Post-Transition-State Dynamics Induced Product Diversity in the Thermal Rearrangement of Cyclopropenyl Azides

Area of Science:

• Organic Chemistry
• Chemical Dynamics
• Computational Chemistry

Background:

• Cyclopropenyl azides undergo thermal rearrangements to form 1,2,3-triazines, degenerate products, or azetes.
• Experimental results on product distribution are conflicting and depend on substituents and temperature.

Purpose of the Study:

• To investigate the thermal rearrangement pathways of substituted cyclopropenyl azides using computational methods.
• To elucidate the role of substituents and temperature in determining product distribution.

Main Methods:

• Quasi-classical trajectory (QCT) calculations were performed on density-functional theory (DFT) potential energy surfaces.
• Simulations covered a range of substituted cyclopropenyl azides (1a-1j).

Main Results:

• Electron-donating substituents yield the degenerate product as the kinetically controlled product (KCP) and influence post-transition state bifurcation (PTSB).
• Electron-withdrawing substituents (F, Cl, Br) result in 1,2,3-triazine as the KCP, suppressing dynamical effects.
• Azete formation can occur via a triazabenzvalene intermediate or by bypassing it, with nonstatistical dynamics playing a crucial role.

Conclusions:

• Substituent type critically determines the kinetically controlled product and influences the branching between different reaction pathways.
• Nonstatistical dynamics beyond the intrinsic reaction coordinate are essential for understanding multiple product channels from cyclopropenyl azides.