Gas-Phase Formation of Fulvenallene (C₇H₆) via the Jahn–Teller Distorted Tropyl (C₇H₇) Radical Intermediate under Single-Collision Conditions

Abstract

The fulvenallene molecule (C 7 H 6 ) has been synthesized via the elementary gas-phase reaction of the methylidyne radical (CH) with the benzene molecule (C 6 H 6 ) on the doublet C 7 H 7 surface under single collision conditions. The barrier-less route to the cyclic fulvenallene molecule involves the addition of the methylidyne radical to the π-electron density of benzene leading eventually to a Jahn−Teller distorted tropyl (C 7 H 7 ) radical intermediate and exotic ring opening−ring contraction sequences terminated by atomic hydrogen elimination. The methylidyne-benzene system represents a benchmark to probe the outcome of the elementary reaction of the simplest hydrocarbon radicalmethylidynewith the prototype of a closed-shell aromatic moleculebenzeneyielding nonbenzenoid fulvenallene. Combined with electronic structure and statistical calculations, this bimolecular reaction sheds light on the unusual reaction dynamics of Huckel aromatic systems and remarkable (polycyclic) reaction intermediates, which cannot be studied via classical organic, synthetic methods, thus opening up a versatile path to access this previously largely obscure class of fulvenallenes.

Gas-Phase Optical Detection of 3-Ethynylcyclopentenyl: A Resonance-Stabilized C7H7 Radical with an Embedded 1-Vinylpropargyl Chromophore

“…Because 1-ethynylcyclopenta-1,3-diene (C 7 H 6 ) has recently been shown from RRKM simulations to be a significant product of the reaction of C 2 H 2 with c -C 5 H 5 (with a predicted yield of ca. 60% at 2500 K), C 7 H 6 + H reactions may provide an additional source of 3ecpr at high temperatures and pressures in environments where propargyl and acetylene are abundant.…”

Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: Abundances of CCH and CN derivatives of hydrocarbon cycles

“…Here, reaction [2] was explored under single-collision conditions in crossed molecular beams as well as computationally (He et al , 2020b). The results reveal a strong energy and hence temperature dependence of the branching ratios with acetylene (C 2 H 2 ) and cyclopentadienyl (C 5 H 5 ) formed almost exclusively at temperatures of 10 K. Both reactions [1] and [3] access the same surface through distinct barrier-less entrance channels of carbon atom addition to the cyclic C 6 H 7 radical (reaction [1]) followed by ring opening and/or hydrogen migration of the collision complex and carbene (CH 2 )-phenyl radical (C 6 H 5 ) recombination that leads to the benzyl radical (C 6 H 5 CH 2 ).…”

Gas-Phase Formation of C5H6 Isomers via the Crossed Molecular Beam Reaction of the Methylidyne Radical (CH; X2Π) with 1,2-Butadiene (CH3CHCCH2; X1A′)

“…The methylidyne (CH; X 2 Π) radical reaction with 1,2-butadiene (CH 2 CCHCH 3 ; X 1 A′) was conducted under single collision conditions using a crossed molecular beams machine at the University of Hawaii . In the primary source chamber, the pulsed methylidyne molecular beam was formed via photodissociation (COMPex 110, Coherent, Inc.; 248 nm; 30 Hz) of bromoform (CHBr 3 , Aldrich Chemistry, ≥99%) seeded in helium (99.9999%; AirGas) at fractions of 0.12% at a backing pressure of 2.2 atm. , The methylidyne beam passed a skimmer and was velocity selected by a four-slot chopper wheel yielding a peak velocity v p of 1827 ± 15 m s –1 and speed ratio S of 12.0 ± 1.2. The rotational temperature of the methylidyne radicals were determined to be 14 ± 1 K via laser-induced fluorescence (LIF) .…”

“…In terrestrial environments, PAHs are considered as toxic byproducts in the incomplete combustion of fossil fuel, coals, and biomass. This causes air and marine pollution eventually resulting in carcinogenic, mutagenic, and teratogenic effects. − Therefore, the exploration of the fundamental reaction pathways leading to a synthesis of PAHs and their precursors in extreme environments is important to better understand the carbon chemistry in terrestrial environments and deep space such as cold molecular clouds like TMC-1 and the dying carbon stars like IRC+10216. − …”