Hindered rotation in N-acyloxy-4-methylthiazole-2(3H)-thiones |
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Authors: | Jens Hartung Christine Schur Sabine Altermann Uwe Bergsträßer Markus Heubes |
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Institution: | a Fachbereich Chemie, Organische Chemie, Technische Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern, Germany b Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany |
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Abstract: | Experimentally determined barriers to O-acyl group topomerization in mixed anhydrides composed of β-disubstituted carboxylic acids and cyclic thiohydroxamic acid N-hydroxy-4-methylthiazole-2(3H)-thione were located in the range of ΔG‡320=68±8 kJ mol−1 (DNMR). According to modeling studies, the underlying exchange process is proposed to occur via rotation about the N,O bond for torsional movement of the O-acyl group past the heterocyclic 4-methyl substituent. The energetically lowest pathway for passing the O-acyl entity by the thione sulfur, is predicted to occur via sequential rocking about the Csp2,O single bond in combination with an interlaced twist about the N,O axis. |
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Keywords: | Mixed anhydride Eyring analysis Hindered rotation Kinetics Modeling Thiazolethione Thiohydroxamic acid Topomerization Variable temperature NMR Strain X-ray diffraction |
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