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 STO-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.