• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Coupling Trans-Bent Double Bonds in Tetragermabutadiene
【24h】

Coupling Trans-Bent Double Bonds in Tetragermabutadiene

机译：Tetragermabutadiene中的跨弯双键耦合

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 coupling of two trans-bent double bonds is examined theoretically through ab initio calculations on tetragermabutadiene H_2Ge velence HGe-GeH velence GeH_2. If a trans-bent arrangement is maintained for each -GeH velence GeH_2 fragment, there are two ways of coupling two trans-bent units, starting from an s-trans conformation around the central bond. The first one preserves an all-trans arrangement of the four pyramidalized germanium atoms. Along the rotational pathway around the central bond, this configuration has no symmetry (C_1), except for dihedral angles of 0 deg (C_s) or 180 deg (C_i). As in butadiene, the potential curve along this coordinate is symmetrical with respect to 0 deg and 180 deg, with a preferred s-trans form, t-1 and two equivalent gauche forms, g-1, lying about 3 kcal/mol above in energy (MP4/DZP//SCF/DZP). The s-cis saddle point separating the two gauche forms is higher in energy than the barrier separating the s-trans and gauche forms. In the second coupling scheme, the molecule maintains a C_2 symmetry axis for any torsional angle, but the energy curve no longer exhibits any symmetry along the entire [0-2#pi#] rotational coordinate. As anticipated by simple overlap arguments within the pseudo #pi# orbital set, the two minima, reminiscent of s-trans and gauche arrangements, are both skewed. The gauche conformer, g-2, is now below the trans one, t-2, but still above t-1. The minima g-2 and t-2 are separated by two rotational barriers, depending on the direction of rotation. Interconversion between these coupling configurations proceeds through planar inversion at one GeH velence GeH_2 unit. Two pathways are possible, linking either the two s-trans forms or the two gauche forms. The barrier along both the t- 1 -> t-2 and g-2 -> g-1 pathways is calculated at 4 kcal/mol, in line with the barrier to planarity found in isolated digermene. In both coupling schemes, adiabatic singlet-triplet separations are calculated at 13 kcal/mol. Intramolecular cyclization of g-2 into the cyclobutene form proceeds with a slight activation barrier, and a large exothermicity of 27 kcal/mol. Alternatives in which one or both double bonds of the butadiene form are replaced by a double hydrogen bridge are not favored. By contrast, the two bond-stretch isomers of the bicyclobutane form are significantly lower in energy than the butadiene forms.
机译：理论上通过对四格玛丁二烯H_2Ge velence HGe-GeH velence GeH_2的从头算来检查两个反弯双键的偶联。如果为每个-GeH velence GeH_2片段维持一个反式排列，则有两种方式耦合两个反式单元，从围绕中心键的s-反式构象开始。第一个保留了四个金字塔状锗原子的全反式排列。沿着围绕中心键的旋转路径，除了0度（C_s）或180度（C_i）的二面角之外，此配置没有对称性（C_1）。像在丁二烯中一样，沿着该坐标的电势曲线相对于0度和180度是对称的，优选的s-反式为t-1，而两种等效的gauche形式为g-1，高于约3 kcal / mol。能量（MP4 / DZP // SCF / DZP）。分离两种薄纱形式的s-顺式鞍点的能量高于分离s-反式和薄纱形式的势垒。在第二种耦合方案中，分子对于任何扭转角均保持C_2对称轴，但能量曲线沿整个[0-2＃pi＃]旋转坐标不再显示任何对称性。如伪＃pi＃轨道集中的简单重叠自变量所预期的那样，两个最小值（使人联想到s-trans和gauche排列）均偏斜。 gauche构象异构体g-2现在低于反式1 t-2，但仍高于t-1。最小值g-2和t-2由两个旋转势垒分隔，具体取决于旋转方向。这些耦合构型之间的相互转换通过一个GeH velence GeH_2单元的平面反转进行。可能有两个途径，将两个s-反式或两个gauche形式连接起来。沿着t-1-> t-2和g-2-> g-1途径的势垒的计算值为4 kcal / mol，这与在孤立的digermene中发现的平面性势垒一致。在这两种耦合方案中，绝热单线态-三重态分离度的计算值为13 kcal / mol。 g-2分子内环化为环丁烯形式时，会出现轻微的激活障碍，放热度为27 kcal / mol。丁二烯形式的一个或两个双键被双氢桥取代的替代方案是不受欢迎的。相反，双环丁烷形式的两个键-拉伸异构体的能量明显低于丁二烯形式。

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