An ab initio study of the rotamers and rotations of propane-1,3-dial by DFT and SCF calculations

Eight planar rotamers of the enol form of malonaldehyde were considered at the HF (Hartree-Fock) and DFT (density functional theory) levels with 6-311 G** and D95** (Dunning/Huzinaga full double-zeta) basis sets with the aim t o establish the most stable of them and to find the energy barriers of thei r conversions. The results show that the rotamer with an intramolecular hyd rogen bond is the most stable one. High energy barriers were ascertained fo r the conversions including rotations around a CC double bond. Most of the reactions connected with breaking of the hydrogen bond display strongly asy mmetric energy barriers. Their transition states were determined as first-o rder saddle points because of one imaginary frequency in the IR spectrum re lated with a negative energy gradient.