Reaction Mechanisms in Aromatic Hydrocarbon Formation Involving the the C_5H_5 Cycylopentadienyl Moiety

摘要

The quantum chemical BAC-MP4 and BAC-MP2 methods have been used to investigate the reaction mechanisms leading to polycyclic aromatic hydrocarbon (PAH) ring formation.in particular we have determined the elementary reaction steps in the conversion of two cyclopentadienyl radicals to naphthalene. This reaction mechanism is shown to be an extension of the mechanism occurring in the H atomassisted conversion of fulvene to benzene. The net reaction involves formation of diyhydrofulvalene, which eliminates a hydrogen atom and then rearranges to form naphthalene through a series of ring closures and openings. The importance of forming the -CR(centre dot)-CHR-CR'=CR"-moiety, which can undergo rearrangement to form three-carbon atom raing structures, is illustrated with the C_4H_7 system. The ability of hydrogen atoms to migrate around the cyclopentadienyl moiety is illustrated both for methyl-cyclopentadiene, C_5H_5CH_3, and dihydrofulvalene, C_5H_5C_5H_5, as well as for their radical species, C_6H_7 and C_5H_5C_5H_4. The mobility of hydrogenin the cyclopentadienyl moiety plays an important role both in providing resonance-stabilized radial products and in creating the -CR(centre dot) CHR-CR'=CR" - moiety for ring formation. The results illustrate the radical pathwayl for converting five-membered rings to aromatic six-membered rings. Furthermore, the results indicate the important catalytic role of H atoms in the aromatic ring formation process.