Zero-point Average Structure of a Molecule Containing Two Symmetric Internal Rotors. Acetone

Abstract

Abstract The theory of vibrational correction to the observed moments of inertia of a molecule which contains an internal rotor has been extended to the case of two symmetric internal rotors, and applied to the analysis of the structure of acetone. The zero-point average structure has been determined by using the moments of inertia obtained by microwave spectroscopy and the bond distances from gas electron diffraction. The zero-point average parameters have been determined as follows: C–C 1.517±0.003 Å; C=O 1.210±0.004 Å; C–H 1.091±0.003 Å; ∠HGH 108° 30′±30′; ∠CCC 116° O′±15′. The isotope effects in the structure parameters have also been observed in terms of the increase caused by deuteration to be δ(DCD)+10′±12′; δ(CCC)−17′±2′. The tilt angle of the methyl top was determined to be 2° 1′±30′.