力诱导的能源景观灾难：下山和上山分叉的机械化学操纵解释了环丙烷的开环选择性
Force-induced Catastrophes on Energy Landscapes: Mechanochemical Manipulation of Downhill and Uphill Bifurcations Explains Ring-opening Selectivity of Cyclopropanes
摘要：
环丙烷衍生物开环反应的机械力化学是一个非常丰富而又令人困惑的研究领域。在表明在热活化极限下，在反式-偕-二氟环丙烷的情况下，当氟被氯、溴和碘取代时，一种罕见的所谓上坡分叉变成下坡分叉后，在机械化学活化领域中系统地研究了二氯衍生物。在Dijkstra路径分析方面的反式宝石-二氯环丙烷的力转换势能面的详细探索揭示了一个迄今为止未知的拓扑灾难，其中的全球形状的能源景观是从根本上改变。从热活化到中等大的力，这是一个上坡分叉，决定了逆旋与对旋开环，然后是沿着两条途径的单独的过渡态。在临界力以上，两个不同的过渡态合并以产生单个过渡态，使得在新建立的下坡分叉处做出关于反旋对旋开环过程的决定。力引起的反应网络拓扑结构的质变的发现大大超越了以前对该物种开环反应的理解。如果没有发现大量机械化学活化反应的这种灾难，那将是令人惊讶的，这将大大扩展操纵化学反应网络的已知机会。
英文摘要：
The mechanochemistry of ring-opening reactions of cyclopropane derivatives turns out to be unexpectedly rich and puzzling. After showing that a rare so-called uphill bifurcation in the case of trans-gem-difluorocyclopropane turns into a downhill bifurcation upon substitution of fluorine by chlorine, bromine and iodine in the thermal activation limit, the dichloro derivative is studied systematically in the realm of mechanochemical activation. Detailed exploration of the force-transformed potential energy surface of trans-gem-dichlorocyclopropane in terms of Dijkstra path analysis unveils a hitherto unknown topological catastrophe where the global shape of the energy landscape is fundamentally changed. From thermal activation up to moderately large forces, it is an uphill bifurcation that decides about dis-versus conrotatory ring-opening followed by separate transition states along both pathways. Above a critical force, the two distinct transition states merge to yield a single transition state such that the decision about the dis-versus conrotatory ring-opening process is taken at a newly established downhill bifurcation. The discovery of a force-induced qualitative change of the topology of a reaction network vastly transcends the previous understanding of the ring-opening reaction of this species. It would be astonishing to not discover a wealth of such catastrophes for mechanochemically activated reactions which will greatly extend the known opportunities to manipulate chemical reaction networks.
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