Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269-3060, United States.
Institute of Industrial Organic Chemistry , Annopol 6, 03-236 Warsaw, Poland.
J Org Chem. 2017 Sep 15;82(18):9279-9290. doi: 10.1021/acs.joc.7b00846. Epub 2017 Sep 6.
Three new homologous TEMPO oxoammonium salts and three homologous nitroxide radicals have been prepared and characterized. The oxidation properties of the salts have been explored. The direct C NMR and EPR spectra of the nitroxide free radicals and the oxoammonium salts, along with TEMPO and its oxoammonium salt, have been successfully measured with little peak broadening of the NMR signals. In the spectra of all ten compounds (nitroxides and corresponding oxoammonium salts), the carbons in the 2,2,6,6-tetramethylpiperidine core do not appear, implying paramagnetic properties. This unpredicted overall paramagnetism in the oxoammonium salt solutions is explained by a redox equilibrium as shown between oxoammonium salts and trace amounts of corresponding nitroxide. This equilibrium is confirmed by electron interchange reactions between nitroxides with an N-acetyl substituent and oxoammonium salts with longer acyl side chains.
已经制备和表征了三种新的同源 TEMPO 氧代铵盐和三种同源氮氧自由基。研究了盐的氧化性质。用直接 C NMR 和 EPR 光谱法成功测量了氮氧自由基和氧代铵盐以及 TEMPO 及其氧代铵盐的 NMR 信号，几乎没有峰展宽。在所有十种化合物（氮氧自由基和相应的氧代铵盐）的光谱中，2,2,6,6-四甲基哌啶核中的碳原子均未出现，表明具有顺磁性。氧代铵盐溶液中这种出乎意料的整体顺磁性可以通过氧化还原平衡来解释，如氧代铵盐与痕量相应氮氧自由基之间的平衡所示。通过具有 N-乙酰取代基的氮氧自由基与具有更长酰侧链的氧代铵盐之间的电子交换反应，证实了这种平衡。
