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Theoretical and spectroscopic studies on the conformational equilibrium of 9-oxabispidines in solution

Title data

Breuning, Matthias ; Paasche, Alexander ; Steiner, Melanie ; Dilsky, Stefan ; Gessner, Viktoria H. ; Strohmann, Carsten ; Engels, Bernd:
Theoretical and spectroscopic studies on the conformational equilibrium of 9-oxabispidines in solution.
In: Journal of Molecular Structure. Vol. 1005 (2011) Issue 1-3 . - pp. 178-185.
ISSN 0022-2860
DOI: https://doi.org/10.1016/j.molstruc.2011.08.047

Abstract in another language

The conformational behavior of N,N-dimethyl-9-oxabispidine and four 2-endo-substituted 9-oxabispidines (3,7-diaza-9-oxabicyclo[3.3.1]nonanes) in solution was investigated by theoretical and spectroscopic methods. The electronic energies of all conformers were calculated on the B3LYP/TZVP level of theory and solvent effects were taken into account by the continuum solvent model COSMO. Only two conformers, the double chair form A1 (both N–R exo) and the boat–chair form B2 (Nchair–R exo, Nboat–R endo), were of energetic relevance (ΔE ⩽ 18.2 kJ mol−1), with the former one strongly dominating (A1:B2 ⩾ 98:2 at room temperature), independent of the existence or nature of the 2-endo-substituent. Compared to the corresponding bispidines, the dominance of the double chair conformers A1 was more pronounced in the 9-oxabispidines, presumably due to stronger N,O-repulsions in their boat–chair conformers B2. 1H NMR studies on 21 2-endo-substituted 9-oxabispidines, using the 3J coupling constants of the exo-methylene protons with the neighboring bridgehead protons as conformational probes, gave no evidence on a noticeable population of the boat–chair conformers B in solution, which is good agreement with the calculations. In addition, the experimentally determined proton shifts of two 2-endo-substituted 9-oxabispidines matched excellently with those calculated for their double chair conformers A1.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: 9-Oxabispidine; Conformation; DFT calculation; Boat–chair equilibrium; Bispidine
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Chemistry > Professor Organic Chemistry > Professor Organic Chemistry - Univ.-Prof. Dr. Matthias Breuning
Result of work at the UBT: No
DDC Subjects: 500 Science > 540 Chemistry
Date Deposited: 11 Jan 2022 13:13
Last Modified: 11 Jan 2022 13:16
URI: https://eref.uni-bayreuth.de/id/eprint/68305