DFT calculations on kinetic data for some [4+2] reactions in solution.

Area of Science:

• Computational Chemistry
• Organic Reaction Mechanisms

Background:

• [4+2] cycloaddition reactions are fundamental in organic synthesis.
• Understanding reaction mechanisms and predicting activation barriers is crucial for reaction design.

Purpose of the Study:

• To investigate the reaction mechanisms of [4+2] cycloadditions using various Density Functional Theory (DFT) methods.
• To evaluate the accuracy of different DFT functionals and solvation models in predicting activation free energy barriers.
• To analyze the influence of substituent and solvent effects on reaction dynamics.

Main Methods:

• Utilized several DFT methods including CAM-B3LYP, BMK, M062x, wB97x, and wB97xd.
• Calculated activation free energy barriers considering both gas-phase and solution translational entropies.
• Employed the I-DCRF solvation model with the 6-31G(d) basis set for solution calculations.
• Analyzed frontier molecular orbital (FMO) interactions and charge transfer in transition states.

Main Results:

• Most [4+2] cycloaddition reactions proceed via synchronous or asynchronous mechanisms.
• Frontier molecular orbital interactions significantly influence transition state stability.
• DFT methods incorporating solution translational entropy (CAM-B3LYP+IDSCRF/6-31G(d), BMK+IDSCRF/6-31G(d), wB97x+IDSCRF/6-31G(d)) yield activation barriers close to experimental values.
• M062x and wB97xd methods generally underestimate the activation free energy barriers.
• Substituent and solvent effects were found to impact reaction dynamics.

Conclusions:

• DFT methods, particularly those accounting for solution effects, are reliable tools for studying [4+2] cycloaddition mechanisms.
• The choice of DFT functional and solvation model is critical for accurate barrier predictions.
• Accurate prediction of reaction dynamics aids in the rational design of chemical reactions.