Structures and conformational dynamics of monomethylated derivatives of acrolein: A quantum-chemical study

For all monomethylated derivatives of acrolein: methyl vinyl ketone СH3C(O)CHCH2, methacrolein CHOC(CH3)CH2, trans- and cis-crotonaldehydes CHOCHCHCH3 in the ground electronic state, the conformer energy differences, barriers to internal rotation, geometric parameters of minima and transitions states corresponding to the barriers of internal rotation were studied by means of various quantum-chemical methods (B3LYP, MP2, QCISD, CCSD(T), CASSCF and others). The conformer energy differences were also estimated using the extrapolative technique VFPA. The vibrational frequencies were calculated at MP2/6-311G(d,p) level in harmonic and different anharmonic approximations. The coupling of two internal rotation motions was investigated by constructing one- and two-dimensional potential energy surface sections and by solving respective vibrational problems.