Ab initio calculations of the rotational barrier in 3-methyl-3-cyclopropenecarboxaldehyde and its fluoride derivative

The structural stability and internal rotation in 3-methyl, 3-cyclopropenecarboxaldehyde and 3-methyl, 3-cyclopropenecarboxylic acid fluoride were investigated by ab initio calculations with 3-21G and 6-31G* (6-311G* for the aldehyde) basis sets. The calculations were carried out at restricted Hartree-Fock (HF) and second-order Moller-Plesset (MP2) levels. From the calculations, the trans form (carbonyl group eclipsing the α-hydrogen) was predicted to be the lower energy conformer for the molecules. Full optimizations were performed at the energy minima and transition states. The calculations predicted an asymmetric potential function with the trans conformer lower in energy for both molecules.