Synthesis, FTIR and FT-Raman spectral analysis and structure-activity relations of N-(4-bromophenyl)-2,2-dichloroacetamide by DFT studies

Article abstract of DOI:10.1016/j.molstruc.2014.01.091

The FTIR and FT-Raman vibrational spectra of N-(4-bromophenyl)-2,2- dichloroacetamide molecule has been recorded and analysed the complete vibrational fundamental modes of the most stable geometry of the compound using the experimental FTIR and FT-Raman data on the basis of peak positions, relative intensities and quantum chemical studies. The observed vibrational frequencies were compared with the theoretical wavenumbers of the optimised geometry of the compound obtained from the DFT-B3LYP gradient calculations employing the high level 6-311++G^** and cc-pVTZ basis sets. The effect of substituent Br in the amide moiety have been analysed and compared. The kinetic and thermodynamic stability and chemical reactivity descriptors of the molecule have been determined. The reactive centres are found from the molecular electrostatic potential and the atomic charges. The limits of electrostatic potential are -9.617e × 10^-3 and +9.617e × 10 ^-3. The molecule has great electronegativity difference, charge is very polarized, and there are significant differences in electron density in different regions of the molecule. The lone pair donor orbital, n_N → π^*_CO interaction possess a strong stabilisation of 64.21 kcal mol^-1.

Full text of DOI:10.1016/j.molstruc.2014.01.091

Journal of Molecular Structure 1064 (2014) 15–26
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, FTIR and FT-Raman spectral analysis and structure–activity
relations of N-(4-bromophenyl)-2,2-dichloroacetamide by DFT studies
a
b
c
V. Arjunan a, , S. Senthilkumari , P. Ravindran , S. Mohan
⇑
a Department of Chemistry, Kanchi Mamunivar Centre for Post-Graduate Studies, Puducherry 605 008, India
b Department of Chemistry, Mahatma Gandhi Govt. Arts College, Mahe 673 311, India
c School of Sciences and Humanities, Vel Tech University, Avadi, Chennai 600 062, India
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
The structural, vibrational and reactivity characteristics have been determined.
The molecule has great electronegativity difference and charge is highly polarized.
The atoms C2, C3, C5, C6, N7, O9 and C10 are more prone to nucleophilic attack.
The LUMO of the molecule feature a larger number of nodes than the HOMO.
The nN
? .
pꢁ interaction possess a strong stabilization of 64.21 kcal molꢂ1
CO
a r t i c l e i n f o
a b s t r a c t
Article history:
The FTIR and FT-Raman vibrational spectra of N-(4-bromophenyl)-2,2-dichloroacetamide molecule has
been recorded and analysed the complete vibrational fundamental modes of the most stable geometry
of the compound using the experimental FTIR and FT-Raman data on the basis of peak positions, relative
intensities and quantum chemical studies. The observed vibrational frequencies were compared with the
theoretical wavenumbers of the optimised geometry of the compound obtained from the DFT-B3LYP gra-
dient calculations employing the high level 6-311++Gꢁꢁ and cc-pVTZ basis sets. The effect of substituent
ABr in the amide moiety have been analysed and compared. The kinetic and thermodynamic stability and
chemical reactivity descriptors of the molecule have been determined. The reactive centres are found
from the molecular electrostatic potential and the atomic charges. The limits of electrostatic potential
are ꢂ9.617e ꢃ 10ꢂ3 and +9.617e ꢃ 10ꢂ3. The molecule has great electronegativity difference, charge is
very polarized, and there are significant differences in electron density in different regions of the mole-
Received 2 September 2013
Received in revised form 11 December 2013
Accepted 27 January 2014
Available online 8 February 2014
Keywords:
FTIR
FT-Raman
N-(4-bromophenyl)-2,2-dichloroacetamide
DFT
Fukui functions
cule. The lone pair donor orbital, nN
?
pꢁCO interaction possess a strong stabilisation of 64.21 kcal molꢂ1
Ó 2014 Elsevier B.V. All rights reserved.
.
1. Introduction
interesting compounds because of their structural similarity to
the lateral chain of natural benzyl penicillin [15,16]. Amides are
also used as ligands due to their excellent coordination abilities
[17,18].
Amides are of fundamental chemical interest as conjugation be-
tween nitrogen lone-pair electrons and the carbonyl p-bond which
possess distinct physical and chemical properties. A planar struc-
ture of amide group has been confirmed by measurement with
X-rays and the trans-configuration is the most stable [1–8]. The
rotational spectrum of acetanilide confirmed that the planar con-
former with the CH3 group anti to the ring is the most stable
[9,10] which is in agreement with the reports of other experimen-
tal investigators [11–14]. Substituted 2-arylacetamides are very
Many N-phenylacetamide derivatives exhibit fungicidal, herbi-
cidal and pharmacological activities which further stimulated the
recent interest in their chemistry. Anilide herbicides such as ala-
chlor, acetochlor, metolachlor, pretilachlor and butachlor are
promising weed control agents for a wide variety of economically
important crops including rice, cotton, potatoes and corns [19–
22]. The choloroacetanilde herbicide alachlor is one of the most
extensively used agro chemical [23,24]. Propanil (3,4-dichloropro-
pioanilide) is a selective contact anilide herbicide commonly used
for the control of broad leveled and grass weeds. N-phenylacet-
amide is used in medicine under the name antifebrin, as a febrifuge
⇑
Corresponding author. Tel.: +91 413 2211111, mobile: +91 9442992223; fax:
+91 413 2251613.
E-mail address: varjunftir@yahoo.com (V. Arjunan).
http://dx.doi.org/10.1016/j.molstruc.2014.01.091
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

16
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
and it has pain relieving properties [25]. Acetanilide is a useful
intermediate in various reactions of aniline in which it is desirable
to protect the amino group.
the exchange part and the Lee–Yang–Parr (LYP) correlation func-
tional [43], calculations have been carried out using 6-311++Gꢁꢁ
and cc-pVTZ basis sets with Gaussian-09 [44] program, invoking
gradient geometry optimisation [45]. Following geometry optimi-
sations with B3LYP method, the optimised structural parameters
were used in the vibrational frequency calculations to characterise
all stationary points as minima. The harmonic vibrational fre-
quency calculations were carried out for 4BNPA resulting in IR
and Raman frequencies together with intensities and Raman depo-
larization ratios. The dipole moment derivatives and polarizability
derivatives were computed analytically. The force constants ob-
tained from the B3LYP/6-311++Gꢁꢁ method have been utilised in
the normal coordinate analysis by Wilson’s FG matrix method
[46–48]. The potential energy distributions corresponding to each
of the observed frequencies were calculated with the program of
Fuhrer et al. [49].
As amides are the simplest model for peptides and also due to
the fungicidal, herbicidal and several pharmacological activities
of many acetanilide derivatives, their exact structure has been
the subject of many experimental and theoretical studies [26–
34]. The room-temperature structure of N-(4-bromophenyl)acet-
amide was reported to crystallise in the orthorhombic space group
Pna21 by Andreetti et al. [35] and recently a new polymorph of the
same compound has been determined at 173 K in the space group
P21/c by Jasinski et al. [36].
The vibrational spectroscopic analysis of acetanilide derivative
N-(4-bromophenyl)-2,2-dichloroacetamide (4BNPA) has not been
studied. Thus, in continuation of earlier studies on N-(chloro
substituted phenyl)-2,2-dichloroacetamides [37] and N-(methyl-
phenyl)-2,2-dichloroacetamides [38,39], N-(dimethyl substituted
phenyl)-2,2-dichloroacetamides [40] and owing to the significance
of the N-arylacetamides in biological systems and in industries, the
compound N-(4-bromophenyl)-2,2-dichloroacetamide has been
prepared and an extensive spectroscopic and quantum chemical
studies are carried out in an effort to provide possible explanations
for vibrational frequencies, to understand the effect of bromine on
the characteristic amide group frequencies and to provide clear
information on the structure–reactivity relations of the molecule.
The Raman scattering activities (Si) of the fundamental modes
were suitably converted to relative Raman intensities (Ii) using
the following relationship derived from the basic theory of Raman
scattering [50].
4
fðm0
ꢂ
miÞ Si
Ii ¼
mi½1 ꢂ expðꢂhc
m
i=kTÞꢄ
where vi is the vibrational wave-
v
0 is the exciting frequency (cmꢂ1),
number of the ith normal mode, h, c and k are universal constants,
and f is the suitably chosen common scaling factor for all the peak
intensities.
2. Experimental
Isoelectronic molecular electrostatic potential surfaces (MEP)
and electron density surfaces [51] were calculated using 6-
311++Gꢁꢁ basis set. The molecular electrostatic potential at a point
‘r’ in the space around a molecule (in atomic units) can be ex-
pressed as:
The compound N-(4-bromophenyl)-2,2-dichloroacetamide
(4BNPA) was prepared from the respective 4-bromoaniline, dichlo-
roacetic acid and phosphorus oxychloride based on the procedure
reported [37]. The pure samples of 4-bromoaniline, dichloroacetic
acid and phosphorus oxychloride were purchased from Aldrich
chemicals, USA and are used as such without further purification.
All other chemicals used are of analar (AR) grade. The synthesised
crude compound was recrystallised from ethanol several times.
The yield of the product is about 70%. The purity of the compound
was confirmed by chemical analysis (found/calculated) for C
(33.82/33.96), H (2.07/2.14) and N (4.90/4.95). The Scheme I de-
picts the preparation of the compound under investigation.
The FTIR spectrum of the compound was recorded in the solid
phase by KBr disc method in a Bruker IFS 66 V spectrometer in
Z
0
0
X
~
ZA
q
ðr Þdr
VðrÞ ¼
ꢂ
0
~
~
~
~
jr ꢂ rj
jRA ꢂ rj
A
where ZA is the charge on nucleus A, located at RA and
q
(r0) is the
electronic density function for the molecule. The first and second
terms represent the contributions to the potential due to nuclei
and electrons, respectively. V(r) is the resultant electrical potential
at each point r, which is the net electrostatic effect produced at
the point r by both the electrons and nuclei of the molecule. The
molecular electrostatic potential (MEP) serves as a useful quantity
to explain hydrogen bonding, reactivity and structure–activity rela-
tionship of molecules including biomolecules and drugs [52]. Struc-
tures resulting from the plot of electron density surface mapped
with electrostatic potential surface depict the shape, size, charge
density distribution and the site of chemical reactivity of a mole-
cule. GaussView 5.0.8 visualisation program [53] has been utilised
to construct the MEP surface, the shape of highest frontier molecu-
lar orbitals.
the range of 4000–400 cmꢂ1. The spectral resolution was 2 cmꢂ1
.
The FT-Raman spectrum of the compound was also recorded with
the same instrument with FRA 106 Raman module. The Raman
spectrum was obtained in the wavenumber range 4000–
100 cmꢂ1. The light scattering was excited using a low-noise diode
pumped Nd:YAG laser source operating at 1.064 lm with 200 mW
powers. A special (enhanced) liquid nitrogen cooled germanium
detector was used. The frequencies of all sharp bands are accurate
to 2 cmꢂ1
.
The stabilisation energy E(2) associated with i (donor) ? j
(acceptor) delocalisation is estimated from the second-order per-
turbation approach [54] as given below
3. Computational details
F2ði; jÞ
The gradient corrected density functional theory (DFT) [41]
with the three-parameter hybrid functional Becke3 (B3) [42] for
Eð2Þ ¼ q
i ej
ꢂ
ei
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments (orbital energies) and F(i,j) is the off-diagonal Fock matrix
element.
Various reactivity and selectivity descriptors such as chemical
hardness, chemical potential, softness, electrophilicity, nucleophi-
licity and the appropriate local quantities employing natural
population analysis (NPA) scheme are calculated. Both the global
and local reactivity descriptors are determined using finite differ-
ence approximation to reveal the intramolecular reactivity of the
Scheme I.

V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
17
molecule. The vertical ionization potential (I), electron affinity (A)
and the electron populations are determined on the basis of
B3LYP/6-311++Gꢁꢁ method. The energy of the N electron species
of the NCEP has been determined by restricted B3LYP method
while N ꢂ 1 and N + 1 electronic species were done by restricted
open B3LYP method using the optimised geometry by B3LYP/6-
311++Gꢁꢁ method. The site-selectivity of a chemical system can
be determined by using Fukui functions [55,56] which can be inter-
preted either as the change of electron density
q(r) at each point r
when the total number of electrons are changed or as the sensitiv-
ity of chemical potential (
l
) of a system to an external perturbation
at a particular point r.
ꢀ
ꢁ
ꢀ
ꢁ
@
q
@N
ðrÞ
d
v
l
ðrÞ
fðrÞ ¼
¼
d
v
ðrÞ
N
Yang and Parr introduced local softness s(r) to predict the reac-
tivity [56]. The s(r) describes the sensitivity of the chemical poten-
tial of the system to the local external perturbation and is obtained
by simply multiplying Fukui function f(r) with global softness S.
The local softness values are generally used in predicting electro-
philic, nucleophilic and free radical reactions, regioselectivity etc.
ꢀ
ꢁ
@
q
ðrÞ
sðrÞ ¼
and sðrÞ ¼ fðrÞS
@
l
v
ðrÞ
where S is the global softness which is inversely related to global
hardness ( ).
The generalised philicity descriptor,
g
x
(r) contains almost all
informations about hitherto known different global and local reac-
tivity and selectivity descriptors, in addition to the information
regarding electrophilic/nucleophilic power of a given atomic site
in a molecule [57]. The local quantity called philictiy associated
Fig. 1. The stable geometry and atom numbering of N-(4-bromophenyl)-2,2-
dichloroacetamide.
with a site k in a molecule can be calculated as xka
¼
x
fka, where
in the plane of the ring. The ACOANHA group also adopts a planar
‘peptide-like’ conformation, as in the case of formamide [59], N-
methylformamide [60], o-methylacetanilide [61] and formanilide
[11,12], N-(methylphenyl)-2,2-dichloroacetamides [38,39], N-(di-
methyl substituted phenyl)-2,2-dichloroacetamides [40]. The theo-
retical amide group bond distances are very well agreed with the
experimental bond distances of N-(4-bromophenyl)acetamide
[36]. The bond lengths between the amide nitrogen and the aro-
matic ring, C1AN7 and between the amide nitrogen and the car-
bonyl group, N7AC8 given in Table 1 reflect the changes in
conjugation. The mesomeric effect (+M) of ABr group on the
C1AN7 bond distances is also having some significance.
x
=
l
2/2
g
and a = +, ꢂ and 0 represents local philic quantities
describing nucleophilic, electrophilic and radical attacks respec-
tively. The condensed philicity summed over a group of relevant
atoms which is defined as the group philicity [58] can also be
P
n
determined by using the relation xga
¼
k¼1xak where, n is the
number of atoms coordinated to the reactive atom and xak is the lo-
cal electrophilicity of the atom k.
4. Results and discussion
4.1. Structural properties
With the electron donating substituents on the benzene ring,
the symmetry of the ring is distorted, yielding ring angles smaller
than 120° at the point of substitution and slightly larger than 120°
at the ortho and meta positions [62]. An opposite trend is observed
in 4BNPA due to the predominance of inductive (ꢂI) effect of the
bromine. The angle at the point of substitution C3AC4AC5 in
4BNPA is 120.6°. Similarly the ortho bond angles C2AC3AC4 and
C4AC5AC6 in 4BNPA are 119.2° and 120.2°, respectively. In the
amide group region the bond angles C1AN7AC8 (128.7°/
(127.5°)), N7AC8AO9 (126.6°/(123.8°)) and O9AC8AC10 (118.4°/
(121.6°)) differ significantly from the experimental values given
in parenthesis of N-(4-bromophenyl)acetamide. The dihedral an-
gles determined theoretically are agreed well with the experimen-
tal values except C2AC1AN7AC8 (179.5°/(164.5°)) and
C6AC1AN7AC8 (0.5°/(ꢂ18.6°)). These are due the role of intermo-
lecular hydrogen bonding present in the solid state. In the crystal,
molecules are linked by NAHꢅ ꢅ ꢅO hydrogen bonds forming chains.
The optimised molecular geometry and atom numbering
scheme of 4BNPA is shown in Fig. 1. The steric interaction of bromo
substituent on the ring is of great importance in determining its
structural and vibrational properties. The steric crowding by adja-
cent substituents on an aromatic ring may be reduced by the rota-
tion of one of the substituents around its bond to the aromatic ring.
The optimised structural parameters bond lengths and the bond
angles for the thermodynamically preferred geometry of 4BNPA
at B3LYP levels with 6-311++Gꢁꢁ and cc-pVTZ basis sets are
presented in Table 1. The theoretical values determined by
B3LYP/6-311++Gꢁꢁ method are used for comparison purposes un-
less otherwise stated. It is observed that the mean CAC bond dis-
tance calculated between the ring carbon atoms of 4BNPA is
1.393 Å, and the CAC and CAH bond lengths are found to be not
significantly deviated with the ABr substitution. The bond length
of the compound 4BNPA determined at the DFT level of theory
are in good agreement with the structural parameters of N-phenyl-
acetamide [13] where the mean bond distance of CAC (ring) is
found to be 1.386 Å and N-(4-bromophenyl)acetamide [36] where
the mean bond distance of CAC (ring) is 1.385 Å. The equal bond
distances of C3AC4 and C4AC5 reveals that the bromine atom lie
Weak CAHꢅ ꢅ ꢅ
p interactions are also present and contribute to the
crystal packing stability [36].
The energy and thermodynamic parameters of the compound
have also been computed at B3LYP methods with 6-311++Gꢁꢁ
and cc-pVTZ basis sets and are presented in Table 2. The frequency

18
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
Table 1
Structural parameters calculated for N-(4-bromophenyl)-2,2-dichloroacetamide (4BNPA) employing B3LYP methods with 6-311++Gꢁꢁ and cc-pVTZ basic sets.
Structural parameters
B3LYP / 6-311++Gꢁꢁ
B3LYP/cc-pVTZ
Expt.a
Expt.b
Internuclear distance (Å)
C1AC2
C1AC6
C1AN7
C2AC3
C2AH13
C3AC4
C3AH14
C4AC5
C4ABr19
C5AC6
C5AH15
C6AH16
N7AC8
N7AH17
C8AO9
C8AC10
C10ACl11
C10ACl12
C10AH18
1.40
1.40
1.41
1.39
1.09
1.39
1.08
1.39
1.92
1.39
1.08
1.08
1.36
1.01
1.22
1.54
1.80
1.80
1.08
1.40
1.40
1.41
1.39
1.08
1.39
1.08
1.39
1.91
1.39
1.08
1.08
1.36
1.01
1.21
1.54
1.80
1.80
1.08
1.397
1.391
1.413
1.379
1.394
1.390
1.401
1.380
0.950
1.384
0.950
1.384
1.891
1.377
0.950
0.950
1.347
0.892
1.226
1.501
1.391
1.384
1.376
1.354
1.219
1.495
0.98
Bond angle (°)
C2AC1AC6
C2AC1AN7
C6AC1AN7
C1AC2AC3
C1AC2AH13
C3AC2AH13
C2AC3AC4
C2AC3AH14
C4AC3AH14
C3AC4AC5
C3AC4ABr19
C5AC4ABr19
C4AC5AC6
C4AC5AH15
C6AC5AH15
C1AC6AC5
119.5
117.2
123.3
120.8
120.0
119.2
119.2
120.1
120.6
120.6
119.6
119.8
120.2
120.3
119.5
119.7
120.1
120.2
128.7
115.3
116.0
126.6
115.0
118.4
112.3
110.9
107.7
111.0
107.4
107.3
119.4
117.2
123.4
120.8
119.9
119.3
119.3
120.2
120.6
120.6
119.6
119.8
120.2
120.2
119.5
119.7
120.0
120.3
128.8
115.5
115.7
126.8
115.2
118.0
113.5
109.6
108.1
110.9
107.2
107.3
119.4
117.1
123.5
120.5
119.7
119.7
119.2
120.4
120.4
121.2
119.1
119.7
119.3
120.3
120.3
120.4
119.8
119.8
127.5
115.1
117.0
123.8
114.5
121.6
C1AC6AH16
C5AC6AH16
C1AN7AC8
C1AN7AH17
C8AN7AH17
N7AC8AO9
N7AC8AC10
O9AC8AC10
C8AC10ACl11
C8AC10ACl12
C8AC10AH18
Cl11AC10ACl12
Cl11AC10AH18
Cl12AC10AH18
109.5
Dihedral angle (°)
ClAN7AC8AO9
ClAN7AC8AC10
C2AC1AN7AC8
C6AC1AN7AC8
C6AC1AC2AC3
N7AC1AC2AC3
C1AC2AC3AC4
C2AC3AC4AC5
C2AC3AC4ABr19
C3AC4AC5AC6
C6AC5AC4ABr19
C4AC5AC6AC1
C2AC1AC6AC5
C5AC6AC1AN7
0.1
1.1
ꢂ3.1
176.7
164.1
ꢂ18.6
0.8
178.2
0.3
ꢂ0.7
179.9
0.0
ꢂ179.2
ꢂ179.5
0.5
ꢂ177.0
ꢂ179.4
0.6
0.1
0.0
ꢂ179.9
ꢂ180.0
0.1
0.0
ꢂ0.0
180.0
0.0
ꢂ0.0
180.0
0.0
ꢂ180.0
ꢂ180.0
179.3
1.2
0.04
0.1
ꢂ0.1
179.9
ꢂ0.1
179.9
ꢂ1.6
ꢂ178.8
a
Values taken from Ref. [13].
Values taken from Ref. [36].
b
calculations compute the zero point energies, thermal correction to
internal energy, enthalpy, Gibbs free energy and entropy as well as
the heat capacity for a molecular system. The larger total dipole
moment (2.106 D) is due to more charge separation.

V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
19
Table 2
The calculated thermodynamic parameters of N-(4-bromophenyl)-2,2-dichloroacet-
amide (4BNPA) employing B3LYP/6-311++Gꢁꢁ and B3LYP/cc-pVTZ methods.
Thermodynamic parameters (298 K)
4BNPA
B3LYP/6-
311++Gꢁꢁ
B3LYP/cc-pVTZ
SCF energy, (Hartrees)
ꢂ3933.1656429
ꢂ3933.3037306
Total energy (thermal), Etotal
87.358
87.474
(kcal molꢂ1
)
Vibrational energy, Evib (kcal molꢂ1
)
85.580
79.447
85.696
79.60
Zeropoint vibrational energy
(kcal molꢂ1
)
Heat capacity (Cv), (cal molꢂ1 kꢂ1
)
44.45
120.75
44.302
119.71
Entropy, S (cal molꢂ1 kꢂ1
)
Rotational constants (GHz)
X
Y
Z
1.467
0.137
0.135
1.474
0.138
0.135
Dipolemoment (Debye)
lx
ly
lz
ltotal
ꢂ0.808
ꢂ1.931
ꢂ0.230
2.106
ꢂ0.950
ꢂ1.943
0.260
Fig. 2. Temperature dependence of entropy, heat capacity at constant pressure (CP)
and enthalpy change (DH) of N-(4-bromophenyl)-2,2-dichloroacetamide.
2.178
EHOMO (eV)
ELUMO (eV)
ꢂ6.6775
ꢂ1.8243
ꢂ7.7970
ꢂ1.1725
4.8532
8.4188
0.24
ꢂ4.3294
4.0894
0.1223
2.2917
4.3294
10.7105
2.05
pressure (Cp), entropy (S) and enthalpy change (DH0?T) with tem-
perature along with the correlation equations. From Table 3, one
can find that the entropies, heat capacities, and enthalpy changes
are increasing with temperature ranging from 50 to 1000 K due
to the fact that the molecular vibrational intensities increase with
temperature [63]. The observed relations of the thermodynamic
functions vs. temperatures with the regression factors (R2) not less
than 0.9995 for 4BNPA are given by
EHOMOꢂ1 (eV)
ELUMO+1 (eV)
ELUMO ꢂ EHOMO (eV)
Ionization potential (I)
Electron affinity (A)
Chemical potential (
Hardness (
Global softness (S)
Electrophilicity (
Electronegativity (
l
)
g
)
x
v
D
D
)
S ¼ 274:3973 þ 0:8609T ꢂ 2:7997 ꢃ 10ꢂ4T2
Cp ¼ 38:4778 þ 0:6235T ꢂ 2:9382 ꢃ 10ꢂ4T2
)
Ee)
En)
Electrofugality (
Nucleofugality (
H ¼ ꢂ6:9551 þ 0:1058T þ 1:5688 ꢃ 10ꢂ4T2
4.2. Thermodynamic analysis
D
The temperature dependence of the thermodynamic properties
heat capacity at constant pressure (Cp), entropy (S) and enthalpy
4.3. Analysis of molecular electrostatic potential
change (DH0?T) for 4BNPA are also determined by B3LYP/6-
311++Gꢁꢁ method and listed in Table 3. The anharmonicity effects
have been eliminated by scaling the thermodynamic properties by
0.97. The Fig. 2 depicts the correlation of heat capacity at constant
The molecular electrostatic potential surface (MEP) which is a
method of mapping electrostatic potential onto the iso-electron
density surface simultaneously displays electrostatic potential
(electron + nuclei) distribution, molecular shape, size and dipole
moments of the molecule and it provides a visual method to
understand the relative polarity [64,65]. Electrostatic potential
maps illustrate the charge distributions of the molecules three
dimensionally. One of the purposes of finding the electrostatic po-
tential is to find the reactive sites of a molecule. The reactive site is
a particularly charged region of a molecule that has an affinity for
interacting with charged particles. The total electron density sur-
face mapped with electrostatic potential of 4BNPA constructed
by B3LYP/6-311++Gꢁꢁ method is shown in Fig. 3. The extreme lim-
its of the total electron density are ꢂ5.709e ꢃ 10ꢂ2 to
+5.709e ꢃ 10ꢂ2. The electrostatic potential contour map for posi-
tive and negative potentials and electrostatic potential surface of
the compound are shown in Fig. 4 and in the Supplementary
Fig. S1, respectively. The colour scheme for the MEP surface is
red, electron rich, partially negative charge; blue, electron defi-
cient, partially positive charge; light blue, slightly electron defi-
cient region; yellow, slightly electron rich region; green, neutral;
respectively. It is obviously from the Figs. 3 and 4 that the region
around oxygen atoms linked with carbon through double bond
represents the most negative potential region (red1). The hydrogen
Table 3
Temperature dependence of the thermodynamic properties of N-(4-bromophenyl)-
2,2-dichloroacetamide (4BNPA) determined by B3LYP/6-311++Gꢁꢁ method.
T (K)
N-(4-bromophenyl)-2,2-dichloroacetamide
Cp (cal molꢂ1 Kꢂ1
)
S (cal molꢂ1 Kꢂ1
)
D
H (kcal molꢂ1
)
50
70.27
97.12
301.12
358.18
402.48
441.44
477.47
510.31
511.54
544.06
575.19
604.99
633.53
660.84
686.99
712.02
736.01
759.01
781.10
802.32
822.74
842.41
861.37
2.67
6.87
12.37
19.18
27.27
36.27
36.64
47.20
58.86
71.53
100
150
200
250
298.15
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
123.09
149.04
174.76
198.63
199.52
222.63
243.67
262.49
279.17
293.91
306.94
318.50
328.80
338.02
346.32
353.82
360.63
366.83
372.49
85.08
99.41
114.44
130.08
146.27
162.94
180.05
197.56
215.43
233.61
252.10
1
For interpretation of colour in Figs. 3 and 4, the reader is referred to the web
version of this article.

20
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
atoms attached to the ends of methyl group posses the maximum
positive charge (blue). The predominance of green region in the
MEP surfaces corresponds to a potential halfway between the two
extremes red and dark blue colour. In other words, red indicates
the lowest electrostatic potential energy, and blue indicates the
highest electrostatic potential energy. Intermediary colours repre-
sent intermediary electrostatic potentials. Areas of low potential,
red, are characterised by an abundance of electrons. Areas of high
potential, blue, are characterised by a relative absence of electrons.
In both the compounds the total electron density surface mapped
with electrostatic potential clearly reveals the presence of high neg-
ative charge on the carbonyl oxygen and in part of the ring while
more positive charge around the NAH region. The region of electro-
static potential is ꢂ9.617e ꢃ 10ꢂ3 to +9.617e ꢃ 10ꢂ3. Electrostatic
potential maps (Figs. 4 and 5) can also be used to determine the nat-
ure of the bonds of the molecules. The molecule 4BNPA has great
electronegativity difference, charge is very polarized, and there are
significant differences in electron density in different regions of
the molecule. This great electronegativity difference leads to regions
that are almost entirely red and almost entirely blue. Thus, a high
electrostatic potential indicates the relative absence of electrons
and a low electrostatic potential indicates an abundance of electrons.
The electrostatic potential maps also illustrate the reactive sites of
molecules whose polarity is not easy to intuitively deduce.
Fig. 4. The contour map of electrostatic potential of the total density of N-(4-
bromophenyl)-2,2-dichloroacetamide.
4.4. Analysis of frontier molecular orbitals
for quantum chemistry [63]. The energies of HOMO LUMO,
LUMO+1 and HOMOꢂ1 and their orbital energy gaps are calculated
using B3LYP/6-311++Gꢁꢁ method and the pictorial illustration of
the frontier molecular orbitals are shown in Fig. 5. Molecular orbi-
tals, when viewed in a qualitative graphical representation, can
provide insight into the nature of reactivity, and some of the struc-
tural and physical properties of molecules. Well known concepts
such as conjugation, aromaticity and lone pairs are well illustrated
by molecular orbitals. Visual analysis of the molecular orbitals al-
lows concepts of structural symmetry to be extended to frontier
electron symmetry. It is actually possible to predict reactivity by
examining the molecular orbitals. The positive and negative phases
are represented in red and green colours, respectively. The LUMO
orbitals of the molecule feature a larger number of nodes than
Highest occupied molecular orbital (HOMO) and lowest unoc-
cupied molecular orbital (LUMO) are very important parameters
the HOMO orbitals. A large extent of localisation of the
p-type
wavefunction on C@O double bond is observed. The HOMO of
the molecule speared out over the ring and the amide parts of
the molecule while the LUMO does spread over the entire parts.
This clearly indicates the n ?
p and p ?
pꢁ transitions are the
most probable. The calculated energy gap (4.8532 eV) of HOMO–
LUMO’s explains the ultimate charge transfer interface within the
molecule.
4.5. Natural bond orbital (NBO) analysis
NBO analyses of molecules illustrate the Lewis structure,
charge, bond order, bond type, hybridization, resonance, donor–
acceptor interactions, etc. The bonding concepts such as type of
bond orbital, their occupancies, the natural atomic hybrids of
which the NBO is composed, giving the percentage of the NBO on
each hybrid, the atom label, and a hybrid label showing the hybrid
orbital (spx) composition (the amount of s-character, p-character,
etc.) of 4BNPA molecule determined by B3LYP/6-311++Gꢁꢁ method
are depicted in the Supplementary Table T1. The occupancies of
NBOs reflect their exquisite dependence on the chemical environ-
ment of the molecule. The NBO energy values show the corre-
sponding spatial symmetry breaking in the direction of unpaired
spin. The Lewis structure that is closest to the optimized structure
is determined.
Fig. 3. The total electron density surface mapped with electrostatic potential of N-
(4-bromophenyl)-2,2-dichloroacetamide.

V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
21
acceptors. This bonding–anti bonding interactions can be quantita-
tively described in terms of the NBO approach that is expressed by
means of second-order perturbation interaction energy E(2)
[54,64,66]. This energy represents the estimate of the off-diagonal
NBO Fock matrix element. The stabilization energy E(2) associated
with i (donor) ? j (acceptor) delocalisation is estimated from the
second-order perturbation approach [67] as given below
F2ði; jÞ
Eð2Þ ¼ q
i ej
ꢂ
ei
where qi is the donor orbital occupancy, ei and ej are diagonal ele-
ments (orbital energies) and F(i,j) is the off-diagonal Fock matrix
element.
All lone pair-bond pair interactions and only bond pair-bond
pair interactions with stabilization energy greater than
3.0 kcal molꢂ1 are listed in the Supplementary Table T2. In 4BNPA
molecule, the lone pair donor orbital, nN
?
pꢁCO interaction be-
tween the nitrogen (N7) lone pair and the C8AO9 antibonding
orbital possess a strong stabilization of 64.21 kcal molꢂ1. The lone
pair donor orbital, nN
?
pꢁCC interaction between the nitrogen (N7)
lone pair and the C1AC6 antibonding orbital has a stabilization en-
ergy 32.63 kcal molꢂ1. The n ? pꢁ stabilization energy of lone pair
of electrons present in the oxygen atom (O9) to the antibonding
orbital
(
rꢁ
)
of (N7AC8) and (C8AC10) are 24.08 and
21.97 kcal molꢂ1, respectively. The bond pair donor orbital, pCC
?
pꢁCC interaction between the C1AC6 bond pair and the C4AC5 anti-
bonding orbital give stabilization of 22.34 kcal molꢂ1 while be-
tween the C4AC5 bond pair and the C2AC3 antibonding orbital
has stabilized by 21.28 kcal molꢂ1
.
5. Vibrational analysis
The FTIR and FT-Raman spectra of N-(4-bromophenyl)- 2,2-
dichloroacetamides are shown in Figs. 6 and 7. All the observed
wavenumbers are assigned in terms of fundamentals, overtones
and combination bands. The observed and calculated frequencies
along with their relative intensities and probable assignments
are presented in Table 4. The geometry of the molecules is consid-
ered by possessing C1 point group symmetry. All the vibrations are
active in both IR and Raman. The theoretical spectra of the com-
pound given in Figs. 6 and 7 are simulated by using Lorentzian
functions.
Fig. 5. The frontier molecular orbitals and their energy gap of N-(4-bromophenyl)-
2,2-dichloroacetamide.
For example, the bonding orbital for N7AC8 with 1.99 electrons
has 62.65% N7 character in a sp1.73 hybrid and has 37.35% C8 char-
acter in a sp2.03 hybrid orbital. In the case of C8AO9 bonding orbital
with 1.992 electrons has 35.66% C8 character in a sp1.95 hybrid and
has 64.34% O9 character in a sp1.46 hybrid orbital. A bonding orbital
for N7AH17 with 1.9821 electrons has 70.68% N7 character in a
sp2.84 hybrid and has 29.32% H17 character in an s orbital. The
CAC bonds of the aromatic ring posses more p character than s
5.1. Carbon–carbon vibrations
The carbon–carbon stretching of 4BNPA molecule is found in
the IR spectrum at 1616, 1590, 1490, 1402 and 1298 cmꢂ1 as med-
ium to very strong bands and at 1631, 1595, 1501, 1412, 1310 and
1192 cmꢂ1 in Raman. These frequencies appear in the respective
range [31–34]. The CCC in-plane and out of plane bending modes
of 4BNPA have been found and presented in Table 4. In 4BNPA
the ring breathing mode is observed at 866 and 880 cmꢂ1 while
the CCC trigonal bending is seen at 1011 and 1009 cmꢂ1, respec-
tively in IR and Raman spectra. All these assignments agree well
with the reported literatures [37–40,68].
character. This is clearly indicates the delocalization of
p electrons
among all the carbon atoms. Similarly C1AN7 bond has also posses
more p character.
4.6. Donor–acceptor interactions
The NBO method demonstrates the bonding concepts like atom-
ic charge, Lewis structure, bond type, hybridization, bond order,
charge transfer and resonance possibility. Strong electron delocal-
isation in the Lewis structure also shows up as donor–acceptor
interactions. This calculation is done by examining all possible
interactions between ‘filled’ (donor) Lewis-type NBOs and ‘empty’
(acceptor) non-Lewis NBOs, and estimating their energetic impor-
tance by 2nd order perturbation theory. The stabilisation of orbital
interaction is proportional to the energy difference between
interacting orbitals. Therefore, the interaction having strongest
stabilisation takes place between effective donors and effective
5.2. CAH vibrations
The CAH bond present in the phenyl group of 4BNPA gives very
strong to very weak stretching bands at 3091 and 3008 cmꢂ1 in IR
spectrum. The band observed in the Raman spectrum at 3020 cmꢂ1
is attributed to the CAH stretching vibration of ACHCl2 group. The
aromatic CAH in-plane bending modes are observed in 4BNPA at
1119, 1074, 979 and 968 cmꢂ1 in the IR and Raman spectra. The
CAH out of plane bending modes of the present compound are

22
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
Fig. 6. (a) FTIR spectrum and Theoretical (b) B3LYP/6-311++Gꢁꢁ, and (c) B3LYP/cc-
pVTZ spectra of N-(4-bromophenyl)-2,2-dichloroacetamide.
Fig. 7. (a) FT-Raman spectrum and (b) Theoretical B3LYP/6-311++Gꢁꢁ, (c) B3LYP/cc-
pVTZ spectra of N-(4-bromophenyl)-2,2-dichloroacetamide.
observed in the said region [38–40,68] and presented in the Table 4.
The alkyl CAH in–plane bending modes are observed in the same
region of CAC stretching. The alkyl CAH in-plane bending modes
are assigned to the frequencies at 1242 and 1256 cmꢂ1 in IR and
Raman spectra, respectively.
4BNPA with that of chloro and methyl substituted N-phenylacet-
amide (NPA) molecules reveals that the substitution of bromine
in the phenyl ring does not make the molecule effectively compete
with the carbonyl oxygen for the electrons of the nitrogen, thus
increasing the force constants of the C@O bond. From Table 5, it
is evident that the C@O stretching frequencies of the compound
under investigation does not show significant variation from that
of the parent compound N-phenyl-2,2-dichloroaetamide, N-(chloro
substituted phenyl)- and N-(methyl substituted phenyl)-2,2-
dichloroacetamides [13,37–40,68].
5.3. Amide group vibrations
The characteristic vibrations of the amide (ACONHA) group of
N-(4-bromophenyl)-2,2-dichloroacetamide are analysed and the
correlation of (–CONH–) group vibrations of some acetanilide are
presented in Table 5. The strong band observed at 3276 cmꢂ1 in
IR is attributed to the NAH stretching. By comparison with NPA,
the NAH stretching of 4BNPA does not vary significantly with the
N-(4-chlorophenyl)-2,2-dichloroacetamide (4CNPA). But it is blue
shifted by 21 and 77 cmꢂ1 from that of N-(2-chlorophenyl)-2,2-
dichloroacetamide (2CNPA) and N-(2,4-dichlorophenyl)-2,2-
dichloroacetamide (24CNPA) molecules, respectively. Similarly
the 4BNPA has 25–36 cmꢂ1 higher NAH stretching frequency than
that of the N-(methyl substituted phenyl)-2,2-dichloroacetamides.
The influence of the ring substituent on NAH stretching frequency
of N-phenylacetamide and its derivatives may be the resultant
steric effect, direct field effects, hydrogen bonding and bond polar-
isation effects. The steric effect of ortho substituent must be con-
sidered in conjunction with the conformations. The increase in
NAH stretching frequency may be expected in introduction of t-
butyl group into the phenyl ring of N-phenylacetamide. This clearly
confirms that the steric effect due to o-methyl and o-chloro groups
is not significantly operating on the NAH stretching vibration and
the electronic effects predominates [37–40,68].
The very strong vibration observed at 1553 and 1563 cmꢂ1 in
IR/Raman spectra are ascribed to the amide-II band, NAH in-plane
bending of 4BNPA. The amide-II bands of NPA, 4CNPAand 4BNPA
does not show any significant variation. By comparing with the
amide-II bands of 2MPA and 24DMPA, a red shift is observed in
4BNPA mode. This shows that the methyl groups excerts more ste-
ric influence on the NAH bond properties.
The CAN stretching mode, the amide-III band, of 4NPA is as-
signed to the wave number observed at 1335 and 1346 cmꢂ1 in
the infrared and Raman spectra, respectively. The fundamental
modes 1338 cmꢂ1 in IR and 1350 cmꢂ1 in Raman are assigned to
the CAN stretching of 4CNA. The amide-III band of NPA is observed
at 1344 cmꢂ1 in the infrared while in Raman it is observed at
1355 cmꢂ1. The spectral data indicates that no appreciable rise in
CAN stretching frequency of 4BNPA and also there is no mesomeric
influence of the bromine towards the CAN bond.
The amide-IV, C@O in-plane bending of 4BNPA is found at 799
and 789 cmꢂ1 in the IR and Raman spectra, respectively. For NPA
compound this mode is assigned to 811 and 810 cmꢂ1. There is a
significant blue shift is observed in the C@O in-plane bending
The very strong IR bands observed at 1678 and 1685 cmꢂ1 are
assigned to the amide-I, the C@O stretching band of 4BNPA mole-
cule. The comparison of the wavenumber of C@O stretching in

V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
23
Table 4
The observed FTIR, FT-Raman and calculated frequencies using B3LYP/6-311++Gꢁꢁ and B3LYP/cc-pVTZ force field along with their relative intensities, probable assignments and
potential energy distribution (PED) of N-(4-bromophenyl)-2,2-dichloroacetamide (4BNPA)a.
Observed
B3LYP/6-311++Gꢁꢁ Calculated wavenumber
Depolarisation B3LYP/cc-pVTZ Calculated
Depolarisation Assignment %PED
ratio
wavenumber
ratio
wavenumber
(cmꢂ1
FTIR
)
FTR
Unscaled Scaled IR
Raman
Unscaled Scaled IR
Raman
(cmꢂ1
)
(cmꢂ1
)
intensity intensity
(cmꢂ1
3593
)
(cmꢂ1
3270
) intensity intensity
3276 s
3203 m
3134 m
3091 s
3594
3271
35.32
5.86
31.07
17.20
0.15
0.16
39.64
5.82
32.97
16.83
0.17
0.19
m
NAH
95mNH
92mCH
2 ꢃ 1616
2 ꢃ 1563
3096
vs
3242
3080
3247
3085
m
CAH
3204
3200
3020 m 3182
3162
3044
3040
3023
3004
0.74
0.63
2.01
9.12
29.12
19.73
23.30
20.36
0.22
0.36
0.18
0.36
3206
3203
3179
3164
3046
3043
3020
3006
0.92
0.81
2.01
9.25
28.65
19.57
25.22
20.21
0.24
0.38
0.18
0.37
m
m
m
m
CAH
CAH
CAH(Cl2) 94mCH
93mCH
90mCH
3008 vw
2948 w
CAH
92mCH
2948 w
2 ꢃ 1490
2 ꢃ 1501
2 ꢃ 1402
2 ꢃ 1177
2 ꢃ 968
2793 vw
2362 w
1894 w
1678 vs
1616 s
1685 m 1762
1631
vw
1674
1600
332.51 30.54
116.33 13.60
0.20
0.35
1765
1634
1677
1601
294.32 25.69
0.20
0.41
m
m
C@O
96mC@O
91mCC
1633
92.03
5.53
CC
1590 m
1595
vs
1631
1598
1.03
100.00
0.44
1633
1600
5.96
100.00
0.30
m
CC
89mCC
1553 vs
1490 vs
1402 s
1335 s
1298 m
1242 s
1563 m 1564
1501 w 1518
1412 w 1427
1346 s 1338
1310 w 1323
1256 s 1275
1261
1252
1192 m 1218
1207
1533
1488
1398
1311
1297
1250
1236
1227
1194
1183
1119
1065
1002
968
953
932
851
834
805
782
751
698
695
636
630
547
530
501
417
413
371
327
306
252
225
200
133
109
82
359.11 43.62
123.95 5.52
0.34
0.19
0.38
0.24
0.26
0.25
0.25
0.69
0.72
0.20
0.20
0.13
0.11
0.74
0.18
0.73
0.07
0.75
0.73
0.75
0.08
0.04
0.73
0.59
0.66
0.53
0.44
0.71
0.05
0.36
0.57
0.72
0.71
0.38
0.21
0.61
0.30
0.75
0.75
0.74
0.75
0.75
1563
1526
1431
1341
1326
1271
1258
1234
1215
1209
1143
1091
1029
996
972
962
870
860
828
795
762
724
715
648
645
580
541
518
423
422
379
339
312
255
232
203
139
114
83
1532
1495
1402
1314
1299
1246
1233
1209
1191
1185
1120
1069
1008
976
953
943
853
843
811
779
747
710
701
635
632
568
530
508
415
414
371
332
306
250
227
199
136
112
81
393.10 47.29
114.75 3.52
0.33
0.26
0.39
0.26
0.25
0.27
0.26
0.65
0.75
0.21
0.19
0.16
0.15
0.75
0.23
0.74
0.09
0.73
0.74
0.74
0.09
0.70
0.10
0.36
0.54
0.51
0.46
0.69
0.06
0.17
0.62
0.66
0.73
0.36
0.23
0.47
0.31
0.72
0.75
0.70
0.75
0.75
bNAH
87bNH
92mCC
87mCC
85mCN
84mCC
87bCH + 10bCC
m
m
m
m
CC
CC
CAN
CC
58.52
80.14
12.36
43.72
33.20
21.23
7.73
4.81
36.73
10.43
16.09
33.78
2.24
0.69
19.06
0.37
11.06
3.23
0.05
3.78
0.11
3.96
0.03
0.03
1.56
4.54
2.59
0.31
2.13
1.59
0.15
0.68
0.15
4.39
0.01
0.72
0.53
0.30
0.96
0.41
0.09
0.53
0.26
0.19
0.10
0.53
1.78
63.37
60.85
26.92
59.30
12.45
18.52
7.12
5.13
22.88
16.28
27.55
13.62
2.44
0.72
16.87
0.39
10.52
2.92
0.05
3.22
0.10
3.90
0.18
0.21
1.51
3.43
0.07
1.99
2.43
2.04
0.55
0.51
0.33
3.67
0.05
0.60
0.47
0.37
1.04
0.34
0.17
0.43
0.23
0.19
0.15
0.55
2.04
bCH(Cl2)
m
c
m
m
NA(C6H5) 80mNC
CH(Cl2)
CC
1210 w
72cCH + 18cCC
91mCC
1177 m
1119 w
1074 s
1011 m
7.14
9.06
CAC(HCl2) 89mCC
1142
12.35
33.76
31.75
0.64
11.93
33.44
26.88
0.52
bCH
bCH
TB
bCH
bCH
70bCH + 12bCCC
67bCH + 21bCCC
77bCCC + 18bCH
70bCH + 14bCCC
67bCH + 15bCCC
1089 m 1087
1009 w 1022
979 m 988
965 vw 972
937 m 951
880 s 868
851
802 m 821
789 w 798
756 m 766
738 m 712
718 m 709
641 s 649
627 s 643
558
968 m
940 vw
866 s
0.62
0.14
0.90
0.41
0.02
2.07
c
CH
65cCH + 20cCCC
RB
78bCCC + 14bCH
825 s
36.25
32.78
57.62
60.12
27.02
0.38
36.58
22.05
45.55
62.52
0.12
c
c
CH
CH
63
62
c
c
CH + 22cCCC
CH + 24cCCC
799 s
765 s
743 s
712 vw
642 m
bC@O
82bC@O + 15bNH
m
c
c
m
c
aCCl2
NAH
CH
sCCl2
C@O
80m
61c
62c
78m
68c
CCl + 10bCH
NH + 21cCO
CH + 20cCCC
CCl + 14bCH
C@O + 12cNH
32.15
74.87
7.02
33.51
7.02
95.03
0.20
34.27
6.98
bCAN
bCCC
mCABr
65bCN + 18bCO
60bCCC + 21bCH
87mCABr
541
506 s
428 w
406 w
511 m 511
431 w 425
403 vw 421
378 m 379
344 m 334
302 m 312
256 w 257
240 w 230
208 s 204
146 w 136
111
29.84
0.75
0.05
27.99
1.26
0.03
bNA(C6H5) 62bNC + 16bCCC
c
CN 59 CN + 22cCO
c
12.09
0.06
18.25
0.61
13.09
0.30
18.01
0.45
bCCC
dCCl2
60bCCC + 17bCH
72dCCl2 + 12bCH
s
CCl2
CCl2
CCl2
bCABr
62
60
64
s
x
CCl2 + 24xCCl2
CCl2 + 20sCCl2
qCCl2 + 18bCH
x
0.05
0.26
2.97
2.07
0.12
0.22
3.02
2.04
q
69bC-Br + 12bCCC
c
c
c
c
c
c
NAC6H5
CABr
CCC
CC
CCC
55c
56c
54c
60c
52c
51c
NC + 21cCCC
C-Br + 20cCCC
CCC + 19cCH
CC + 20cCH
CCC + 24cCH
CCC + 18cCH
84
56
31
10
0.07
5.03
0.04
2.46
0.07
4.36
0.11
1.69
55
30
10
54
32
15
53
31
15
CCC
a
m
– stretching; b – in-plane bending; d – deformation;
q
– rocking; c – out of plane bending; x – wagging and s – twisting; TB-trigonal bending and RB-ring breathing.
Raman intensity is normalised to 100.
frequency of 4BNPA when compared with the N-(chloro/methyl
substituted phenyl)-2,2-dichloroacetamide compounds.
715 cmꢂ1. Thus, the bromo substitution raised the NAH out of
plane bending. The C@O out of plane bending of 4BNPA is observed
at 627 cmꢂ1 in Raman spectrum. In NPA this amide-VI band is
observed in IR at 558 and 568 cmꢂ1. The amide-VI out of plane
The amide-V, the NAH out of plane bending is observed at 743
and 738 cmꢂ1 in 4BNPA. This mode in NPA is seen at 712 and

24
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
bending mode of 4BNPA is significantly raised than that of NPA.
The o-methyl group in 2MPA excerts more blue shift on the
amide-VI frequency than other compounds.
Initially, all scaling factors have been kept fixed at a value of 1.0
to produce the pure DFT calculated vibrational frequencies (un-
scaled) which are given in Table 4. Subsequently, the scale factors
0.91, 0.95 and 0.98 for NAH, CAH/C@O and all other vibrations,
respectively, were used with 6-311++Gꢁꢁ and cc-pVTZ basis sets.
The resultant scaled frequencies are also listed in Table 4. The
RMS value using the with 6-311++Gꢁꢁ and cc-pVTZ basis sets are
9.9 and 8.4, respectively. The correlation diagram for the calculated
and the experimental frequencies are shown in the Supplementary
Fig. S2.
5.4. CABr vibrations
Bromine compounds absorb strongly in the region 650–
485 cmꢂ1 due to CABr stretching vibrations. The in-plane bending
vibrations are identified at 325–140 cmꢂ1. Thus, the strong inten-
sity bands observed at 506 in the infrared spectrum and
208 cmꢂ1 in Raman spectrum are attributed to the CABr stretching
and in-plane bending modes, respectively. These assignments are
in good agreement with the literature [69].
7. Topological charge distribution
The atomic charges of the neutral, cationic and anionic species
of 4BNPA determined by natural population analysis (NPA) and
the local reactivity properties of N-(4-bromophenyl)-2,2-dichloro-
acetamide using B3LYP/6-311++Gꢁꢁ method are presented in Ta-
ble 6. Among the ring carbon atoms C1 has a positive charge
while others have negative charge. The positive charge of C1 is
due to the attachment of highly electronegative nitrogen atom
(N7) to it. The carbon attached with the bromo group has less neg-
ative charge than that of others. This is due to the electron attract-
ing nature of the bromine by means of inductive effect. The very
high positive charge on the amide carbon C8 is due to the partial
polar nature of C@O group. This also leads to a high negative
charge on the oxygen atom O9. The bromine atom has small
positive charge because of the mesomeric (+M) effect. The
correlation of the atomic charges of the neutral, anion and cation
of N-(4-bromophenyl)-2,2-dichloroacetamide is shown in the
Supplementary Fig. S3.
5.5. CCl2 group vibrations
The CACl absorption is observed in the broad region between
850 and 550 cmꢂ1. When several chlorine atoms are attached to
one carbon atom, the band is usually more intense and at high fre-
quency end of the assigned limits. The very strong and medium
bands in IR at 765 and having the Raman counterpart at
765 cmꢂ1 are assigned to the asymmetric CCl2 stretching vibration
of 4BNPA. The medium to strong symmetric CCl2 stretching in
4BNPA is observed at 642 cmꢂ1 in IR and 641 cmꢂ1 in Raman spec-
tra. The CCl2 asymmetric and symmetric stretching frequency does
not show any appreciable variation from that of the corresponding
frequencies in NPA. The in-plane CCl2 deformation vibration of
4BNPA is obtained at a low frequency region of the Raman spectra
as medium band corresponding to 344 cmꢂ1. The out of plane CCl2
twisting and wagging modes are assigned and given in the Table 4.
These assignments are in good agreement with the literature val-
ues [38–40]. In the low frequency region the fundamental modes
of acetanilide [68] differ from the compound under investigation
because of the observation of the vibrations of heavy atoms.
8. Analysis of structure–activity descriptors
In studying the importance of nucleophilicity excess descrip-
tor, a careful analysis on the electronic structure, property and
reactivity of 4BNPA compound is performed. The complete mole-
cule is considered as a single unit. This unit can easily take part in
charge transfer process within the coordinating atoms in the mol-
ecule. Table 6 and Supplementary Table T3 presents the philicity
values of the 4BNPA compound. The understanding of chemical
reactivity and site selectivity of the molecular systems has been
effectively handled by the conceptual density functional theory
(DFT) [78]. Chemical potential, global hardness, global softness,
electronegativity and electrophilicity are global reactivity descrip-
tors, highly successful in predicting global chemical reactivity
trends. The global parameters like ionization potential (I), elec-
6. Scale factors
Computed harmonic frequencies typically overestimate vibra-
tional fundamentals due to basis set truncation and neglect of elec-
tron correlation and anharmonicity [70]. To compensate these
shortcomings and to correlate the experimentally observed and
theoretically computed frequencies for each vibrational modes of
the compound scale factors are introduced. A better agreement
between the computed and experimental frequencies can be ob-
tained by using different scale factors for different types of funda-
mental vibrations. To determine the scale factors, the procedure
used previously [71–77] have been followed that minimises the
residual separating the experimental and theoretically predicted
vibrational frequencies. The optimum scale factors for vibrational
frequencies were determined by minimising the residual
tron affinity (A), electrophilicity (x), electronegativity (v), hard-
ness ( ), and softness (S) of the molecule are determined and
g
displayed in Table 2. The site-selectivity of a chemical system,
cannot, however, be studied using the global descriptors of
reactivity.
N
ꢂ
ꢃ
X
2
D
¼
k
xTi heor
ꢂ
mEi xpt
Fukui functions and local softness are extensively applied to
probe the local reactivity and site selectivity. The formal defini-
tions of all these descriptors and working equations for their com-
putation have been described [78–80]. The Fukui functions of the
individual atoms of the neutral, cationic and anionic species of
4BNPA calculated by B3LYP/6-311++Gꢁꢁ method are presented in
the Supplementary Table T3. It is clearly understood that the atoms
C2, C3, C5, C6, N7, O9 and C10 are favourable for nucleophilic
attack. The other atoms of 4BNPA are favourable for electrophilic
attack. The molecule under investigation mainly gives substitution
reactions.
i
where xiTheo and miExpt are the ith theoretical harmonic frequency
and ith experimental fundamental frequency (in cmꢂ1), respectively
and N is the number of frequencies included in the optimisation
which leads to
rffiffiffiffi
D
RMS ¼
N
A uniform scaling factor is recommended for all frequencies
<1800 cmꢂ1 at the B3LYP method with 6-311++Gꢁꢁ basis set and
is adopted in this study. Due to the large anharmonicities of CAH
and NAH stretching frequencies >2700 cmꢂ1 were scaled by two
different scale factors [75,76].
The local softness, relative electrophilicity (sþk /skꢂ) and relative
nucleophilicity (sꢂk =skþ) indices, the dual local softness
D
sk and
the multiphilicity descriptors (Dxk) have also been determined

V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
25
Table 5
Correlation of amide (ACONHA) group vibrations of the compounds investigated.
Compounds name
mC@O
bNAH
mCAN
bC@O
cNAH
cC@O
mNAH
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
FTIR
FTR
aNPA
1672
1678
1676
1682
1677
1680
1669
1692
1670
1678
1680
1685
1682
1685
1674
1678
1669
1691
1668
1685
1555
1545
1555
1569
1588
1554
1551
1591
1567
1553
1568
1551
1558
1567
1590
1555
1546
1595
1570
1563
1344
1340
1338
–
1341
1335
1348
1345
1340
1335
1355
1346
1350
1342
1350
1335
1340
1350
1341
1346
811
807
801
812
807
806
810
822
805
799
810
804
800
815
800
804
809
820
807
789
712
739
745
–
717
726
745
–
715
742
749
752
725
730
744
–
558
574
574
570
667
658
636
661
601
–
568
–
3270
3255
3277
3199
3250
3245
3240
3266
3296
3276
3275
3253
3269
3201
3247
3247
3236
–
a2CNPA
a4CNPA
a24CPA
b2MPA
c3MPA
584
567
675
658
638
–
b4MPA
d24DMPA
d35DMPA
e4BNPA
–
743
–
738
602
627
–
–
a
b
c
Values taken from Ref. [13].
Values taken from Ref. [37].
Values taken from Ref. [38].
Values taken from Ref. [39].
d
e
Values from the present investigation.
Table 6
The partial charges of the atoms determined by natural population analysis (NPA) and the local reactivity properties of N-(4-bromophenyl)-2,2-dichloroacetamide using B3LYP/6-
311++G** method.
Atom
Neutral
Anion
0.0491
Cation
0.1134
Df(k)
D
sk
D
xk
Electrophilicity
Nucleophilicity
C1
C2
C3
C4
C5
C6
N7
C8
0.1517
ꢂ0.2092
ꢂ0.2105
ꢂ0.1142
ꢂ0.2036
ꢂ0.2101
ꢂ0.5963
0.6447
ꢂ0.5838
ꢂ0.2820
ꢂ0.0046
0.0042
0.2075
0.2246
0.2245
0.2503
0.4029
0.2356
0.0684
ꢂ0.1409
0.0468
0.0783
ꢂ0.0172
0.0057
0.0096
ꢂ0.3229
0.1073
0.1794
ꢂ2.6789
1.9979
4.6589
0.1728
2.7514
ꢂ0.3733
0.5005
0.2146
5.7877
0.3634
ꢂ0.1155
ꢂ0.1108
ꢂ0.0996
ꢂ0.1084
ꢂ0.1161
ꢂ0.3353
0.3217
ꢂ0.2775
ꢂ0.1514
0.0139
0.0193
0.1196
0.1280
0.1278
0.1375
0.2139
0.1260
0.0577
ꢂ0.2561
ꢂ0.2319
ꢂ0.1987
ꢂ0.2382
ꢂ0.2369
ꢂ0.5993
0.5195
ꢂ0.7074
ꢂ0.3105
ꢂ0.1197
ꢂ0.1484
0.1905
0.2019
0.2025
0.2460
0.3860
0.2099
ꢂ0.0228
ꢂ0.0699
ꢂ0.0085
ꢂ0.1602
0.0606
0.0074
0.1389
0.0672
0.2580
0.0082
0.0315
0.1540
0.5913
3.5075
0.2851
0.0115
87.0000
ꢂ2.5799
2.4782
4.5825
0.1607
ꢂ0.4482
ꢂ0.0548
ꢂ1.0271
ꢂ0.3876
O9
0.1827
0.0223
0.4187
0.4035
C10
Cl11
Cl12
H13
H14
H15
H16
H17
H18
Br19
0.1021
0.0125
0.2340
0.2182
6.2216
ꢂ0.0966
ꢂ0.1375
ꢂ0.1049
ꢂ0.1193
ꢂ0.1187
ꢂ0.1171
ꢂ0.2059
ꢂ0.1353
ꢂ0.1019
ꢂ0.0118
ꢂ0.0168
ꢂ0.0128
ꢂ0.0146
ꢂ0.0145
ꢂ0.0143
ꢂ0.0252
ꢂ0.0165
ꢂ0.0125
ꢂ0.2214
ꢂ0.3151
ꢂ0.2404
ꢂ0.2734
ꢂ0.2720
ꢂ0.2684
ꢂ0.4719
ꢂ0.3101
ꢂ0.2335
0.0990
10.1060
ꢂ0.1934
ꢂ0.2350
ꢂ0.2275
ꢂ0.0381
ꢂ0.0894
ꢂ0.2345
ꢂ8.5234
ꢂ5.1706
ꢂ4.2555
ꢂ4.3955
ꢂ26.2326
ꢂ11.1834
ꢂ4.2646
ꢂ0.1173
to predict the reactive sites of the molecule and are summarised in
Table 6. From the dual local softness sk and the multiphilicity
descriptors ( k) one can confirm that the atoms C2, C3, C5, C6,
(ii) The molecule has great electronegativity difference, charge
is very polarized, and there are significant differences in
electron density in different regions of the molecule.
D
D
x
N7, O9 and C10 are favourable for nucleophilic attack. The other
atoms of 4BNPA are favourable for electrophilic attack. The local
reactivity descriptors of the individual atoms of the molecule
(iii) The lone pair donor orbital, nN
?
pꢁCO interaction possess a
strong stabilization of 64.21 kcal molꢂ1
.
(iv) There is no systematic variation in CAC stretching vibrations
with the bromine substitution in the ring. The effect of sub-
stituent ABr in the amide moiety have been analysed and
compared.
(v) The kinetic and thermodynamic stability and chemical reac-
tivity descriptors of the molecule have been determined. The
atoms C2, C3, C5, C6, N7, O9 and C10 are favourable for
nucleophilic attack while others are favourable for electro-
philic attack.
(vi) There is no significant shift in the amide-I, C@O stretching;
amide-II, N-H in-plane bending and amide-III, the C–N
stretching vibrational frequencies of N-(4-bromophenyl)-
2,2-dichloroacetamide
(vii) There is a significant blue shift is observed in the amide-IV,
C@O in-plane bending frequency when compared with the
N-(chloro/methyl substituted phenyl)-2,2-dichloroacet-
amide compounds.
sak ¼ fkaS, xak
¼
x
fka and fka where, a = +, ꢂ and 0 represents local phi-
licity quantities describing for nucleophilic, electrophilic and free
radical attack, respectively presented in Tables 6 and T3 are clearly
express the nature of activity of the individual atoms.
9. Conclusion
The FTIR and FT-Raman vibrational spectra of N-(4-bromophe-
nyl)-2,2-dichloroacetamide molecule has been recorded and ana-
lysed the complete vibrational fundamental modes of the most
stable geometry of the compound using the experimental FTIR
and FT-Raman data on the basis of peak positions, relative intensi-
ties and quantum chemical studies. The following observations are
made
(i) The reactive centres are found from the molecular electro-
static potential and the atomic charges. The limits of electro-
(viii) The bromo substitution raised the NAH out of plane
bending.
static potential are ꢂ9.617e ꢃ 10ꢂ3 and +9.617e ꢃ 10ꢂ3
.

26
V. Arjunan et al. / Journal of Molecular Structure 1064 (2014) 15–26
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