Singlet oxygen

Singlet oxygen
Names
IUPAC name
Singlet oxygen
Systematic IUPAC name
Dioxidene
Identifiers
3D model (JSmol)
ChEBI
491
  • InChI=1S/O2/c1-2
    Key: MYMOFIZGZYHOMD-UHFFFAOYSA-N
  • O=O
Properties
O2
Molar mass 31.998 g·mol−1
Reacts
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as 1
[O
2] or 1
O
2), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambient temperature, but the rate of decay is slow.

The lowest excited state of the diatomic oxygen molecule is a singlet state. It is a gas with physical properties differing only subtly from those of the more prevalent triplet ground state of O2. In terms of its chemical reactivity, however, singlet oxygen is far more reactive toward organic compounds. It is responsible for the photodegradation of many materials but can be put to constructive use in preparative organic chemistry and photodynamic therapy. Trace amounts of singlet oxygen are found in the upper atmosphere and in polluted urban atmospheres where it contributes to the formation of lung-damaging nitrogen dioxide.[1]: 355–68  It often appears and coexists confounded in environments that also generate ozone, such as pine forests with photodegradation of turpentine.[citation needed]

The terms 'singlet oxygen' and 'triplet oxygen' derive from each form's number of electron spins. The singlet has only one possible arrangement of electron spins with a total quantum spin of 0, while the triplet has three possible arrangements of electron spins with a total quantum spin of 1, corresponding to three degenerate states.

In spectroscopic notation, the lowest singlet and triplet forms of O2 are labeled 1Δg and 3Σ−
g, respectively.[2][3][4]

  1. ^ Wayne RP (1969). "Singlet Molecular Oxygen". In Pitts JN, Hammond GS, Noyes WA (eds.). Advances in Photochemistry. Vol. 7. pp. 311–71. doi:10.1002/9780470133378.ch4. ISBN 9780470133378.
  2. ^ Klán P, Wirz J (2009). Photochemistry of Organic Compounds: From Concepts to Practice (Repr. 2010 ed.). Chichester, West Sussex, U.K.: Wiley. ISBN 978-1405190886.
  3. ^ Atkins P, de Paula J (2006). Atkins' Physical Chemistry (8th ed.). W.H.Freeman. pp. 482–3. ISBN 978-0-7167-8759-4.
  4. ^ Hill C. "Molecular Term Symbols" (PDF). Archived from the original (PDF) on 5 September 2017. Retrieved 10 October 2016.