Understanding the kinetics and mechanism of thermal cheletropic elimination of N2 from (2,5-dihydro-1H-pyrrol-1-ium-1-ylidene) amide using RRKM and ELF theories

Abstract

The cheletropic elimination process of N2 from (2,5-dihydro-1H-pyrrol-1-ium-1-ylidene) amide (C4H6N2) has been studied computationally using density functional theory, along with the M06-2X/aug-cc-pVTZ level of theory. The calculated energy profile has been supplemented with calculations of kinetic rate constants using transition state theory (TST) and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. This elimination process takes place spontaneously with an activation energy around 33 kJ/mol. Pressure dependence of the rate constants revealed that the TST approximation breaks down and fall-off expression is necessary for the kinetic modeling. At temperatures ranging from 240 to 360 K and atmospheric pressure, the unimolecular rate constant is evaluated from RRKM theory as k=(1.0249*1012)*exp (-33.11/RT) s-1. Bonding changes along the reaction coordinate have been studied using bonding evolution theory. Electron localization function topological analysis reveals that the cheletropic elimination is characterized topologically by four successive structural stability domains (SSDs). Breaking of C–N bonds (Rx = 0.1992 amu1/2 Bohr) and the other selected points separating the SSDs along the reaction coordinate occur in the vicinity of the transition state.