CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, STRUCTURAL PARAMETERS, ABINITIO CALCULATIONS, AND VIBRATIONAL ASSIGNMENT OF CYCLOPROPANECARBOXALDEHYDE

The asymmetric torsional potential function, conformational energy difference, vibrational frequencies, and structural parameters of cyclopropanecarboxaldehyde have been obtained from ab initio calculations at the 3-21 G and/or 6-31 G* basis set levels. These results have allowed for a reinterpretation or clarification of some of the corresponding results obtained from experiment. The conformations that have the oxygen atom oriented cis and trans to the three-membered ring are observed and calculated to be the most stable and high energy forms in the gaseous phase, respectively. From the ab initio calculations using the 6-31 G* basis set, the energy difference between the two conformers is 114 cm-1. For the liquid, the trans conformer is more stable and is the only rotamer present in the annealed solid. Based on a combination of results obtained from ab initio calculations, microwave spectroscopy, and the electron diffraction technique, r(o) structural parameters have been obtained for both conformations.