Pulling on bonds counterintuitively Experimental mechanochemistry has largely focused on the application of force along chemical bonds to accelerate their cleavage. Akbulatov et al. now demonstrate that force can also play a more subtle role. They generated strained macrocyclic rings photochemically and then studied the influence of that strain on the rates of reactions that cleaved either phosphorus-oxygen or silicon-oxygen bonds. P-O cleavage was accelerated by force orthogonal to the bond axis, whereas the Si-O cleavage was inhibited by force along the bond. Both results were consistent with the respective transition states predicted by theory. Science, this issue p. 299 Molecular strain has a complex effect on cleavage of P–O and Si–O bonds that depends on the respective transition states. Stretching polymer chains accelerates dissociation of a variety of internal covalent bonds, to an extent that correlates well with the force experienced by the scissile bond. Recent theory has also predicted scenarios in which applied force accelerates dissociation of unloaded bonds and kinetically strengthens strained bonds. We report here unambiguous experimental validation of this hypothesis: Detailed kinetic measurements demonstrate that stretching phosphotriesters accelerates dissociation of the unloaded phosphorus-oxygen bond orthogonal to the pulling axis, whereas stretching organosiloxanes inhibits dissociation of the aligned loaded silicon-oxygen bonds. Qualitatively, the outcome is determined by phosphoester elongation and siloxane contraction along the pulling axis in the respective rate-determining transition states. Quantitatively, the results agree with a simple mechanochemical kinetics model.

中文翻译：

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实验实现的机械化学不同于负载键的力加速断裂

与直觉相反地拉动键 实验机械化学主要集中在沿化学键施加力以加速其裂解。阿克布拉托夫等人。现在证明力也可以发挥更微妙的作用。他们以光化学方式生成应变大环，然后研究该应变对裂解磷-氧或硅-氧键的反应速率的影响。PO 裂解被与键轴正交的力加速，而 Si-O 裂解被沿键的力抑制。两个结果都与理论预测的相应过渡态一致。科学，这个问题 p。299 分子应变对 P-O 和 Si-O 键的裂解具有复杂的影响，这取决于各自的过渡态。拉伸聚合物链会加速各种内部共价键的解离，其程度与易裂键所承受的力密切相关。最近的理论还预测了施加力加速卸载键的解离并在动力学上加强应变键的情况。我们在这里报告了这一假设的明确实验验证：详细的动力学测量表明，拉伸磷酸三酯会加速与拉伸轴正交的未加载磷-氧键的解离，而拉伸有机硅氧烷会抑制对齐加载的硅-氧键的解离。定性地，结果是由磷酸酯伸长率和硅氧烷收缩决定的，沿拉动轴在各自的决定速率的过渡态。数量上，