15N NMR spectroscopy of labeled alkoxyamines. 15N-Labeled model compounds for nitroxide-trapping studies in free-radical (co)polymerization

Eight 15N-labeled derivatives of 1-ethoxy-2,2,6,6-tetramethylpiperidine were synthesized in order to investigate the effects of their structural units on 15N NMR spectra. A single peak is found for each alkoxyamine. The chemical shift depends extensively on the nature of the α carbon atom of the alkoxy group. The remote functional group attached to position 4 of the piperidine ring has a smaller but still significant effect. The results of the 15N NMR measurements are supported by the detection of the N−H and N−C spin−spin coupling from the 1H and 13C NMR. The investigated alkoxyamines are model compounds for the radical-trapping products of styryl, methyl methacryloyl, α-methylstyryl, and methyl acryloyl radicals by 15N-labeled nitroxides. The potential of 15N NMR spectroscopy to analyze such products is discussed. In addition, it is shown that the 13C chemical shifts of the α carbon atom of the alkoxy group fall in an empty part of the 13C NMR spectrum, which allows the identification of trapped (macro)...