Synthesis and structural and vibrational analysis of (5,7-dichloro- quinolin-8-yloxy) acetic acid

Article abstract of DOI:10.1016/j.molstruc.2012.03.013

We have prepared the (5,7-dichloro-quinolin-8-yloxy) acetic acid and characterized it by infrared and Raman spectroscopies in the solid phase and by nuclear magnetic resonance (NMR) spectroscopy in a CDCl₃ solution. The density functional theory (DFT) together with the 6-31G and 6-311++G basis sets were used to study its structure and vibrational properties. Two stable conformations of the compound were theoretically determined in the gas phase and probably these conformations are present in the solid phase. The harmonic vibrational wavenumbers for the optimized geometries were calculated at the same theory levels. For a complete assignment of all the observed bands in the vibrational spectra the DFT calculations were combined with Pulay's scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental ones. The force constants for the (5,7-dichloro-quinolin-8-yloxy) acetic acid were calculated and compared with those obtained for the (5-chloro-quinolin-8-yloxy) acetic acid and 2-(quinolin-8-yloxy)-acetic acid compounds. Furthermore, the characteristics of the electronic delocalization, the topological properties of the electronic charge density together with the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps were studied.

Full text of DOI:10.1016/j.molstruc.2012.03.013

Journal of Molecular Structure 1018 (2012) 149–155
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and structural and vibrational analysis of (5,7-dichloro-quinolin-8-yloxy)
acetic acid
Elida Romano a, María V. Castillo a, Jorgelina L. Pergomet b, Juan Zinczuk b,1, Silvia A. Brandán a,
⇑
a Cátedra de Química General, Instituto de Química Inorgánica, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Ayacucho 471, 4000 San Miguel de
Tucumán, Tucumán, Argentina
b Instituto de Química Rosario (CONICET-UNR), Facultad de Ciencias Bioquímicas y Farmacéuticas, Suipacha 531, 2000 Rosario, Santa Fé, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
We have prepared the (5,7-dichloro-quinolin-8-yloxy) acetic acid and characterized it by infrared and
Raman spectroscopies in the solid phase and by nuclear magnetic resonance (NMR) spectroscopy in a
CDCl3 solution. The density functional theory (DFT) together with the 6-31Gꢀ and 6-311++Gꢀꢀ basis sets
were used to study its structure and vibrational properties. Two stable conformations of the compound
were theoretically determined in the gas phase and probably these conformations are present in the solid
phase. The harmonic vibrational wavenumbers for the optimized geometries were calculated at the same
theory levels. For a complete assignment of all the observed bands in the vibrational spectra the DFT cal-
culations were combined with Pulay’s scaled quantum mechanical force field (SQMFF) methodology in
order to fit the theoretical wavenumber values to the experimental ones. The force constants for the
(5,7-dichloro-quinolin-8-yloxy) acetic acid were calculated and compared with those obtained for the
(5-chloro-quinolin-8-yloxy) acetic acid and 2-(quinolin-8-yloxy)-acetic acid compounds. Furthermore,
the characteristics of the electronic delocalization, the topological properties of the electronic charge den-
sity together with the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital
(LUMO) energy gaps were studied.
Received 22 November 2011
Received in revised form 6 March 2012
Accepted 7 March 2012
Available online 20 March 2012
Keywords:
(5,7-Dichloro-quinolin-8-yloxy) acetic acid
Vibrational spectra
Molecular structure
Force field
DFT calculations
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
and 6-311++Gꢀꢀ basis sets accomplished by means of the SQMFF
methodology [7–9] in order to fit the theoretical wavenumber val-
The syntheses of heterocyclic compounds containing the (quin-
olin-8-yloxy) moiety have been object of numerous studies for the
last few years because they exhibit a wide range of biological prop-
erties [1–4]. Recently, a complete vibrational analysis of all ob-
served bands in the vibrational spectra of 2-(quinolin-8-yloxy)
[5] and (5-chloro-quinolin-8-yloxy) acetic acids [6] were studied
by means of the DFT calculations combined with Pulay’s scaled
quantum mechanical force field (SQMFF) methodology [7–9]. In
both studies, the normal mode calculations were accomplished
by using a generalized valence force field (GVFF) [8,9] and by
considering three different structures for each compound. The
presence of the chloro atom in the structure of (5-chloro-quino-
lin-8-yloxy) acetic acid decreases the dipole moment value of the
most stable structure in relation to the 2-(quinolin-8-yloxy)-acetic
acid and, accordingly, their properties are slightly different. In this
case, we carried out a structural, experimental and theoretical
vibrational study of (5,7-dichloro-quinolin-8-yloxy) acetic acid
(DQA) based on B3LYP theoretical calculations by using 6-31Gꢀ
ues to the experimental ones. In this work, the compound was syn-
thesized and characterized by infrared and Raman spectroscopies
in the solid phase and also by NMR spectroscopy for diluted solu-
tions in CDCl3. On the other hand, as the crystal and molecular
structure of DQA were not previously determined and in order to
carry out a complete assignment of all the observed bands in the
vibrational spectra, the optimized geometries and the correspond-
ing frequencies for the normal modes of vibration were calculated
by taking into account two different stable structures of DQA. In
order to obtain the corresponding force fields for those structures,
Rauhut and Pulay [9] transferable scaling factors were used while
the harmonic force constants were subsequently scaled to repro-
duce as much as possible the experimental frequencies. Thus, a
complete assignment of the compound in terms of the potential
energy distribution was performed and the force constants were
calculated and compared with those corresponding to the (quino-
lin-8-yloxy) [5] and (5-chloro-quinolin-8-yloxy) acetic acids [6]. In
addition, the nature of the different rings and bonds of the two
studied structures of DQA were analyzed by means of NBO studies
[10–12], while the topological properties of electronic charge den-
sity were determined by using Bader’s atoms in molecule theory
(AIM) [13,14].
⇑
Corresponding author. Tel.: +54 381 4247752; fax: +54 381 4248169.
E-mail address: sbrandan@fbqf.unt.edu.ar (S.A. Brandán).
1
Member of the Carrera de Investigador Científico, CONICET, Argentina.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.03.013

150
E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
structure of the 8-(Carboxymethoxy) quinolinium nitrate monohy-
2. Experimental methods
drate compound [15]. The atom structures and labelling for all con-
formers of DQA can be seen in Fig. 1. The electronic charge density
topological analysis for those structures and NBO calculations were
performed by using the AIM200 program package [14] and the NBO
3.1 [16] program, as implemented in the GAUSSIAN 03 package [17].
The natural internal coordinates for the compound were defined as
reported in the literature [5,6,18] and are listed in Table S1 (Sup-
porting material). The resulting force fields were transformed to
‘‘natural’’ internal coordinates by using the MOLVIB program
[19,20]. Then, following the SQMFF procedure [7–9,21], the har-
monic force fields only for the CI and CII structures were evaluated
at the B3LYP/6-31Gꢀ level because the CIII structure has an imagi-
nary frequency. The potential energy distribution components
(PED) higher than or equal to 10% were subsequently calculated
with the resulting SQMFF. Vibrational modes were analyzed by
using the GaussView program [22].
2.1. Synthesis of methyl [(5,7-dichloroquinolin-8-yl)oxy]acetate
A
mixture of 5,7-dichloro-8-hydroxyquinoline (2.14 g,
0.01 mol), potassium carbonate powder (2.76 g, 0.02 mol) and
methyl bromoacetate (1.84 g, 0.012 mol) in acetone(100 mL) was
heated at reflux monitored by TLC. After 4 h, the reaction was com-
pleted; the mixture was filtered and concentrated in vacuo. The
residue (2.67 g) was crystallized from isopropyl ether (120 mL) to
give (5,7-dichloroquinolin-8-yloxy) acetic acid methyl ester
(2.08 g, 73%) m.p. 128.5–129 °C.
2.2. Synthesis of (5,7-dichloroquinolin-8-yloxy) acetic acid
A
solution of methyl [(5,7-dichloroquinolin-8-yl)oxy]acetate
(1.01 g, 3.5 mmol) and LiOHꢁH2O (0.315 g, 7.5 mmol). in 10 mL of
dimethylsulfoxide was stirred and heated at 50 °C for 12 h. The
resulting white suspension was adjusted to pH 3 with 1 N HCl.
The precipitate was filtered, washed with water and ethanol and
dried to give (5,7-dichloroquinolin-8-yloxy) acetic acid (0.865 g,
91%) m.p. 221–222 °C.
4. Results and discussion
4.1. Geometry
1H NMR (300 MHz, CDCl3) d: 4.77 (2H, s, OACH2); 7.64 (1H dd
J = 4,28; J = 8,73 H3); 7.67 (1H, s, H6), 8,61 (1H dd J = 8,73;
J = 1,28, H4); 8.92 (1H dd J = 4,28; J = 1,28, H2).
A comparison of the total energies together with the corre-
sponding dipole moment values for all conformers of (5,7-dichlo-
roquinolin-8-yloxy) acetic acid is shown in Table 1. The CI energy
is lower than that of the other two conformers, as was observed
in the monochloro compound [6]. The potential energy difference
between the CI and CII forms, by using the B3LYP/6-31Gꢀ and
B3LYP/6-311++Gꢀꢀ methods are 45.64 and 38.56 kJ/mol, respec-
tively. These energy differences between both conformations are
lower than the ones of (5-chloro-quinolin-8-yloxy) acetic acid
[6]. In DQA, the presence of two Cl atoms probably indicates that
the largest dipole moment value stabilizes the molecule, in accor-
dance with the results obtained for other compounds [6,23,24].
Table 2 shows the geometrical parameters for the CI and CII struc-
tures of DQA. The stabilities of the two conformers of DQA were
investigated by using natural atomic charges [25–28] and the
results are given in Table S2. Notice that the natural charge values
(NPA) corresponding to the C21 atoms have higher positive values
in both structures, while the more negative values correspond to
the O23 atoms. Bond orders, expressed by Wiberg’s index for both
conformers of DQA are given in Table S3. C9 and C12 atoms in both
conformers have higher bond order values than the other ones
because both atoms are linked to the Cl atoms.
13C NMR (75 MHz, CDCl3) d: 70.85 (CH2); 123.42(C3);
125,24(C7); 125.24 (C5); 126.04 (C4a); 128.03 (C6); 133.67 (C4);
142.31 (C8a); 151.15(C2); 149.45(C8); 170.35 (CO2H) (atom num-
bering according to naphthalene).
Nuclear magnetic resonance (NMR) spectra were recorded for
dilute solutions in CDCl3 by using a Bruker 300 FT spectrometer
at 300 MHz for 1H and 75 MHz for 13C.
The infrared spectrum of the solid in KBr pellets from 4000 to
400 cmꢂ1 was recorded with an FTIR GX1 spectrophotometer,
equipped with a globar source and a DGTS detector at a resolution
of 1 cmꢂ1 and 64 scans. The Raman spectrum (resolution 4 cmꢂ1
,
200 scans) was recorded between 4000 and 0 cmꢂ1 with a Bruker
RF100/S spectrometer equipped with a Nd: YAG laser source (exci-
tation line 1064 nm, 150 mW power).
3. Computational details
The potential energy curves associated with rotation around the
O17AC18 bond, described by the C10AO17AC18AC21 dihedral an-
gle for the compound, were studied at the B3LYP/6-31Gꢀ and B3LYP/
6-311++Gꢀꢀ levels. The results show two stable conformations,
namely, CI and CII, according to the OH group position in relation
to the N atom of the quinoline ring. Besides, another plane structure
was also considered (CIII) in accordance with the experimental
4.2. NMR
Table 3 shows the 1H NMR and 13C NMR shifts of DQA in deuter-
ated chloroform. Five signals corresponding to five different H
Fig. 1. Theoretical structures and labelling of the atoms for the stable CI and CII conformers of (5,7-dichloro-quinolin-8-yloxy) acetic acid.

E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
151
Table 1
Calculated total energy (E) and dipolar moments for the structures of (5,7-dichloro-quinolin-8-yloxy) acetic acid at different theory levels.
(5,7-dichloro-quinolin-8-yloxy) acetic acid
Method
CI
CII
CIII
E1 (Hartrees)
l
(D)
E2 (Hartrees)
l
(D)
D
E = E1–E2 (kJ/mol)
EP (Hartrees)
l (D)
B3LYP/6-31Gꢀ
ꢂ1624.2030
ꢂ1624.4561
6.55
6.79
ꢂ1624.1856
ꢂ1624.4414
4.50
4.79
45.64
38.56
ꢂ1624.1856
ꢂ1624.4391
0.40
0.70
B3LYP/6-311++Gꢀꢀ
atoms can be seen in the spectrum. Peaks at 7.64, 8.61, and
8.92 ppm belong to three H atoms on 7, 8, and 11 positions of
the hetero ring, respectively, while the peak at 7.67 belongs to H
atom on position 15 of the carbocyclic ring. The peak belonging
to H atoms of the CH2 group appears at 4.77 ppm. These chemical
shift values are in agreement with those reported in the literature
[6]. A slight shift of these peaks towards lower fields implies the
existence of some intermolecular interaction between nonbonding
electrons. In the 13C NMR spectrum the peak at 170.35 ppm be-
longs to the C21 atom of the carboxy group and the peak at
70.85 ppm corresponds to the C18 atom of the methylene group.
The observed chemical shifts are in agreement with those reported
in the literature for the 13C NMR of (5-chloro-quinolin-8-yloxy)
acetic acid [6].
conformers of DQA. On the other hand, the LP(1)N16 ?
rꢀO23AH24 delocalization, possible only for the CI conformer
and that confers a high stability is calculated. The calculated total
energy values favor the CI conformer, whose structure, by using
both basis sets, is the most stable in the gas phase. In this way,
the stabilization energies justify the different stabilities between
both conformers.
4.4. AIM analysis
The two most stable structures of DQA were also analysed by
means of Bader’s charge electron density topological analysis
[13]. The calculated electron density (
»
q), and the Laplacian values,
2q(r) in the bond critical points (BCPs) and in the ring critical
points (RCPs) for those structures are shown in Table S6. The BCP
has the typical properties of the closed–shell interaction and for
4.3. NBO study
this reason, the value of
q(r) is relatively low, the relationship be-
tween |k1|/k3 and <1
»
2q(r) is positive, indicating that the interac-
The stability of the CI and CII structures of DQA was also inves-
tigated by means of NBO calculations [10–12]. Tables S4 and S5
show the second order perturbation energies E(2) (donor ? accep-
tor) that involve the most important delocalization for CI and CII
conformers of DQA, respectively. In this work, the contributions
tion is dominated by the charge contraction away from the
interatomic surface toward each nucleus. Notice that the results
are slightly dependent on the size basis set. Thus, the analysis
shows the same BCPs for the CI and CII structures by using both ba-
sis sets. These results, together with the NBO analysis, justify the CI
structure stability due to the presence of a short intramolecular
N16AH24 bond (1.872 Å by using 6-31Gꢀ basis set), as observed
in Table S6. Also, the topological properties are more significant
in this stable structure than CII. This study reveals that the H bonds
are different in both conformers. In CI, the H bond is between
N16AH24 while in CII between N16AH19.
of the stabilization energies for the dET
charge transfers are
r?r⁄
similar to those obtained for all conformers of the (5-chloro-quin-
olin-8-yloxy) acetic acid [6], while the LP(3)Cl14 ? rꢀC10AC12
delocalizations due to other Cl atom are observed for the two
Table 2
Calculated geometrical parameters for the two stable conformers of (5,7-dichloro-
quinolin-8-yloxy) acetic acid.
aB3LYP/6-31Gꢀ
CI
aB3LYP/6-311++Gꢀꢀ
CI CII
4.5. Vibrational analysis
Parameter
CII
In this study, in accordance with the NBO and AIM results, only
the CI and CII structures of DQA in the gas phase were considered.
Bond length (Å)
C3AC4
C4AN16
C5AN16
C4AC10
1.430
1.359
1.440
1.535
1.755
1.745
1.210
1.332
1.430
1.359
1.440
1.434
1.359
1.414
1.529
1.759
1.746
1.201
1.360
1.434
1.359
1.414
1.429
1.358
1.439
1.534
1.755
1.745
1.205
1.329
1.429
1.358
1.439
1.431
1.362
1.417
1.526
1.759
1.744
1.195
1.362
1.431
1.362
1.417
Table 3
Experimental chemical shifts (in ppm) for (5,7-chloro-quinolin-8-yloxy) acetic acid.
C9ACl6
C12ACl14
C10AO17
C18AO17
C18AC21
C21AO22
C21AO23
H atoms
d (ppm)
Integ. multiplicity (JHz)
1H NMR in CDCl3
11
7
8
15
8.92
7.64
8.61
7.67
4.77
1H dd (4,28; 1,28)
1H dd (4,28; 8,73)
1H dd (8,73; 1,28)
1H s
Bond angle (°)
C4AN16AC5
19, 20
2H s
118.8
118.7
118.4
122.8
119.1
111.8
117.2
119.5
123.3
118.9
118.4
125.1
116.3
123.6
113.3
114.0
124.9
121.1
118.9
118.9
118.5
123.9
117.3
122.3
113.5
113.9
125.3
120.8
C4AC10AC12
C4AC10AO17
C12AC10AO17
C10AO17AC18
O17AC18AC21
C18AC21AO23
C18AC21AO22
O22AC21AO23
118.6
118.2
123.0
119.8
112.5
117.6
119.3
123.0
C atoms
Multiplicity
13C NMR in CDCl3
5
1
2
3
151.15
123.42
133.67
126.04
125.24
128.03
125.24
149.45
142.31
170.35
70.85
Doblete
Doblete
Doblete
Singlete
Singlete
Doblete
Singlete
Singlete
Singlete
Singlete
Triplete
9
13
12
10
4
21
18
Dihedral angles (°)
C21AC18AO17AC10
C4AC10AO17AC18
C12AC10AO17AC18
ꢂ121.3
102.2
ꢂ81.9
ꢂ53.8
ꢂ35.5
149.6
ꢂ117.2
104.6
ꢂ80.4
ꢂ58.1
ꢂ46.4
139.3
a
This work.

152
E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
The DQA structures have C1 symmetries and 66 normal vibration
modes, all active in the infrared and Raman spectra. Figs. 2 and 3
show the registered infrared and Raman spectra for the compound
in the solid phase. The assignment of the experimental bands to
the expected normal vibration modes were made on the basis of
PED in terms of symmetry coordinates, and by taking into account
the corresponding assignment of related molecules [5,29–37].
Tables 4, S7 and S8 shows the experimental and calculated fre-
quencies, potential energy distribution based on the 6-31Gꢀ basis
set, and assignment for the CI and CII structures of DQA. The
observed broad band in the IR spectrum of the solid sample with
several shoulders between 2800 and 1900 cmꢂ1 are probably
attributed to the NAH and OAH hydrogen bondings formed by
the spatial arrangement of molecules in the lattice crystal, as ob-
served in the molecular packing of the 2-(20-furyl)-1H-imidazole
[23], 2-(20-furyl)-4,5-1H-dihydroimidazole [26] and tolazoline
hydrochloride molecules [35,36]. Here, B3LYP/6-31Gꢀ calculations
were considered because the used scale factors are defined for this
basis set. The SQM force fields for this compound can be obtained
upon request. Below, we discuss the assignment of the most
important groups.
Fig. 3. Experimental Raman spectrum of the solid (5,7-dichloro-quinolin-8-yloxy)
acetic acid in a glass capillary.
4.5.1.3. CH2 modes. The IR bands at 3002 and 2956 cmꢂ1 are
assigned to the antisymmetric and symmetric stretching modes
of this group in agreement with similar compounds [25,32]. The
scissoring modes for both conformers of DQA can be assigned to
the strong IR band at 1491 cmꢂ1. The IR bands at 1342 and
1256 cmꢂ1 are assigned to the wagging modes of this group, as
predicted by calculation, while the strong bands and the shoulder
at 1455 and 1362 cmꢂ1 are respectively assigned to the rocking
modes. The twisting mode for both conformers are associated with
the weak IR band at 1048 cmꢂ1 as observed in similar compounds
[5,6].
4.5.1. Assignments
4.5.1.1. OH modes. The bands in the IR spectra at 3952 and
3448 cmꢂ1 are assigned to the OAH stretching vibrations of both
conformers, in accordance with the values reported for similar
molecules [30,32–34]. The width and shape of the latter band
clearly shows the typical spectroscopic signature of an H-bond
interaction. In accordance with the reported value for benzoic acid
[33,34] and with theoretical calculations, the corresponding defor-
mation modes of this group are assigned to the strong IR bands at
1455 and 1342 cmꢂ1, for the CI and CII conformers, respectively.
The out-of-plane deformation mode (sOH or cOH) is assigned for
4.5.1.4. COO modes. As predicted by calculations, the expected C@O
stretching modes for both conformers are assigned at 1754 cmꢂ1
[5,6] while the CAO stretching modes are clearly assigned to the
IR bands at 1342 and 1144 cmꢂ1 for the CI and CII conformers,
respectively. Theoretical calculations for 4-hidroxybenzoic acid di-
the CI conformer to the strong band in Raman spectrum at
75 cmꢂ1 whereas, for the CII conformer, it is assigned to the very
weak band in the same spectrum at 419 cmꢂ1, as can be seen in
the 4-hydroxybenzoic acid dimer [30].
mer predict [30] the two c
(COO) modes at 772 cmꢂ1, whereas the
two d(COO) modes are predicted at 771 and 620 cmꢂ1. Here, the
modes for the CI and CII conformers are predicted at different
wavenumbers, hence the IR bands at 655 and 610 cmꢂ1 are associ-
ated with the d(COO) modes, while the IR band at 562 cmꢂ1 is as-
4.5.1.2. CH modes. The CAH stretching modes can be clearly
assigned, due to their positions, to the group of bands in the
3125–3041 cmꢂ1 region of the IR and Raman spectra. The in-plane
deformation modes of the quinoline ring are assigned to the bands
at 1580, 1491, 1455, 1237 and 1214 cmꢂ1, as observed in similar
compounds [30–32,36]. On the other hand, the four expected
out-of-plane deformations of CAH group for the two conformers
of DQA are assigned to the IR and Raman bands located at 1002,
949, 874 and 818 cmꢂ1, as observed in Table 5.
signed to the c(COO) modes, as observed in Table 5. The rocking
modes of COO groups for the CI and CII conformers are predicted
at 470 and 264 cmꢂ1, as in similar compounds [30,33,34]; hence,
they are assigned respectively to the IR and Raman bands at 475
and 254 cmꢂ1. The SQM clearly predicts the twisting modes be-
tween 121 and 38 cmꢂ1, for this reason, only the first mode was as-
signed to the Raman band at 121 cmꢂ1
.
4.5.1.5. Skeletal modes. In this compound, the skeletal stretching
modes are predicted to be strongly mixed (Tables 4, S7 and S8).
In accordance with the values reported for similar molecules
[30,32,36] and at our theoretical results, the strong IR bands at
1754, 1600 and 1580 cmꢂ1 are mainly associated with the C@C
stretching modes, while the IR bands at 1402, 1375, 1256, 1237,
1101, 857 and 681 cmꢂ1 are associated with the CAC stretching
modes, as observed in Table 4. The strong IR band at 1455, 1362,
1342 and 1296 cmꢂ1 are associated with the CAN stretching
modes, while the IR bands at 742 and 403 cmꢂ1 and the Raman
band at 378 cmꢂ1 are assigned to the CACl stretching modes for
both conformers, as observed in (5-Chloro-quinolin-8-yloxy) acetic
acid [6]. On the other hand, the six quinoline ring deformations and
torsions are assigned to the expected regions, as observed in
similar molecules [5,6,32–34]. Finally, the butterfly modes are
Fig. 2. Experimental infrared spectrum of the solid (5,7-dichloro-quinolin-8-yloxy)
acetic acid in KBr pellets.

E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
153
Table 4
Observed and calculated wavenumbers (cmꢂ1) and assignment for the (5,7-dichloro-quinolin-8-yloxy) acetic acid.
Experimentala
IR solid
CI
CII
Raman solid
SQMb
Assignment
SQMb
Assignment
3952 m
3938 w
3448 w, br
3125
3715
m
(O23AH24)
3309
3243
3235
3220
3190
3152
3075
1865
1657
1629
1613
1537
1507
1491
1440
1431
1419
1392
m
m
m
m
m
m
m
m
m
m
m
(O23AH24)
(C13AH15)
(C2AH8)
(C1AH7)
(C5AH11)
aCH2
3244
3233
3214
3169
3126
3069
1898
1658
1630
1608
1540
1500
1483
1437
1435
1413
m
m
m
m
m
m
m
m
m
m
(C13AH15)
(C2AH8)
(C1AH7)
(C5AH11)
aCH2
sCH2
(C21AO22)
(C1AC2);
(C13AC9)
(C12AC10)
3084 w
3041 vw
3002 vw
2956 w
1754 vs
1754 vs
1600 s
1580 s
1580 s
1491 s
1491 s
1455 s
1455 s
1402 s
1402 s
1375 s
1362 w
1362 w
1342 s
1342 s
1296 w
1256 w
1237 m
1237 m
1214 w
1144 m
1101 s
1101 s
1048 w
1048 w
1002 m
1002 m
949 s
3081 vw
3038 vvw
3005 vvw
2958 vw
sCH2
(C21AO22)
(C1AC2);
(C13AC9)
m(C2AC3)
m(C2AC3)
1601 vw
1581 vw
1570 vw
(C12AC10)
bC1AH7
dCH2
bC5AH11
dOH
bC13AH15
bC1AH7
d CH2
bC5AH11
1492 vw
1415 vw
q
CH2
m
m
(C5AN16)
(C10AC4)
m
m
(C10AC4)
(C3AC4)
1380 m
1369 w
1346 vw
1380
m(C3AC9)
1370
qCH2
1332
1320
1310
1277
1260
m(C4AN16)
1329
1310
1273
1266
1243
1231
1175
m(C4AN16)
m(C21AO23)
m(C5AN16)
dOH
wag CH2
m
m
(C10AO17)
(C13AC12)
wag CH2
m
m
(C13AC12)
(C3AC9)
1233
1177
1168
1139
1078
1060
1032
bC13AH15
bC2AH8
bC2AH8
1148 vw
m(C21AO23)
m(C18AO17)
m(C1AC5)
1128
1076
m
m
(C10AO17)
(C1AC5)
bR1 (A2)
sw CH2
1049 vw
1009 vw
951 vw
1032
1016
1004
977
960
896
swCH2
m(C18AO17)
c
c
C2AH8
C5AH11
1000
968
959
894
c
c
C2AH8
C5AH11
949 s
884 s
bR1(A1)
bR1(A2)
bR1 (A1)
bR1 (A2); m(C12ACl14); bR3 (A2); bR3 (A1)
874 m
857 s
818 s
877 vw
861 vw
885
879
827
811
796
746
740
694
c
m
s
c
c
C13AH15
(C18AC21)
R1 (A2)
C1AH7
C10AO17
887
870
823
c
m
C13AH15
(C18AC21)
cC2AH8
818 s
795 m
742 w
730 w
681 m
681 m
655 m
623 vw
610 w
610 w
575 w
562 w
533 vw
508 vw
502 vw
489 vw
475 vw
429 m
417 w
403 w
789
747
sR1 (A2)
m
(C9ACl6)
bR2 (A2); bR3 (A2); bR2 (A1)
C12ACl14
bR2 (A1)
729 w
678 vw
c
712
700
662
m
(C3AC4)
dCCO
sR1 (A1)
659
632
619
dCOO
bR3 (A2)
sR1 (A1)
618
609
587
567
516
dCOO
C9ACl6
bR2 (A2)
c
575 vw
511 w
584
560
518
513
bR2 (A2)
COO
R2 (A1)
bR3 (A1)
c
c
c
COO
C12ACl14
s
501
485
bR3 (A2)
bR3 (A1)
470
438
422
q
COO
sR3 (A2)
434
426
399
s
s
m
R3 (A2)
OH
(C9ACl6)
419 vw
c
C9ACl6
378 m
378 m
349 vw
374
m
(C12ACl14)
369
349
291
264
244
234
211
193
m
c
(C12ACl14)
C10AO17
346
309
252
240
220
bR2 (A1)
C10AO17
q
dCOC
q
q
Butt
bC9ACl6
bC12ACl14
254 w
254 w
227 vw
212 vw
188 w
dCCO
Butt
bC9ACl6
COO
C10AO17
203
dCOC
(continued on next page)

154
E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
Table 4 (continued)
Experimentala
IR solid
CI
CII
Raman solid
SQMb
Assignment
SQMb
Assignment
162 w
145 w
121 w
75 vs
182
143
121
99
77
51
bC12ACl14
s
s
s
s
s
R2 (A2)
wCOO
OH
CCOC
R3 (A1)
143
124
75
s
s
s
CCOC
R2 (A2)
R2 (A1)
75 vs
53
38
10
sR3 (A1)
swCOO
sw Ring
20 vw
28
swRing
Abbreviations: m, stretching; b, deformation in the plane; c, deformation out of plane; wag, wagging; s, torsion; bR, deformation ring sR, torsion ring; q, rocking; sw, twisting;
d, deformation; Butt, butterfly; a, antisymmetric; s, symmetric; A1, Ring 1; A2, Ring 2.
a
This work.
b
B3LYP/6-31Gꢀ.
Table 5
Comparison of scaled internal force constants for the two conformers of (5,7-dichloro-quinolin-8-yloxy) acetic acid.
B3LYP/6-31Gꢀ
Force constant
(5,7-Dichloro-quinolin-8-yloxy) acetic acida
(5-Chloro-quinolin-8-yloxy) acetic acidb
2-(Quinolin-8-yloxy) acetic acidc
CI
CII
CI
CII
CIII
CI
CII
f(C@O)
f(CAO)
f(OAH)
f(CAH2)
f(CAH)
f(CACl)
f(CAN)
f(CAC)
f(O@C@O)
f(HACAH)
f(CAOAH)
f(CAOAC)
13.65
6.36
6.10
5.34
5.69
3.65
7.89
6.65
1.34
0.91
1.06
0.94
14.22
6.08
7.73
5.29
5.67
3.61
7.76
6.61
1.23
0.83
0.79
1.60
13.62
6.33
6.11
5.31
5.68
3.51
7.90
6.65
1.33
0.91
1.01
0.99
14.16
5.93
7.71
5.23
5.67
3.49
7.77
6.59
1.24
0.87
0.79
1.16
14.10
6.15
7.65
5.10
5.66
3.42
7.84
6.61
1.26
0.88
0.77
1.46
12.53
6.73
5.55
4.87
5.17
13.07
5.50
7.10
4.80
5.16
7.26
6.22
1.33
0.84
0.91
0.98
7.12
6.17
1.23
0.80
0.70
1.18
Units are mdyn Åꢂ1 for stretching and stretching/stretching interaction and mdyn Å radꢂ2 for angle deformations.
a
This work.
Anhydrous from Ref. [6].
Anhydrous from Ref. [5].
b
c
assigned to the weak Raman bands at 254 and 227 cmꢂ1, as ob-
served in Table 4.
the values of the energy separation between those orbitals are high-
er in the (5-chloro-quinolin-8-yloxy) acetic acid than in DQA. This
large HOMO–LUMO gap for the (5-chloro-quinolin-8-yloxy) acetic
acid automatically means high excitation energies for many excited
states, good stability and high chemical hardness. For these reasons,
the presence of other Cl atom in DQA increases the reactivity as
compared with the (5-chloro-quinolin-8-yloxy) acetic acid.
4.6. Force field
The calculated force constants for the two DQA’s conformers
were calculated by means of Pulay et al. [7–9] scaling procedure
together with the MOLVIB program [19,20] and they can be
seen in Table 5 compared with the corresponding values for the
(5-chloro-quinolin-8-yloxy) acetic acid [6] and 2-(quinolin-8-yloxy)
acetic acid [5]. The analyses show that in both chloro compounds all
values are approximately the same with the exception of the f(CACl)
force constant that is higher in DQA than in (5-chloro-quinolin-
8-yloxy) acetic acid [6]. The lower CACl distance in DQA justifies a
higher value in the f(CACl) of this compound related to (5-chloro-
quinolin-8-yloxy) acetic acid [6]. On the other hand, the presence
of the Cl atoms slightly increases the force constant values as com-
pared with the 2-(quinolin-8-yloxy) acetic acid [5] in relation to
the other ones.
5. Conclusions
The (5,7-dichloro-quinolin-8-yloxy) acetic acid was synthesized
and characterized by infrared, Raman and NMR spectroscopic tech-
niques. The presence of CI and CII conformers was detected in both
spectra, and a complete assignment of the vibrational modes was
accomplished. Two stable conformers for the DQA in the gas phase
were determined by B3LYP/6-31Gꢀ and B3LYP/6-311++Gꢀꢀ calcula-
tions. The SQM/B3LYP/6-31Gꢀ force fields were obtained for both
structures of DQA and also for the force constants for the stretching
and deformation modes. The NBO and AIM analyses confirm the
presence of H bonds in the CI conformer of DQA. The presence of
two Cl atoms in the quinoline ring increases the molecule reactiv-
ity as compared to the (5-chloro-quinolin-8-yloxy) acetic acid.
4.7. HOMO–LUMO energy gap
The frontier molecular HOMO and LUMO orbitals play an impor-
tant role in the reactivity of the compounds and in many properties
[37]. Here, those orbitales were calculated for DQA and compared
with the corresponding values for the (5-chloro-quinolin-8-yloxy)
acetic acid, as observed in Table S9. The results show that both
orbitals are mainly localized on the rings, indicating that the
Acknowledgements
This work was supported with grants from CIUNT (Consejo de
Investigaciones, Universidad Nacional de Tucumán), CONICET
(Consejo Nacional de Investigaciones Científicas y Técnicas, R.
Argentina) and ANPCYT PICT 0394. The authors thank Prof. Tom
HOMO–LUMO are mostly the p-antibonding-type orbitals and that

E. Romano et al. / Journal of Molecular Structure 1018 (2012) 149–155
155
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2012.
03.013.
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