Hydrogen Peroxide

Hydrogen peroxide is a chemical compound with the formula H
2O
2
. In its pure form, it is a very pale blue liquid, slightly more viscous than water. Hydrogen peroxide is the simplest peroxide (a compound with an oxygen–oxygen single bond). It is used as an oxidizer, bleaching agent, and antiseptic. Concentrated hydrogen peroxide, or “high-test peroxide”, is a reactive oxygen species and has been used as a propellant in rocketry. Its chemistry is dominated by the nature of its unstable peroxide bond.

Hydrogen peroxide is unstable and slowly decomposes in the presence of light. Because of its instability, hydrogen peroxide is typically stored with a stabilizer in a weakly acidic solution in a dark coloured bottle. Hydrogen peroxide is found in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as peroxidases.

Properties

The boiling point of H2O2 has been extrapolated as being 150.2 °C (302.4 °F), approximately 50 °C (90 °F) higher than water. In practice, hydrogen peroxide will undergo potentially explosive thermal decomposition if heated to this temperature. It may be safely distilled at lower temperatures under reduced pressure

Description

Structure

O−O bond length = 147.4 pm O−H bond length = 95.0 pm
Structure and dimensions of H2O2 in the gas phase
O−O bond length = 145.8 pm O−H bond length = 98.8 pm
Structure and dimensions of H2O2 in the solid (crystalline) phase

Hydrogen peroxide (H
2O
2
) is a nonplanar molecule with (twisted) C2 symmetry; this was first shown by Paul-Antoine Giguère in 1950 using infrared spectroscopy. Although the O−O bond is a single bond, the molecule has a relatively high rotational barrier of 2460 cm−1 (29.45 kJ/mol); for comparison, the rotational barrier for ethane is 1040 cm−1 (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 H
2O
2
 are significantly different. This difference is attributed to the effects of hydrogen bonding, which is absent in the gaseous state. Crystals of H
2O
2
 are tetragonal with the space group D4
4P4121.

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