title: Studies on the s-cis-trans isomerism for some furan derivatives through IR and NMR spectroscopies and theoretical calculations.
abstract: The s-cis-trans isomerism of two furan derivatives [2-acetyl- (AF) and 2-acetyl-5-methylfuran, (AMF)] was analyzed, using data from the deconvolution of their carbonyl absorption band in two solvents (CH(2)Cl(2) and CH(3)CN). These infrared data showed that the O,O-trans conformers predominate in the less polar solvent (CH(2)Cl(2)), but these equilibria change in a more polar solvent (CH(3)CN) leading to a slight predominance of the O,O-cis conformers, in agreement with the theoretical calculations. The later results were obtained using B3LYP-IEFPCM/6-31++g(3df,3p) level of theory, which taking into account the solvent effects at IEFPCM (Integral Equation Formalism Polarizable Continuum Model). Low temperature (13)CNMR spectra in CD(2)Cl(2) (ca. -75 °C) showed pairs of signals for each carbon, due to the known high energy barrier for the cis-trans interconversion leading to a large predominance of the trans isomers, which decreases in acetone-d(6). This was confirmed by their (1)HNMR spectra at the same temperatures. Moreover, despite the larger hyperconjugative interactions for the O,O-cis isomers, obtained from NBO data, these isomers are destabilized by the their Lewis energy.
authors.affiliation: Physical Organic Chemistry Laboratory, Chemistry Institute, State University of Campinas, Caixa Postal 6154, 13083-970 Campinas, SP, Brazil. rittner@iqm.unicamp.br
authors.forename: Roberto
authors.initials: R
authors.lastname: Rittner
authors.forename: Lucas C
authors.initials: LC
authors.lastname: Ducati
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Cormanich
authors.forename: Barbara C
authors.initials: BC
authors.lastname: Fiorin
authors.forename: Carolyne B
authors.initials: CB
authors.lastname: Braga
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Abraham
mesh_terms: D000107:Acetylation; D005663:Furans / Q000737:chemistry*; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D008968:Molecular Conformation; D012997:Solvents; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D005663:Furans; D012997:Solvents