Properties of Spin-Labeled Alkynylpyrazoles

The structure of spin-labeled acetylenes includes 7r-electron-rich pyrazole and 

The spectrum of radical 101 appears as a quintet (1 2 3 2 1) caused by the hyperfine interaction (HFI) with two equivalent nitroxide nitrogen nuclei ( 2n = 0.74 mT), each line of the quintet being additionally split due to hyperfine 

The g-factors of radicals 101 and 102 are 2.0065 and 2.0059, respectively. The pyrazolylnitroxides have effective magnetic moments at room temperature corresponding to the standard values for one unpaired electron per molecule (1.71 0.05 B.M.). The values of effective magnetic moments of the nitroxyls practically do not change in the temperature range 5-300K. 

Eigure 6 shows the EPR spectra with deflned g-tensor and HFI components for radicals 101 and 102. 

EPR spectia (2-mm band) of radical 101 and 102 (5 x 10 M) in oxygen-free toluene at 130-140K. 

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