DFT studies of N-alkoxyaminyl radicals: ESR parameters, UV–vis absorptions and generations

Although aminoxyl radicals (RR′NO˙) are well-known as organic stable free radicals, the isomeric radicals, N  -alkoxyaminyl radicals (RN˙OR′), are scarcely studied in the area of theoretical study. We carried out the theoretical calculation of the isotropic 14N hyperfine coupling constants (aN), g-factors, electronic absorbances, and generation mechanisms of N-alkoxyaminyl radicals. For thirty one N-alkoxyaminyl radicals, the PCM-DFT calculation at B3LYP/6-31+G(d,p) could well reproduce the experimental data of aN and g-factors, where R2 were 0.9796 and 0.9439, respectively. The UV–vis spectra were moderately reproduced by PCM-TD-DFT (PBE0/6-31+G(d,p)), where R2 was 0.9205. Additionally, the use of a linear scaling procedure precisely reproduced the UV–vis spectrum. The activation Gibbs free energies for the generation of N-alkoxyaminyl radicals and aminoxyl radicals in the competing reactions of nitroso compounds with alkyl radicals were estimated by DFT and coupled cluster calculations. The activation free energies for the generation of N-alkoxyaminyl radicals were estimated to be 9–18 kcal/mol at B3LYP/6-31+G(d,p). The reported product ratios in the competing reactions could be reasonably explained by the differences in the activation free energies.

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