Steric Consequences on the Conformation of Medium-Sized Rings: Solution NMR, Solid-State Crystallographic, ab Initio Molecular Orbital Calculations, and Molecular Mechanics Studies on Substitut

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• 作者：Lilibeth P. Burke ; Anthony D. DeBellis ; Herman Fuhrer ; Hansrudolf Meier ; Stephen D. Pastor ; Grety Rihs ; Guenther Rist ; Ronald K. Rodebaugh ; and Sai P. Shum
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：September 3, 1997
• 年：1997
• 卷：119
• 期：35
• 页码：8313 - 8323
• 全文大小：326K
• 年卷期：v.119,no.35(September 3, 1997)
• ISSN：1520-5126

文摘

The conformation of the eight-membered membered12H-dibenzo[d,g][1,3,2]dioxasilocinring system wasinvestigated both in the solid-state by X-ray crystallography and insolution by NOE experiments. Ab initioHartree-Fock calculations were performed to locate all stationary points for theunsubstituted12H-dibenzo[d,g][1,3,2]dioxasilocin ring system. The MM2* force field was parametrized toreproduce our ab initio results, and these datawere compared to the experimental data. The transition states forconformational interchange were identified. Thepseudoequatorial preference for a methyl substituent on either theC(12) carbon atom or silicon is greater than thedifference in energy between a boat-chair and twist-boat conformationin 2,4,8,10-tetra-tert-butyl-substituted12H-dibenzo[d,g][1,3,2]dioxasilocins.The conformations observed in the solid-state X-ray crystalstructures of 12H-dibenzo[d,g][1,3,2]dioxasilocinsare sensitive to crystal-packing forces and may be different from thatin solution.