Aromaticity on the fly: cyclic transition state stabilization at finite temperature

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Organic Chemistry

Background:

• Pericyclic reactions are fundamental in organic chemistry.
• Understanding reaction mechanisms at elevated temperatures is crucial.
• The influence of high temperatures on transition state properties is not fully understood.

Purpose of the Study:

• To investigate the nature of the transition state in pericyclic reactions at elevated temperatures.
• To determine if aromaticity is preserved in the transition state under dynamic thermal conditions.
• To explore the role of cyclic delocalization in synchronizing atomic motion.

Main Methods:

• Utilizing unbiased ab initio molecular dynamics simulations.
• Analyzing structural, magnetic, and electronic properties of the transition state.
• Performing free-energy calculations to assess the validity of transition state theory.

Main Results:

• The transition state for intramolecular rearrangements in barbaralane and bullvalene remains aromatic at high temperatures.
• Significant thermal atomic motions do not disrupt the concertedness and aromatic character of the dynamical transition state.
• Free-energy calculations confirm the applicability of transition state theory for these reactions.

Conclusions:

• Cyclic delocalization is a powerful factor that synchronizes atomic motions even at high temperatures.
• The aromatic character of the transition state is robust and persists under dynamic thermal conditions.
• Transition state theory is a valid framework for studying these high-temperature rearrangement reactions.