DFT study in the kinetics and mechanism of the thermal decomposition of N-benzoyl-N′-phenylthiourea derivatives

This work presents a theoretical study on the mechanism of the gas phase elimination of five derivatives of N-benzoyl-N′-phenylthiourea (BPT), with substituents at the N′-phenyl ring. The reaction profiles, energy vs. reaction coordinate, were evaluated using the force of reaction and electronic flux. We investigated the electron density distribution employing CHELPG charges. Bond breaking and bond formation were analyzed using Mayer's bond order and intrinsic bond strength index (IBSI) calculations. Calculations were performed using Density Functional Theory (DFT), with Gaussian 16 software, at the B3LYP-GD3/Def2TZVPP level of theory. The results suggest that strong electron-withdrawing substituents at the N′-phenyl stabilize the initial state and raise the activation barrier. Moderate electron-withdrawing effects, e.g., 3-chloro and 4-chlorophenyl, promote a more efficient electronic reorganization leading to the transition state, lowering the energy of activation. These findings provide a quantitative framework to predict the reactivity of similar systems and optimize the design of novel compounds with specific properties.