Computational Study of the Kinetics and Mechanism of Gas-Phase Decomposition of N-diacetamides Using Density Functional Theory

In this research work, we examined the decomposition mechanisms of N-substituted diacetamides. We focused on the substituent effect on the nitrogen lone pair electron delocalization, withdrawing and electron donor groups. DFT functionals used included: B1LYP, B3PW91, CAMB3LYP, LC-BLYP, and X3LYP. Dispersion functions gd3bj were applied when necessary to improve non-covalent interactions in the transition state. Pople with higher angular moments and def2-TZVP basis sets were also applied and were crucial for obtaining consistent thermodynamic parameters. The proposed mechanism involves a six-membered transition state with the extraction of an α hydrogen. Several conformers of N-diacetamides were used to account for the decrease in entropy in the transition state in the rate-determining state. All calculations, including Natural Bond Orbital (NBO) analyses, were performed using the Gaussian16 computational package and its GaussView 6.0 visualizer, along with VMD and GNUPLOT software. The isosurfaces and IBSI indexes were calculated using MultiWFN and IGMPlot, respectively.