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Type: Artigo de periódico
Title: Influence of intramolecular hydrogen bonding on the conformational equilibrium of cis-3-N,N-dimethylaminocyclohexanol compared with trans-3-N,N-dimethylaminocyclohexanol and cis- and trans-3-N,N-dimethylamino-1-methoxycyclohexane
Author: de Oliveira, PR
Ribeiro, DS
Rittner, R
Abstract: H-1 NMR data show that concentration increase shifts the conformational equilibrium of cis-3-N,N-dimethylaminocyclohexanol (1) (cis-3-DACH) from the 1aa conformer, stabilized by an intramolecular hydrogen bond (IAHB), to the lee conformer [43% (0.01 m) to 70% (0.40 m), in CCl4], which can form intermolecular hydrogen bonds (IEHB). The percentage of lee conformer also increases with the solvent basicity from 36% in C6D to 89% in DMSO. The conformational equilibrium of the trans isomer (trans-3-DACH) is also dependent on concentration, since 1ae increases from 77% (0.05 m) to 84% (0.40 m) in CCl4 but not with the solvent polarity. The occurrence of an IAHB in cis-3-DACH was confirmed by the study of a model compound, cis-3-N,N-dimethylamino-l-methoxycyclohexane (2) (cis-3-DAMCH), lacking an OH group and presenting a single conformer 2ee (similar to 95%). The corresponding trans isomer (trans-3-DAMCH) behaves similarly to trans-3-DACH, since the 2ae conformer occurs as similar to 83%, in the studied solvents. The PCMODEL program gave very good coupling constant values for the qualitative analysis of energy changes in the study of concentration and solvent effects, since the energy values obtained for cis and trans isomers of 3-DACH were in good agreement with the theoretically calculated [B3LYP/6311 +g(d,p) level] values. The averaged calculated energy of the IAHB, for conformer 1aa of cis-3-DACH, with optimization of the reference structure and at several levels of theory, is 5.74 kcal mol(-1) (1 kcal = 4.184 kJ). Copyright (c) 2005 John Wiley & Sons, Ltd.
Subject: conformational analysis
theoretical calculations
intramolecular hydrogen bond
NMR spectroscopy
Country: Inglaterra
Editor: John Wiley & Sons Ltd
Citation: Journal Of Physical Organic Chemistry. John Wiley & Sons Ltd, v. 18, n. 6, n. 513, n. 521, 2005.
Rights: fechado
Identifier DOI: 10.1002/poc.896
Date Issue: 2005
Appears in Collections:Unicamp - Artigos e Outros Documentos

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