Two-dimensional character of internal rotation of furfural and other five-member heterocyclic aromatic aldehydes.

The features of nuclear motion corresponding to the rotation of the formyl group (CHO) are studied for the molecules of furfural and some other five-member heterocyclic aromatic aldehydes by the use of MP2/6-311G** quantum chemical approximation. It is demonstrated that the traditional one-dimensional models of internal rotation for the molecules studied have only limited applicability. The reason is the strong kinematic interaction of the rotation of the CHO group and out-of-plane CHO deformation that is realized for the molecules under consideration. The computational procedure based on the two-dimensional approximation is considered for low lying vibrational states as more adequate to the problem.

The barriers to internal rotation of benzaldehyde and benzoyl fluoride: "reconciliation" between theory and experiment.

This work is devoted to investigation of the known problem of the discrepancy between the experimental and theoretical values for the barrier to internal rotation of the molecules comprised of a benzene ring and a π-conjugated substituent, such as benzaldehyde and benzoyl fluoride. The possible reasons of such discrepancy are considered. As a result the conclusion was drawn that the origin of the problem is incorrectness of the assignments of the torsional levels higher than first, both for benzaldehyde and benzoyl fluoride. In addition the significant kinematic interaction between torsional vibration and out-of-plane CHO deformation was found for benzaldehyde.