666
K. Sarojini et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 96 (2012) 657–667
Frontier molecular orbitals (FMOs)
ular hydrogen bonds in the crystal structure. Theoretical 1H and
13C chemical shift values (with respect to TMS) were reported
and compared with experimental data, showing good agreement
for both 1H and 13C. The comparison between experimental results
and theoretical data presents that the calculation level preferred is
powerful approach for understanding the identification of all the
molecules studied in this work. NBO result reflects the charge
transfer mainly due to C–C group. Atomic charges are also deter-
mined for the identification of the molecule. Moreover, frontier
molecular orbitals and molecular electrostatic potential were visu-
alized. Electronic transition and energy band gap of the title mole-
cule were investigated and interpreted. HOMO–LUMO gap with
4.23 eV indicates that the title compound has a good chemical sta-
bility. The tile compound is chemically stable up to 295 °C. In con-
clusion, all the calculated data and experimental results not only
show the way to the characterization of the molecule but also use-
ful in the application in industry and fundamental researches in
chemistry and biology in the future.
Both the highest occupied molecular orbitals (HOMOs) and low-
est unoccupied molecular orbitals (LUMOs) are the main orbitals
taking part in chemical stability. The HOMO represents the ability
to donate an electron, LUMO as an electron acceptor representing
the ability to obtain an electron. The HOMO and LUMO energy cal-
culated by B3LYP/6-31G(d,p) method as shown below.
HOMO energy (B3LYP) = 5.5547 eV
LUMO energy (B3LYP) = 1.3154 eV
HOMO–LUMO energy gap (B3LYP) = 4.2392 eV
This electronic absorption corresponds to the transition from
the ground to the first excited state and is mainly described by
one electron excitation from the highest occupied molecular orbi-
tal (HOMO) to the lowest unoccupied molecular orbital (LUMO).
The HOMO is located over the naphthalene ring, NH and SO2 group.
LUMO is delocalized on the entire compound except the CH2 of the
methyl group. The HOMO to LUMO transition implies an electron
density transfer from the naphthyl amino moiety to toluene sulfo-
nyl moiety. Fig. 8. Shows the surfaces of HOMO and LUMO. The
HOMO–LUMO energy gap explains the eventual charge transfer
interactions taking place within the molecule.
Acknowledgement
The authors thank SAIF, IIT Madras, Chennai, providing facilities
for taking single crystal XRD.
Thermal analysis
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