Conformational studies of performic acid, peracetic acid, and methyl performate by ab initio calculations

ORGN 299

Eric A. Noe, Department of Chemistry, Jackson State University, 1400 J. R. Lynch Street, Jackson, MS 39217-0510 and Charles H. Langley, Chemistry, Jackson State University, 1400 J. R. Lynch St., JAP Science Bldg, Jackson, MS 39217.
Calculations were carried out for the title compounds at levels to MP2/6-311++G(df,pd) and MP2/6-311++G(2d,2p). Dihedral drives for the Z,Z to Z,E and E,E to E,Z potential barriers were done at these levels for the three compounds. As expected, the two peracids have the planar Z,Z conformation with an internal hydrogen bond. The second-lowest energy conformers for performic acid and peracetic acid are above the global minima by 2.59 and 5.94 kcal/mol at the MP2/6-311G(2d,2p) level. At this level, the lowest-energy conformer of methyl performate has O=C-O-O and C-O-O-C dihedral angles of +178.6° and +120.4°. For the conformation second-highest in free energy, these dihedral angles are -4.7° and +92.5°, and the relative free energy is 0.13 kcal/mol.