• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Journal of mass spectrometry: JMS >Density functional theory and RRKM calculations of decompositions of the metastable E-2,4-pentadienalmolecular ions
【24h】

Density functional theory and RRKM calculations of decompositions of the metastable E-2,4-pentadienalmolecular ions

机译：亚稳E-2,4-戊二烯分子离子分解的密度泛函理论和RRKM计算

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The potential energy profiles for the fragmentations that lead to [C _5H_5O]~+ and [C_4H_6] ~(+?) ions from the molecular ions [C_5H _6O]~(+?) of E-2,4-pentadienal were obtained from calculations at the UB3LYP/6-311G++(3df,3pd)//UB3LYP/6-31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice-Ramsperger-Kassel-Marcus calculations of individual rate coefficients for a large number of reaction steps. The preequilibrium and rate-controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C-H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E-2,4-pentadienal ions. The direct dissociation, however, can only become important in the high-energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2-hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion-neutral complex which, in turn, decomposes rapidly to the s-trans-1,3-butadiene ion [C_4H_6]~(+?). The predominating metastable channel is the second one, that is, a multi-step ring closure which starts with a rate-limiting cis - trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C_5H_5O]~+. These results can be used to rationalize the CID mass spectrum of E-2,4-pentadienal in a low-energy regime.
机译：从E-2,4-戊二烯醛的分子离子[C_5H _6O]〜（+？）生成[C _5H_5O]〜+和[C_4H_6]〜（+？）离子的碎片的势能图在UB3LYP / 6-311G ++（3df，3pd）// UB3LYP / 6-31G（d，p）理论水平上进行计算。然后将通过密度泛函方法获得的动力学势垒和谐波频率用于Rice-Ramsperger-Kassel-Marcus的大量反应步骤的单个速率系数的计算中。平衡前和速率控制步骤的近似值被应用于复杂势能表面的不同区域，从而可以计算总分解速率并在三个竞争途径之间进行区分：C-H键断裂，脱羰基作用和环化作用。这些过程必须竞争四种E-2,4-戊二烯离子构象异构体的平衡混合物。但是，直接离解仅在高能状态下才变得重要。相反，在亚稳态动力学窗口中，CO的损失和环化是可观察到的过程。前者涉及从羰基缓慢的1,2-氢转移，随后立即形成离子中性络合物，然后离子中性络合物迅速分解为s-trans-1,3-丁二烯离子[C_4H_6] 〜（+？）。最主要的亚稳态通道是第二个通道，即一个多步闭环反应，它以限速的顺-反异构化反应开始。该过程产生相互转化的吡喃离子的混合物，其解离为吡啶离子[C_5H_5O]〜。这些结果可用于合理化低能量条件下E-2,4-戊二烯醛的CID质谱图。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号