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Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone-the more polar the molecule the more stable the axial conformer

  • The esters of 4-hydroxy-cyclohexanone and a series of carboxylic acids R-COOH with R of different electronic and steric influence (R=Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, sec-Bu, t-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, and CBr3) were synthesized and the conformational equilibria studied by H-1 and C-13 NMR spectroscopy at 103 K and at 295 K, respectively. The geometry of optimized structures of the axial 'equatorial chair conformers was computed at the ab initio MO and DFT levels of theory. Only one preferred conformation was obtained for the axial and the equatorial conformer as well. When comparing the conformational equilibria of the cyclohexanone esters with those of the corresponding cyclohexyl esters a certain polarity contribution of the cyclohexanone framework was revealed, which is independent of the substituent effects and increases the stability of the axial conformers by a constant amount.

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Author:Erich Kleinpeter, Matthias Heydenreich, Andreas Koch, Torsten LinkerORCiDGND
ISSN:0040-4020 (print)
Parent Title (English):Tetrahedron
Place of publication:Oxford
Document Type:Article
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Tag:4-Substituted cyclohexanones; ALTONA equation; Conformational analysis; Dynamic NMR; Quantum chemical calculations; Simulation of H-1 NMR spectra
First Page:2363
Last Page:2373
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert