Probing quantum mechanical tunneling (QMT) in chemical reactions is crucial to understanding and developing new transformations. Primary H/D kinetic isotopic effects (KIEs) beyond the semiclassical maximum values of 7‒10 (room temperature) are commonly used to assess substantial QMT contributions in one‐step hydrogen transfer reactions, because of the much greater QMT probability of protium vs. deuterium. Nevertheless, we report here the discovery of a reaction model occurring exclusively by H‐atom QMT with residual primary H/D KIEs. A 2‐hydroxyphenylnitrene, generated in N2 matrix, was found to isomerize to an imino‐ketone via sequential (domino) QMT involving anti to syn OH‐rotamerization (rate determining step) and [1,4]‐H shift reactions. These sequential QMT transformations were also observed in the OD‐deuterated sample, and unexpected primary H/D KIEs between 3 and 4 were measured at 3 to 20 K. Analogous residual primary H/D KIEs were found in the anti to syn OH‐rotamerization QMT of 2‐cyanophenol in a N2 matrix. Evidence strongly indicates that these intriguing isotope‐insensitive QMT reactivities arise due to the solvation effects of the N2 matrix medium, putatively through coupling with the moving H/D tunneling particle. Should a similar scenario be extrapolated to conventional solution conditions, then QMT may have been overlooked in many chemical reactions.

中文翻译：

---

氢隧道表现出意想不到的小初级动力学同位素效应

探索化学反应中的量子力学隧道效应（QMT）对于理解和开发新的转变至关重要。超出半经典最大值 7-10（室温）的初级 H/D 动力学同位素效应 (KIE) 通常用于评估一步氢转移反应中的实质性 QMT 贡献，因为氕与氢的 QMT 概率要大得多。氘。尽管如此，我们在这里报告了仅由 H 原子 QMT 发生的反应模型的发现，以及残留的初级 H/D KIE。发现在 N2 基质中生成的 2-羟基苯基氮烯通过顺序（多米诺）QMT 异构化为亚氨基酮，涉及反顺式 OH-旋转异构化（速率决定步骤）和 [1,4]-H 变换反应。这些连续的 QMT 转化也在 OD 氘化样品中观察到，并且在 3 至 20 K 下测量了 3 至 4 之间的意外初级 H/D KIE。在反顺式 OH 旋转异构化中发现了类似的残留初级 H/D KIE。 N2 基质中 2-氰基苯酚的 QMT。有力的证据表明，这些有趣的同位素不敏感 QMT 反应性是由于 N2 基质介质的溶剂化效应而产生的，推测是通过与移动的 H/D 隧道粒子耦合而产生的。如果将类似的情况外推到常规溶液条件，那么 QMT 在许多化学反应中可能会被忽视。