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Published on: September 16, 2019
Acetyl Methyl Torsion in Pentan-2-one As Observed by Microwave Spectroscopy
Maike Andresen1,2, Isabelle Kleiner2, Martin Schwell2
1Institute of Physical Chemistry , RWTH Aachen University , Landoltweg 2 , D-52074 Aachen , Germany.
Abstract:
The rotational spectra of two conformers of pentan-2-one (also known as methyl propyl ketone) were recorded in the frequency range from 2 to 40 GHz using two molecular jet Fourier transform microwave spectrometers. Fine splittings due to the internal rotations of the acetyl methyl group CH3CO- and the butyryl methyl group -COCH2CH2CH3 were resolved and analyzed with high accuracy. The torsional barriers of the acetyl and the butyryl methyl groups are 238.14 and 979 cm-1, respectively, for the lowest energy conformer, as well as 188.384 and 1032 cm-1, respectively, for the other one. From the results obtained for the acetyl methyl group, a general rule to predict its torsional barrier in ketones based on the molecular symmetry is proposed.
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