Conformational analysis of a seven-membered ring azasugar, (3R,4R,6S)-trihydroxyazepane: Comparison of GIAO calculation and experimental NMR spectra on 13C chemical shifts

Pao Ling Yeh, Chin Kuen Tai, Tzenge Lien Shih*, Hui Ling Hsiao, Bo Cheng Wang

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

8 Scopus citations

Abstract

DFT/B3LYP/6-311++G(d,p) calculation of the relative stable conformations of (3R,4R,6S)-trihydroxyazepane are presented. The GIAO/DFT/OPBE, GIAO/DFT/B3LYP and GIAO/HF single point calculations with 6-311++G(d,p), 6-311+G(2d,p), cc-pVDZ and cc-pVTZ basis sets of (3R,4R,6S)-trihydroxyazepane were conducted to generate their 13C NMR chemical shifts. According to calculation results, 14 (3R,4R,6S)-trihydroxyazepane with optimized structure were generated. There were three conformers which contain the intramolecular hydrogen bonding exhibit a lowest electronic energies and TCN1(eq) was the most stable conformer than others. Boltzmann weighting factor analysis exhibits that TCN1(eq), TCN3(eq) and TCN5(eq) dominate a major contribution among the 14 conformers. The individual calculated NMR results of TCN1(eq), TCN3(eq) and TCN5(eq) represents a quite close correlation with experimental data. Moreover, the experimental 13C NMR chemical shifts gave only the average contribution of all conformers. In our investigation, the calculated 13C NMR chemical shifts of mixture (3R,4R,6S)-trihydroxyazepane exhibit a good agreement with the experimental NMR data. Calculated NMR results of mixture (3R,4R,6S)-trihydroxyazepane conformers display a remarkable MAE and RMS improvement over that of each individual conformer. A good calculation method and basis set choice to evaluate the theoretical chemical shifts for these conformers is HF/cc-pVTZ.

Original languageEnglish
Pages (from-to)64-71
Number of pages8
JournalJournal of Molecular Structure
Volume1018
DOIs
StatePublished - 27 06 2012
Externally publishedYes

Keywords

  • Conformational analysis
  • NMR calculation
  • Trihydroxyazepane

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