The microwave spectrum and potential function of propanal

Abstract

The potential function for internal rotation of the aldehyde group in propanal has been determined. All available microwave and far-infrared data are fitted to the potential V(α)=½ [graphic omitted] V_n(1 – cos nα) and where (in cm^–1)V₁= 251(2), V₂= 736(8), V₃= 550(4), V₄=–179(5) and V₅=–7(4). The energy difference between the two stable conformers has been redetermined from microwave relative intensities to be ΔW(gauche–cis)= 420(27) cm^–1. Torsional fundamentals measured in the infrared have also been used in the potential function calculation. Isotopic data have been measured providing insight into the torsional motion in CH₃CH₂CH¹⁸O and CH₃CH₂CDO. The resulting potential is compared with some isoelectronic molecules. The dipole moment of gauche propanal has been measured as 2.864(8) D orientated within 0.6° of the CO bond.