The microwave spectrum of n-butyl acetate

We recorded the rotational spectrum of n-butyl acetate (CH3-COO-C4H9) using molecular beam Fourier transform microwave spectroscopy. The rotational constants and the centrifugal distortion constants of the most abundant and of the two less abundant conformers were determined. The main conformer with C-1 symmetry has a strong spectrum. The other two conformers have C-s and C-1 symmetries. Their intensities are considerably weaker. The quantum chemical calculations of specific conformers were carried out at the MP2/6-311++G(d,p) level. Harmonic frequency calculations were done to exclude imaginary frequencies. Furthermore, calculations at different levels of theory were performed for the main conformer. To analyze the internal rotation of the acetyl methyl groups the codes XIAM and BELGI were used. The molecular structures of the three conformers were determined and the values of the experimental rotational constants were compared with those obtained by ab initio methods. For all conformers torsional barriers of approximately 100 cm(-1) were found. (C) 2013 Elsevier Inc. All rights reserved.