Triplet oxygen
Encyclopedia : T : TR : TRI : Triplet oxygen
Triplet oxygen is the ground state of the oxygen molecule. The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals. These orbitals are classified as antibonding, so the O-O bond is weaker than the N-N bond in molecular nitrogen, where all bonding molecular orbitals are filled.
Unpaired electrons in degenerate orbitals can have the same spin, so the total spin S of the molecule is 1. This is known as a triplet configuration because the spin has three possible alignments in an external magnetic field.
Because the molecule has a non-zero spin magnetic moment, liquid oxygen is paramagnetic i.e. it can be attracted to the poles of a magnet. The Lewis structure O=O does not accurately represent the diradical nature of molecular oxygen; molecular orbital theory must be used to adequately account for the unpaired electrons.
The unusual electron configuration prevents molecular oxygen from reacting directly with other molecules, which are in the singlet state. Conservation of spin quantum number would require a triplet transition state in such a reaction. The extra energy required is sufficient to prevent direct reaction at ambient temperatures with all but the most reactive substrates e.g. white phosphorus. At higher temperatures or in the presence of suitable catalysts the reaction proceeds more readily. For instance, most flammable substances are characterised by an autoignition temperature at which they will undergo combustion in air without an external flame or spark.
Singlet oxygen, where the electron spins are opposed in a higher energy state, is many times more reactive than triplet oxygen.
References
- http://www.missouri.edu/~chemrg/wade4e/chapter15/dioxygen_t.html
- http://www.meta-synthesis.com/webbook/16_diradical/diradical.html
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.