Triplet oxygen

Triplet oxygen
Names
	IUPAC name Triplet oxygen
	Systematic IUPAC name Dioxidanediyl (substitutive); dioxygen(2•)(triplet) (additive)
Identifiers
CAS Number	7782-44-7 ;
3D model (JSmol)	Interactive image; Interactive image;
ChEBI	CHEBI:27140;
ChemSpider	952;
EC Number	231-956-9;
Gmelin Reference	492
KEGG	D00003 ;
MeSH	Oxygen
PubChem CID	977;
RTECS number	RS2060000;
UNII	S88TT14065 ;
UN number	1072
	InChI InChI=1S/O2/c1-2 Key: MYMOFIZGZYHOMD-UHFFFAOYSA-N;
	SMILES [O]#[O]; [O][O];
Properties
Chemical formula	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
Molecular shape	Linear
Dipole moment	0 D
Thermochemistry
Std molar; entropy (S⦵298)	205.152 J K−1 mol−1
Std enthalpy of; formation (ΔfH⦵298)	0 kJ mol−1
Pharmacology
ATC code	V03AN01 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H270
Precautionary statements	P220, P244, P370+P376, P403
NFPA 704 (fire diamond)	0 0 1 OX
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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]

^ ^a ^b "Triplet Dioxygen (CHEBI:27140)". Chemical Entities of Biological Interest (ChEBI). UK: European Bioinformatics Institute.
^ 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.
^ 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.

[Triplet_Dioxygen_(CHEBI:27140)-1] "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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