Synthesis, conformational and theoretical studies of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes

Article abstract of DOI:10.1016/j.molstruc.2015.10.006

1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3 were synthesis and characterized by FT-IR, UV-Vis, ¹H, ¹³C NMR and mass spectral studies. The stable conformations of 1-3 were predicted theoretically and selected geometrical parameters were derived from optimized structures. The molecular parameters of HOMO-LUMO energies, polarizability, hyperpolarizability, natural bond orbital (NBO), atom in molecule (AIM) analysis and molecular electrostatic potential (MEP) surfaces were determined by the density functional theory (DFT) method and analysed.

Full text of DOI:10.1016/j.molstruc.2015.10.006

Journal of Molecular Structure 1104 (2016) 70e78
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, conformational and theoretical studies of
1,n-di(2-formyl-4-phenylazophenoxy)alkanes
,
R. Balachander a *, A. Manimekalai b
a Department of Chemistry, Periyar Arts College, Cuddalore 607 001, Tamilnadu, India
b Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)
benzene 3 were synthesis and characterized by FT-IR, UVeVis, 1H, 13C NMR and mass spectral studies.
The stable conformations of 1e3 were predicted theoretically and selected geometrical parameters were
derived from optimized structures. The molecular parameters of HOMO-LUMO energies, polarizability,
hyperpolarizability, natural bond orbital (NBO), atom in molecule (AIM) analysis and molecular elec-
trostatic potential (MEP) surfaces were determined by the density functional theory (DFT) method and
analysed.
Received 13 June 2015
Received in revised form
11 August 2015
Accepted 9 October 2015
Available online xxx
Keywords:
Synthesis
© 2015 Published by Elsevier B.V.
Computational
Conformational
1,n-di(2-formyl-4-phenylazophenoxy)
alkanes
1. Introduction
extensively reported in the literature [13,14]. Azo ligands are most
important objects of the modern coordination chemistry [15e18].
Azobenzene dyes have long been investigated because of their
interesting cis-trans photoisomerization phenomena [1e4]. The
dynamics of cis-trans photoisomerization and configuration of
azochromophores has been the target of many studies [5,6].
Azoaromatic derivatives cover a wide variety of compounds which
main structural characteristic is the presence of an azo group (eN]
Ne) connecting two phenyl rings (PheN]NePh). The attachment
of electron donor and/or acceptor groups in different positions of
the phenyl rings can shift the absorption and emission bands of
these compounds to the visible region. This effect is highly
dependent on the solvent [7e10]. Azo compounds can be affected
by the solvent properties and temperature changes [11]. Bearing in
mind that the trans isomer is the most stable conformation in the
absence of steric hindrance, the temperature dependence suggests
that torsional changes in the azoaromatic compound structure af-
fects their electronic delocalization, thus, their optical properties.
The oxidation-reduction behaviour of these compounds play an
important role in their biological activity [12]. The pharmaceutical
importance of compounds containing an arylazo group have been
The preparation of new ligands is perhaps the most important step
in the development of metal complexes with unique properties and
novel reactivity [19]. The second order NLO organic materials are
typically based on NLO chromophores that can be incorporated in
polymer [20e24] or hybrid organic-inorganic [24,25] or in cross
linked system [26]. The dendritic approach, in which the chromo-
phore is functionalized with branched bulky groups to hinder its
tendency to crystallize has also been largely employed in the recent
years [27,28]. In all these approaches the choice of the proper
chromophore plays
a fundamental role: high NLO activity,
expressed as the value first order molecular hyperpolarizability
b,
along with a fair good photo- and thermal stability and a good
solubility are required molecular. Typically, second order NLO
chromophores are constituted by an electron acceptor moiety
linked to an electron donor group through a conjugation bridge
that allows a charge transfer of p-electrons. Both the strength of the
electron donor and acceptor groups and the nature of the conju-
gation bridge are important parameters in defining the activity of
the chromophore.
Recently, we have synthesized and determined the conforma-
tions of some arylazosalicylaldehyde and their oximes by theoret-
ical methods and spectral studies [29]. These aldehydes can be used
as starting materials to synthesize of some dialdehydes, which in
* Corresponding author.
E-mail address: svrbalu@gmail.com (R. Balachander).
http://dx.doi.org/10.1016/j.molstruc.2015.10.006
0022-2860/© 2015 Published by Elsevier B.V.

R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
71
Table 1
Physical and mass spectral values of 1e3.
Compds.
Physical
Colour
Mass (m/z)
Yield (%)
m.p. (ꢀC)
1
2
3
Yellowish orange
Yellowish orange
Yellow
66
52
40
194e195
220e221
240e241
478.0 [M], 448.1 [Mꢁ1], 418.3 [Mꢁ2]
506.0 [M], 475.3 [Mꢁ2], 446.7 [Mꢁ1]
554.1 [M], 524.2 [Mꢁ1], 494.3 [Mꢁ2], 331.2 [Mþ1]
turn can be used as colourimetric receptor for some ions. Further
these dialdehydes can be used to synthesize several coordination
complexes, fused macrocycles, oxazolidines, pyrimidines and so on.
In continuation of this work, some 1,n-di(2-formyl-4-
phenylazophenoxy)alkanes 1e3 were synthesized and character-
ized in the present study, and their conformations have been pre-
dicted from theoretical studies. Selected geometrical properties,
NBO, AIM analysis, HOMO-LUMO, MEP surface, dipole moment,
polarizability and first order hyperpolarizability were determined
by the density functional theory (DFT) method and analysed.
2. Experimental
2.1. Synthesis of 5-arylazosalicylaldehyde
5-Arylazosalicylaldehyde was prepared following the procedure
mentioned in the literature [30]. A mixture of aniline (z0.93 g,
1 mmol), water (15 mL) and 5 N HCl (10 mL) was cooled to 0e5 ꢀC
and to this a solution of sodium nitrite (0.69 g, 1 mmol) in water
was added. The mixture was stirred for 30 min in an ice bath.
Diazonium salt was obtained and this was added in drop wise to an
ice-cold solution of salicylaldehyde (1 mL, 1 mmol) and 10% sodium
hydroxide (10 mL) for 1 h with constant stirring. The solid mass
separated out was removed by filtration, dried and recrystallized
from ethanol.
Table 2
IR spectral values (cmꢁ1) of 1e3.
Assignments
1
2
3
2.2. Synthesis of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes 1
and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3
naromatic(CeH)
3063
1686
1569
1480
1248
1092
817
3041
1683
1593
1485
1253
1090
824
3063
1687
1594
1483
1255
1092
822
nC
nC
]
]
O
C
A mixture of 5-arylazosalicylaldehyde (0.46 g, 2 mmol), alkyl-
dibromides (1 mmol) [1,2-dibromoethane (0.12 mL), 1,4-
dibromobutane (0.11 mL) and m-dibromoxylene (0.26 g)] and po-
tassium carbonate (0.5 g) in acetonitrile (15 mL) was refluxed for
24 h. The reaction mixture was filtered and the solvent was evap-
orated to obtain 1,n-di(2-formyl-4-phenylazophenoxy)alkanes 1
and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3.
nN
]
N
nCeO
Aromatic CH out-of-plane bending vibration
764
686
770
686
770
689
Fig. 1. IR spectrum of 1.

72
R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
Scheme 1. Steps involved in the synthesis of 1e3.
The pure product was obtained by recrystallization from ethanol.
The physical and mass spectral data of all the synthesized com-
pounds 1e3 are displayed in Table 1. The mass spectrum of 2 is
given in Fig. S1.
Avatar-330 FT-IR spectrophotometer was used for recording IR
spectra (KBr pellet). The mass spectra were performed using JEOL
Gcmate spectrometer. The UVevisible spectra were recorded in
Shimadzu UV-1800 UVevisiblespectrophotometer using N,N-
dimethylformamide as solvent at ambient room temperature.
2.3. Spectral measurements
2.4. Computational study
The 1H (500 MHz) and 13C NMR (125 MHz) were recorded at
room temperature on Bruker 500 MHz instrument using 10 mm
sample tube. Samples were prepared by dissolving about 10 mg of
the sample in 2.5 mL of chloroform-d containing 1% TMS for 1H and
50 mg of the sample in 2.5 mL of chloroform-d containing a few
drops of TMS for 13C. The solvent chloroform-d also provided the
internal field frequency lock signal. The 1He1H and 1He13C COSY
spectra were performed on a Bruker 500 NMR spectrometer.
Geometry optimizations were carried out according to density
functional theory available in Gaussian-03 package using B3LYP/6-
31G(d,p) basis set [31] available in Gaussian-03 package. The po-
larizabilities and hyperpolarizabilities were determined from the
DFT optimized structure by finite field approach using B3LYP/6-
31G* basis set, NBO calculations using the basis set B3LYP/6-
311þG(d,p) available in Gaussian-03 and AIM calculations were
Fig. 2. 1H NMR spectrum of 1.

R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
73
Fig. 3. 13C NMR spectrum of 1.
done using B3LYP/6-31G(d,p) basis set.
3. Results and discussion
3.1. FT-IR spectra
The sharp peaks around 1680 cmꢁ1 in the FT-IR spectra of 1e3
O of aldehydic group. Strong peaks for eN]Ne (azo)
are due to nC
]
group are observed in the region 1250 cmꢁ1. The aromatic and
aliphatic CeH stretching vibration appeared around 3060 and
2870 cmꢁ1, respectively. The peaks around 1090 cmꢁ1 are attrib-
uted to aliphatic nCeO mode. The FT-IR spectral data of 1e3 are
listed in Table 2 and FT-IR spectrum of 1 as shown in Fig. 1.
3.2. NMR spectra
1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-
di(2-formyl-4-phenylazophenoxymethyl)benzene
3
were
Fig. 4. Possible conformations of 1e3.
Table 3
1H Chemical shifts (ppm) of 1e3.
Compds. H-3
H-5
H-6
H-10 and H-14 H-11 and H-13 H-12
H-16
H-18 and H-180 H-19 and H-190 H-20 H-21 and H-22
1
2
3
8.46 (d, 2.50) 8.20 (dd, 2.50, 8.50) 7.22 (d, 8.50) 7.92 (d, 7.50) 7.52 (t)
8.46 (d, 2.50) 8.19 (dd, 2.75, 8.75) 7.17 (d, 8.50) 7.93 (d, 7.00) 7.54 (t)
8.48 (d, 2.50) 8.18 (dd, 2.75, 8.75) 7.21(d, 9.00) 7.93 (d, 8.25) 7.49e7.55
7.49 (t)
7.50 (t)
7.49e7.55 10.63 (s) 5.36 (s)
10.53 (s) 4.67 (s)
10.58 (s) 4.34 (t)
e
e
e
e
e
2.21 (t)
e
7.60 7.49e7.55
Values within parentheses are the observed coupling constants in Hz.
Table 4
13C Chemical shifts (ppm) of 1e3.
Compds. C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(9)
C(10) and C(14) C(11) and C(13) C(12)
C(16)
C(18) C(19)
C(20)
C(21)
C(22)
1
2
3
162.03 125.47 123.93 147.02 129.84 113.02 152.42 122.88
162.68 125.11 123.89 146.54 129.97 112.81 152.46 122.83
162.34 125.44 123.91 146.76 129.82 113.41 152.44 122.85
129.13
129.12
129.13
131.14 188.71 67.26
131.01 189.05 68.46 25.91
131.07 189.14 70.66 136.39 126.13 127.43 129.46
e
e
e
e
e
e
e

74
R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
synthesized as shown in Scheme 1 and characterized by 1H, 13C
NMR, 1He1H and 1He13C COSY spectra. The labelling of the atoms
followed in the present study was indicated in Scheme 1. The sig-
nals in the 1H NMR spectrum were assigned based on their posi-
tions, integrals and multiplicities. The 500 MHz NMR spectrum of 1
(Fig. 2) reveals a sharp singlet at 4.67 ppm for the methylene pro-
tons attached to oxygen atom O(15) i.e., H(18) and H(180). The low
frequency doublet centered at 7.22 ppm is assigned to the ortho
proton with respect to OCH2 moiety i.e., H(6). The doublet centered
at 8.46 ppm (integral corresponds to two protons) and doublet of
doublet centered at 8.20 ppm (integral corresponds to two protons)
are assigned to the ring protons H(3) and H(5), respectively [32].
The doublet nature of the signal for H(3) (J ¼ 2.50 Hz) is due to meta
coupling with respect to OCH2 moiety and another coupling is also
observed in the signal of H(5) (J ¼ 2.50, 8.50 Hz), which appeared as
doublet of doublet due to 4J3,5 coupling of H(5). The NMR spectrum
further reveals high frequency doublet at 7.92 ppm for the ortho
protons of the phenyl ring attached to the nitrogen atom N(8) i.e.,
H(10) and H(14). Two triplets at 7.52 (integral corresponds to four
protons) and 7.49 ppm (integral corresponds to two protons) are
also observed for meta [H(11) and H(13)] and para [H(12)] protons,
respectively of the phenyl ring attached to nitrogen atom N(8). The
high frequency singlet at 10.53 ppm is assigned to aldehydic proton
H(16). This assignment is further confirmed by the correlation
Fig. 5. Optimized structures of 1e3.

R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
75
observed in the 1He1H COSY spectrum (Fig. S2). In a similar manner
assignments were done for other compounds 2 and 3.
which is attached to the nitrogen atom N(8). The remaining signals
at 131.14, 129.84 and 123.93 ppm are assigned to the carbons C(12),
C(5) and C(3), respectively. This assignment is based on correlations
observed in the 1He13C COSY spectrum (Fig. S3). In a similar
manner assignments were done for other compounds 2 and 3. The
1H and 13C chemical shifts obtained in this manner are listed in
Tables 3 and 4, respectively.
In 13C NMR spectra at 125 MHz have been recorded in CDCl3 for
1e3. The assignment of signals in 1 is made as follows (Fig. 3). The
low frequency signal at 67.26 ppm is due to the methylene carbon
attached to oxygen atom O(15) i.e., C(18). The high frequency signal
at 188.71 ppm is due to aldehydic carbon C(16). The signal at
113.02 ppm is due to ortho carbon with respect to oxygen atom
O(15) i.e., C(6). The high intense signals at 122.88 and 129.13 ppm
are due to ortho [C(10) and C(14)] and meta [C(11) and C(13)] car-
bons of the phenyl ring attached to nitrogen atom N(8). The 13C
NMR spectrum reveals four signals for quaternary carbons C(1),
C(2), C(4) and C(9) at 162.03, 125.47, 147.02 and 152.42 ppm, which
can easily be distinguished from other carbons based on small in-
tensities. Among the signals for quaternary carbons, the high fre-
quency signal at 162.03 ppm is assigned to the ipso carbon C(1) and
this assignment is based on the high deshielding nature of the
oxygen atom compared to nitrogen and carbon atoms. The signal at
125.47 ppm is assigned to the ipso carbon C(2), since it is ortho with
respect to oxygen atom O(15). Among the remaining signals at
152.42 and 147.02 ppm, the signal at 147.02 ppm is assigned to the
carbon C(4) which is para with respect to the OCH2 moiety. Obvi-
ously, the signal at 152.42 ppm is assigned to the ipso carbon C(9)
3.3. UVevis absorption spectra
UVeVis absorption spectra are recorded for 1e3 in dime-
thylformamide in the region 260e400 nm. The maximum ab-
sorption bands exhibit of 328.5, 335.0 and 339.5 nm for the
dialdehydes 1e3, respectively. All the absorption bands are due to
the
pep* transition of the eN]Ne unit. The higher lmax is
observed for 3, when compared to other 1 and 2 due to the pres-
ence of m-xylene moiety linked between two arylazosalicylalde-
hyde moiety. The UVeVis absorption spectra of 1e3 are shown in
Fig. S4.
3.4. Conformational analysis
The presence of only one set of signals for phenyl-
azosalicylaldehyde moiety and methylene moiety indicates that the
dialdehydes are symmetric molecules. Therefore there are two
possible conformations for 1e3. In conformation A the two alde-
hydic moieties (CH]O groups) are opposite to each other whereas
in conformation B the two aldehydic moieties are [CH]O group] on
the same side (Fig. 4). The possibility of existing in conformation B
is ruled out since severe steric crowding exists between the two
aldehydic moieties. Therefore, the dialdehydes exist in conforma-
tion A only. In order to confirm this, geometry optimizations were
done for both the possibilities for 1. The energies are found to
be ꢁ1600.0535 and ꢁ1600.0429 Hartree for conformations A and B,
Table 5
Selected geometric parameters [bond lengths (Å), bond angles (ꢀ) and torsional
angles (ꢀ)] of 1e3.
Geometric parameters
1
2
3
Bond length
C1eC2
C2eC3
C2eC16
C1eC6
C1eO15
C4eN7
O15eC18
N7eN8
C16eO17
C16eH16
N8eC9
C18eC180
C18eC19
C19eC190
Bond angle
C1eC2eC3
1.41
1.40
1.48
1.41
1.36
1.42
1.42
1.26
1.22
1.11
1.42
1.52
e
1.42
1.40
1.48
1.41
1.36
1.42
1.43
1.26
1.22
1.05
1.42
e
1.42
1.40
1.48
1.41
1.38
1.42
1.47
1.28
1.25
1.10
1.42
e
Table 6
HOMO-LUMO energies (eV) and dipole moment m(D) of 1e3.
Compds.
HOMO
LUMO
D
E
Dipole moment
1.52
1.53
1.51
e
1
2
3
ꢁ6.196
ꢁ6.123
ꢁ6.096
ꢁ2.399
ꢁ2.318
ꢁ2.469
3.797
3.085
3.627
1.01
1.09
7.08
e
119.0
121.9
120.0
116.5
123.5
119.5
123.4
115.7
120.9
105.9
e
119.1
121.7
119.7
116.5
123.7
119.7
123.4
115.7
120.9
107.3
112.0
118.9
121.4
120.3
116.2
123.6
119.9
123.3
116.3
120.5
108.0
e
C1eC2eC16
C2eC1eC6
C2eC1eO15
C6eC1eO15
Table 7
Polarizabilities and hyperpolarizabilities for 1e3.
C1eO15eC18
C2eC16eO17
C2eC16eH16
O17eC16eH16
O15eC18eC19/O15eC18eC180
C18eC19eC190
Torsional angle
C3eC2eC1eO15
C16eC2eC1eC6
C1eC2eC16eO17
C1eC2eC16eH16
C3eC2eC16eO17
C3eC2eC16eH16
O15eC1eC6eC5
C6eC1eO15eC18
C3eC4eN7eN8
C1eO15eC18eC19
N7eN8eC9eC10
O15eC18eC19eC20
O15eC18eC19eC21
O15eC18eC19eC190
O15eC18eC180eO150
1
2
3
axx
axy
ayy
axz
ayz
azz
776.458
ꢁ78.092
370.784
ꢁ0.011
0.002
118.487
421.910
62.527
ꢁ3.823
ꢁ2.038
7.961
798.067
93.064
397.808
ꢁ0.008
0.011
135.876
443.917
65.788
2.820
782.773
ꢁ37.324
435.432
46.610
14.290
ꢁ180.0
ꢁ180.0
ꢁ180.0
0.0
180.0
180.0
180.0
ꢁ0.0
0.0
ꢁ179.6
ꢁ179.6
ꢁ178.7
1.4
252.026
490.077
72.629
ꢁ173.595
ꢁ1979.258
194.219
ꢁ199.901
50.035
ꢁ67.127
125.441
23.573
125.497
171.366
1690.415
14604.005
<
a
> (a.u)
atot
1024
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
ꢂ
0.0
1.3
ꢁ9.781
ꢁ180.0
180.0
ꢁ0.0
ꢁ180.0
ꢁ180.0
0.0
ꢁ180.0
ꢁ180.0
0.1
179.9
179.8
ꢁ0.1
e
ꢁ178.6
179.7
ꢁ1.8
179.9
ꢁ179.0
ꢁ0.2
47.0
14.060
ꢁ0.345
ꢁ18.074
ꢁ15.182
ꢁ7.451
2.525
ꢁ0.985
ꢁ2.455
ꢁ0.879
36.805
317.967
4.596
2.581
ꢁ1.546
ꢁ1.775
2.231
e
e
e
ꢁ134.7
ꢁ4.902
e
180.0
e
e
btot (a.u)
1033
btot (esu)
9.034
ꢁ180.0
e
ꢂ
78.044

76
R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
respectively. From the values the favoured conformation is pre-
dicted to be A for 1. The other dialdehydes also exist in conforma-
tion A only. The optimized structures of favoured conformations are
displayed in Fig. 5.
C(19)eC(190) are found to be ꢁ180.0ꢀ and 180.0ꢀ, respectively.
3.6. Energies, dipole moments and polarizabilities
HOMO-LUMO energies, dipole moments, polarizability and first
order hyperpolarizability for the dialdehydes 1e3 were calculated
and the values are listed in Tables 6 and 7. HOMO-LUMO pictures
are reproduced in Fig. 6. From Table 6 it is seen that the energies of
both HOMO and LUMO orbitals are increased as the number of
carbon atoms in the side chain increased but the energy gap
decreased. The order of dipole moments are 3 > 2 > 1.
HOMO orbitals are mainly derived from pz orbitals of carbon
nitrogen and oxygen atoms except pz orbitals of aldehydic carbon
C(16), pz orbital of alkoxy carbons (CH2)n in dialdehydes 1 and 2. In
3, the pz orbitals of one of the 2-formyl-4-phenylazo-
3.5. Molecular properties
3.5.1. Geometric parameters
From the optimized structures of geometric parameters were
derived in Table 5. The observed torsional angles O(15)eC(18)e
C(19)eC(20) [47.0ꢀ] and O(15)eC(18)eC(19)eC(21) [e134.7ꢀ]
in dialdehyde 3 indicate that the phenyl ring of xylene moiety
is
highly
distorted
from
the
plane
containing
4-
phenylazobenzaldehydic moiety. In dialdehydes 1 and 2, the
torsional angles O(15)eC18eC(180)eO(150) and O(15)eC(18)e
Fig. 6. HOMO-LUMO pictures of 1e3.

R. Balachander, A. Manimekalai / Journal of Molecular Structure 1104 (2016) 70e78
77
phenoxymethyl moiety and pz orbitals of central benzene ring are
not taking part in the formation HOMO orbitals. LUMO orbitals are
derived from pz orbitals of carbon, nitrogen and oxygen atoms
except pz orbitals of C(6), C(11), C(13) and pz orbital of alkoxy car-
bons in 1 and 2. In 3 the pz orbitals of one of the 2-formyl-4-
phenylazophenoxymethyl moiety, pz orbitals of central benzene
ring and pz orbitals of C(6), C(11) and C(13) are not taking part in
the formation LUMO orbitals.
The polarizabilities and first-order polarizabilities were also
calculated by DFT method using the basis set B3LYP/6-31G* avail-
able in Gaussian-03 package and these values are listed in Table 7.
Increase in the number of carbon atoms in the side chain increased
both the polarizabilities and hyperpolarizabilities. The NLO char-
acter decreases according to the following order: 3 > 2 > 1.
orbital with the antibonding orbitals of vicinal C(2)eC(3), N(7)e
N(8) and C(6)eC(5) bonds are found to be very high (z78, 63,
74 kcal molꢁ1) and this is the primary delocalization in dialdehydes
1e3.
3.8. AIM analysis
Atoms in molecules electron density topological analysis carried
out for aldehyde 1 revealed the existence of 56 bond critical points
(BCPs) with a (3, ꢁ1) topology between the atoms connected by
covalent bond (Table S2). The negative values obtained for the
Laplacian are clear indication that the electronic charge is locally
concentrated within the region of inter atoms leading to an inter-
action named as covalent bonds and being characterized by large rb
values. Besides these one more bond critical point is observed be-
tween the atoms C(16) and O(17) (aldehyde carbonyl group). The
value of rBCP at the BCP is found to be 0.402 and V2rBCP value is
found to be 0.279 (C16eO17). The positive magnitude of V2rBCP
indicates the highly ionic nature of carbonyl group in aldehyde 1. In
other aldehydes 2 and 2 also ionic nature of carbonyl (C16eO17)
group (Table S2) is confirmed by the positive Laplacian density at
bond critical point and high rBCP values. Ring critical point (RCP) of
phenyl ring attached to N(8) [(C9eC10eC11eC12eC13eC14)] is
slightly having higher electron density compared to the phenyl ring
of the benzaldehyde moiety [C1eC2eC3eC4eC5eC6].
3.7. NBO analysis
NBO analysis at B3LYP/6-311þG(d,p) level were carried out for
the dialdehydes 1e3 and the important second-order perturbative
estimates of donoreacceptor interactions are displayed in Table S1.
The p-bonded electrons of C(2)eC(3) and C(6)eC(5) bonds in 1e3
are delocalized on to the non-bonding p-orbitals available on C(4)
carbon atom, which in turn delocalized on to the nearby anti-
bonding orbitals of the vicinal C(2)eC(3), N(7)eN(8) and C(6)eC(5)
bonds. The hyperconjugative interaction energies involving C(4) p-
3.9. MEP surfaces
Three-dimensional distribution of molecular electrostatic po-
tential (MEP) is highly useful in predicting the reactive behaviour of
the molecule. The MEP surface has been plotted for aldehydes and
representative diagram is given in Fig. 7. Region of negative charge
(red colour (in the web version)) is seen around the electronegative
oxygen O(17) and O(170) in dialdehydes 1e3. The red colour region
is susceptible for electrophilic attack. Blue colour represents
strongly positive region and the predominant green region in the
MEP surfaces corresponds to a potential half way between the two
extreme [red and blue] regions in aldehydes 1e3.
4. Conclusions
Structure of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes
1
and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3
were analysed by 1D, 2D NMR and mass spectral studies. The stable
conformation of 1e3 were predicted theoretically and molecular
parameters of HOMO-LUMO energies, polarizabilities, hyper-
polarizabilities, NBO and AIM analysis were calculated using
Gaussian-03 package.
Acknowledgement
The authors thank the NMR Research Centre, Indian Institute of
Technology, Madras, for recording the NMR spectra.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2015.10.006.
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