Unimolecular isomerizations of C₆H₆^•+ radical cations: a computational study

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Kinetics

Background:

• Benzene radical cation (C₆H₆^•+) is a key intermediate in various chemical processes.
• Understanding its isomerization pathways is crucial for predicting reaction outcomes.

Purpose of the Study:

• To computationally investigate 18 concerted isomerization reactions of C₆H₆^•+ species.
• To determine reaction pathways, transition states, and energy barriers.
• To estimate rate coefficients and activation energies for these reactions.

Main Methods:

• Density Functional Theory (DFT) with B3LYP and M06-2X functionals.
• Complete Basis Set (CBS-QB3) approach for accurate energy calculations.
• Canonical Transition State Theory (TST) to calculate rate coefficients and activation energies.

Main Results:

• Identified well-defined transition states for all 18 isomerization reactions.
• Observed general agreement with Hammond's postulate regarding transition state positions.
• Estimated rate coefficients over a temperature range of 200-500 K.
• Derived 15 multi-step conversion routes to the most stable benzene radical cation isomer.

Conclusions:

• The study provides a comprehensive computational analysis of C₆H₆^•+ isomerization.
• The findings offer valuable data for understanding the reactivity and stability of benzene radical cations.
• The identified pathways and kinetic parameters can aid in predicting chemical reaction mechanisms involving these species.