Competitive Nitrogen versus Carbon Tunneling.

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Chemical Dynamics

Background:

• Heavy atom quantum mechanical tunneling (QMT) was historically considered improbable.
• Recent findings indicate that heavy-atom QMT occurs more frequently than anticipated.

Purpose of the Study:

• To investigate the competitive nature of carbon vs. nitrogen heavy-atom QMT.
• To demonstrate that distinct products can arise from the same starting material via competing QMT pathways.

Main Methods:

• Generation of amino-substituted benzazirine in solid argon at cryogenic temperatures (3-18 K).
• Monitoring spontaneous decay in the dark and determining reaction half-life.
• Utilizing quantum chemical computations to analyze reaction pathways.

Main Results:

• Observed spontaneous decay of amino-substituted benzazirine with a half-life of 210 min.
• Identified two distinct products: p-aminophenylnitrene and amino-substituted ketenimine.
• Reaction rate was found to be temperature-independent, contradicting classical transition state theory.
• Quantum chemical calculations confirmed two competing carbon vs. nitrogen QMT pathways.

Conclusions:

• Carbon and nitrogen heavy-atom QMT can be competitive, leading to multiple products from a single precursor.
• The temperature-independent reaction rate highlights quantum mechanical effects over classical predictions.
• This work underscores the significant role of quantum phenomena in chemical reactivity and molecular behavior.