Triplet oxygen

Triplet oxygen
Names
IUPAC name
Triplet oxygen
Systematic IUPAC name
Dioxidanediyl[1] (substitutive)
dioxygen(2•)(triplet)[1] (additive)
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 231-956-9
492
KEGG
MeSH Oxygen
RTECS number
  • RS2060000
UNII
UN number 1072
  • InChI=1S/O2/c1-2
    Key: MYMOFIZGZYHOMD-UHFFFAOYSA-N
  • [O]#[O]
  • [O][O]
Properties
O2
Molar mass 31.998 g·mol−1
Appearance Colorless gas
Melting point −218.2 °C; −360.7 °F; 55.0 K
Boiling point −183.2 °C; −297.7 °F; 90.0 K
Structure
Linear
0 D
Thermochemistry
205.152 J K−1 mol−1
0 kJ mol−1
Pharmacology
V03AN01 (WHO)
Hazards
GHS labelling:
GHS03: Oxidizing
Danger
H270
P220, P244, P370+P376, P403
NFPA 704 (fire diamond)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Triplet oxygen, 3O2, refers to the S = 1 electronic ground state of molecular oxygen (dioxygen). Molecules of triplet oxygen contain two unpaired electrons, making triplet oxygen an unusual example of a stable and commonly encountered diradical:[2] it is more stable as a triplet than a singlet. According to molecular orbital theory, the electron configuration of triplet oxygen has two electrons occupying two π molecular orbitals (MOs) of equal energy (that is, degenerate MOs). In accordance with Hund's rules, they remain unpaired and spin-parallel, which accounts for the paramagnetism of molecular oxygen. These half-filled orbitals are antibonding in character, reducing the overall bond order of the molecule to 2 from the maximum value of 3 that would occur when these antibonding orbitals remain fully unoccupied, as in dinitrogen. The molecular term symbol for triplet oxygen is 3Σ
g
.[3]

  1. ^ a b "Triplet Dioxygen (CHEBI:27140)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute.
  2. ^ Borden, Weston Thatcher; Hoffmann, Roald; Stuyver, Thijs; Chen, Bo (2017). "Dioxygen: What Makes This Triplet Diradical Kinetically Persistent?". Journal of the American Chemical Society. 139 (26): 9010–9018. doi:10.1021/jacs.7b04232. PMID 28613073.
  3. ^ Atkins, Peter; De Paula, Julio; Friedman, Ronald (2009) Quanta, Matter, and Change: A Molecular Approach to Physical Chemistry, pp. 341–342, Oxford: Oxford University Press, ISBN 0199206066, see [1]. accessed 11 August 2015.

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