Structural stability and analysis of vibrational spectra of 1,2,4,5-tetroxane and 3,6-diphenyl-1,2,4,5-tetroxane

The diperoxide 3,6-diphenyl-1,2,4,5-tetroxane was synthesized and its infrared and Raman spectra were measured. The structural stability and the vibrational spectra of 1,2,4,5-tetroxane and 3,6-diphenyl-1,2,4,5-tetroxane were investigated by the DFT-B3LYP and the ab initio MP2 calculations with the 6-311G∗∗ basis set. From the calculations, the chair form of 1,2,4,5-tetroxane was predicted to be about 9, 20, and 50 kcal/mol lower in energy than the twist, boat, and planar structures, respectively. The ring inversion in 1,2,4,5-tetroxane is concluded to take place most probably through the twist structure of the ring. In the case of 3,6-diphenyl-1,2,4,5-tetroxane, the planar-equatorial (Peq) conformation was predicted by both levels of theory to be the lowest energy and predominant form of the molecule. The planar  ⇋⇋perpendicular and axial  ⇋⇋equatorial interconversion barriers were calculated to be about 2 and 12 kcal/mol, respectively. Reliable vibrational assignments were provided for the spectra of 1,2,4,5-tetroxane and 3,6-diphenyl-1,2,4,5-tetroxane by combining experimental and theoretical data of the two molecules.