1014
H. Raissi et al. / Spectrochimica Acta Part A 62 (2005) 1004–1015
to the CH3 deformation modes and the band at about 1195
was assigned to the olefinic CH in plane bending mode. The
bands at about 1105, 1040, 1015 and 1005 cm−1 are assigned
mainly to the CH3 rocking modes.
The N· · ·O stretching mode in the APO spectrum at
360 cm−1 also shows considerable upward frequency shift
(412 cm−1) by CH3 substitution on the Nitrogen atom. This
frequency shift also supports the presence of stronger hydro-
gen bond in MeAPO compared to that in APO.
4.3.3. Below 1000 cm−1
In this region, we expect to observe C CH3 stretching,
C3C2O6 and C3C4N7 deformations, N H and C H␣ out of
plane bending modes and in plane and out of plane ring defor-
mation modes.
5. Conclusion
The structure, intramolecular hydrogen and vibrational
spectra of MeAPO have been measured and analyzed by the
aid of calculations at the density functional theory (DFT) lev-
els and post-Hartree–Fock (MP2) level and considering its
spectral behaviors upon deuteration. Superior results were
obtained with B3LYP/6-31G**. All theoretical calculations
and experimental results reveal that the intramolecular H-
bond by methyl substitution on the Nitrogen atom of APO
become stronger than that APO.
Theoretical calculations show that the hydrogen of
NHCH3 group is in the plane of the chelated ring. Analysis
of the vibrational spectra indicates strong coupling between
the chelated ring modes.
Theoretical calculations suggest that the band at about
930 cm−1 is due to asymmetric C CH3 stretching mode,
which is somewhat, coupled to the in plane C3 C2 O6 and
CH␣ bending modes. Upon deuteration this band shows an
upward frequency shift of about 10 cm−1. The corresponding
band in APO (980 cm−1) [2] shows also an upward frequency
shift upon deuteration. The infrared band at 859 cm−1 shows
a downward frequency shift upon deuteration, which is in
agreement with our theoretical calculations, we assign this
band to the C CH3 stretching mode coupled to the in plane
C3 C4 N7 and CH␣ bending modes.
The vibrational spectra of MeAPO indicate two bands at
about 830 and 730 cm−1, which the former completely dis-
appear in DMeAPO. According to our calculations, these
two bands are caused by (γNH10 + γCH␣) out of phase, and
in phase, respectively. In DMeAPO, decoupling of γCH␣
and γND10 causes that these two bands to be observed at
675 and 735 cm−1, respectively, which is in agreement with
the calculated results. In the case of APO, the out of plane
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)
than that for MeAPO (830 cm−1). This frequency shift also
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