Triplet oxygen, O2, 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: 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 Ο 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 Ξ£
g.
β Core Definition: Triplet oxygen
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π Triplet oxygen in the context of Radical (chemistry)
In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron.With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes.
A notable example of a radical is the hydroxyl radical (HOΒ·), a molecule that has one unpaired electron on the oxygen atom. Two other examples are triplet oxygen and triplet carbene (κCH
2) which have two unpaired electrons.
Triplet oxygen in the context of Dioxygen
There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are:
- Atomic oxygen (O1), a free radical.
- Singlet oxygen (O
2), one of two metastable states of molecular oxygen. - Tetraoxygen (O4), another metastable form.
- Solid oxygen, existing in six variously colored phases, of which one is octaoxygen (O8, red oxygen) and another one metallic (ΞΆ-oxygen).
Triplet oxygen in the context of Singlet oxygen
Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with two oxygen atoms in a quantum state where all electrons are spin-paired, known as a singlet state. It is the lowest excited state of the diatomic oxygen molecule, which in general has the chemical structure O=O and chemical formula O
2. Singlet oxygen can be written more specifically as
[O
2] or
O
2. The more prevalent ground state of O
2 is known as triplet oxygen. At room temperature, singlet oxygen will slowly decay into triplet oxygen, releasing the energy of excitation.
Singlet oxygen is a gas with physical properties differing only subtly from the ground state. 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. It often appears and coexists confounded in environments that also generate ozone, such as pine forests with photodegradation of turpentine.