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Stabilization of Free Radicals by Adsorption: Detection by Paramagnetic Resonance


IT is known that quinhydrones are weak acids and may therefore form ions in strongly alkaline solutions. Due to the loss of two hydrogen atoms of the quinhydrone compound, two identical semiquinone ions can be expected; for example: These semiquinone ions, having an odd number of electrons, should be paramagnetic. Michaelis has proved the existence of free radical ions of this type during alkaline reduction of phenanthrene-quinone-3-sulphonate1 by potentiometric and magnetic measurements. It would be difficult to demonstrate the existence of free radical ions in the case of many quinhydrones, for example, p-benzoquinhydrone, as they are too unstable in alkaline solution. It occurred to us, however, that it might be possible to stabilize such unstable radical ions by adsorption of quinhydrone on suitable basic surfaces. A sufficiently basic surface could have the same effect as the alkaline solution, and the adsorption might stabilize the free radicals formed.

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BIJL, D., KAINER, H. & ROSE-INNES, A. Stabilization of Free Radicals by Adsorption: Detection by Paramagnetic Resonance. Nature 174, 830–831 (1954).

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