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R.T. Ulahannan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 404–414
1262 cmꢂ1 in IR, 1202 cmꢂ1 in Raman and at 1270, 1230 cmꢂ1 the-
oretically (SDD) are assigned as CN stretching modes. Panicker et.al
reported the CN stretching mode at 1215 cmꢂ1 theoretically [36].
According to Socrates [33] the C@C stretching is expected
around 1600 cmꢂ1 when conjugated with C@O. The C20@O22 and
1490 and 1440 cmꢂ1 are good group vibrations [34]. The bands ob-
served at 1590, 1540, 1486, 1445, 1376 cmꢂ1 in the IR spectrum,
1537, 1488, 1445, 1366 cmꢂ1 in the Raman spectrum and at
1578, 1535, 1491, 1433, 1368, 1340 cmꢂ1 theoretically (SDD) are
assigned as phenyl ring stretching modes. These modes are ex-
pected in the region 1250–1620 cmꢂ1 [34]. In the case of tri-substi-
tuted benzenes, with mixed substituent, the ring breathing mode is
expected in the range 600–750 cmꢂ1 [40] and in the present case,
the band observed at 788 cmꢂ1 in the Raman spectrum and at
769 cmꢂ1 (SDD) is assigned as the ring breathing mode of the phe-
nyl ring. Mary et al., [43] reported the ring breathing mode of the
C
15@C18 stretching bands are assigned at 1627 (SDD), 1610 cmꢂ1
(IR), 1609 cmꢂ1 (Raman) and at 1607 cmꢂ1 (SDD), 1610 cmꢂ1
(IR), 1609 cmꢂ1 (Raman), respectively. The deformation bands of
C@O and C@C are also identified and assigned (Table 2).
The carboxylic group is characterized by the OH stretch, C@O
stretch and OH out-of-plane deformation and even by the CAO
stretch and OH in-plane deformation. The C@O stretching vibration
in the spectra of carboxylic acids give rise to a strong band in the
region 1600–1700 cmꢂ1 [34]. The band observed at 1651 cmꢂ1 in
the IR spectrum1652 cmꢂ1 in the Raman spectrum and at
1634 cmꢂ1 (SDD) is assigned as C@O stretching mode. The OH in-
plane deformation, coupled to the CAO stretching mode is ex-
pected in the region 1390 55 cmꢂ1 [34], and the band at
1262 cmꢂ1 (IR), 1270 cmꢂ1 (SDD) is assigned as the in-plane bend-
ing of OH group which is not pure but contains contributions from
other modes also. The C(@O)O stretching mode coupled to OH in-
plane bending exhibits a band in the region 1250 80 cmꢂ1 and
tri-substituted benzene ring at 738 cmꢂ1
.
In the present case, the quinoline ring modes are observed at
1610, 1445, 1020 (CC stretching modes), 1262 (CN stretch) in IR,
1609, 1051, 1022 (CC stretching modes), 1202 (CN stretch) in Ra-
man, 1607, 1433, 1045, 1035 (CC stretching modes), 1270,
1230 cmꢂ1 (CN stretch) theoretically (SDD). For the title com-
pound, the in-plane vibrations of the quinoline ring are observed
at 519 cmꢂ1 in IR, 500, 422 cmꢂ1 in Raman and 528, 435 cmꢂ1 in
SDD. The torsional modes are seen at 285, 216 cmꢂ1, in Raman
and 285, 225 cmꢂ1 in SDD. The other deformations modes of the
phenyl and quinoline ring are also identified and assigned (Table 2).
The in plane bending of quinoline ring is reported by Chowdhury
et al. [44] at 526, 472, 508, 624, 829, 869 cmꢂ1 and the ring vibra-
tions at 1245, 1383, 1434, 1470, 1593, 1621 cmꢂ1 in the Raman
spectrum and 760 cmꢂ1 as the ring breathing mode. Krishnakumar
et al. reported the out of plane bending of quinoline derivatives at
586, 601, 634, 505, 538, 612 cmꢂ1 theoretically [45]. The substitu-
ent sensitive modes of the rings are also identified and assigned
(Table 2).
the SDD calculation give CAO stretching mode at 1313 cmꢂ1
.
Experimentally bands are observed at 1298 cmꢂ1 in the IR spec-
trum and at 1319 cmꢂ1 in the Raman spectrum. The deformation
bands, out-of-plane OH, in-plane C@O and out-of-plane C@O are
expected in the regions, 905 65, 725 95 and 595 85 cmꢂ1
,
respectively [34]. These bands are assigned at 913 cmꢂ1 (Raman),
926 (SDD), and 755 (IR), 752 (Raman), 766 cmꢂ1 (SDD) and 703
(IR), 706 (Raman), 719 cmꢂ1 (SDD) respectively. The AC(@O)O
rocking mode is expected in the region 445 120 cmꢂ1 [34], and
in the present case the SDD calculations give this mode at
476 cmꢂ1. Varghese et al., [38] reported COOH deformation bands
Optimized geometrical parameters
at 785 cmꢂ1 and 378 cmꢂ1
.
To best of our knowledge, no X-ray crystallographic data of the
title compound have yet been reported. However, the theoretical
results (SDD) obtained are almost comparable with the reported
structural parameters of similar derivates. For the title compound
the bond length of C5AC6 is observed as 1.4092 Å and this length
is greater than that of C4AC5 (1.3860 Å) because of the delocalisa-
tion of electron density of C5AC6 due to the presence of C@O group.
The C15@C18 could be assumed a double bond character due to the
lesser bond length 1.3608 Å. The greater bond length of C1AC2
(1.4020 Å) is due to delocalisation of electron density due to the
adjacent quinoline ring. It has been reported that the bond lengths
of C1AC2 is 1.4188 Å, C5AC6 is 1.415 Å and C15@C18 is 1.3679 Å
[46]. The bond angle C1AC2AC3 (119.6°) and C2AC3AC4 (119.4°)
is lesser than 120° because of the presence of quinoline ring. The
angles C2AN14AC20 and C3AC15AC18 are 125.8 and 121.3° respec-
tively, which can be assumed as due to the presence of OH group
which is electropositive. The presence of higher electronegative
group C@O would be the reason for the greater bond angle of N14-
AC20AC18 (114.2°). Yurdakul and Yurdakul reported the bond an-
gles as C1AC2AC3 (118.9), C2AC3AC4 (119.3), C2AN14AC20
(118.93), C3AC15AC18 (119.85), N14AC20AC18 (122.82) [46]. The
For the hydroxyl group, the OH group provides three normal
vibrations; the stretching vibration OH, in-plane and out-of-plane
deformations dOH and cOH. The in-plane OH deformation [34] is
expected in the region1440 40 cmꢂ1 and the band at 1409 in Ra-
man spectrum and at 1412 cmꢂ1 (SDD) is assigned as this mode.
The stretching of hydroxyl group CAO appears at 1214 cmꢂ1 in
the IR spectrum and the calculated value is 1206 cmꢂ1 (SDD) and
this band is not pure, but contains significant contributions from
other modes also. This band is expected in the region
1220 40 cmꢂ1 [39–41]. The out-of-plane deformation is expected
generally in the region 650 80 cmꢂ1 [34] and in the present case
it is assigned at 636 cmꢂ1 theoretically (SDD). For paracetamol, the
CAO stretching mode and out-of-plane OH are reported at 1240
and 620 cmꢂ1, respectively [42]. The SDD calculations give OH
stretching at 3563 cmꢂ1
.
Aromatic compounds commonly exhibit multiple weak bands in
the region 3100–3000 cmꢂ1, due to aromatic CH stretching vibra-
tions [34]. However, these bands are rarely useful because they
overlap with one another resulting in stronger absorption in this re-
gion. The SDD calculations give the CH stretching modes of the phe-
nyl ring at 3138, 3117, 3094 cmꢂ1
.
The bands observed at
C10@O12 group is slightly tilted from the tri-substituted phenyl ring
3077 cmꢂ1 in the IR spectrum and at 3126, 3077 cmꢂ1 in the Raman
spectrum are assigned as CH stretching modes of the phenyl ring.
For the title compound, the bands at 1118 (IR), 1113, 1240 (Raman)
and 1120, 1130, 1247 cmꢂ1 (SDD) are assigned as the CH in-plane
bending modes of the phenyl ring. The CH out-of-plane deforma-
tions are expected below 1000 cmꢂ1 [34] and for the title com-
pound, the SDD calculations give bands at 947, 897 and 869 cmꢂ1
as evident from the dihedral angle C1AC6AC10AO11 = ꢂ19.9°.
HOMO and LUMO
HOMO (Highest Occupied Molecular Orbital) and LUMO (Low-
est Unoccupied Molecular Orbital) are the very important parame-
ters for quantum chemistry. The conjugated molecules are
characterized by a HOMO–LUMO separation, which is the result
of a significant degree of ICT (Intra-molecular Charge Transfer)
from the end-capping electron-donor groups to the efficient elec-
as c
CH modes. Experimentally bands are observed at 900 cmꢂ1 in
the IR spectrum and at 947, 885 cmꢂ1 in the Raman spectrum.
The benzene ring possesses six ring stretching modes of which
the four with the highest wavenumbers occurring near 1600, 1580,
tron-acceptor groups through
p-conjugated path. The strong
Ulahannan, Rajeev T.
