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Concentration and solvent effects on the conformational equilibrium of cis-3-ethoxycyclohexanol by 1H NMR and IR spectroscopy

✍ Scribed by Paulo R. de Oliveira; Danilo S. Ortiz; Roberto Rittner

Publisher: Elsevier Science
Year: 2006
Tongue: English
Weight: 149 KB
Volume: 788
Category: Article
ISSN: 0022-2860
DOI: 10.1016/j.molstruc.2005.11.009

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✦ Synopsis

NMR data, in CCl 4 , show that an increase in the concentration of cis-3-ethoxycyclohexanol (cis-3-ECH) shifts the conformational equilibrium from the ax-ax conformer (X ax-ax Z51% at 0.01 mol L K1 ), stabilized by an intramolecular hydrogen bond (IAHB), to the eq-eq conformer (X eq-eq Z67% at 0.40 mol L K1 ), which forms intermolecular hydrogen bonds (IEHB), as confirmed by IR data. The Dn values, obtained by IR spectra, indicated that cis-3-ECH presents a stronger IAHB than the cis-3-methoxycyclohexanol, due to the increase in substituent steric and group electronegativity effects. The percentage of eq-eq conformer also increases with the solvent basicity, from 51% (DG eqeqaxax ZK0.03 kcal mol K1 in CCl 4 to 97% (DG eqeqaxax ZK2.05 kcal mol K1 ) in DMSO. Values of 4.58 and 5.39 kcal mol K1 , for the IAHB strength in cis-3-ECH, were obtained from the theoretical data at CBS-4M and B3LYP/6-311CG** levels, respectively.

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