Dynamics-driven reaction pathway in an intramolecular rearrangement

Area of Science:

• Physical organic chemistry
• Computational chemistry
• Chemical dynamics

Background:

• Traditionally, transition states (TSs) and intrinsic reaction coordinates (IRCs) are used to interpret organic reactivity.
• This interpretation overlooks the impact of vibrational and kinetic energy at finite temperatures.
• Recent findings suggest reactions may not always follow intermediates along the IRC.

Purpose of the Study:

• To investigate the influence of molecular dynamics (MD) on chemical reaction pathways.
• To explore how finite temperature effects alter the mechanisms of organic reactions.
• To provide new interpretations of organic reactivity beyond traditional TS/IRC models.

Main Methods:

• Utilized molecular dynamics (MD) simulations.
• Analyzed the heterolysis rearrangement of protonated pinacolyl alcohol (Me3C-CHMe-OH2+).
• Compared MD-derived pathways with intrinsic reaction coordinate (IRC) pathways.

Main Results:

• MD simulations revealed a stepwise mechanism involving C-O bond cleavage followed by methyl group migration.
• The IRC pathway suggested a concerted mechanism for the same reaction.
• Dynamics effects were shown to significantly alter the reaction pathway compared to static models.

Conclusions:

• Finite temperature dynamics effects can fundamentally change the course of organic reactions.
• Traditional interpretations relying solely on IRCs may be insufficient for understanding complex reactivity.
• MD simulations offer a more comprehensive approach to interpreting organic reactivity, revealing alternative mechanisms.