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

Abstract

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