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TY - THES AU - Attig, Theo TI - Konformerenanalyse von langkettigen Essigsäureestern mit Hilfe quantenchemischer und mikrowellenspektroskopischer Untersuchungen CY - Aachen M1 - RWTH-CONV-143953 SP - 128 S. : graph. Darst. PY - 2013 N1 - Zsfassung in dt. und engl. Sprache N1 - Aachen, Techn. Hochsch., Diss., 2013 AB - The rotational spectra of n-butyl acetate (CH3-COO-C4H9), n-pentyl acetate (CH3-COO-C5H11), and n-hexyl acetate (CH3-COO-C6H13) were recorded using molecular beam Fourier transform microwave spectroscopy. First of all, ab initio calculations were carried out for every conformer at MP2/6 311++G(d,p) level. The theoretical rotational constants were used to predict the spectra. In the next step, broadband scans were recorded in selected ranges and the measured lines were re-measured in the high resolution mode. Three conformers were assigned for the molecule n-butyl acetate, two for the molecule n-pentyl acetate, and one for the molecule n-hexyl acetate. Comparing the experimental with the theoretical values, the structures of these assigned conformers were obtained. The strongest lines of each spectrum belong to the conformer with the lowest energy, which has C1 symmetry. A conformer with CS symmetry was assigned for each of the molecules n-butyl acetate and n pentyl acetate. Comparing the structures of the conformers with lowest energy, the results show, that by extending the carbon chain successively, the previous structure is conserved. The new carbon atoms are added antiperiplanar. For the energetically lowest conformers of n-butyl acetate, n-pentyl acetate, and n hexyl acetate quantum chemical calculations with different methods and basis sets were carried out. The used methods are Hartee-Fock (HF), second order Møller-Plesset perturbation theory (MP2), Density Functional Theory (DFT) with the Becke Lee Yang functional (B3LYP). The used basis sets are 6-31G(d,p), 6 31+G(d,p), 6-31++G(d,p), 6 311G(d,p), 6-311+G(d,p), and 6 311++G(d,p). The investigations have shown, that the best agreement between the experimental and theoretical values are observed at the MP2/6-311+G(d,p) level. The MP2/6 311++G(d,p) level, which has been used in this work has also a good agreement and is suitable for predicting rotational constants of acetic acetate esters. KW - Mikrowellenspektroskopie (SWD) KW - Essigsäureester (SWD) KW - Quantenchemie (SWD) LB - PUB:(DE-HGF)11 UR - https://publications.rwth-aachen.de/record/228916 ER -