The internal rotation potential function of monochloroacetaldehyde in the ground electronic state: A quantum-chemical calculation

The applicability of the quantum-chemical approximations of various levels (RHF, MP2, CASSCF and CISD) as methods for describing an internal rotation potential energy curve which, in essence, has two potential wells is consid ered. Such a curve, unusual for molecules with substituted methyl tops, is characteristic of the monochloroacelaldehyde CClH2CHO molecule in the groun d electronic state. All quantum-chemical approximations mentioned above, wh ich differ in the method for taking into account electron correlation and t he completeness of the basis set of atomic orbitals (including the effectiv e core potential approximation), correctly describe the complex shape of th e internal rotation potential function in the region corresponding to the t rans conformer. The torsional motion is to a substantial degree coupled wit h molecular skeleton vibrations. The calculation results are in close agree ment with the experimental data.