Generation of nitroxides with a chloro or nitro substituent in β‐position

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Abstract
Nitroxides 1 with a chloro or nitro substituent in the ß‐position can be generated by three methods: addition of radicals to gem‐chloro nitroso‐ or gem‐nitro nitroso compounds (reaction 1), addition of chloro‐ or nitroalkyl radicals to nitroso compounds (reaction 2), and addition of atomic chlorine to nitrones (reaction 3). With nitrogen dioxide instead of chlorine, ß‐nitronitroxides cannot be obtained, because NO2 adds to nitrones via oxygen in a presumably charge‐controlled process. The presence of the chloro or nitro substituent in the ß‐position influences the unpaired spin density at nitrogen and thus lowers the nitroxide splitting constant.The ESR signals of the nitroxides 1 clearly show the hyperfine splittings caused by the ß‐substituent. In the presence of nitric oxide, ß‐chloronitroxides cannot be detected and ß‐nitronitroxides only with difficulty.

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