• 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 >Synergism of porphyrin-core saddling and twisting of meso-aryl substituents
【24h】

Synergism of porphyrin-core saddling and twisting of meso-aryl substituents

机译：卟啉核马鞍化和中芳基取代基的扭曲

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 structural chemistry of meso-aryl-substituted porhyrins has uncovered a bewildering variety of macrocycle distortions. Saddling angles range up to 40 degrees, while the plane of the phenyl groups at the meso positions may be anywhere between perpendicular to the porphyrin plane (theta = 90 degrees) and tilted to quite acute angles (theta = 30 degrees or even less). These two distortions appear to be correlated. This has naturally been explained by steric hindrance: when the phenyls rotate toward the porphyrin plane, for instance, coerced by packing forces, the pyrrole rings can alleviate the steric hindrance by tilting away to a saddled conformation. We demonstrate, however, that the two motions are intrinsically coupled by electronic factors and are correlated even in the absence of external forces. A saddling motion makes it sterically possible for the phenyl rings to rotate toward the porphyrin plane, which will always happen because of increasingly favorable pi-conjugation interaction with smaller angles theta. The considerable energy lowering due to pi conjugation counteracts the energy cost of the saddling, making the concerted saddling/rotation motion very soft. Unsubstituted meso-aryl porphyrins just do not distort, but an additional driving force may tip the balance in favor of the combined distortion motion. Internal forces having this effect are repulsion of the four hydrogens that occupy the central hole of the ring in porphyrin diacids but also steric repulsion in peripherally crowded porphyrins. These findings lead to a clarification and systematization of the observed structural variety, which indeed shows a remarkable correlation between saddling and phenyl ring tilting.
机译：介孔芳基取代的卟啉的结构化学发现了令人困惑的大环畸变。鞍形角的范围最大为40度，而内消旋位置的苯基平面可以在垂直于卟啉平面（θ= 90度）并倾斜到非常锐角（θ= 30度或更小）之间的任何位置。这两个失真似乎是相关的。这自然可以用位阻解释：当苯基朝着卟啉平面旋转时，例如在堆积力的作用下，吡咯环可以通过倾斜成马鞍形构象来减轻位阻。但是，我们证明了这两个运动在本质上是由电子因素耦合的，即使在没有外力的情况下也相互关联。鞍形运动使得苯环在空间上可能朝着卟啉平面旋转，这总是会发生，这是因为在较小的角度theta上pi偶联作用越来越有利。由于π共轭而导致的大量能量降低抵消了马鞍的能量成本，使得协调的马鞍/旋转运动非常柔软。未取代的中芳基卟啉不会变形，但是额外的驱动力可能会使平衡失衡，从而有利于组合的畸变运动。具有这种作用的内力是在卟啉二酸中占据环中心孔的四个氢的排斥力，以及在周围拥挤的卟啉中的空间排斥力。这些发现导致所观察到的结构变化的澄清和系统化，这确实显示了鞍形结构和苯环倾斜之间的显着相关性。

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