A potential energy scan is mainly used to describe the relationship
between potential energy and molecular geometry. The
conformational analysis was used through the potential surface
scan in order to determine the most optimized geometry of the
(2E)-IPHC molecule. The torsional barrier rotations are in reference
to the CeN and CeC bonds. The first two potential energy scan
curves were carried out with dihedral angles C17eC18eN4eN5 and
C17eC18eC19eC22, the link between the phenyl ring with semicarbazide
and imidazole moieties, respectively. The third scan was
carried out with dihedral angle C19eC18eN4eN5, the link between
the imidazole ring and the semicarbazide moiety. During the scan,
all the geometrical parameters were simultaneously relaxed and
were varied in steps of 30 from 0 to 360. The curves of the potential
energy as a function of the dihedral angle were presented in
Fig. 1. Thirteen conformers were obtained in each scan. Conformational
analysis revealed that the most stable conformer was
obtained in the third scan at a torsion angle of 180 with a global
minimum energy of 81.1997 kcal/mol (0.129361 hartrees). After
optimization with the global minimum energy, the phenyl ring and
semicarbazide moiety are in one plane and the imidazole ring is
parallel to that plane. The energies of the conformers of the (2E)-
IPHC molecule were calculated by AM1 theory and they are listed in
Table 1. The standard deviations of the conformational energies
were calculated as 1.3929, 13.4253, and 10.9250 kcal/mol in scans 1,
2, and 3, respectively.