13C GIAO DFT calculation as a tool for configuration prediction of N–O group in saturated heterocyclic N‐oxides |
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Authors: | Radek Pohl Francisc Potmischil Martin Dračínský Václav Vaněk Lenka Slavětínská Miloš Buděšínský |
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Affiliation: | 1. Institute of Organic Chemistry and Biochemistry, Academy of Science of the Czech Republic, , CZ‐166 10 Prague 6, Czech Republic;2. Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, , RO‐030018 Bucharest‐1, Romania |
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Abstract: | Tropane, tropinone, pseudopelletierine and cocaine were oxidized in situ in a nuclear magnetic resonance (NMR) tube providing mixtures of exo/endo N‐oxides. Observed 13C chemical shifts were correlated with values calculated by gauge‐including atomic orbitals density functional theory (DFT) OPBE/6‐31G* method using DFT B3LYP/6‐31G* optimized geometries. The same method of 13C chemical shift calculation was applied on series of methyl‐substituted 1‐methylpiperidines and their epimeric N‐oxides described in literature. The results show that using this undemanding calculation method enables assignment of configuration of N–O group in N‐epimeric saturated heterocyclic N‐oxides. The approach enables assigning of the configuration with high degree of certainty even if NMR data of only one isomer are available. An improved method of in situ oxidation of starting amines in an NMR tube is also described. Copyright © 2012 John Wiley & Sons, Ltd. |
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Keywords: | NMR 13C 1H saturated heterocyclic N‐oxides chemical shift calculations DFT |
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