29 kJ/mol. The maximum energy delocalization take part in the
index (
electrophilic nature of a molecule Parr et al. [49] have proposed
electrophilicity index ( ) as a measure of energy lowering due to
maximal electron flow between donor and acceptor. They defined
x), which defines a quantitative classification of the global
x
p–
pꢃ transition. The E(2) values and types of the transition is shown
in Table 7.
electrophilicity index (x) as follows
Hyperpolarizability calculations
l2
x
¼
2
g
The first order hyperpolarizability (btotal) of the title compound
PN4MPN along with related properties (
l
, h
a
i and
Da) are calcu-
using the above equations, the chemical potential, hardness and
electrophilicity index have been calculated for PN4MPN and their
values are shown in Table 6. The usefulness of this new reactivity
quantity has been recently demonstrated in understanding the
toxicity of various pollutants in terms of their reactivity and site
selectivity [54–56]. The calculated value of electrophilicity index
describes the biological activity of PN4MPN.
lated using HF and DFT-B3LYP methods and 6-311++G(d,p) basis
set, based on the finite-field approach. In the presence of an
applied electric field, the energy of a system is a function of the
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 ꢄ 3 ꢄ 3 array. The 27 components of the
3D matrix can be reduced to 10 components due to Kleinmam
symmetry [61]. It can be given in the lower tetrahedral format.
The components of btotal are defined as the coefficients in the Tay-
lor series expansion of the energy in the external electric field.
When the external electric field is weak and homogeneous, when
the external electric field is weak and homogeneous, this expan-
sion becomes
NBO analysis
The natural bonding orbital’s (NBO) calculations are performed
using NBO 3.1 program as implemented in the Gaussian 03W [11]
package at the B3LYP/6-311++G(d,p) level in order to understand
various second order interactions between the filled orbital of
one subsystem, which is a measure of the intermolecular delocal-
ization or hyper conjugation.
E ¼ Eo ꢁ laFa ꢁ 1=2aabFaFb ꢁ 1=6ba FaFbFc . . .
bc
where Eo is the energy of unperturbed molecule, F the field at the
a
NBO analysis gives the most accurate possible natural Lewis
origin, la
polarizability and the first order hyperpolarizabilities, respectively.
The total static dipole moment , the mean dipole polarizabilitiy
), the anisotropy of the polarizability and the total first order
,
aa and b
are the components of dipole moment,
b
a
bc
structure picture of
U because all orbital are mathematically
chosen to include the highest possible percentage of the electron
density. Interaction between both filled and virtual orbital spaces
information is correctly explained by the NBO analysis, it could
enhance the analysis of intra and inter molecular interactions.
The second order Fock matrix was carried out to evaluate donor
(i)–acceptor (j) i.e. donor level bands to acceptor level bonds inter-
action in the NBO analysis [57]. The result of interaction is a loss of
occupancy from the concentration of electron NBO of the idealized
Lewis structure into an empty non-Lewis orbital. For each donor (i)
and acceptor (j), the stabilization energy E (2) associates with the
delocalization i ? j is estimated as
l
(a
Da
hyperpolarizability btotal, using x, y, z components they are defined
as
1=2
l
¼ ðl2x
þ
lY2
þ
lZ2
Þ
axx
þ
ayy
3
þ
azz
ha
i ¼
2
2
1=2
D
a
¼ 2ꢁ1=2½ðaxx
ꢁ
ayyÞ þ ðayy
ꢁ
azzÞ þ ðazz
ꢁ
axxÞ2 þ 6a2xx
ꢂ
2
Eð2Þ
¼
D
Eij ¼ qiFði; jÞ =ðej
ꢁ eiÞ
1=2
btotal ¼ ðb2x þ by2 þ b2z Þ
where qi is the donor orbital occupancy, ej
ꢁ
ei are diagonal ele-
and
ments and F(i,j) is the off diagonal NBO Fock Matrix element. NBO
analysis provides an efficient method for interaction among bonds,
and also provides a convenient basis for investigating charge trans-
fer or conjugative interaction in molecular systems. Some electron
donor orbital, acceptor orbital and the interacting stabilization
energy resulted from the second order micro-disturbance theory
are [58,59]. The larger E2 value the more intensive is the more dona-
tion tendency from electron donors to electron acceptors and the
greater the extent of conjugation of the whole system [60]. Delocal-
ization of electron density between occupied Lewis type (bond or
lone pair) NBO orbital and formally unoccupied (anti bond or Ryd-
berg) non-Lewis NBO orbital correspond to a stabilizing donor–
acceptor interaction. NBO analysis has been formed on the PN4MPN
molecule at the DFT/B3LYP 6-31G(d,p) level in order to elucidate,
the intra molecular rehybridization and delocalization of electron
density within the molecule. The intramolecular hyperconjugative
bx ¼ bxxx þ byyy þ bzzz
by ¼ byyy þ bxxy þ byzz
bz ¼ bzzz þ bxxz þ byyz
The HF/6-311++G(d,p) results of electronic dipole moment li
(i = x,y,z), polarizability aij and first order hyperpolarizability bijk
are listed in Table 8. The calculated dipole moment and hyperpolar-
izability values obtained from HF/6-311++G(d,p) and B3LYP/
6-311++G(d,p) methods are collected in Table 8. The total molecular
dipole moment of PN4MPN from HF and B3LYP with 6-311++G(d,p)
basis set are 2.2302 D and 1.8259 D respectively, which are nearer
to the value of urea (l = 1.3732 D). Similarly the first order hyper-
polarizability of PN4MPN with B3LYP/6-311++G(d,p) basis set is
5.3775 ꢄ 10ꢁ30 fourteen times greater than the value (bo = 0.372 -
ꢄ 10ꢁ30 esu). From the computation the high values of PN4MPN
are probably attributed to the charge transfer existing between
interactions of
strong stabilization energy of 20.24 kJ/mol and 21.86 kJ/mol,
respectively. Incase of
(C4–C9) orbital to pꢃ (C5–C6) shows the
p p (C7–C8) leads to
(C5–C6) orbital to pꢃ (C4–C9),
p

74
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Table 7
Second-order perturbation theory analysis of Fock matrix in NBO Basis for PN4MPN.
Donor (i)
ED (i) (e) e
Type
Acceptor (j)
Type
ED (j) (e)
E(2)a (kJ/mol)
E (j)–E (i)b (a.u)
F (i,j)c (a.u)
C1–N2
1.98805
r
C1–C11
N2–C4
rꢃ
rꢃ
0.02579
0.07165
1.91
3.27
1.38
1.27
0.046
0.058
C1–N2
C5–C6
1.94449
1.97374
P
r
C1–N2
C4–C9
Pꢃ
Pꢃ
Pꢃ
0.39361
0.36575
0.38014
4.43
3.56
3.71
0.35
0.41
0.41
0.039
0.037
0.038
C
11–C12
N2–C4
C4–C5
C5–H18
C6–C7
C6–H19
C7–C10
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
0.07165
0.02384
0.01336
0.02493
0.01468
0.01641
4.17
3.44
1.33
3.59
1.08
3.52
1.05
1.29
1.17
1.29
1.16
1.12
0.060
0.059
0.035
0.061
0.032
0.056
C5–C6
C4–C9
1.67170
1.97106
P
r
C4–C9
C7–C8
Pꢃ
Pꢃ
0.36575
0.32847
20.24
21.86
0.28
0.29
0.068
0.072
N2–O3
C4–C5
C5–H18
C8–C9
C8–H20
C9–H29
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
0.02304
0.02384
0.01397
0.01503
0.01466
0.01371
1.36
4.99
2.00
3.24
2.21
1.33
1.12
1.30
1.19
1.31
1.17
1.17
0.035
0.072
0.044
0.058
0.046
0.035
C4–C9
C7–C8
1.68045
1.97407
P
r
C1–N2
C5–C6
C7–C8
Pꢃ
Pꢃ
Pꢃ
0.39361
0.29742
0.32847
6.19
20.30
17.57
0.24
0.30
0.31
0.035
0.070
0.065
C6–H7
C6–H19
C7–C10
C8–C9
C8–H20
C9–H29
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
0.02493
0.01468
0.01641
0.01503
0.01466
0.01371
3.38
2.54
1.71
3.37
1.21
2.12
1.29
1.15
1.12
1.29
1.16
1.15
0.059
0.048
0.039
0.059
0.033
0.044
C7–C8
1.65156
1.97159
P
r
C4–C9
C5–C6
Pꢃ
Pꢃ
0.36575
0.29742
22.59
18.40
0.28
0.29
0.072
0.066
C11–C12
C1–N2
C1–C11
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
rꢃ
0.03371
0.02579
0.02735
0.01609
0.01403
0.01390
0.01426
1.83
1.89
4.17
3.09
1.08
2.013
2.49
1.28
1.16
1.28
1.29
1.15
1.16
1.16
0.043
0.042
0.065
0.051
0.032
0.045
0.048
C
C
C
C
C
11–C16
12–C13
12–H25
13–H26
16–H21
C11–C12
1.64650
P
C1–N2
Pꢃ
Pꢃ
Pꢃ
0.39361
0.33285
0.1403
13.25
20.21
19.81
0.23
0.29
0.29
0.050
0.068
0.068
C
C
13–C14
15–C16
LP(1) O3
LP(2) O3
1.98253
1.93089
r
P
C1–N2
N2–C4
rꢃ
rꢃ
Pꢃ
0.03371
0.07165
4.89
3.00
1.34
1.11
0.073
0.052
C4–C9
0.36575
1.29
0.27
0.018
ED, Electron Density.
a
Energy of hyper conjugative interaction (stabilization energy).
Energy difference between donor and acceptor i and j NBO orbital.
Fock matrix element between i and j NBO orbital.
b
c
the phenyl rings within the molecular skeleton. We conclude that
the title compound is an attractive object for future studies of
non-linear optical properties.
matic ring. Among the hydrogen atoms present in the molecule
the charge on H17, H18, H21, H28 and H29 atoms has the maximum
magnitude of 0.2522, 0.2523, 0.2344, 0.2246 and 0.2397 respec-
tively by HF method and 0.2181, 0.2172, 0.1916, 0.1802 and
0.1967 respectively by B3LYP method. It is to be noticed that all
the hydrogen atoms exhibit a net positive charge both in HF and
DFT methods. The presence of negative charge on O and N atoms
and net positive charge on H atom may suggest the formation of
intramolecular interaction and intermolecular interaction in solid
forms [64].
Atomic charge analysis
The atomic charge in molecules is fundamental to the chemis-
try. For instance, atomic charge has been used to describe the pro-
cesses of electro negativity equalization and charge transfer in
chemical reactions [62,63]. Milliken and natural atomic charges
calculated at the RHF and B3LYP/6-311++G(d,p) method is col-
lected in Table 9. It is worthy to mention that electro negative
atoms N2, O3, C4, C6, C8, C9, C10, C13, C14, C15 and C16 atoms of
PN4MPN exhibit negative charge, while C1, C5 and C7 atoms exhibit
positive charges. Oxygen O3 atom has a maximum negative charge
value. The maximum positive atomic charge obtained for C1 which
is a carbon surrounded by nitrogen and oxygen atoms in the aro-
Fukui functions
DFT is one of the important tools of quantum chemistry to
understand popular chemical concepts such as electronegativity,
electron affinity, chemical potential and ionization potential [65].
The electron density-based local reactivity descriptors such as Fu-

N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
75
Table 8
Table 10
The dipole moments
anisotropy of the polarizability
l
(D), polarizability
, and the first hyperpolarizability b of PN4MPN
calculated by HF and B3LYP methods using 6-311++G(d,p) basis set.
a
,
the average polarizability ao
,
the
Condensed Fukui table fk and descriptors (sf)k for PN4MPN.
Da
fkꢁ
ðsfÞꢁk
fkþ
fk0
ðsfÞþk
0
Atom
ðsfÞk
C1
0.5908
ꢁ0.0820
ꢁ0.2132
ꢁ0.0385
ꢁ0.0400
ꢁ0.1445
0.2869
ꢁ0.4205
ꢁ0.1908
ꢁ0.6519
0.6606
ꢁ0.1674
ꢁ0.1322
ꢁ0.4563
ꢁ0.3763
ꢁ0.0743
0.4062
ꢁ0.2195
0.2141
0.5030
0.0910
0.0018
0.0119
0.0004
0.0004
0.0054
0.0215
0.0461
0.0095
0.1109
0.1138
0.0073
0.0046
0.0543
0.0369
0.0014
0.0431
0.0126
0.0120
0.0002
0.0000
0.0024
0.0086
0.0371
0.0076
0.0901
0.0457
0.0000
0.0017
0.0330
0.0221
0.0004
0.0660
0.0053
0.0013
0.0007
0.0000
0.0023
0.0134
0.0405
0.0079
0.1013
0.0486
0.0005
0.0025
0.0408
0.0253
0.0010
Parameters
PN4MPN
N2
O3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
ꢁ0.1430
ꢁ0.0694
ꢁ0.0523
ꢁ0.0006
ꢁ0.0931
0.2265
ꢁ0.3941
ꢁ0.1738
ꢁ0.6232
0.4318
ꢁ0.0456
ꢁ0.0980
ꢁ0.3957
ꢁ0.3117
ꢁ0.0634
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
0.0293
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
59.6797
74.4508
58.5311
383.7584
50.4701
105.3677
96.3429
40.6720
366.1348
82.8539
63.2940
ꢁ0.0040
ꢁ0.0955
0.1820
ꢁ0.3771
ꢁ0.1707
ꢁ0.5875
0.4183
33.9918
ꢁ82.4325
ꢁ79.2595
29.0237
41.4494
0.0018
109.8754
ꢁ91.5415
5.1811 ꢄ 10ꢁ30
ꢁ0.8187
124.2249
ꢁ93.4428
5.3775 ꢄ 10ꢁ30
ꢁ0.8396
ꢁ0.0802
ꢁ0.3557
ꢁ0.2909
ꢁ0.0412
btotal (esu)
lx
ly
1.4931
1.0397
lz
l
ꢁ1.4401
ꢁ1.2443
(D)
2.2302
1.8259
axx
axy
ayy
axz
ayz
azz
175.6214
35.0001
189.5245
10.4451
ꢁ22.6034
143.3992
2.5122 ꢄ 10ꢁ23
4.588 ꢄ 10ꢁ23
186.5256
37.2095
203.2659
14.4937
ꢁ26.5075
152.4521
2.3152 ꢄ 10ꢁ23
4.3672 ꢄ 10ꢁ23
tron, which we chemist interpret as which are more prone to un-
dergo a nucleophilic or an electrophilic attack, respectively. The
Fukui function is defined as [68]
d
q
@N
ðrÞ
fðrÞ ¼
r
hai esu
D
a
where
q(r) is the electronic density, N is the number of electrons
and r is the external potential exerted by the nucleus. The Fukui
function is a local reactivity descriptor that indicates the preferred
regions where a chemical species will change its density when
the number of electrons is modified. Therefore, it indicates the pro-
pensity of the electronic density to deform at a given position upon
accepting or denoting electrons [68–70]. Also, it is possible to define
the corresponding condensed or atomic Fukui functions on the kth
atom site as,
Table 9
Mulliken atomic charges.
Atom with numbering
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
C1
N2
O3
C4
C5
C6
C7
C8
0.5624
ꢁ0.1098
ꢁ0.5737
ꢁ0.0367
0.0183
0.5030
ꢁ0.1430
ꢁ0.5694
ꢁ0.0523
0.0096
ꢁ0.0931
0.2265
ꢁ0.3941
ꢁ0.1738
ꢁ0.6232
0.4318
0.0986
ꢁ0.0980
ꢁ0.3957
ꢁ0.3117
ꢁ0.0634
0.2181
0.2172
0.1885
0.1582
0.1916
0.1644
0.1401
fkþ ¼ qkðN þ 1Þ ꢁ qkðNÞ for nucleophilc attack
ꢁ0.0541
0.1921
ꢁ0.5094
ꢁ0.2279
ꢁ0.6622
0.5852
fkꢁ ¼ qkðNÞ ꢁ qkðN ꢁ 1Þ for electrophilic attack
C9
C10
C11
C12
C13
C14
C15
C16
H17
H18
H19
H20
H21
H22
H23
H24
H25
H26
H27
H28
H29
1
2
fk0
¼
½qkðN þ 1Þ ꢁ qkðN ꢁ 1Þꢂ for radical attack
0.1239
ꢁ0.1182
ꢁ0.5390
ꢁ0.3549
ꢁ0.3151
0.2522
0.2523
0.2286
0.2121
0.2344
0.1637
0.1477
0.1564
0.2155
0.2194
0.1873
0.2246
0.2397
where +, ꢁ, 0 signs show nucleophilic, electrophilic and radical at-
tack, respectively. In these equations, qk is the atomic charge (eval-
uated from Mulliken population analysis, electrostatic derived
charge, etc.) at the kth atomic site is the neutral (N), anionic
(N + 1) or cationic (N ꢁ 1) chemical species. The Fukui function al-
lows determining the pin point distribution of the active sites on
a molecule, the value of this function is completely dependent of
the kind of charges used. In order to solve the negative Fukui func-
tion problem, different attempts have been made by various groups
[71–73]. Kolandaivel et al. [74] introduced the atomic descriptor to
determine the local reactive sites of the molecular system. In the
present study, the optimized molecular geometry was utilized in
single-point energy calculations, which have been performed at
the DFT for the anions and cations of the title compound using
the ground state with doublet multiplicity. The individual atomic
charges calculated by Mulliken population analysis (MPA) have
been used to calculate the Fukui function. In order to confirm that
the atomic descriptor would produce the reactive sites without dis-
turbing the trend; we have performed the calculation for the reac-
tive sites of the stable structures of PN4MPN. Table 10 shows the fk
and (sf)k values for the compound PN4MPN, using which one can
find the complexities associated with fk values due to the negative
values being removed in the (sf)k values. It has been found that
MPA schemes predict C11 has higher fkꢁ value indicates the possible
site for electrophilic attack. From the values reported in Table 10,
0.1577
0.1799
0.1720
0.1444
0.1802
0.1967
kui functions are proposed to explain the chemical selectivity or
reactivity at a particular site of a chemical system [66]. Electron
density is a property that contains all the information about the
molecular system and plays an important role in calculating almost
all these chemical quantities. Parr and Yang [67] proposed a finite
difference approach to calculate Fukui function indices, i.e. nucleo-
philic, electrophilic and radical attacks. Fukui indices are, in short,
reactivity indices; they give us information about which atoms in a
molecule have a larger tendency to either loose or accept an elec-

76
N.R. Sheela et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 62–77
Fig. 9. Molecular Electrostatic Potential (MEP) Map for PN4MPN.
Table 11
MPA schemes predict the reactivity order for the electrophilic case
as C11 > C1 > C7 > C4 > C12. The observation of the reactive sites by
Theoretically computed energies (a.u), zero-point vibrational energies (kcal molꢁ1),
rotational constants (GHz), entropies (cal molꢁ1), dipole moment (D), heat capacity
(kcal molꢁ1 Kꢁ1) and rotational temperature (K).
ðsfÞꢁk is found almost identical to fꢁ. Even though the (sf)k values
k
are numerically less it should be worth noting that the values are
positive and the ordering of the reactivity has not changed in any
case. The calculated fkþ value predicts that the possible sites for
nucleophillic attack is C11, C7 and C10 site and the radical attack
was predicted at C11 and C1 site. From the tabulated values it is evi-
dent that reactivity order for the electrophilic case was C11 > C1 > C7.
If one compares the three kinds of attacks it is possible to observe
that, nucleophilic attack is bigger reactivity comparison with the
electrophilic and radical attack.
Parameters
HF/6-311++G(d,p)
B3LYP/6-311++G(d,p)
Total energy
Zero point energy
Rotationa constants
ꢁ667.0971
156.5863
0.86148
0.36136
0.28488
ꢁ671.3945
146.6854
0.88199
0.34681
0.27398
Entropy
Total
Translational
Rotational
Vibrational
Electronic
164.672
0.889
0.889
162.894
0.000
155.306
0.889
0.889
153.528
0.000
Dipole moment
Rotational temperature
5.7289
0.0413
0.0173
0.0136
4.5443
0.0423
0.0166
0.0131
Molecular electrostatic potential surface
The Molecular Electrostatic Potential surface (MEPs) for HPN
molecule in 3D plots is illustrated in Fig. 9. The MEP’s is a plot of
electrostatic potential mapped onto the constant electron density
surface. The MEP’s is a plot of electrostatic potential mapped onto
the electron density surface. The MEP’s is a plot of electrostatic po-
tential mapped onto the constant electron density surface. The
MEP’s superimposed on top of the total energy density as a shell.
The different values of the electrostatic potential at the surface
are represented by different colors. The color code of these maps
in the range between ꢁ0.05 a.u (deepest red) and 0.05 a.u (white)
in compound, where white indicates the strongest attraction
(nucleophilic attack) and red indicates the strongest repulsion
(electrophilic attack). The importance of MEP’s lies in the fact that
it simultaneously displays molecular size, shape as well as positive,
negative and neutral electrostatic potential regions in terms of col-
or grading and is very useful in research of molecular structure
with its physicochemical property relationship [75,76]. As can be
seen from the MEP’s map of the title molecule the regions having
the negative potential are over the oxygen atom (O3). From these
results we can say that the hydrogen atoms indicates the strongest
attraction and the oxygen atom indicates the strongest repulsion.
Thermodynamic properties
The calculated thermodynamic parameters are presented in
Table 9. Scale factors have been recommended [65] for an accurate
prediction in determining Zero point vibration energy (ZPVE) and
the entropy. The variations in the ZPVE’s seem to be insignificant.
The total energies and the change in the total entropy of PN4MPN
at room temperature by different methods are also presented in
Table 11, along with dipole moment. The highest value of ZPVE
of PN4MPN is 160.8147 kcal molꢁ1 obtained by HF/6-311++G
(d,p), whereas the lowest one is 149.8758 kcal molꢁ1, obtained by
B3LYP/6-311++G(d,p) method. Dipole moment reflects the molecu-
lar charge distribution and is given as a vector in three dimensions.
Therefore, it can be used as an illustrator to depict the charge
movement across the molecule. As a result, the dipole moment
of PN4MPN was observed at 5.4070 D in HF/6-311++G(d,p) method
whereas 4.1171 D in B3LYP/6-311++G(d,p) method.

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of title compound are examined by using FT-IR, FT-Raman and
NMR spectra and tools derived from the density functional theory.
Due to the lack of experimental information on the structural
parameters in the literature, the optimized geometric parameters
(bond length and bond angles) was theoretically determined at
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PN4MPN show that the negative potential sites are on electroneg-
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hydrogen atoms. These sites give information about the region
from where the compound can undergo non-covalent interactions.
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