Thermal Decomposition Kinetics of the Indenyl Radical: A Theoretical Study

Abstract

Quantum chemistry and statistical reaction rate theory calculations have been performed to investigate the products and kinetics of indenyl radical decomposition. Three competitive product sets are identified, including formation of a cyclopentadienyl radical (c-C5H5) and diacetylene (C4H2), which has not been included in prior theoretical kinetics investigations. Rate coefficients for indenyl decomposition are determined from master equation simulations at 1800–2400 K and 0.01–100 atm, and temperature- and pressure-dependent rate coefficient expressions are incorporated into a detailed chemical kinetic model for indene pyrolysis. Indenyl is found to predominantly decompose to o-benzyne (o-C6H4) + propargyl (C3H3), with lesser amounts of fulvenallenyl (C7H5) + C2H2 and c-C5H5 + C4H2.

New Carbenes and Cyclic Allenes Energetically Comparable to Experimentally Known 1-Azulenylcarbene

“… 52 − 56 The recent discovery of four neutral molecules, cyclopentadiene (C 5 H 6 ), two isomers of ethynylcyclopentadiene (C 7 H 6 ), and indene (C 9 H 8 ), along with two of the C 5 H 2 carbenes aforementioned in the Taurus Molecular Cloud-1, 12 , 13 , 57 reinforces the possibility of polycyclic aromatic hydrocarbon (PAH) formation in space through resonance-stabilized carbene intermediates. 58 − 61 In this endeavor, C 11 H 8 is the next higher homologue potentially suitable for laboratory and radioastronomical studies. 62 Our recent theoretical account on C 11 H 8 isomers established a fact that six low-lying indene isomers (2aH-cyclopenta[ cd ]indene, 7-ethynyl-1 H -indene, 4-ethynyl-1 H -indene, 6-ethynyl-1Hindene, 5-ethynyl-1 H -indene, and 7bH-cyclopenta[cd]-indene) remain elusive till date in the laboratory.…”

“…Unequivocally, if a molecule is polar (μ ≠ 0), then the laboratory rotational transitions are a pre-requisite for potential confirmation of the same molecules many light-years away. − Thus, a firm experimental and theoretical understanding of carbene and its related chemistry has become necessary for many related fields such as astrochemistry, combustion, and soot formation . Along the same lines, phenyl/naphthyl/azulenyl rings containing carbenes (arylcarbenes) have drawn considerable attention to the astrochemistry community because of their ease of thermal and photochemical transformations. − The recent discovery of four neutral molecules, cyclopentadiene (C 5 H 6 ), two isomers of ethynylcyclopentadiene (C 7 H 6 ), and indene (C 9 H 8 ), along with two of the C 5 H 2 carbenes aforementioned in the Taurus Molecular Cloud-1, ,, reinforces the possibility of polycyclic aromatic hydrocarbon (PAH) formation in space through resonance-stabilized carbene intermediates. − In this endeavor, C 11 H 8 is the next higher homologue potentially suitable for laboratory and radioastronomical studies . Our recent theoretical account on C 11 H 8 isomers established a fact that six low-lying indene isomers (2aH-cyclopenta­[ cd ]­indene, 7-ethynyl-1 H -indene, 4-ethynyl-1 H -indene, 6-ethynyl-1Hindene, 5-ethynyl-1 H -indene, and 7bH-cyclopenta­[cd]-indene) remain elusive till date in the laboratory .…”

Six Low-Lying Isomers of C11H8 Are Unidentified in the Laboratory–A Theoretical Study

“…C 11 H 8 is a prototypical elemental composition for organic chemists as it encompasses a diverge set of structural isomers. − Lately, aromatic molecules, especially indenyl radical (C 9 H 7 • ), indene (C 9 H 8 ), and its derivatives (C 11 H 8 and C 13 H 8 ), are considered to be key intermediates of astronomical interest for the formation of polycyclic aromatic hydrocarbons − in the interstellar medium. − As C 11 H 8 is home for several indene derivatives, we have explored the various isomers of this elemental composition in this work. The most stable isomer, 1 H -cyclopenta­[ cd ]­indene ( 1 ; see Figure ) was isolated by different groups in the early 1970s. , Wentrup and co-workers synthesized 1 by flash vacuum pyrolysis of 1-(2-diazoethylidene)­indene at 600 °C.…”

“…While several derivatives of 7bHcyclopenta[cd]indene (10) have been isolated elsewhere, 35−38 the parent molecule remains elusive, which outlines that it is the kinetic control that governs the formation of a particular molecule in the laboratory. Other low-lying neutral molecules of C 11 H 8 that are synthetically characterized are as follows: 1H-cyclopropa[b]naphthalene (12; see Figure 2), 39,40 1Hcyclopropa[a]naphthalene (13), 41 penta-1,3-diyn-1-ylbenzene (15), 42,43 1-(buta-1,3-diyn-1-yl)-4-methylbenzene (20), 44, 45 1-(buta-1,3-diyn-1-yl)-2-methylbenzene (22), 46,47 1-ethynyl-2-(prop-1-yn-1-yl)benzene (28; see Figure 3), 48, 49 1,4-diethynyl-2-methylbenzene (31), 50 1,3-diethynyl-5-methylbenzene (33), 51 1,2-diethynyl-4-methylbenzene (36), 52 and 1,2-diethynyl-3-methylbenzene (37). 53 On the contrary, on the high-energy side, reactive intermediates such as 1-naphthylcarbene (52; see Figure 5) and 2-naphthylcarbene (51) have been trapped by matrix isolation within their triplet ground electronic state.…”