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>ESR Study of Radical Structure and Symmetrical Hydrogen Bond in a Single Crystal of Potassium Hydrogen Maleate Irradiated at 77deg;K
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ESR Study of Radical Structure and Symmetrical Hydrogen Bond in a Single Crystal of Potassium Hydrogen Maleate Irradiated at 77deg;K
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机译：ESR Study of Radical Structure and Symmetrical Hydrogen Bond in a Single Crystal of Potassium Hydrogen Maleate Irradiated at 77deg;K
ESR study has been carried out on the structure of radicals produced in an irradiated single crystal of potassium hydrogen maleate which is known as a typical compound having a symmetrical intramolecular hydrogen bond. It was found that in the radical formed by removal of the acidic proton the unpaired electron occupies the sgr; antibonding orbital between the inhyphen;planeporbitals of the two ring oxygen atoms, when the crystal is irradiated at 77deg;K. The principal values of thegtensor for this radical were determined to begxxequals;2.0043,thinsp;gyyequals;2.0039, andgzzequals;2.0079. The hyperfine couplings for the two vinylene protons are equivalent and have the nearly isotropic value of5plusmn;1G. On the other hand, if the crystal is warmed up to room temperature after irradiation at 77deg;K, the same species of radical is formed but the unpaired electron occupies the delocalized pgr; orbital. This radical is the same as that found in roomhyphen;temperature irradiation which was previously reported. Both the radicals possess the mirror symmetry perpendicular to theCdblbnd;Cbond as does the mother molecule. The formations of such symmetrical radicals are closely related to the symmetrical structure and the extremely short Omiddot;middot;middot;O distance of the parent molecule, which are due to the symmetrical hydrogen bond. The cause of the formations of the sgr; and pgr; electron radicals from the same mother molecule is also discussed.
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