Theoretical Investigation of Lone Pair Inversions, Ring Openings, and Hydride Shifts in O-Methylated Epoxides

详细信息    查看全文

• 作者：Jeffrey W. Schubert ; Timothy J. Dudley ; Brian K. Ohta
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：March 30, 2007
• 年：2007
• 卷：72
• 期：7
• 页码：2452 - 2459
• 全文大小：218K
• 年卷期：v.72,no.7(March 30, 2007)
• ISSN：1520-6904

文摘

WFIGR ID=jo0624492n00002>Mechanisms associated with the isomerization of the O-methylethylene oxonium ion and its tetramethyl-substituted analogue have been explored using correlated electronic structure calculations. The minimaand transition states associated with inversion at the oxygen atom, as well as those associated with openingof the epoxide ring, have been characterized. The calculated barrier to inversion at the oxygen atom forthe O-methylethylene oxonium ion, 15.7 kcal/mol, agrees well with the experimentally determined value,10 ± 2 kcal/mol. Our calculations indicate that a significantly higher barrier exists for the ring-openingmechanism that leads to more thermodynamically stable structures. This work includes the first knowncalculations on the O-methyl-2,3-dimethyl-2-butene oxonium ion along with transition states andintermediates associated with ring opening and inversion at the oxygen atom. Results show that there isa significantly lower barrier to ring opening as compared to the O-methylethylene oxonium ion species,leading to a lower probability of isolating this species. The effects of basis sets and correlation techniqueson these ions were also analyzed in this work. Our results indicate that the B3LYP/6-31G* level isreliable for obtaining molecular geometries for both minima and transition states on the C₃H₇O⁺ andC₇H₁₅O⁺ potential energy surfaces.