Hindered rotation in N

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• 作者：Jens Hartung ; Christine Schur ; Irina Kempter ; Sabine Altermann ; Georg Stapf ; Uwe Bergsträ ; ß ; er ; Thomas Gottwald ; Markus Heubes
• 关键词：Mixed anhydride ; Eyring analysis ; Hindered rotation ; Kinetics ; Modeling ; Thiazolethione ; Thiohydroxamic acid ; Topomerization ; Variable temperature NMR ; Strain ; X-ray diffraction
• 刊名：Tetrahedron
• 出版年：2009
• 出版时间：5 September 2009
• 年：2009
• 卷：65
• 期：36
• 页码：7527-7532
• 全文大小：375 K

文摘

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 C_sp²,O single bond in combination with an interlaced twist about the N,O axis.