The molecular structure of hydrogen peroxide, HOOH

The gas phase structures of the OH radical, the hydroxide ion, and the oxonium ion H3O+ have all been determined by spectroscopic methods. Bond distances and valence angles are listed in Table 17.3. The near-constant length of the OH bonds is striking. 

H3O+ is isoelectronic with the ammonia molecule NH3 and has a similar trigonal pyramidal shape. The HOH valence angle is slightly larger than the corresponding angle in NH3 (ZHNH = 107°) and the inversion barrier (11 kJ mol ) in less than half the barrier in ammonia, perhaps because 0-H bond distance is about 5 pm shorter than the N-H bond distance. 

Problem 17.5 Suggest a molecular orbital description of the bonding in the hydroxide ion. 

The molecular structure of gaseous HOOH is shown in Fig. 17.4. The molecule has a twofold symmetry axis through the midpoints of the 0-0 bond and the line connecting the two H atoms. The molecule is nonplanar, the angle between the two OOH planes T (HOOH) = 118°. The O-H bond distance is similar to that in the water molecule, the 0-0 

The mean O-H bond dissociation energy is hydrogen peroxide, defined as half the standard energy of the reaction 

---