ChemPhysChem 2015-06-22

Acetyl Methyl Torsion in N-Ethylacetamide: A Challenge for Microwave Spectroscopy and Quantum Chemistry.

Raphaela Kannengießer, Marcel J Lach, Wolfgang Stahl, Ha Vinh Lam Nguyen

Index: ChemPhysChem 16 , 1906-11, (2015)

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Abstract

The gas-phase structures and parameters describing acetyl methyl torsion of N-ethylacetamide are determined with high accuracy, using a combination of molecular beam Fourier-transform microwave spectroscopy and quantum chemical calculations. Conformational studies at the MP2 level of theory yield four minima on the energy surface. The most energetically favorable conformer, which possesses C1 symmetry, is assigned. Due to the torsional barrier of 73.4782(1) cm(-1) of the acetyl methyl group, fine splitting up to 4.9 GHz is found in the spectrum. The conformational structure is not only confirmed by the rotational constants, but also by the orientation of the internal rotor. The (14) N quadrupole hyperfine splittings are analyzed and the deduced coupling constants are compared with the calculated values. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.