Singlet oxygen , systematically called 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 in which all the electrons are paired in pairs. This is kinetically unstable at room temperature, but its decay rate is slow.
The lowest inhaled state of the diatomic oxygen molecule is the singlet's status. These are gases with different physical properties only subtly from those of the more common triplet base state of O 2 . However, in terms of chemical reactivity, singlet oxygen is much more reactive to organic compounds. It is responsible for the photodegradation of many materials but can be used constructively in preparative organic chemistry and photodynamic therapy. The number of single oxygen tracks is found in the upper atmosphere and also in the contaminated urban atmosphere where it contributes to the formation of nitrogen dioxide that damages the lungs. It often appears and coexist in the environment which also produces ozone, such as pine forests with photodegradation of turpentine.
The terms 'singlet oxygen' and 'triplet oxygen' are derived from the number of rotating electrons. Singlets have only one possible spin of electrons with a total quantum rotation of 0, while triplets have three possible spin arrangements of electrons with a total quantum rotation of 1, which corresponds to three degenerate conditions.
In spectroscopic notation, the singlets and triplets O 2 are labeled 1 ? g and 3 ? -
g , respectively.
Video Singlet oxygen
Electronic structure
Singlet oxygen refers to one of two excited electronic singlet states. Both singlet status denoted 1 ?
g and 1 ? g (the previous post that read "1" shows it as a singlet state). The singlet state of oxygen is 158 and 95 kilojoules per mole higher in energy than the base state of the oxygen triplet. Under the most common laboratory conditions, the higher the energy 1 ?
g status singlet quickly converts to more stable energy and lower 1 ? g singlet status; this is, more stable than the two excited states, one with the remaining electrons in separate degenerating orbitals but no longer with such spin, called the title term, oxygen singlet , commonly abbreviated as 1 O 2 , to distinguish them from triplet base state molecules, 3 O 2 .
Molecular orbital theory predicts the basic state of electronics symbolized by the symbol of the term molek 3 ? -
g and two low singlet states, with the symbol of the term 1 ? g and 1 ?
g . These three electronic conditions differ only in spin and occupancy of two oxygen antibodies? g -korbit, which degenerates (equivalent in energy). Both of these orbitals are classified as anti-bonding and have higher energy. Following the first rule of Hund, in the ground state, these electrons are unpaired and have the same (same) rotation. The state of this open triplet molecule of oxygen molecules is different from the most stable diatomic molecule, which has a singlet ( 1 ?
g ).
Two less stable, higher energy-spirited states easily accessible from this ground state, again in accordance with Hund's first rule; the first one removes one unpaired high-energy electron from one degenerate orbital to another, where it "flips" and matches the other, and creates a new state, a singlet condition known as 1 ? g state (the term symbol, where the previous superscript "1" shows it as the singlet status). Alternatively, the two electrons can remain in the degenerate state orbitals, but the spins of one can "flip" so that it is now opposite to the second (ie, still in a separate degeneration orbital, but no longer like a spin); this also creates a new state, the singlet status called as 1 ?
g state. The soil and two singlet oxygen status can be explained by a simple schematic in the picture below.
Singlet status 1 ? g is 7882.4 cm -1 above the triplet 3 ? -
g ground state., which in other units corresponds to 94.29 kJ/mol or 0.9773 eV. 1 ? g singlet is 13 120.9 cm -1 (157,0 kJ/mol or 1.6268 eV) above the ground state.
The transition of radiation between three low-oxygen electronic states is formally prohibited as an electric dipole process. Two singlet-triplet transitions are strictly prohibited because of the spin selection rule? S = 0 and because of the parity rule that the g-g transition is off limits.
The lower, the status of O 2 ( 1 ? g ) is commonly referred to as singlet oxygen . The energy difference of 94.3 kJ/mol between the ground state and singlet oxygen corresponds to the transition of infrared near-infrared singlets at ~ 1270m. As a result, singlet oxygen in the gas phase is very long (72 minutes), although interaction with the solvent reduces the life span to microseconds or even nanoseconds.
The higher 1 ? g is very short. In the gas phase, it relaxes primarily into basic state triplets with an average age of 11.8 seconds. However, in solvents such as CS 2 and CCl 4 , it will loosen to a lower singlet 1 ? g in milliseconds due to nonradiative spoilage channels.
Paramagnetism due to orbital angular momentum
Both singlet oxygen states have no unpaired electrons and therefore no clean electron spins. However, 1 ? g is paramagnetic as shown by observation of electron paramagnetic resonance (EPR) spectrum. Paramagnetism is due to net orbital (and not rotating) electronic angular momentum. In a magnetic field degeneration level * * is divided into two levels corresponding to the molecular orbital with angular momentum 1 ? and -1 ? around the molecular axis. In a 1 state? g one of these orbitals is double-loaded and the other is empty, so the transition is possible between the two.
Maps Singlet oxygen
Production
Various methods for singlet oxygen production exist. Irradiation of oxygen gas in the presence of organic dyes as sensitizers, such as rose bengal, methylene blue, or porphyrins - photochemical methods - produce their production. Singlet oxygen can also be in non-photochemical preparative chemical procedures. One chemical method involves the decomposition of triethylsilyl hydrotronide produced in situ from triethyl silane and ozone.
- (sub 2 3 3 SiH O 3 -> (C 3 SiOOOH -> (C 2 H 5 ) 3 SiOH O 2 ( 1 ? g )
Another method uses an aqueous reaction of hydrogen peroxide with sodium hypochlorite:
- H 2 2 NaOCl -> O 2 ( 1 ? g ) NaCl H 2 O
The third method frees singlet oxygen through phosphite ozonide, which, in turn, produces in situ. The phosphite ozonide will decompose to provide a single oxygen: 3 -> (RO) 3 PO 3
The advantage of this method is that it can accept non-water conditions.
Reaction
Due to differences in their electron shells, singlet and oxygen triplets differ in their chemical properties; singlet oxygen is very reactive. The singlet oxygen life depends on the medium. In a normal organic solvent, a lifetime is only a few microseconds whereas in a solvent that does not have a C-H bond, its life can be for seconds.
Organic chemistry
Unlike basic ground oxygen, singlet oxygen participates in Diels-Alder reaction reactions [4 2] - and [2 2] -loaded loads and integrated integrated ene reactions. It oxidizes thioethers to sulfoxides and organometallic complexes. With some substrates, 1,2-dioxetane is formed; cyclic dienes such as 1,3-cyclohexadiene form [4 2] cyclic adduction.
In a single oxygen reaction with an alpha alpha allele, for example, lemon grass, indicated, by the abstraction of the ally proton, in the enzyme-like reaction, yields allyl hydroperoxide, RO-OH (R = alkyl), which can then be reduced to the corresponding aliphatic alcohol.
In reaction with water trioxidane, an unusual molecule with three connected oxygen atoms respectively, is formed.
Biochemistry
In photosynthesis, singlet oxygen can be produced from light harvesting chlorophyll molecules. One of the roles of carotenoids in photosynthesis systems is to prevent damage caused by well-produced singlet oxygen to remove excess light energy from chlorophyll molecules or quenching singlet oxygen molecules directly.
In mammalian biology, singlet oxygen is one species of reactive oxygen, which is associated with oxidation of LDL cholesterol and produces cardiovascular effects. Polyphenol antioxidants can scavenge and reduce the concentration of reactive oxygen species and can prevent damaging oxidative effects.
Ingestion of a pigment capable of generating single oxygen with activation by light can result in severe skin photosensitivity (see phototoxicity, human photosensitivity, photodermatitis, phytophotodermatitis). This is particularly of concern to animal herbivores (see Photosensitivity in animals).
Singlet oxygen is an active species in photodynamic therapy.
Analytical and physical chemistry
Direct detection of singlet oxygen is possible by using sensitive laser spectroscopy or through its very weak phosphorus at 1270 nm, which is not visible. However, at high singlet oxygen concentrations, the fluorescence of singlet oxygen species "dimol" - the simultaneous emission of two singlet oxygen molecules in a collision - can be observed as red light at 634 nm.
References
Further reading
- Bodner, G.M. (2002) Film Film Demonstration Lecture: 8.4 Liquid Oxygen - Paramagnetism and Color, West Lafayette, IN, USA: The Purdue University Department of Chemistry, see [1] and [2], accessed August 11, 2015; or, see Bodner, G.M.; K. Keyes & amp; T.J. Greenbowe (1995) Purdue University Lecture Demonstration Manual, 2nd Edn, p. TBD, New York, NY, USA: John Wiley and Sons. [The preceding reference to the magnetic properties of the oxygen state.]
External links
- NIST's web book on oxygen
- Photochemistry & amp; Photobiology Tutorial on Singlet Oxygen
- Demonstration of Red Singlet Oxygen Dimol Emission (Purdue University)
Source of the article : Wikipedia
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