Chemical Reactions and Mechanisms

Quantum tunneling allows atoms and molecules to pass through energy barriers that classical physics would deem impassable, and chemists have increasingly recognized that this phenomenon can determine not just the rate but the very outcome of a reaction—a concept called tunneling control. Research in this area focuses on highly reactive intermediates such as carbenes and nitrenes, where the low mass of hydrogen and, more surprisingly, heavier atoms like carbon and nitrogen enables tunneling to compete with or override thermally driven pathways, sometimes directing reactions toward products that would otherwise be inaccessible. Techniques like matrix isolation, which traps short-lived species in frozen inert gases at cryogenic temperatures, combined with high-level computational modeling, have made it possible to observe and rationalize these effects in detail. Open questions center on predicting when heavy-atom tunneling will dominate in more complex molecules, and on harnessing tunneling control deliberately in organic synthesis to achieve selectivity that no conventional catalyst could provide.

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Keywords

Tunneling ControlChemical ReactionsNitrenesCarbenesPhotochemistryOrganic Synthesis