The structure of the H2O2 molecules

When it comes to the structure of hydrogen peroxide, many think of its chemical brother H2O. But you should also keep an eye out for O2 because H2O2 lies chemically right in the middle.

Here are some rough structures that come up:

The structures drawn in red are more or less correct.

So, as so often in chemistry, not everything is as you imagine it to be. The oxygen molecule in no way has a double bond. Rather, it is a biradical.

It is well known that the water molecule is angled. The angle H-O-H is not exactly a tetrahedral angle, since the non-bonding electron pairs form larger orbitals than the bonding ones. Therefore, the binding electron pairs and thus also the hydrogen atoms are somewhat “compressed”. The bond angle is therefore 104.5° instead of the theoretical 109.5°.

The bond angle H-O-O in the molecule of H2O2 is only 94.8°. The molecule is also not built in a planar manner, but rather twisted. This angle around the O-O axis is 111.5°.

Only in this way is the mutual repulsion of the H atoms and the big, non-bonding sp3 orbitals the least.

Of course, the two hydroxyl groups of the molecule can rotate internally around the O-O axis. But this is not so easy and requires energy to overcome the repulsions of the opposing H atoms and the non-bonding orbitals.