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13 C GIAO DFT calculation as a tool for configuration prediction of N–O group in saturated heterocyclic N ‐oxides
Author(s) -
Pohl Radek,
Potmischil Francisc,
Dračínský Martin,
Vaněk Václav,
Slavětínská Lenka,
Buděšínský Miloš
Publication year - 2012
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.3810
Subject(s) - chemistry , chemical shift , density functional theory , atomic orbital , computational chemistry , carbon 13 nmr , group (periodic table) , atomic charge , stereochemistry , molecule , organic chemistry , quantum mechanics , physics , electron
Tropane, tropinone, pseudopelletierine and cocaine were oxidized in situ in a nuclear magnetic resonance (NMR) tube providing mixtures of exo / endo N ‐oxides. Observed 13 C 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 13 C 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.