Ab initio calculation study on conformation and vibrational frequencies of 3-methyl-3-penten-2-one

Geometries of nine conformers of 3-methyl-3-penten-2-one have been optimized by ab initio method using both of ST0-3G and 3-21G basis sets. The stabilities of different conformers are compared, and the properties and barriers of internal rotations are discussed. Calculated results show that ( i ) there are three possible stabler conformers; ( ii ) both of (trans, s-trans) and (trans, s-cis) conformers.can simultaneously exist and can be tranformed into each other; ( iii ) calculated vibrational frequencies are in good agreement with experimental spectra.