When multiple reaction steps occur before thermal equilibration, kinetic energy from one reaction step can influence overall product distributions in ways that are not well predicted by transition state theory. An understanding of how the structural features of mechanophores, such as substitutions, affect reactivity, product distribution, and the extent of dynamic effects in the mechanochemical manifolds is necessary for designing chemical reactions and responsive materials. We synthesized two tetrafluorinated [4]-ladderanes with fluorination on different rungs and found that the fluorination pattern influenced the force sensitivity and stereochemical distribution of products in the mechanochemistry of these fluorinated ladderanes. The threshold forces for mechanochemical unzipping of ladderane were decreased by α-fluorination and increased by γ-fluorination; these changes correlated to the different stabilizing or destabilizing effects of fluorination patterns on the first transition state. Using ab initio steered molecular dynamics (AISMD), we compared the product distributions of synthesized and hypothetical ladderanes with different substitution patterns. These calculations suggest that fluorination on the first two bonds of ladderane gives rise to a larger fraction of dynamic trajectories and a larger fraction of E-alkene product through a mechanism resulting from larger momentum because of the greater atomic mass of fluorine. Fluorination on the third and fourth rungs instead gives a larger fraction of E-alkene product primarily due to electronic effects. These combined experimental and computational studies of the mechanochemical unzipping of fluorinated ladderanes provide an example of how relatively simple substituents can affect the extent of nonstatistical dynamics and, thus, mechanochemical outcomes.

中文翻译：

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氟化影响梯形烷机械化学解压的力敏感性和非平衡动力学


当热平衡之前发生多个反应步骤时，一个反应步骤的动能可以以过渡态理论无法很好地预测的方式影响整体产物分布。了解机械基团的结构特征（例如取代）如何影响机械化学歧管中的反应性、产物分布和动态效应的程度对于设计化学反应和响应材料是必要的。我们合成了两种在不同梯级上氟化的四氟化 [4]-梯烷，发现氟化模式影响了这些氟化梯烷机械化学中产物的力敏性和立体化学分布。α-氟化降低了阶梯烷机械化学解拉链的阈值力，而γ-氟化提高了梯烷的机械化学解拉链力;这些变化与氟化模式对第一过渡态的不同稳定或不稳定作用相关。使用从头到尾引导分子动力学 （AISMD），我们比较了具有不同取代模式的合成和假设梯烷的乘积分布。这些计算表明，梯烷前两个键上的氟化作用会产生更大比例的动态轨迹和更大比例的 E-烯烃产物，这是由于氟的原子质量较大，因此动量更大。相反，由于电子效应，第三级和第四级的氟化会产生更大比例的 E-烯烃产物。 这些对氟化梯烷的机械化学解开的实验和计算研究提供了一个例子，说明相对简单的取代基如何影响非统计动力学的程度，从而影响机械化学结果。