A theoretical study of pyrolysis mechanisms of pyrrole

Density functional theory and ab initio calculations were carried out to in vestigate the pyrolysis mechanisms of pyrrole. All equilibrium and transiti on state structures of the proposed reaction channels were fully optimized by the density functional B3LYP method using the 6-31G(d,p) basis set. Rela tive energies were evaluated at the QCISD(T)/6-311G(d,p) level of theory. L n addition to the mechanism proposed in experimental studies, alternative u nimolecular pathways for the formation of cis-crotonitrile and allyl cyanid e, major nitrogen-containing isomerization products, were proposed and inve stigated. The results suggest that a mechanism proposed in the present stud y is more likely responsible for the formation of allyl cyanide. For the fo rmation of cis-crotonitrile, a mechanism proposed in the present study shou ld also be competitive, especially under low-pressure conditions. Although extensive calculations were carried out, we failed to identify a unimolecul ar decomposition pathway generating HCN, another major nitrogen-containing pyrolysis product, with an activation barrier close to the experimental val ue.