ABSTRACT

For very small molecules this is straightforward. For example, consider the chiral substituted oxiranes, methyl-oxirane, 1, and phenyl-oxirane, 2.

The oxirane ring is conformationally rigid, as are also the methyl and phenyl substituents. However, in 1 the methyl group can rotate about the C-C bond, connecting it to the oxirane ring, and in 2, the phenyl group can rotate about the C-C bond, connecting it to the oxirane ring. To determine the number of stable conformations of 1 and 2, relaxed scans of their PESs with respect to rotation of the CH3 and C6H5 groups are carried out. Specically, the dihedral angles C1C2C3H1 of 1 and C1C2C3C4 of 2 are varied from 0 to 360°. For each value of the dihedral angle, optimization of the molecule is carried out, giving the relaxed energy. The plot of the relaxed energies vs. the dihedral angle values is the relaxed PES scan.