Theoretical investigation of the conformation and hydrogen bonding ability of 5-arylazosalicylaldoximes

Article abstract of DOI:10.1016/j.molstruc.2012.06.012

Conformations of 5-arylazosalicylaldoximes 6-10 have been predicted from spectral and theoretical studies. The orientation of OH bond is predicted to be anti to CN bond from the PES analysis. The presence of intramolecular hydrogen bonding in oximes 6-10 and their parent aldehydes 1-5 is supported by the additional bond and ring critical points from AIM analysis, hyperconjugative interaction energies determined from NBO analysis and selected geometrical parameters derived from optimized structures. Molecular properties such as dipole moment, polarizability and hyperpolarizabilities for oximes 6-10 and their parent aldehydes 1-5 were also determined by computational studies.

Full text of DOI:10.1016/j.molstruc.2012.06.012

Journal of Molecular Structure 1027 (2012) 175–185
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Theoretical investigation of the conformation and hydrogen bonding ability
of 5-arylazosalicylaldoximes
⇑
A. Manimekalai , R. Balachander
Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, Tamilnadu, India
h i g h l i g h t s
"
"
"
Conformations of oximes have been predicted from spectral and theoretical studies.
Intramolecular hydrogen bonding in oximes and aldehydes.
Molecular properties for oximes and aldehydes were determined from computational studies.
a r t i c l e i n f o
a b s t r a c t
Article history:
Conformations of 5-arylazosalicylaldoximes 6–10 have been predicted from spectral and theoretical
studies. The orientation of OH bond is predicted to be anti to C@N bond from the PES analysis. The pres-
ence of intramolecular hydrogen bonding in oximes 6–10 and their parent aldehydes 1–5 is supported by
the additional bond and ring critical points from AIM analysis, hyperconjugative interaction energies
determined from NBO analysis and selected geometrical parameters derived from optimized structures.
Molecular properties such as dipole moment, polarizability and hyperpolarizabilities for oximes 6–10
and their parent aldehydes 1–5 were also determined by computational studies.
Received 24 November 2011
Received in revised form 1 April 2012
Accepted 1 June 2012
Available online 12 June 2012
Keywords:
5-Arylazosalicylaldoximes
Hydrogen bonding
Computational studies
Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction
from self-assembled aggregates of azo benzene units. Incorpora-
tion of azobenzene in bilayer assemblies exhibit novel photochem-
The azobenzene chromophore has elicited considerable interest
because of its novel photoisomerization and photocyclization reac-
tions [1] as well as its technological applications in the dye and
pigment industry [2]. Their oxidation–reduction behavior play
important role in biological activity [3,4]. Some of the photore-
sponsive azobenzene derivatives show enhanced transport of me-
tal ions across a liquid membrane on irradiation [5,6]. Derivatives
of azobenzene can be used as intermediates as well as ligands to
synthesize several organic compounds and coordination com-
plexes [7–10]. Generally organic chromophores and polymers are
strongly fluorescent in dilute solution and aggregate formation
leads to reduction in fluorescent efficiency in the solid state. How-
ever an asymmetric disulfide compound consisting of a photoisom-
erizable azobenzene unit coupled to a biphenyl fluorophore [11]
whose isolated species is weakly fluorescent in initial solution,
spontaneously self-assembles into strongly fluorescent aggregates
under UV light irradiation. Several reports in literature reveal
enhancement of fluorescence [12,13] and photoreactivity [14,15]
ical reactivity and energy transfer on excitation [16]. The
photochemical behavior and energy transfer of azobenzene deriv-
atives in microphorous crystals have also been reported in litera-
ture [17–21].
Second-order non-linear optical materials consisting of azo
dyes poled in polymer matrices have been synthesized and their
NLO behavior was studied in detail [22,23]. Azobenzene dendri-
mers with a branch point at each of the donor–acceptor function-
alized azobenzene monomeric units, have large first
hyperpolarizabilities [24–26] and quantum chemical calculations
have also been made to predict interaction in various conforma-
tions between monomeric unit of donor–acceptor functionalized
azobenzene dendrimers [27]. Because of the wide applicability of
azobenzene derivatives we thought that synthesis and character-
ization of some simple azo derivatives is of considerable impor-
tance and hence the study has been carried out. In the present
study five 5-arylazosalicylaldoximes 6–10 were synthesized and
their conformations have been predicted from spectral and
theoretical studies. Single crystal measurements made for 5-p-
tolylazosalicylaldoxime
derived from computational studies. The presence of intramolecular
7 also predict the same conformation
⇑
Corresponding author. Tel.: +91 9486283468.
E-mail address: profmeka1@gmail.com (A. Manimekalai).
0022-2860/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.06.012

176
A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
hydrogen bonding in oximes 6–10 and their parent aldehydes 1–5
is evidenced from AIM, NBO and selected geometrical properties.
13C NMR spectroscopy. 1HA1H, 1HA13C COSY spectra and one-dimen-
sional NMR spectra were recorded in DMSO-d6 due to poor solubility
of the compounds in CDCl3 and analyzed. Odabasoglu et al. [28] have
recorded 1H and 13C NMR spectra for the parent aldehydes 1, 2, 4 and 5
at 200 MHz in CDCl3. In the present study spectra were also recorded
for the parent aldehydes 1–5 in CDCl3 at 500 MHz.
2. Experimental
2.1. Synthesis of 5-arylazosalicylaldoximes 6–10
3.1. IR spectral analysis
5-Arylazosalicylaldehydes 1–5 were prepared according to the
procedure reported by Odabasoglu et al. [28]. A mixture of 5-ary-
lazosalicylaldehyde (1 mmol) and sodium acetate (0.5 g) was dis-
solved in boiling ethanol and hydroxylamine hydrochloride
(0.13 g; 2 mmol) was added. The mixture was refluxed for 3 h.
The reaction mixture was poured into water. The 5-aryl-
azosalicylaldoxime separated out was filtered and recrystallized
from ethanol. (6) aryl = phenyl, m.p. 153 °C, yield 70%; (7) ar-
yl = p-tolyl, m.p. 155 °C, yield 70%; (8) aryl = p-methoxyphenyl,
m.p. 160 °C, yield 75%; (9) aryl = p-fluorophenyl, m.p. 175 °C, yield
75% and (10) aryl = p-nitrophenyl, m.p. 180 °C, yield 70%.
The sharp peaks around 1610 cmꢂ1 in the IR spectra of 6–10 are
due to mC@N group. The stretching vibration of the OH (mOH) group
was observed in the region 3410 cmꢂ1. Aromatic C@C stretching
vibrations are seen around 1580 and 1500 cmꢂ1. The out of plane
bending vibration of OH group appeared around 1390 cmꢂ1. The
peaks around 1200 cmꢂ1 are due to mCAO mode. Aromatic CAH
out of plane bending vibrations appeared around 800 and
750 cmꢂ1. Strong peaks for N@N group were observed around
1260 cmꢂ1. Aromatic CAH stretching vibration was appeared
around 3060 cmꢂ1. The sharp peaks around 1010 cmꢂ1 are due to
mNAO mode. In oxime 10 peaks for mNO appeared at 1520 and
2
2.2. Spectral measurements
1338 cmꢂ1. The IR data of 6–10 are listed in Table 1.
The proton spectra at 500 MHz and proton decoupled 13C NMR
spectra at 125 MHz were recorded at room temperature on DRX
500 NMR spectrometer using 10 mm sample tube. Samples were
prepared by dissolving about 10 mg of the sample in 0.5 mL of
DMSO-d6 containing 1% TMS for 1H and 0.5 g of the sample in
2.5 mL of DMSO-d6 containing a few drops of TMS for 13C. The sol-
vent chloroform-d also provided the internal field frequency lock
signal. The 1HA1H and 1HA13C COSY spectra were performed on
a DRX-500 NMR spectrometer. Avatar-330 FT-IR spectrophotome-
ter was used for recording IR spectra (KBr pellet). For the parent
aldehydes NMR spectra were recorded in chloroform-d.
3.2. NMR spectral analysis
The signals in the 1H NMR spectra were assigned based on their
positions, integrals and multiplicities and confirmed by the corre-
lations observed in the COSY spectra. The two high frequency sing-
lets observed at 11.51 and 10.89 ppm in 6 are assigned to phenolic
proton H(15) and oxime OH proton H(18) respectively. The signal
at 8.43 ppm is assigned to H(16) proton. The low frequency dou-
blet observed at 7.10 ppm (J = 8.5 Hz) is assigned to the ortho pro-
ton with respect to OH group i.e., H(3). For H(6), a doublet (meta
coupling of J = 2.5 Hz) at 8.14 ppm was observed. The 1H NMR
spectrum further reveals two triplets at 7.58 and 7.53 ppm (inte-
gral corresponds to three protons) and a doublet at 7.86 ppm with
spacing 8.00 Hz (integral corresponds to three protons) for the aro-
matic protons of phenyl ring and for the proton H(4). The high in-
tense triplet at 7.58 ppm is obviously due to the meta protons of
the phenyl ring i.e., H(11) and H(13). The remaining triplet at
7.53 ppm is due to para proton of the phenyl ring i.e., H(12). The
doublet at 7.86 ppm is therefore assigned to H(4) proton and ortho
protons of the phenyl ring [H(10) and H(14)]. This assignment is
further confirmed by the correlations observed in the 1HA1H COSY
spectrum. In a similar manner assignments were done for other
oximes and their parent aldehydes.
2.3. Computational study
Geometry optimizations were carried out according to density
functional theory available in Gaussian-03 package using B3LYP/
6-31G(d,p) basis set [29] for the structures of oximes and their par-
ent aldehydes. The polarizabilities and hyperpolarizabilities were
determined from the DFT optimized structures by finite field ap-
proach using B3LYP/6-31Gꢀ basis set available in Gaussian-03
package and NBO calculations using the basis set B3LYP/6-
31G(d,p) and B3LYP/6-311+G(d,p). AIM parameters were deter-
mined using AIM-All package [30] from B3LYP/6-31G(d,p) opti-
mized structures.
In 13C NMR spectra quaternary carbons can be easily distin-
guished from other carbons based on small intensities. Assign-
ments of the aromatic ring carbons were made on the basis of
cross peaks observed in 1HA13C COSY spectra. The downfield signal
at 146.51 ppm in the oxime 6 is assigned to AC@N carbon. The hy-
droxy bearing carbon [C(2)] resonates at 159.34 ppm. For the ipso
carbons C(1), C(5) and C(9) signals were observed at 119.73,
145.60 and 152.45 ppm. Among these signals the low frequency
signal at 119.73 ppm is assigned to the quaternary carbon C(1)
since it is ortho with respect to electron releasing OH group. Among
the remaining signals at 145.60 and 152.45 ppm, the signal at
152.45 ppm is assigned to the ipso carbon C(9) which is attached
to the nitrogen atom N(8). Obviously, the signal at 145.60 ppm is
due to C(5) which is para with respect to OH group. The low fre-
quency signal at 117.31 ppm is assigned to C(3) carbon and this
assignment is based on the known shielding magnitude of OH
group. The C(4) and C(6) carbons resonate at 125.84 and
122.34 ppm respectively. From the intensities, the signals at
122.70 and 129.85 ppm are assigned to ortho [C(10) and C(14)]
and meta [C(11) and C(13)] carbons and the signal at 131.30 ppm
is assigned to para carbon [C(12)]. In a similar manner assignments
2.4. X-ray analysis
Single crystal measurements of oxime 7 with the dimensions
0.30 ꢁ 0.20 ꢁ 0.15 mm was chosen for X-ray diffraction study.
Crystallographic measurements were done at 293(2) K with Bruker
axis Kappa CCD diffractometer using graphite monochromated Mo
Ka radiation (k = 0.71073 Å). The crystal structure was solved by
direct method and refined by full-matrix least square technique
on F2 using the SHELX-97 set of program [31]. The parameters in
the CIF form are available as Electronic Supplementary Information
from the Cambridge Crystallographic Database Centre (CCDC
853941).
3. Results and discussion
5-Phenylazosalicylaldoxime (6), 5-p-tolylazosalicylaldoxime (7),
5-p-methoxyphenylazosalicylaldoxime (8), 5-p-fluorophenylazo-
salicylaldoxime (9) and 5-p-nitrophenylazosalicylaldoxime (10) were
synthesized according to theScheme1and characterized by IR, 1H and

A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
177
H
CHO
17
O
13
14
10
C
18
X
8
N
1
Con. HCl
0−
5 oC
OH
16
6
X
NH2
NaNO2
+
X
N
Cl
N
H
9
12
2
20% NaOH
N
O
11
5
0
−
5 oC
15
7
3
4
1
−
5
18
OH
H
17
N
13
11
14
C
19
8
N
1
16
2
6
X
H
9
NH2OH HCl
12
N
O
10
5
CH3COONa / EtOH
Reflux 3 h
15
7
3
4
6
−
10
X
H
1 6
, ;
2 7
, ;
CH3
3 8
, ;
4 9
, ;
OCH3
F
5 10
,
;
NO2
Scheme 1. Structures of synthesized compounds and synthetic steps adopted.
Table 1
IR spectral data (cmꢂ1) of 6–10.
Assignments
6
7
8
9
10
3414
3060
1622
1574
1485
1392
1265
1195
1013
785
3189
3095
1601
1577
1497
1386
1256
1154
1021
834
3415
3107
1625
1589
1493
1393
1228
1269
1015
842
3429
2923
1619
1574
1487
1391
1262
1158
1004
824
3370
3103
1615
1579
1487
1387
1271
1103
1011
859
OAH
CAH (aromatic)
C@N
C@C
OH
N@N
CAO
NAO
Aromatic CH out of plane bending vibration
761
769
779
682
751
685
–
–
–
–
NO2
–
–
–
–
1517
1338
Table 2
1H NMR chemical shifts (ppm) of oximes (DMSO-d6) 6–10 and their parent aldehydes (CDCl3) 1–5.
Compds.
H-3
H-4
H-6
H-16
H-15
H-18
H-19
H-10 and H-14
H-11 and H-13
H-12
6
7
8
9
10
1
7.10 (d, 8.50 Hz)
7.08 (d, 10.00 Hz)
7.07 (d, 9.00 Hz)
7.09 (d, 9.00 Hz)
7.13 (d, 9.00 Hz)
7.16 (d, 8.50 Hz)
(7.19)
7.15 (d, 8.50 Hz)
(7.16)
7.13 (d, 9.00 Hz)
7.15(d, 9.00 Hz)
(7.18)
7.86
8.14 (d, 2.50 Hz)
8.11 (s)
8.43
8.43
8.43
8.43
11.51
11.46
11.49
11.51
11.55
11.34
(11.51)
11.32
(11.29)
11.29
11.35
(11.54)
11.48
(11.46)
10.89
11.46
10.78
10.89
11.15
–
–
7.86
7.75
7.85
7.93–7.90
8.04
7.94–7.92
(7.85)
7.85–7.82
(7.73)
7.93–7.92
7.96–7.94
(7.92)
7.58 (d)
7.37
7.11
7.41
8.41
7.57–7.53
(7.57)
7.36–7.34
(7.34)
7.05–7.04
7.25–7.21
(7.40)
7.53 (t)
–
–
–
7.81 (dd, 2.50, 8.50 Hz)
7.80 (dd, 2.25, 8.75 Hz)
7.84 (dd, 2.50, 8.50 Hz)
7.93 (dd, 2.50, 8.75 Hz)
8.21 (dd, 2.50, 9.00 Hz)
(8.08)
8.19 (dd, 2.50, 9.00 Hz)
(8.04)
8.16 (dd, 2.00, 8.50 Hz)
8.19 (dd, 2.25, 8.50 Hz)
(8.06)
2.40
3.86
–
–
–
–
–
–
–
–
–
–
–
8.08 (d, 2.50 Hz)
8.13 (d, 2.50 Hz)
8.21 (d, 2.50 Hz)
8.24 (d, 2.50 Hz)
(8.17)
8.21 (d, 2.00 Hz)
(8.13)
8.17 (d, 2.00 Hz)
8.22 (d, 2.50 Hz)
(8.16)
8.42
–
10.07
(10.36)
10.06
(10.34)
10.04
10.06
(10.35)
10.08
(10.33)
7.52–7.49
(7.56)
–
2
2.47
(2.36)
3.92
–
–
–
–
–
–
–
–
–
–
3
4
5
7.19 (d, 8.50 Hz)
(7.19)
8.25 (dd, 2.25, 8.50 Hz)
(8.09)
8.31 (d, 2.00 Hz)
(8.18)
8.05
(7.98)
8.42
(8.37)
–
Values within parentheses are taken from Ref. [28] for aldehydes 1, 2, 4 and 5.
were made for other compounds 7–10 and their parent aldehydes.
The 1H and 13C chemical shifts obtained in this manner are listed in
Tables 2 and 3 respectively.
3.3. Conformational analysis
There are four possible conformations for the oximes as shown
in Fig. 1. In conformation A intramolecular hydrogen bonding ex-

178
A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
Table 3
13C NMR chemical shifts (ppm) of oximes (DMSO-d6) 6–10 and their parent aldehydes (CDCl3) 1–5.
Compds. C-3
C-4
C-6
C-16
C-19/
C-18
C-1
C-2
C-5
C-9
C-12
C-10 and
C-14
C-11 and
C-13
6
7
8
9
10
1
117.31
125.84
125.71
125.45
125.84
126.63
130.71
(123.86)
122.59
(123.72)
128.71
124.73
(123.89)
130.65
(124.93)
122.34
122.68
121.97
122.28
122.99
129.33
(129.47)
129.04
(129.52)
124.66
129.32
(129.49)
130.68
(129.93)
146.51
146.58
146.63
146.41
146.08
196.57
(187.36)
196.59
(187.43)
196.61
196.51
(187.56)
196.37
(187.93)
–
119.73
119.72
119.58
119.76
120.08
120.32
(122.48)
121.06
(122.53)
120.33
120.31
(122.51)
120.37
(122.74)
159.34
159.58
158.75
162.88
155.84
167.77
(163.09)
163.54
(162.97)
162.13
163.79
(163.15)
155.52
(164.26)
145.60
145.40
145.63
149.21
145.69
145.94
(144.78)
146.01
(144.88)
146.05
145.76
(144.65)
145.77
(144.84)
152.45
150.55
146.71
159.35
148.46
152.38
(151.80)
150.49
(149.96)
146.73
148.91
(148.53)
148.72
(155.16)
131.30
141.30
161.95
164.86
160.56
131.07
(130.88)
141.69
(141.22)
163.25
165.39
(163.40)
164.87
(148.13)
122.70
122.68
115.00
124.93
125.51
123.61
(122.18)
122.77
(122.29)
114.31
124.80
(124.48)
123.36
(123.18)
129.85
130.34
124.59
116.71
145.69
129.17
(129.21)
129.75
(129.83)
130.60
118.63
(116.18)
124.81
(123.19)
117.37
117.22
117.32
117.54
118.59
(118.26)
118.52
(118.29)
118.46
116.23
(118.27)
118.99
(118.58)
21.44
56.05
–
–
–
2
21.51
(20.91)
55.61
–
3
4
5
–
Values within parentheses are taken from Ref. [28] for aldehydes 1, 2, 4 and 5.
ists between hydroxyl proton and oxime nitrogen and hence it is
stabilized over the other conformers in which there is no such
hydrogen bonding. Further single crystal measurements were
made for the oxime 7 and it also reveals the stable conformation
as ‘A’ only. The ORTEP structure and close packed diagram for 7
are shown in Fig. 2.
For the oxime 8 in the favoured conformation ‘A’ there are two
possible orientations of methoxy group as shown in Fig. 3. In con-
formation A, the methoxy methyl group is anti to N@N bond
whereas in A0 it is syn. Theoretical study [relative energies are 0.0
(A) and 0.22 (A0) kcal molꢂ1] predicts the favoured conformation
as ‘A’ only for the oxime 8. For the aldehydes 1–5 also there are
four possible conformations as shown in Fig. 4. The relative ener-
gies determined by computational method for aldehyde 1 are
Crystal data
C14H13N3O2
V = 1213.01(10) Å3
Z = 4
found to be 0.0 (A), 13.74 (B), 12.17 (C) and 10.04 (D) kcal molꢂ1
.
Mr = 255.27
Thus, the theoretical study predicts the favoured conformation
‘A’ only for the aldehydes. To investigate the barrier for isomerisa-
tion process in the favoured conformation ‘A’ in aldehydes 1–5, po-
tential energy scan over C(1)AC(16) bond was carried out for a
Monoclinic, P21/n
a = 13.7543(7) Å
b = 4.6276(2) Å
c = 19.0577(10) Å
b = 90.170(2)°
Mo K
l
a radiation
= 0.097 mmꢂ1
T = 293(2) K
0.30 ꢁ 0.20 ꢁ 0.15 mm
representative
aldehyde
1.
The
torsional
angle
C(6)AC(1)AC(16)AO(17) was varied in steps of 15° from 0° to
180° and the potential energy scan (PES) diagram is reproduced
in Fig. 5. The barrier for the isomerisation process is predicted to
In order to confirm the favoured conformation computational
calculations (geometry optimizations) were preformed for the
oxime 6 according to DFT method using B3LYP/6-31G(d,p) basis
set available in Gaussian-03 package [29] for the four possible con-
formations and the relative energies determined are found to be
0.0 (A), 9.76 (B), 10.39 (C) and 7.98 (D) kcal molꢂ1. Thus, the theo-
retical study predicts the favoured conformation as ‘A’ only. For
other oximes also one can expect conformation ‘A’ as the favoured
conformation.
be 22.38 kcal molꢂ1
.
Potential energy scan over NAO bond was also carried out to
predict the orientation of OH group of oxime moiety in conforma-
tion A. The torsional angle C(16)AN(17)AO(18)AH(18) was varied
in steps of 10° from 0° to 180° and PES diagram thus obtained is
illustrated in Fig. 6. From the scan diagram, it is concluded that
OAH bond is anti to C@N bond [C(16)AN(17)AO(18)A
H(18) = 180°] and this arrangement is favoured over the syn
H
O
N
O
H
H
H
C
C
N
C
H
X
X
N
N
X
N
H
N
N
O
N
O
A
C
B
D
H
O
O
H
H
H
N
C
N
H
X
N
O
N
O
H
Fig. 1. Possible conformations of oximes.

A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
179
Fig. 2. ORTEP and close packed structures of oxime 7.
arrangement [C(16)AN(17)AO(18)AH(18) torsional angle = 0°].
The barrier is predicted to be 6.98 kcal molꢂ1. Geometry optimiza-
tions were done for the intramolecular hydrogen bonded struc-
tures of the other aldehydes and oximes and the optimized
structures are reproduced in Fig. 7. To investigate the nature of
hydrogen bond, molecular properties such as geometrical parame-
ters, hydrogen bond energies, NBO and AIM parameters have been
determined by computational methods.
lengths are closer to the XRD values. However for the bond angles
and torsional angles, deviation is noticed and the maximum devi-
ation in torsional angle is found to be 4°. Selected geometrical
parameters which give information about the intramolecular
hydrogen bonding are listed in Table 5. The usual geometric
parameters related with hydrogen-bonding are the H15ꢃ ꢃ ꢃND17
,
O
A15AH15 and OA15ꢃ ꢃ ꢃND17 distances as well as OA15AH15ꢃ ꢃ ꢃND17
angle in oximes 6–10 where OA15 and ND17 are the electron accep-
tor oxygen and donor nitrogen atoms, respectively. For aldehydes,
the geometric parameters related with hydrogen-bonding are the
3.4. Molecular properties
H15ꢃ ꢃ ꢃOD17
A15AH15ꢃ ꢃ ꢃOD17 angle. The cutoff limit generally accepted for
the establishment of a hydrogen bond are H15ꢃ ꢃ ꢃND17 < 3.0 Å and
15AAHꢃ ꢃ ꢃN17D > 110° [32,33]. Table 5 reveals that these criteria
are satisfied in oximes as well as in their respective aldehydes.
,
O
A15AH15 and OA15ꢃ ꢃ ꢃOD17 distances as well as
O
3.4.1. Geometric parameters
From the optimized structures, geometrical parameters were
derived and they are compared with the parameters derived from
XRD values in the oxime 7 (Table 4) alone. The theoretical bond
O
H
H
O
H
H
H
O
H
H3C
C
N
C
N
O
N
O
N
N
O
N
O
H3C
A
A'
Fig. 3. Possible rotamers of methoxy group in oxime 8.

180
A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
H
O
C
C
O
H
X
N
H
X
X
N
N
N
H
O
N
N
O
B
D
A
C
H
O
C
C
O
O
H
X
N
N
O
H
H
Fig. 4. Possible conformations of aldehydes.
Moreover the distances between the atoms involved in long range
interactions depicted in Table 5 are always shorter than the sum of
van der Walls radii [34] i.e., the distances observed between the
oxygen atom O15 and nitrogen atom N17 in oximes are within
the sum of van der Waals radii (Oꢃ ꢃ ꢃN < 307 pm) and the distances
observed between the oxygen atom O15 and oxygen atom O17 in
aldehydes is less than 300 pm. Therefore, geometric parameters
listed in Table 5 support intramolecular hydrogen bonding in 1–
10. The higher ND17ꢃ ꢃ ꢃH15 and OA15ꢃ ꢃ ꢃND17 distances in oximes rel-
ative to the H15ꢃ ꢃ ꢃOD17 and OA15ꢃ ꢃ ꢃOD17 distances in the parent
aldehydes reveal that the extent of intramolecular hydrogen bond-
ing is higher in aldehydes compared to their oximes.
Comparison of energies of a rotamer of a given hydrogen
bonded structure with the rotamer with no hydrogen bonding
interaction will give an idea of hydrogen bond interaction energies.
More specifically rotamer A is compared with the rotamer C for
oxime 6 and aldehyde 1. The relative energies are actually the
hydrogen bond interaction energies (EHB). For other oximes 7–10
and aldehydes 2–5 energies were determined for rotamers with
no hydrogen bonding (Fig. 8) and from comparison with the ener-
gies of hydrogen bonded structures (conformation A) hydrogen
bond interaction energies were determined and they are also listed
in Table 5. The relative energies are not corrected for ZPE differ-
ences and may depend on such differences. The higher intramolec-
ular hydrogen bonding interaction in aldehydes compared to their
oximes is evidenced from the higher EHB values in aldehydes rela-
tive to their oximes.
3.4.2. Natural bond orbital analysis
NBO analysis were carried out for the oximes 6–10 and their
parent aldehydes 1–5 and the important second order perturbative
estimates of donor–acceptor interactions are displayed in Table 6.
The hyperconjugative interaction energies involving C(5) p-orbital
with the antibonding orbitals of vicinal C(1)AC(6), N(7)AN(8) and
C(3)AC(4) bond are found to be very high (ꢄ81, 70 and
69 kcal molꢂ1) and this is the primary delocalization seen in the
oximes 6–9. In the parent aldehydes 1–4 the hyperconjugative
interaction energy involving C(1) p-orbital with the antibonding
orbital of vicinal C(16)AO(17) bond is found to be very high
(ꢄ77 kcal molꢂ1) and this is the primary delocalization present in
their parent aldehydes 1–4. However in oxime 10 and its parent
aldehyde 5 primary delocalization occurs within the orbitals of
the nitro group attached to the para position of the phenyl ring at-
tached to N(8).
Most stabilizing interactions take place between vicinal NBOs.
Besides these some interactions between remote filled and unfilled
orbitals are also present. The main stabilized interaction involves
the N(17) lone pair as donor and the O(15)AH(15) antibond orbital
Fig. 6. PES diagram of oxime 6.
Fig. 5. PES diagram of aldehyde 1.

A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
181
[
rꢀO(15)AH(15)] as acceptor in oximes 6–9 and O(17) lone pair as
unit G/qBCP values for some selected bonds of oximes and their
aldehydes [N7AN8, C2AO15, O15AH15, C16AO17, C16AN17,
donors and O(15)AH(15) antibonding orbital [rꢀO(15)AH(15)] as
acceptor in aldehydes 1–4. However in oxime 10 and its aldehyde
5 the strong interaction involve N(17)/O(17) lone pair as donor and
the antibonding pure s-orbital of H(15) [rꢀH(15)] as acceptor. The
delocalization energy corresponding to the intramolecular hydro-
gen bonding is slightly lower in oximes than in aldehydes. Among
the various substituted compounds studied the nitro derivative is
found to have higher stabilizing energy indicating that the intra-
molecular hydrogen bond formation efficiency is higher in nitro
derivatives 5 and 10 compared to other derivatives.
N17AO18, O18AH18, O17ꢃ ꢃ ꢃH15 and N17ꢃ ꢃ ꢃH15] and
ring critical points (RCPs). The negative values obtained for the
Laplacian of electron density for N7AN8, C2AO15,
q values of
( )
2q
r
O15AH15, C16AO17, C16AN17, N17AO18 and O18AH18 bonds
are a clear indication that the electronic charge is locally concen-
trated within the region of inter atoms leading to an interaction
named as covalent or polarized bonds and being characterized by
large
q values [35–37]. Besides these BCP was located between
the non-bonded H(15) and N(17) atoms in oximes and H(15) and
O(17) atoms in aldehydes. Popelier proposed that the establish-
ment of a hydrogen bond should be accompanied by four local
topological properties of the electron density [38,39]; (i) existence
of a (3, ꢂ1) BCP between the atoms involved in the interaction, (ii)
3.4.3. Atoms-in-molecules analysis
Atoms-in-molecules (AIM) electron density topological analy-
ses were carried out for oximes 6–10 and aldehydes 1–5. Table 7
2qBCP
, e, the three eigen values k1, k2 and k3, the rela-
density at the BCP (
cian of the density at the same point
the range 0.015–0.15 au and (iv) existence of mutual penetration
of hydrogen and the electron-donor atoms nitrogen and oxygen.
q
BCP) in the range 0.002–0.040 au, (iii) Lapla-
lists qBCP
,
r
r
2qBCP is positive and in
tionship between the perpendicular and parallel curvatures |k1|/
k3, the potential energy density V, the kinetic energy density G,
the total energy density H and the kinetic energy density for charge
Fig. 7. Optimized structures of oximes 6–10 and their parent aldehydes 1–5.

182
A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
Table 4
Selected geometric parameters [bond lengths (Å), bond angles (°) and torsional angles (°)] in oximes 6–10 and their parent aldehydes 1–5.
Geometric parameters
7
6
8
9
10
1
2
3
4
5
XRD
Theor.
Bond length
C1AC2
C1AC6
C1AC16
C2AC3
C2AO15
C3AC4
C6AC5
C5AC4
C5AN7
N7AN8
1.407
1.395
1.455
1.388
1.359
1.378
1.379
1.401
1.427
1.246
1.271
0.930
1.395
1.428
1.501
1.426
1.427
1.400
1.458
1.402
1.343
1.386
1.399
1.406
1.412
1.263
1.286
1.092
1.397
1.418
–
1.426
1.399
1.457
1.402
1.344
1.386
1.399
1.406
1.412
1.264
1.287
1.092
1.398
1.411
1.361
1.427
1.398
1.458
1.402
1.343
1.386
1.399
1.406
1.411
1.263
1.286
1.092
1.397
1.415
1.348
1.429
1.396
1.458
1.403
1.340
1.384
1.401
1.408
1.405
1.265
1.286
1.092
1.394
1.417
1.469
1.426
1.399
1.455
1.404
1.335
1.384
1.395
1.410
1.413
1.262
1.233
1.106
1.437
1.400
1.456
1.404
1.336
1.385
1.395
1.411
1.414
1.263
1.234
1.107
1.427
1.400
1.455
1.404
1.337
1.385
1.395
1.411
1.414
1.264
1.234
1.107
1.427
1.400
1.456
1.404
1.335
1.384
1.396
1.411
1.413
1.262
1.234
1.107
1.428
1.397
1.458
1.405
1.332
1.383
1.397
1.412
1.408
1.263
1.233
1.106
1.398
1.458
1.402
1.344
1.386
1.399
1.406
1.412
1.263
1.286
1.092
1.397
1.415
1.509
C16AO17/N17
C16AH16
N17AO18
N8AC9
–
–
–
–
–
1.417
–
1.415
1.509
1.410
1.360
1.415
1.347
1.417
1.470
C12AX18
Bond angle
C2AC1AC16
C6AC1AC16
C1AC2AO15
C3AC2AO15
C6AC5AN7
C4AC5AN7
C2AO15AH15
C5AN7AN8
C1AC16AN17/O17
C16AN17AO18
N7AN8AC9
N8AC9AC10
N17AO18AH18
122.6
121.9
121.9
121.9
121.9
121.9
119.8
120.3
121.6
119.2
125.1
116.0
107.1
114.8
121.5
–
119.8
119.8
120.2
121.6
119.2
125.3
116.0
107.1
114.7
121.5
–
119.8
120.3
121.6
119.2
125.2
115.9
107.1
114.8
121.4
–
119.8
120.3
121.5
119.1
125.1
115.9
107.3
115.1
121.2
–
119.2
121.3
118.4
115.4
125.5
109.5
114.1
124.1
112.2
113.9
125.0
109.5
119.0
122.3
118.1
125.0
116.1
108.6
115.0
124.1
112.1
114.9
125.0
103.1
119.9
122.3
118.1
124.9
116.0
108.6
115.0
124.2
112.1
114.8
125.8
103.1
120.0
122.3
118.1
125.0
116.1
108.5
114.9
124.1
113.0
115.0
125.1
103.1
119.0
122.3
118.1
125.0
116.0
108.6
115.1
123.9
112.1
114.8
124.0
103.1
119.1
122.2
118.1
124.9
115.9
108.7
115.3
121.0
112.2
114.3
124.7
103.3
120.3
121.6
119.4
125.2
116.0
107.1
114.2
121.4
–
–
115.0
124.8
–
115.0
125.0
115.9
125.1
–
115.5
124.8
–
114.4
124.7
–
Torsional angle
C6AC1AC2AO15
C6AC1AC16AN17
C6AC1AC10–O17
C2AC1AC16AN17
C1AC2AO15AH15
C3AC2AO15AH15
C16AN17AO18AH18
C1AC16AN17AO18
C5AN7AN8AC9
N7AN8AC9AC10
C1AC16AN17AH15
C16AN17AH15AO15
C2AO15AH15AN17
178.7
ꢂ180.0
ꢂ180.0
–
180.0
180.0
–
0.0
0.0
ꢂ180.0
ꢂ180.0
–
180.0
ꢂ180.0
ꢂ180.0
–
180.0
–
180.0
–
0.0
180.0
–
180.0
180.0
–
180.0
–
0.0
180.0
–
180.0
–
180.0
–
0.0
180.0
–
180.0
–
180.0
–
0.0
180.0
–
ꢂ177.4
ꢂ180.0
–
–
–
ꢂ180.0
2.8
–
–
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
–
0.0
ꢂ180.0
ꢂ180.0
ꢂ180.0
180.0
180.0
0.0
180.0
ꢂ180.0
ꢂ180.0
180.0
180.0
0.0
180.0
180.0
ꢂ180.0
180.0
0.0
ꢂ180.0
ꢂ180.0
180.0
ꢂ180.0
0.0
–
ꢂ179.3
ꢂ179.4
3.9
ꢂ180.0
ꢂ180.0
ꢂ180.0
0.0
–
–
–
–
–
–
180.0
0.0
0.0
–
ꢂ180.0
180.0
0.0
0.0
–
180.0
0.0
0.0
–
180.0
0.0
0.0
–
0.0
0.0
–
–
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
–
–
–
–
–
–
The qBCP values obtained in the present study and positive magni-
tude of
2qBCP reported in Table 7 are in the high limit of the
requirements to define a hydrogen bond and thus a strong interac-
of a strong intramolcular hydrogen bond for the oximes and alde-
hydes. The electron density at RCP is found to be less in oximes than
in aldehydes. As pointed by Bader [40,41] a relationship exists be-
tween the hydrogen bond strength and the density in the BCP. Com-
r
tion may be inferred.
Moreover a ring critical point (RCP) is also observed in both the
oximes [C(1)AC(2)AO(15)AH(15)AN(17)AC(16)] and aldehydes
[C(1)AC(2)AO(15)AH(15)AO(17)AC(16)] thus reinforcing the idea
parison of qBCP and
aldehydes 1–5 indicate that the values are higher in aldehydes than
r
2qBCP for the oximes 6–10 and parent
in oximes. As a consequence the hydrogen bond presents a stronger
Table 5
EHB and intramolecular hydrogen bonding geometrical parameters in 1–10.
Compds.
O
(Å)
A15AH15
OD17ꢃ ꢃ ꢃH15
OD17ꢃ ꢃ ꢃOA15
O
(°)
A15AH15ꢃ ꢃ ꢃOD17
ND17ꢃ ꢃ ꢃH15
ND17ꢃ ꢃ ꢃO15A
O
(°)
15AAH15ꢃ ꢃ ꢃND17
EHB
(Å)
(Å)
(Å)
(Å)
(kcal molꢂ1
)
1
2
3
4
5
6
7
0.991
0.991
0.991
0.991
0.991
0.986
–
1.723
1.724
1.726
1.723
1.721
–
0.820
0.986
–
2.616
2.616
2.617
2.615
147.8
147.8
147.8
147.8
–
–
–
–
–
–
–
–
–
–
–
–
12.171
12.181
12.168
12.145
12.132
10.394
–
10.380
10.330
10.375
10.464
2.613
147.6
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1.784
–
2.653
1.786
1.784
1.777
2.653
1.903
1.785
2.654
2.652
2.647
145.0
146.6
145.0
145.0
145.0
145.0
XRD
Theor.
–
8
9
10
0.985
0.986
0.987
–
–

A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
183
O
H
H
O
H
H
H
H
C
N
C
N
X
X
N
N
X
N
N
N
O
N
C
A
A
C
C
6 10
−
H
H
C
O
C
O
X
N
H
N
O
O
H
1 5
−
Fig. 8. Conformations of rotamers with and without hydrogen bonding.
Table 6
NBO analysis of 1–10 by DFT method.
Donor NBO
Acceptor NBO
E2 (kcal molꢂ1
)
1
2
3
4
5
6
7
8
9
10
BD(2)N7AN8
BD(2)C14AC9
BD(2)C6AC5
BD(2)C6AC5
BD(2)C3AC4
BD(2)C6AC5
LP(2)O15
BD⁄(2)C14AC9
BD⁄(2)N7AN8
BD⁄(2)N7AN8
BD⁄(2)C3AC4
LP⁄(1)C2
10.48
(10.45)
20.62
(21.02)
16.21
(16.46)
21.92
(22.06)
60.96
(61.25)
44.58
(45.13)
77.51
(76.09)
72.22
10.46
(10.41)
21.7
10.47
(10.17)
22.42
(23.83)
15.87
(16.77)
21.94
(22.17)
60.72
(62.62)
44.84
(44.54)
76.49
(72.55)
71.24
(72.24)
83.59
(79.55)
21.07
(17.79)
–
10.46
(10.45)
20.87
(21.21)
16.40
(16.69)
21.87
(22.00)
60.86
(61.17)
21.87
(45.08)
77.66
(76.28)
72.46
(72.53)
82.04
(77.17)
21.23
(17.82)
–
10.59
(10.55)
13.55
(13.74)
22.96
(23.45)
–
10.67
(10.63)
20.13
(20.53)
–
10.66
10.65
(10.59)
21.82
(22.29)
–
10.68
(10.66)
20.39
(20.74)
–
10.66
(10.85)
–
(10.60)
20.76
(21.22)
–
(21.74)
16.03
(16.27)
21.96
(22.10)
60.90
(61.17)
44.68
(45.22)
77.10
(75.66)
71.85
(71.89)
82.87
(78.02)
21.22
(17.80)
–
–
–
–
–
–
–
–
59.94
(60.20)
–
59.80
(60.06)
–
59.59
(59.82)
–
59.84
(60.11)
–
–
LP(1)C1
–
–
LP⁄(1)C2
77.10 (–)
70.21
(68.99)
–
69.85
(68.61)
–
69.27
(68.04)
–
70.38
(69.19)
–
–
LP(1)C1
BD⁄(2)C6AC5
–
–
(72.26)
LP(2)C1
BD⁄(2)C16AO17 82.31
–
–
–
–
–
–
(77.48)
LP(2)O17/
LP(1)N17
LP(1)N17/O17
BD(2)C1–C6
BD⁄(1)O15AH15 21.25
(17.83)
23.16 (–)
22.37
(17.31)
–
22.30
(17.24)
–
22.20
(17.15)
–
22.41
(17.35)
–
23.09 (–)
LP⁄(1)H15
–
–
25.51
–
24.53
23.67
(23.79)
–
BD⁄(2)C16–N17
–
–
–
24.20
(24.32)
80.75
(81.10)
68.32
(68.74)
66.95
(69.48)
55.54
(55.80)
39.74
(39.95)
39.33
(39.66)
17.81
(17.70)
–
24.7
24.38
(24.51)
81.69
(82.09)
68.78
(69.22)
67.03
(69.65)
55.42
(55.66)
39.87
(40.10)
39.31
(39.64)
18.14
(18.03)
–
24.13
(24.24)
80.53
(80.83)
68.08
(68.46)
68.64
(71.42)
55.38
(55.65)
39.79
(40.02)
39.38
(39.72)
17.75
(17.62)
–
(24.39)
81.10
(81.49)
68.54
(69.00)
66.60
(69.14)
55.54
(55.80)
39.77
(39.99)
39.30
(39.62)
17.94
(17.84)
–
LP(1)C5
BD⁄(2)C1–C6
BD⁄(2)C3–C4
BD⁄(2)N7–N8
LP⁄(1)C2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
LP(1)C5
–
–
–
–
–
–
LP(1)C5
BD(2)C1–C6
BD(2)C1–C6
BD(2)C3–C4
BD(2)N7–N8
LP(2)O19
LP⁄(1)C5
LP(1)C5
LP(1)C5
BD⁄(2)N18–O20
163.76
(163.43)
28.79
(27.68)
16.03
163.30
(162.95)
23.79
(23.67)
2.10
BD(2)C1–C6
BD(2)C5–C4
LP(3)O15
BD⁄(2)C16–017/
N17
BD⁄(2)N7–N8
–
–
–
–
–
–
–
–
–
–
–
–
(23.85)
438.52
(24.31)
485.38
LP⁄(1)H15
Values within parentheses are the values derived from B3LYP/6-311+G(d,p).
Bold values indicates intramolecular hydrogen bonding parameters.
interaction in aldehydes than in oximes. This is also in line with the
distances observed between the oxygen atom O15 and oxygen atom
O17 in aldehydes (lower values) and the distances between the oxy-
gen atom O15 and nitrogen atom N17 in oximes (higher values).

184
A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
Table 7
Topological properties at BCP (3, –1) in relevant bonds of 1–10.
Compds.
1
Bond (Aꢃ ꢃ ꢃB)
N7AN8
qBCP
ꢂ
r
2qBCP
e
k1
k2
k3
|k1|/k3
G
V
H
Gb/qBCP
0.4547
1.0452
0.3507
1.9319
0.1330
0.0025
0.0164
0.0433
0.0008
0.0903
0.1518
0.0188
0.1108
0.0028
0.1340
0.0013
0.0166
0.0430
0.0001
0.1340
0.0022
0.0164
0.0435
0.0007
0.1295
0.0042
0.0160
0.0444
0.0001
0.1327
0.0055
0.0177
0.2610
0.0417
0.0366
0.0569
0.1329
0.0060
0.0178
0.2605
0.0418
0.0367
0.0569
0.1338
0.0069
0.0179
0.2597
0.0421
0.0367
0.0569
0.1337
0.0057
0.0177
0.2615
0.0416
0.0366
0.0569
0.1285
0.0030
0.0172
0.2648
0.0406
0.0364
0.0572
ꢂ1.0870
ꢂ0.6715
ꢂ1.7538
ꢂ0.9923
ꢂ0.0733
ꢂ1.0021
ꢂ0.6259
ꢂ1.4867
ꢂ0.9290
ꢂ0.0734
ꢂ1.0799
ꢂ0.6676
ꢂ1.7563
ꢂ0.9911
ꢂ0.0727
ꢂ1.0856
ꢂ0.6721
ꢂ1.7548
ꢂ0.9928
ꢂ0.0733
ꢂ1.0839
ꢂ0.6802
ꢂ1.7525
ꢂ0.9964
ꢂ0.0738
ꢂ1.0849
ꢂ0.6457
ꢂ1.7775
ꢂ0.8904
ꢂ0.0646
ꢂ1.8935
ꢂ0.7329
ꢂ1.0829
ꢂ0.6446
ꢂ1.7777
ꢂ0.8902
ꢂ0.0644
ꢂ1.8928
ꢂ0.7319
ꢂ1.0786
ꢂ0.6436
ꢂ1.7788
ꢂ0.8896
ꢂ0.0642
ꢂ1.8923
ꢂ0.7303
ꢂ1.0831
ꢂ0.6465
ꢂ1.7767
ꢂ0.8904
ꢂ0.0647
ꢂ1.8938
ꢂ0.7336
ꢂ1.0791
ꢂ0.6547
ꢂ1.7712
ꢂ0.8914
ꢂ0.0665
ꢂ1.8956
ꢂ0.7402
ꢂ0.9594
ꢂ0.6698
ꢂ1.7254
ꢂ0.9511
0.0733
1.0012
0.9906
1.5473
2.0946
0.2756
1.1182
0.6587
1.4489
1.4463
0.3085
0.9981
0.9816
1.5486
2.0901
0.2739
1.0002
0.9928
1.5481
2.0965
0.2660
1.0008
1.0150
1.5472
2.1102
0.2770
1.0005
0.9425
1.5639
1.0639
0.2352
1.5869
0.9914
0.9998
0.9396
1.5638
1.0631
0.2347
1.5863
0.9909
0.9978
0.9334
1.5643
1.0609
0.2341
1.5858
0.9900
0.9995
0.9447
1.5635
1.0633
0.2355
1.5872
0.9918
0.9993
0.9703
1.5616
1.0676
0.2400
1.5889
0.9954
1.0857
0.6779
1.1334
0.4737
0.2660
0.8962
0.9502
1.0261
0.6423
0.2380
1.0820
0.6801
1.1341
0.4742
0.2654
1.0854
0.6770
1.1335
0.4736
0.2660
1.0830
0.6702
1.1326
0.4717
0.2669
1.0843
0.6850
1.1366
0.8369
0.2747
1.1932
0.7393
1.0830
0.6861
1.1368
0.8373
0.2746
1.1932
0.7386
1.0810
0.6895
1.1372
0.8385
0.2742
1.1932
0.7377
0.1084
0.6844
1.1364
0.8374
0.2750
1.1932
0.7397
1.0800
0.6747
1.1342
0.8350
0.2769
1.1930
0.7436
0.2742
0.4033
0.0719
0.6893
0.0341
0.2260
0.2930
0.0566
0.5220
0.0425
0.2720
0.4009
0.0720
0.6882
0.0339
0.2738
0.4039
0.0719
0.6898
0.0341
0.2726
0.4098
0.0715
0.6932
0.0342
0.2735
0.3898
0.0741
0.5152
0.0291
0.0729
0.1940
0.2729
0.3890
0.0741
0.5150
0.0290
0.0729
0.1938
0.2717
0.3874
0.0742
0.5143
0.0290
0.0730
0.1935
0.2730
0.3904
0.0741
0.5151
0.0291
0.0728
0.1941
0.2711
0.3973
0.0738
0.5164
0.0295
0.0724
0.1955
ꢂ0.8097
ꢂ0.8943
ꢂ0.6268
ꢂ1.3408
ꢂ0.0359
ꢂ0.6528
ꢂ0.7138
ꢂ0.4874
ꢂ1.1237
ꢂ0.0446
ꢂ0.8025
ꢂ0.8901
ꢂ0.6279
ꢂ1.3392
ꢂ0.0357
0.8083
ꢂ0.5355
ꢂ0.4910
ꢂ0.5549
ꢂ0.6515
ꢂ0.0018
ꢂ0.4268
ꢂ0.4208
ꢂ0.4308
ꢂ0.6017
ꢂ0.0021
ꢂ0.5305
ꢂ0.4892
ꢂ0.5559
ꢂ0.7510
ꢂ0.0018
ꢂ0.5345
ꢂ0.4915
ꢂ0.5552
ꢂ0.6518
0.0018
ꢂ0.5333
ꢂ0.4954
ꢂ0.5541
ꢂ0.6533
ꢂ0.0019
ꢂ0.5341
ꢂ0.4761
ꢂ0.5641
ꢂ0.6484
ꢂ0.0019
ꢂ0.6061
ꢂ0.3028
ꢂ0.5327
ꢂ0.4755
ꢂ0.5643
ꢂ0.6483
ꢂ0.0019
ꢂ0.6060
ꢂ0.3022
ꢂ0.5297
ꢂ0.4742
ꢂ0.5648
ꢂ0.6481
0.0018
0.6031
1.2998
0.2152
1.7723
0.7494
0.5420
1.0068
0.1831
1.4115
0.0958
0.6014
1.2948
0.2152
1.7706
0.7483
0.6029
1.3008
0.2151
1.7728
0.7494
0.6010
1.3120
0.2143
1.7783
0.7493
0.6024
1.2836
0.2180
1.3720
0.6912
0.1978
0.6061
0.6020
1.2823
0.2181
1.3718
0.6905
0.1980
0.6061
0.6012
1.2793
0.2181
1.3704
0.6921
0.1982
0.6061
0.6023
1.2848
0.2181
1.3721
0.6912
0.1977
0.6061
0.5996
1.2979
0.2181
1.3747
0.6876
0.1967
0.6062
C2ꢃ ꢃ ꢃO15
0.3103
0.3342
0.3889
0.0455
0.4170
0.2910
0.3089
ꢂ0.3698
ꢂ0.4436
0.4523
0.3095
0.3347
0.3887
0.0453
0.4542
0.3105
0.3343
0.3891
0.0455
0.4536
0.3123
0.3335
0.3898
0.0456
0.4540
0.3037
0.3399
0.3755
0.0421
0.3682
0.3201
0.4533
0.3034
0.3400
0.3754
0.0420
0.3682
0.3198
0.4519
0.3028
0.3403
0.3753
0.0419
0.3683
0.3193
0.4533
0.3039
0.3397
0.3754
0.0421
0.3682
0.3203
0.4521
0.3061
0.3384
0.3756
0.0429
0.3679
0.3225
O15ꢃ ꢃ ꢃH15
C
16AO17
ꢂ0.1512
ꢂ0.1290
0.8030
0.5107
1.4972
3.1890
0.1619
1.0340
0.3527
1.9353
ꢂ0.1488
ꢂ0.1285
1.0427
0.3499
1.9330
ꢂ0.1522
ꢂ0.1290
1.0426
0.3426
1.9302
ꢂ0.1598
ꢂ0.1294
1.0422
0.3454
1.9600
0.5326
ꢂ0.1085
2.1332
0.4350
1.0391
0.3458
1.9605
0.5333
ꢂ0.1084
2.1323
0.4335
1.0322
0.3474
1.9620
0.5349
ꢂ0.1083
2.1317
0.4314
1.0389
0.3447
1.9590
0.5329
ꢂ0.1086
2.1336
0.4359
1.0359
0.3371
1.9509
0.5287
ꢂ0.1097
2.1357
0.4450
O17ꢃ ꢃ ꢃH15
2
3
4
5
6
N7AN8
ꢂ0.9191
ꢂ0.5434
ꢂ1.4594
ꢂ0.8363
ꢂ0.0732
ꢂ0.9523
ꢂ0.6667
ꢂ1.7276
ꢂ0.9502
ꢂ0.0727
ꢂ0.9573
ꢂ0.6706
ꢂ1.7265
ꢂ0.9515
ꢂ0.0733
ꢂ0.9596
ꢂ0.6774
ꢂ1.7249
ꢂ0.9540
ꢂ0.0738
0.9578
ꢂ0.6421
ꢂ1.7465
ꢂ0.7061
ꢂ0.0620
ꢂ1.8266
ꢂ0.6935
ꢂ0.9559
ꢂ0.6408
ꢂ1.7466
ꢂ0.7062
ꢂ0.0618
ꢂ1.8258
ꢂ0.6925
ꢂ0.9513
ꢂ0.6382
ꢂ1.7474
ꢂ0.7062
ꢂ0.0616
ꢂ1.8252
ꢂ0.6910
ꢂ0.9553
ꢂ0.6429
ꢂ1.7458
ꢂ0.7058
ꢂ0.0622
ꢂ1.8269
ꢂ0.6941
ꢂ0.9562
ꢂ0.6527
ꢂ1.7413
ꢂ0.7048
ꢂ0.0639
ꢂ1.8290
ꢂ0.7002
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AO17
O17ꢃ ꢃ ꢃH15
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AO17
O17ꢃ ꢃ ꢃH15
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
ꢂ0.8954
ꢂ0.6271
ꢂ1.3416
ꢂ0.0359
ꢂ0.8059
ꢂ0.9052
ꢂ0.6256
ꢂ1.3465
ꢂ0.0361
ꢂ0.8076
ꢂ0.8659
ꢂ0.6382
ꢂ1.1636
ꢂ0.0310
ꢂ0.6790
ꢂ0.4968
ꢂ0.8056
ꢂ0.8645
ꢂ0.6384
ꢂ1.1633
ꢂ0.0309
ꢂ0.6789
ꢂ0.4960
ꢂ0.8014
ꢂ0.8616
ꢂ0.6390
ꢂ1.1624
ꢂ0.0308
ꢂ0.6789
ꢂ0.4948
ꢂ0.8058
ꢂ0.8670
ꢂ0.6379
ꢂ1.1634
ꢂ0.0310
ꢂ0.6790
ꢂ0.4973
ꢂ0.8011
ꢂ0.8788
ꢂ0.6353
ꢂ1.1649
ꢂ0.0316
ꢂ0.6787
ꢂ0.5022
C
16AO17
O17ꢃ ꢃ ꢃH15
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AO17
O17ꢃ ꢃ ꢃH15
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AN17
N17ꢃ ꢃ ꢃH15
H
N
18AO18
17AO18
7
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AN17
N17ꢃ ꢃ ꢃH15
H
N
18AO18
17AO18
8
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AN17
N17ꢃ ꢃ ꢃH15
H
N
18AO18
17AO18
ꢂ0.6059
ꢂ0.3013
ꢂ0.5328
ꢂ0.4766
ꢂ0.5638
ꢂ0.6483
ꢂ0.0031
ꢂ0.6062
0.3032
ꢂ0.5300
ꢂ0.4815
ꢂ0.5615
ꢂ0.6485
0.0021
9
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AN17
N17ꢃ ꢃ ꢃH15
H
N
18AO18
17AO18
10
N7AN8
C2ꢃ ꢃ ꢃO15
O15ꢃ ꢃ ꢃH15
C
16AN17
N17ꢃ ꢃ ꢃH15
H
N
18AO18
17AO18
ꢂ0.6063
ꢂ0.3067
The energetic properties of BCP associated with the intramolec-
ular hydrogen bonding also provide valuable information about the
characteristics of this interaction. Kinetic energy density G, is al-
[42,43]. H value is almost null pointing again to strong hydrogen
bond. As a rule the larger the G values, the stronger the interaction
and thus a strong intramolecular hydrogen bond may be inferred
from the values reported in Table 7. The critical point found in
the intramolecular hydrogen bond has two negative (k1 and k2)
and one positive eigen values (k3). The relationship between the
negative and positive curvatures |k1|/k3 is less than 1.0, as it gener-
ally occurs in an hydrogen bond interaction [37].
ways positive and its ratio to electron density (G/qBCP) may be used
to define the character of the interaction. This ratio may be larger
than 1.0 for closed shell (hydrogen bonding, ionic bonds and van
der Waals interaction) and less than 1.0 for shared interactions
(covalent bonds) [35]. The ratio G/qBCP reported in Table 7 is lower
than 1.0 for the intramolecular hydrogen bonding, although for
closed shell interactions as these ones should be larger than 1.0.
Nevertheless values slightly lower than 1.0 have been reported
for remarkably strong hydrogen bonding in other compounds
3.4.4. Dipole moments and polarizabilities
The dipole moments, polarizabilities and first order polarizabil-
ities were also calculated by finite field approach using the basis

A. Manimekalai, R. Balachander / Journal of Molecular Structure 1027 (2012) 175–185
185
Table 8
Dipole moment
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l
(D), polarizability
(
atot ꢁ 1023 esu) and hyperpolarizability
(btot ꢁ 1033 esu) for oximes 6–10 and their parent aldehydes 1–5.
Compds.
Dipole moment
Polarizability
Hyperpolarizability
6
7
8
9
10
1
2
3
4
5
1.26
1.13
2.66
2.18
7.06
2.76
3.51
4.57
1.47
3.46
30.448
33.222
34.766
31.800
35.549
27.853
30.614
32.218
28.217
32.471
22340.68
16377.74
1502.71
16109.50
89263.27
13141.49
6598.80
9710.80
7011.95
65781.88
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Acknowledgement
The authors thank the NMR Research Centre, Indian Institute of
Science, Bangalore for recording the NMR spectra.
Appendix A. Supplementary material
IR, 1H and 13C NMR spectra (Figs. S1–S3) for the oxime 6 are
provided. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
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