Dinitrogen tetroxide

Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide, is the chemical compound N₂O₄. It is a useful reagent in chemical synthesis. It forms an equilibrium mixture with nitrogen dioxide.

Dinitrogen tetroxide is a powerful oxidizer that is hypergolic (spontaneously reacts) upon contact with various forms of hydrazine, which makes the pair a popular bipropellant for rockets.

Structure and properties

Dinitrogen tetroxide forms an equilibrium mixture with nitrogen dioxide. The molecule is planar with an N-N bond distance of 1.78 Å and N-O distances of 1.19 Å. The N-N distance corresponds to a weak bond, since it is significantly longer than the average N-N single bond length of 1.45 Å.

Unlike NO₂, N₂O₄ is diamagnetic since it has no unpaired electrons. The liquid is also colorless but can appear as a brownish yellow liquid due to the presence of NO₂ according to the following equilibrium:

Higher temperatures push the equilibrium towards nitrogen dioxide. Inevitably, some dinitrogen tetroxide is a component of smog containing nitrogen dioxide.