Ring expansion and isomerization in methyl indene and methylene indene radicals. Quantum chemical and transition‐state theory calculations

Abstract

Ring expansion and isomerization in 1‐ and 2‐methylene indene radicals and isomerizations among the three isomers of methyl indene were studied by the Becke three‐parameter hybrid method with Lee‐Yang‐Parr correlation functional approximation (B3LYP). Structure, energy, and frequency calculations were carried out with the Dunning correlation consistent polarized doubleζ, (cc‐pVDZ) basis set. In contrast to methyl cyclopentadiene, transition states for ring expansion starting from the molecule methyl indene could not be located. The potential energy surfaces for ring expansion in methylene indene radicals consist of several intermediates and transition states and involve two principal pathways. One pathway is associated with cleavage of the five‐membered ring adjacent to the methylene group and formation of a six‐membered ring. In the second pathway, the transition states of the first stage consist of a newly‐formed three‐membered ring fused to the original cyclopentadiene ring. In all cases, the reaction pathways leading to ring expansion include an intermediate that, via an additional transition state, produces an α‐ or (β‐hydronaphthalene radical. The latter, by a fast H‐atom ejection, forms naphthalene. The structure, energetics, and additional parameters on the potential energy surfaces are shown. Several transition states and intermediates are common to both ring expansion and isomerization, so that there are competing parallel pathways that determine the final distribution among the isomerization and ring expansion products. Potential energy surfaces for interisomerization among the various isomers of methyl indene were calculated, and several reaction pathways were suggested.

Investigating repetitive reaction pathways for the formation of polycyclic aromatic hydrocarbons in combustion processes

“…4suggests the presence of m/z = 130 u that might be formed through a HAMA sequence starting at m/z = 116 u (indene), followed by a dehydrogenation sequence (-2 H) ending in naphthalene. These ring enlargement reactions have also been reported by Lifshitz et al[73,74], Jasper and Hansen[75], and Shukla et al[39,76].A similar sequence is expected to convert five-membered ring structures at m/z = 166 u species via m/z = 180 u intermediates into anthracene and/or phenanthrene at m/z = 178 u. Even though these sequences are consistent with our mass spectra, the anticipated complexity of the chemistry precludes a reliable estimation of their importance.…”

Five vs. six membered-ring PAH products from reaction of o-methylphenyl radical and two C3H4 isomers

“…Cyclisation of C1 produces C2 (−75.2 kcal mol −1 ), via TS C1→C2 (−34.2 kcal mol −1 ) then produces 1-methylindene + H (C5). Previous studies report that 1-methylindene and 3methylindene readily isomerize at 600 K, [64][65] so both isomers would result by this pathway in our experiment.…”

Ring Expansion and Isomerization in N-Methylindole and N-Methyleneindole Radical. Quantum Chemical and Kinetics Calculations

“…Other important parameters of this reaction are listed in Table . The first step is the production of an intermediate that is very similar to the equivalent intermediates in the processes of the ring expansion in 5-methylenecyclopentadiene, N -methylenepyrrole, and 1-methyleneindene . These intermediates are characterized by bicyclic structures with five- and three-membered rings fused together.…”