2) is a nonplanar molecule with (twisted) C2 symmetry; this was first shown by Paul-Antoine GiguÃ¨re in 1950 using infrared spectroscopy. Although the OâO bond is a single bond, the molecule has a relatively high rotational barrier of 2460 cmâ1 (29.45 kJ/mol); for comparison, the rotational barrier for ethane is 1040 cmâ1 (12.5 kJ/mol). The increased barrier is ascribed to repulsion between the lone pairs of the adjacent oxygen atoms and results in hydrogen peroxide displaying atropisomerism.
The molecular structures of gaseous and crystalline
2 are significantly different. This difference is attributed to the effects of hydrogen bonding, which is absent in the gaseous state. Crystals of
2 are tetragonal with the space group D4