Possible Production of Radicals by Mechanical Means

A diradical is an atom or molecule containing two impaired electrons. The properties of diradicals are for the most part like those of monoradicals. They are paramagnetic and show paramagnetic resonance absorption. Although they are very reactive chemically, this is not a reliable criterion for the diradical state. Spectroscopically the diradical will probably be a triplet state if a double bond structure coupling the two electrons is geometrically possible. But when the two electrons are fairly well isolated from each other the state is probably a double doublet, like two independent radicals. 

Any unsaturated molecule has diradical as well as singlet (nonradical) states. Usually one of the non-radical states will have a decisively lower free energy than the most stable of the diradical states, in which case the substance is not paramagnetic. Special circumstances can make the diradical state the ground state then the singlet state is an excited one. Some substances have detectable amounts of both forms in equilibrium. It is unknown whether the radical-like reactions of some compounds are characteristic of their singlet states directly or due to an undetectable amount of a more reactive triplet state in equilibrium. 

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