Conformational preferences for some 5-substituted 2-acetylthiophenes through infrared spectroscopy and theoretical calculations

► cis-trans isomerism of 5-substituted 2-acetylthiophenes was analyzed and quantified. ► Theoretical calculations were performed for isolated state and solutions (IEFPCM). ► A close agreement between infrared data and theoretical calculations was obtained. ► Low temperature C-13 NMR spectra confirmed the low energy barrier (∼8 kcal mol−1).