Thermal isomerization of acetylnitrene: a quantum-chemical study

The electronic structure and pathways of thermal isomerization of formylnitrene and acetylnitrene were studied by the B3LYP/6-311G(d,p) density functional method and ab initio G2(MP2,SVP) computational procedure using the geometries obtained from B3LYP calculations. According to G2 calculations, both nitrenes have singlet ground states while the energies of the corresponding triplet states are 2.8 and 5.7 kcal mol–1 higher. For acetylnitrene, the activation barrier to the nitrene → isocyanate isomerization was estimated at 28.9 kcal mol–1 (G2). Calculations revealed no pathway for single-step isomerization of nitrene into cyanate in both systems. The formation of methyl cyanate from isocyanate is thermodynamically unfavorable (ΔE = 26.5 kcal mol–1) and requires a high activation barrier (89.4 kcal mol–1) should be overcome. Based on the results obtained, the pathways of transformation of nitrene formed in thermal decomposition of acetyl azide (Curtius rearrangement) were analyzed.