Ab initio study of malonaldehyde rotamers

Malonaldehyde rotamer geometries were optimized using ab initio calculations at the HF level with STO-3G** and 6-21G** basis sets. The most stable rotamer is the omega-shaped one with cyclic structure and intramolecular hydrogen bond. The most unstable rotamer is that obtained by rotation of the omega-rotamer around the CO single bond by 180 degrees due to the loss of the additional stabilization contributed by the intramolecular H-bond. The energy barriers separating the different rotamers vary between 13 and 233 kJ.mol(-1). The structure of the transition states is non-planar with rotation angles varying between 72 and 98 degrees.