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Perhydrohelicenes and other diamond-lattice based hydrocarbons: the choreography of inversion
Chemical Science ( IF 7.6 ) Pub Date : 2017-07-17 00:00:00 , DOI: 10.1039/c7sc01759f
Roger W. Alder 1, 2, 3, 4 , Craig P. Butts 1, 2, 3, 4 , Richard B. Sessions 2, 3, 4, 5
Affiliation  

Overall inversion in fused cyclohexane oligomers 2, 3, and 4 (all based on cis-decalin 1) occurs by a rolling process involving no more than two adjacent rings in twist-boat conformations at any time. These inverting rings move along the oligomer in processes that are precisely choreographed by the adjacent chairs. Actual inversion mechanisms can be stepwise [CC → TC → TT → C′T → C′C′], as for cis-decalin, but it is shown that a concerted alternative [CC → TC → C′T → C′C′] is enforced in 2. The all-cis,anti,cis-isomers of perhydrohelicenes 4 are based on the diamond lattice and have remarkably low strain energies. Helix inversion in 4 is compared with that in helicenes 5. For both, the intermediates and transition states have shapes broadly like kinked old-style telephone cables. In both cases barriers increase with the length of the system to eventually reach a plateau value of ca. 120 kJ mol−1 for 4, much lower than that for 5 (320–350 kJ mol−1). While rolling inversion only requires two adjacent rings in twist-boat conformations at any instant, inversion in propellane 6 requires all three rings be converted to twist-boats, and the S4 symmetric hydrocarbon 7 requires all four rings to be converted to twist-boats. As a consequence, 7 probably has the highest barrier of any non-oligomeric cis-decalin derived structure (87.3 kJ mol−1 at B3LYP/6-31G*).

中文翻译:

全氢螺旋体和其他基于菱形晶格的碳氢化合物:反演的编排

在稠合的环己烷的低聚物整体反转23,和4(全部基于-decalin 1)通过在任何时间不涉及在扭船构象多于两个相邻的环轧制过程中发生。这些倒置环在低聚物中移动,其过程由相邻的椅子精确地编排。对于顺式-萘,实际的转化机理可以是逐步的[CC→TC→TT→C′T→C′C′] ,但已证明有一个协同的替代方案[CC→TC→C′T→C′C′ ]在2中强制执行。在清一色perhydrohelicenes的异构体4基于金刚石晶格,并且具有非常低的应变能。将4中的螺旋反转与螺旋5中的螺旋反转进行了比较。对于两者而言,中间体和过渡态的形状都大致类似于扭结的老式电话电缆。在这两种情况下,势垒都随着系统长度的增加而增加,最终达到平台值ca左右。120千焦耳摩尔-14,多比用于降低5(320-350千焦摩尔-1)。滚动反转在任何时候都只需要扭船构型中的两个相邻环,而螺旋桨6的反转则需要将所有三个环都转换为扭船,而S 4对称碳氢化合物7要求将所有四个环都转换为旋船。结果,在任何非寡聚的顺式-萘衍生的结构中,7可能具有最高的势垒(在B3LYP / 6-31G *处为87.3 kJ mol -1)。
更新日期:2017-07-22
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