The relationship between the shape of a molecule and its chemical reactivity is a central tenet in chemistry. However, the influence of the molecular geometry on reactivity can be subtle and result from several opposing effects. Here, using a crossed-molecular-beam experiment in which individual rotational quantum states of specific conformers of a molecule are separated, we study the chemi-ionization reaction of hydroquinone with metastable neon atoms. We show that collision-induced alignment of the reaction partners caused by geometry-dependent long-range forces influences reaction pathways, which is, however, countered by molecular rotation. The present work provides insights into the conformation-specific stereodynamics of complex polyatomic systems and illustrates the capability of advanced molecule-control techniques to unravel these effects.

分子形状与其化学反应性之间的关系是化学的一个中心原则。然而，分子几何形状对反应性的影响可能很微妙，并且是由几个相反的效应引起的。在这里，使用交叉分子束实验，其中分离分子特定构象异构体的单个旋转量子态，我们研究了对苯二酚与亚稳氖原子的化学电离反应。我们表明，由几何依赖性远程力引起的碰撞诱导的反应伙伴对齐会影响反应途径，然而，分子旋转会抵消这种反应途径。这项工作提供了对复杂多原子系统的构象特异性立体动力学的见解，并说明了先进的分子控制技术能够揭示这些影响。