Gas‐Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C₈H₇) via Triplet Aromatic Cyclooctatetraene (C₈H₈) and Non‐Aromatic Cyclooctatriene (C₈H₈) Intermediates

Abstract

The 1,2,4,7-cyclooctatetraenyl radical (C H ) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C H ) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C H ) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C H ). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods.

Formation of the Elusive Silylenemethyl Radical (HCSiH2; X2B2) via the Unimolecular Decomposition of Triplet Silaethylene (H2CSiH2; a3A″)

“…Both distributions terminate at 69° due to limitations in the machine configuration that prevents scanning at larger angles. To account for these broad and asymmetric distributions, a second reaction channel arising from dicarbon (C 2 )a known byproduct of graphite ablation , and silane was required. In the selected part of the beam, the dicarbon (C 2 ) to atomic carbon (C) ratio of 0.5 ± 0.05:1 was determined, that is, a fraction of about 33%.…”

“…The reaction of atomic carbon with silane (Voltaix; 99.9999%) was performed utilizing a crossed molecular beams machine at the University of Hawaii. , The carbon atoms were produced in their electronic ground state by ablation of a rotating graphite rod using the focused fourth harmonic of a Nd:YAG laser operating at a reduced output energy of 10 mJ per pulse. − The ablated carbon atoms were subsequently entrained in a pulsed beam of neon gas (99.999%; Specialty Gases of America), skimmed, and then velocity-selected using a four-slot chopper wheel rotating at 120 Hz. This part of the pulse was characterized by a peak velocity v p of 1505 ± 10 m s –1 and a speed ratio S of 3.3 ± 0.1; note that under these experimental conditions, dicarbon (C 2 ) is also produced with the same beam properties . A neat silane beam ( v p = 841 ± 10 m s –1 ; S = 10.2 ± 0.3) was spatially and temporally aligned to intersect perpendicularly the carbon atom beam resulting in a nominal collision energy of 13.0 ± 0.2 kJ mol –1 and a center-of-mass angle (CM) of 56.1 ± 0.4° (Table ).…”

“…This part of the pulse was characterized by a peak velocity v p of 1505 ± 10 m s −1 and a speed ratio S of 3.3 ± 0.1; note that under these experimental conditions, dicarbon (C 2 ) is also produced with the same beam properties. 56 A neat silane beam (v p = 841 ± 10 m s −1 ; S = 10.2 ± 0.3) was spatially and temporally aligned to intersect perpendicularly the carbon atom beam resulting in a nominal collision energy of 13.0 ± 0.2 kJ mol −1 and a centerof-mass angle (CM) of 56.1 ± 0.4°(Table 1). The reactively scattered products entered a triply differentially pumped universal detector rotatable in the plane defined by the reactant beams.…”

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

“…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. − …”