title: Assignment of the absolute configuration of alpha-chiral carboxylic acids by 1H NMR spectroscopy
abstract: The prediction of the absolute configuration of alpha-chiral carboxylic acids from the 1H NMR spectra of their esters with (R)- and (S)-ethyl 2-hydroxy-2-(9-anthryl) acetate [(R)- and (S)-9-AHA, 5] is discussed. Low-temperature NMR experiments, MM, semiempirical, and aromatic shielding effect calculations allowed the identification of the main conformers and showed that, in all esters studied, conformer ap is the most stable. A simple model for the assignment of the absolute configuration from NMR data is presented, and its reliability is corroborated with acids 6-31 of known absolute configuration. In addition to 5, other auxiliary reagents with open (32-38) and cyclic (39-42) structures have also been studied. trans-(+)- and (-)-2-phenyl-1-cyclohexanol (41) was found to be particularly efficient and produced delta delta RS values similar to those of 5.
authors.affiliation: Departamento de Quimica Organica, Facultad de Quimica, Universidad de Santiago de Compostela, Spain.
authors.initials: MJ
authors.lastname: Ferreiro
authors.initials: SK
authors.lastname: Latypov
authors.initials: E
authors.lastname: Quinoa
authors.initials: R
authors.lastname: Riguera