Electric field-catalyzed single-molecule Diels-Alder reaction dynamics

Area of Science:

• Chemical kinetics and reaction mechanisms
• Physical organic chemistry
• Single-molecule spectroscopy

Background:

• The Diels-Alder reaction is a fundamental cycloaddition reaction in organic chemistry.
• Understanding its mechanism is crucial for synthetic chemistry and materials science.
• Previous studies suggested a concerted mechanism, but detailed dynamic pathways remained elusive.

Purpose of the Study:

• To directly observe the time trajectories and reaction pathways of the Diels-Alder reaction at the single-molecule level.
• To elucidate the role of charge transfer complexes in the reaction mechanism.
• To investigate the influence of electric fields on the reaction pathway and explore potential catalytic effects.

Main Methods:

• Utilizing an in situ label-free single-molecule electrical detection platform for high-resolution observation.
• Employing single-molecule detection to track reaction dynamics in real-time.
• Combining experimental data with theoretical calculations to validate findings.

Main Results:

• Direct observation confirmed the well-accepted concerted mechanism of the Diels-Alder reaction.
• The study clarified the influence of endo and exo configurations of charge transfer complexes on the reaction path.
• An unprecedented stepwise pathway was observed at high temperatures under a high-voltage electric field.
• An electric field-catalyzed mechanism involving a zwitterionic intermediate was identified.

Conclusions:

• The Diels-Alder reaction mechanism can be controlled by external electric fields.
• Electric field catalysis offers a novel approach for mechanistic control in chemical reactions.
• This work provides new insights into the fundamental understanding of cycloaddition reactions and catalytic processes.