Rotational isomerism, barrier to internal rotation and electric dipole moment of acrylic acid by microwave spectroscopy

Microwave spectra have been observed for the normal and acid deuterated isotopic species of the s-cis and s-trans rotamers of acrylic acid in the ground and a number of excited torsional states. Both rotameric forms are planar with the hydroxyl group adopting the cis conformation relative to the carbonyl group. The dipole moments determined from Stark effect measurements are [graphic omitted].The difference in zero point vibrational energy between the two rotamers and the 1 â†� 0 torsional frequencies have been determined from relative intensity measurements as E°s-trans—E°s-cis= 58 ± 20 cm–1, νs-cis= 105 ± 20 cm–1, νs-trans= 95 ± 20 cm–1. The potential function hindering the internal rotation is essentially two-fold with a barrier of 1340 ± 500 cm–1(16.0 ± 6.0 kJ mol–1) at an angle of 89 ± 4° from the s-cis configuration.