Off the Beaten Path: Almost Clean Formation of Indene from the <i>ortho</i>-Benzyne + Allyl Reaction

McCabe, Morgan N.; Hemberger, Patrick; Reusch, Engelbert; Bodi, Andras; Bouwman, Jordy

doi:10.1021/acs.jpclett.0c00374

Cited by 43 publications

(65 citation statements)

References 39 publications

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“…Whereas indene has been shown to be the product in high-temperature processes involving reactions of phenyl radicals (C 6 H 5 ) with allene (H 2 CCCH 2 ) and methylacetylene (CH 3 CCH) ( 61 , 62 ) along with the benzyl radical (C 7 H 7 )–acetylene (C 2 H 2 ) system ( 63 ), the MACA mechanism operates at low temperatures such as in molecular clouds. The only other barrierless reaction, which has been recently shown to form indene, is o -benzyne (C 6 H 4 ) plus allyl (C 3 H 5 ) ( 64 ), but it involves two unstable species not detected in deep space. MACA has the potential to convert any vinyl group (C 2 H 3 ) linked to an aromatic, six-membered ring eventually to a cyclopentadiene moiety via reaction of a methylidyne radical ( Fig.…”

Section: Discussionmentioning

confidence: 99%

Low-temperature gas-phase formation of indene in the interstellar medium

et al. 2021

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Polycyclic aromatic hydrocarbons (PAHs) are fundamental molecular building blocks of fullerenes and carbonaceous nanostructures in the interstellar medium and in combustion systems. However, an understanding of the formation of aromatic molecules carrying five-membered rings—the essential building block of nonplanar PAHs—is still in its infancy. Exploiting crossed molecular beam experiments augmented by electronic structure calculations and astrochemical modeling, we reveal an unusual pathway leading to the formation of indene (C9H8)—the prototype aromatic molecule with a five-membered ring—via a barrierless bimolecular reaction involving the simplest organic radical—methylidyne (CH)—and styrene (C6H5C2H3) through the hitherto elusive methylidyne addition–cyclization–aromatization (MACA) mechanism. Through extensive structural reorganization of the carbon backbone, the incorporation of a five-membered ring may eventually lead to three-dimensional PAHs such as corannulene (C20H10) along with fullerenes (C60, C70), thus offering a new concept on the low-temperature chemistry of carbon in our galaxy.

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Section: Discussionmentioning

confidence: 99%

Low-temperature gas-phase formation of indene in the interstellar medium

et al. 2021

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“…An in situ formation mechanism for benzene, cyclopentadiene, indene, and naphthalene must involve abundant hydrocarbons containing from two to five carbon atoms (Kaiser & Hansen 2021). Moreover, some of these species should allow an easy cyclisation in bimolecular reactions to efficiently form the first aromatic ring -benzene (c-C 6 H 6 ), benzyne (c-C 6 H 4 ), the phenyl radical (c-C 6 H 5 ), or any other species -from which larger PAHs can grow (Jones et al 2011;Parker et al 2012;McCabe et al 2020;Doddipatla et al 2021). The progargyl radical and the closed-shell hydrocarbons methyl-, vinyl-, and ethynylallene have been detected in TMC-1 with high abundances (Agúndez et al 2021a;Cernicharo et al 2021b,c).…”

Section: Introductionmentioning

confidence: 99%

Discovery of benzyne, o-C₆H₄, in TMC-1 with the QUIJOTE line survey

Cernicharo

Agúndez

Kaiser

et al. 2021

A&A

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106

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We report the detection, for the first time in space, of a new non-functionalised hydrocarbon cycle in the direction of TMC-1: o-C6H4 (ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5.0 ± 1.0) × 1011 cm−2. The abundance of this species is around 30 times lower than that of cyclopentadiene and indene. We compare the abundance of benzyne with that of other pure hydrocarbons, cycles or chains, and find that it could be formed from neutral-radical reactions such as C2H + CH2CHCCH and C + C5H5, and possibly through C4H + C2H4, C3H + CH2CCH2, and C3H2 + C3H3. Hence, the rich content of hydrocarbon cycles observed in TMC-1 could arise through a bottom-up scenario involving reactions of a few radicals with the abundant hydrocarbons recently revealed by the QUIJOTE line survey.

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“…Although, some success is reported for observations on Tu Tau; a binary star system hosting a carbon-rich AGB star and a blue companion (Buss et al 1991;Speck & Barlow 1997;Boersma et al 2006). Knowledge available from the combustion community has been used to explain the bottom-up formation of PAHs in the outflows of such stars (e.g., Frenklach & Feigelson 1989;Cherchneff et al 1992) and suggests that pentagon-containing PAH species are also produced (Bouwman et al 2015;Johansson et al 2018;Schulz et al 2019;McCabe et al 2020). Inclusion of pentagons can also be achieved through top-down erosion of large aromatic species, which is considered the prime mechanism for creating fullerenes (Berné & Tielens 2012).…”

Section: Astronomical Implicationsmentioning

confidence: 99%

“…A large variety of mechanisms are expected to contribute to the formation of PAHs in the combustion of fossil fuels (Richter & Howard 2000;Moriarty & Frenklach 2000;Parker et al 2014;Kaiser et al 2015;Yang et al 2017), some of which are applied to astrochemistry to explain the formation of interstellar aromatic molecules in the outflows of carbon-rich stars (e.g., Frenklach & Feigelson 1989;Cherchneff et al 1992). The sequences of chemical reactions involved not only produce clean hexagon containing aromatic molecules, but they have also been shown in the laboratory to result in pentagon containing species (Bouwman et al 2015;Johansson et al 2018;Commodo et al 2019;Schulz et al 2019;McCabe et al 2020). Pentagon inclusion is also invoked to explain the formation of fullerenes through erosion of large PAHs as this provides a way to bowl the planar PAH plane (Berné & Tielens 2012).…”

Section: Introductionmentioning

confidence: 99%

Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)

Bouwman

Boersma

Bulak

et al. 2020

A&A

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Infrared bands at 3.3, 6.2, 7.6, 7.8, 8.6, and 11.2 μm have been attributed to polycyclic aromatic hydrocarbons (PAHs) and are observed toward a large number of galactic and extragalactic sources. Some interstellar PAHs possibly contain five-membered rings in their honeycomb carbon structure. The inclusion of such pentagon defects can occur during PAH formation, or as large PAHs are eroded by photo-dissociation to ultimately yield fullerenes. Pentagon formation is a process that is associated with the bowling of the PAH plane, that is, the ability to identify PAH pentagons in space holds the potential to directly link PAHs to cage and fullerene structures. It has been hypothesized that infrared (IR) activity around 1100 cm−1 may be a spectral marker for interstellar pentagons. We present an experimentally measured gas-phase IR absorption spectrum of the pentagon-containing rubicene cation (C26H14•+) to investigate if this band is present. The NASA Ames PAH IR Spectroscopic Database is scrutinized to see whether other rubicene-like species show IR activity in this wavelength range. We find that a specific molecular characteristic is responsible for this IR band. Namely, the vibrational motion attributed to this IR activity involves pentagon-containing harbors. An attempt to find this specific mode in Spitzer observations is undertaken and tentative detections around 9.3 μm are made toward the reflection nebula NGC 7023 and the H II-region IRAS 12063-6259. Simulated emission spectra are used to derive upper limits for the contributions of rubicene-like pentagonal PAH species to the IR band at 6.2 μm toward these sources.

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Off the Beaten Path: Almost Clean Formation of Indene from the ortho-Benzyne + Allyl Reaction

Cited by 43 publications

References 39 publications

Low-temperature gas-phase formation of indene in the interstellar medium

Low-temperature gas-phase formation of indene in the interstellar medium

Discovery of benzyne, o-C₆H₄, in TMC-1 with the QUIJOTE line survey

Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)

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Off the Beaten Path: Almost Clean Formation of Indene from the ortho-Benzyne + Allyl Reaction

Cited by 43 publications

References 39 publications

Low-temperature gas-phase formation of indene in the interstellar medium

Low-temperature gas-phase formation of indene in the interstellar medium

Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey

Gas-phase infrared spectroscopy of the rubicene cation (C26H14•+)

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Discovery of benzyne, o-C₆H₄, in TMC-1 with the QUIJOTE line survey

Gas-phase infrared spectroscopy of the rubicene cation (C₂₆H₁₄^•+)