The Structure and Torsional Dynamics of Two Methyl Groups in 2-Acetyl-5-methylfuran as Observed by Microwave Spectroscopy

International audienceThe molecular beam Fourier transform microwave spectra of 2-acetyl-5-methylfuran were recorded in the frequency range 2-26.5 GHz. Quantum chemical calculations calculated two conformers with a trans and a cis configuration of the acetyl group, both of which were assigned in the experimental spectrum. All rotational transitions split into quintets due to the internal rotations of two non-equivalent methyl groups. Using the program XIAM, the experimental spectra can be simulated with standard deviations within the measurement accuracy, yielding well-determined rotational and internal rotation parameters, inter alia the V3 potentials. While the V3 barrier height of the ring methyl rotor does not change for both conformers, that of the acetyl methyl rotor differs by about 100 cm−1. The predicted values from quantum chemistry are only in the correct order of magnitude