Triplet oxygen
| Names | |
|---|---|
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Preferred IUPAC name
Triplet oxygen
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Systematic IUPAC name
Dioxidanediyl (substitutive)
dioxygen(2•)(triplet) (additive) |
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| Identifiers | |
7782-44-7 
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| 3D model (Jmol) |
Interactive image Interactive image Interactive image |
| ChEBI | CHEBI:27140 |
| ChemSpider | 952 |
| EC Number | 231-956-9 |
| 492 | |
| KEGG |
D00003
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| MeSH | Oxygen |
| PubChem | 977 |
| RTECS number | RS2060000 |
| UN number | 1072 |
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| Properties | |
| O2 | |
| Molar mass | 32.00 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 | |
|
Std molar
entropy (S |
205.152 J K−1 mol−1 |
|
Std enthalpy of
formation (ΔfH |
0 kJ mol−1 |
| Pharmacology | |
| V03AN01 (WHO) | |
| Hazards | |
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EU classification (DSD)
|
 O |
| R-phrases | R8 |
| S-phrases | S17 |
| NFPA 704 | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Triplet oxygen, systematically but less commonly, 1,2-dioxidanediyl, is normal, gaseous oxygen (O2, dioxygen) in its ground state. It is therefore classified as an inorganic chemical, and more specifically as a particular electronic state of one allotrope of the inorganic chemical element, oxygen. In this particular state, according to one type of modern bonding theory, the electron configuration of the oxygen molecule has two electrons occupying two molecular orbitals (MOs) of equal energy (that is, degenerate MOs), therefore remaining unpaired. These orbitals are classified as antibonding and are of higher energy, so the resulting bonding structure between the oxygen atoms is weakened (i.e., is higher in energy)—for instance, it is higher in energy than the bonding in dinitrogen, where the corresponding antibonding orbitals are empty. The spectroscopic molecular term symbol for triplet (ground state) oxygen is 3Σ−
g.
The s = 1⁄2 spins of the two electrons in degenerate orbitals gives rise to 2 × 2 = 4 independent spin states in total. Exchange interaction splits these into a singlet state (total spin S = 0) and a set of 3 degenerate triplet states (S = 1). In agreement with Hund's rules, the triplet states are energetically more favorable, and correspond to the ground state of the molecule with a total electron spin of S = 1. Excitation to the S=0 state results in much more reactive, metastable singlet oxygen.
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