Isotopic dependence of the hydrogen-transfer-triggered methyl-group rotation in deuterated 5-methyltropolone

Abstract

We present here the first experimental study of the microwave spectrum of deuterated 5-methyltropolone, a molecule which exhibits two large-amplitude motions: an intramolecular hydrogen transfer (deuterium transfer in the current case of deuterated 5-methyltropolone) and a methyl torsion. The main goal of this study was to get information on the isotopic dependence of the main tunneling parameters of 5-methyltropolone in the framework of the two dimensional tunneling formalism, which previously has shown some counterintuitive results for isotopic dependence of tunneling parameters in 2-methylmalonaldehyde. Measurements were carried out by Fourier-transform microwave spectroscopy in the 9GHz to 26GHz frequency range. Theoretical analysis was carried out using a tunneling-rotational Hamiltonian based on a G12m extended-group-theory formalism. Our global fit of 384 transitions to 17 molecular parameters gave a weighted root-mean-square deviation of 0.8. The current study on the isotopic dependence of the main tunneling parameters in 5-methyltropolone supports the assumption of possible “leakage” between tunneling parameters in the two-dimensional tunneling formalism in use.