Theoretical investigation on the gas phase thermolysis mechanism and rate constant of diacetamide

The gas-phase thermolysis mechanism of diacetamide (CH₃C(O)NHC(O)CH₃) was investigated using ab initio method at HF/6-31G (d,p) level, Moler- Plesset method at MP2/6-31G (d,p) level and hybrid density functional theory (DFT) at B3LYP/6-31G (d,p) level. It was found that Hartree-Fock method is not suitable to predict the mechanism for this reaction. A semiconcerted mechanism with a six-membered cyclic transition state was found at MP2/6-31G (d,p) and B3LYP/6-31G (d,p) levels of theory. The refined barrier at B3LYP/6- 311+G [df, p) level of theory is about 179.50 kJ mol^-1 with the Zero-Point- Vibrational-Energy (ZPVE) correction; Microcanonical transition state theory was used to calculate rate constants for the reaction. The calculated rate constants are in good agreement with experimental values.