Biradicals electron spin resonance

The nitroxide biradical 35 has approximate Z)2 symmetry. The electron spin resonance (ESR) spectrum has been obtained in ethanol and computer simulated in frozen ethanol <1995MRCS129>. 

The electron spin resonance (ESR) spectra of the radical anion of 2,2 -bipyridine, sometimes in the form of its alkali metal com-plgx, 71.175,177.299-304 radical anion of 3,3 -bipyridine, ° and the radical anion of 4,4 -bipyridine, ° ° usually obtained by reduction of the bipyridines with an alkali metal, have been measured, and hyperfine splitting constants were assigned. Related biradical species have also been investigated. The ESR spectrum of the 4,4 -bipyridinium radical cation, of which... 

Electron-spin resonance (e.s.r.) spectroscopy is a technique for the study of species containing one or more unpaired electrons. The scope of the method includes the detection and characterization of some transition-metal ions, simple molecules and ions (e.g. O2, NO, NOg, COi"), and organic radicals, including biradicals and triplet states. 

P. Maruthamuthu and J. C. Scaiano, Biradicals double trapping by nitric oxide. An electron spin resonance study,/. Phys. Chem. 82, 1588-1591 (1978). 

This assumption is consistent with experimental data obtained recently by Campredon el al49 These authors trapped a biradical intermediate during electron spin resonance (ESR) experiments. Signals attributed to the radicals 61-64 were monitored when NO was added to solutions of spiropyrans 56-59. Similar results were obtained with spirooxazines 29 and 60 leading to radicals 65 and 66. Nevertheless there is no direct evidence indicating that the trapped biradicals are on the reaction path leading to the merocyanine. 

Electron spin resonance (ESR) spectroscopy is also known as electron paramagnetic resonance (EPR). spectroscopy or electron magnetic resonance (EMR) spectroscopy. The main requirement for observation of an ESR response is the presence of unpaired electrons. Organic and inorganic free radicals and many transition metal compounds fulfil this condition, as do electronic triplet state molecules and biradicals, semicon-ductor impurities, electrons in unfilled conduction bands, and electrons trapped in radiation-damaged sites and crystal defect sites. 

Buchwalter, S. L., and Closs, G. L. "Electron Spin Resonance and CIDNP Studies on 1,3-Cyclo-pentadiyls. A Localized 1,3 Carbon Biradical System with a Triplet Ground State. Tunneling in Carbon-Carbon Bond Formation." J. Am. Chem. Soc., 101,4688-4694 (1979). 

Cheletrophic spin trapping of nitric oxide. Ultraviolet light converts the phenolic compound to a biradical, which rapidly reacts with nitric oxide to form a stable nitroxyl radical that is readily observable by electron paramagnetic resonance. 

Milov, A. D., Ponomarev, A. B., and Tsvetkov, Y. D. (1984). Electron—electron double resonance in electron spin echo Model biradical systems and the sensitized photolysis of decalin. Chem. Phys. Lett. 110, 67—72. 

By including electron correlation in the wave function the UHF method introduces more biradical character into the wave function than RHF. The spin contamination part is also purely biradical in nature, i.e. a UHF treatment in general will overestimate the biradical character. Most singlet states are well described by a closed-shell wave function near the equilibrium geometry, and in those cases it is not possible to generate a UHF solution which has a lower energy than the RHF. There are systems, however, for which this does not hold. An example is the ozone molecule, where two types of resonance structure can be drawn. Figure 4.8. 

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