Unconventional Pathway in the Gas-Phase Synthesis of 9H-Fluorene (C13 H10 ) via the Radical-Radical Reaction of Benzyl (C7 H7 ) with Phenyl (C6 H5 )

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring-9H-fluorene (C₁₃ H₁₀ )-is produced isomer-specifically in the gas phase by reacting benzyl (C₇ H₇ ⋅) with phenyl (C₆ H₅ ⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1-(6-methylenecyclohexa-2,4-dienyl)benzene intermediates (C₁₃ H₁₂ ) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical-radical reactions are initiated through recombination at their radical centers. The structure of 9H-fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings.

A combined DFTB nanoreactor and reaction network generator approach for the mechanism of hydrocarbon combustion

We explored the mechanism of ethylene combustion by combining a density functional tight-binding based nanoreactor molecular dynamic method (DFTB-NMD) and a hidden Markov model (HMM) based reaction network generator approach. The results demonstrate that the DFTB-NMD is a promising method to predict the mechanism of complicated combustion reactions.

From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy

Synchrotron radiation provides insight into spectroscopy and dynamics in clusters and nanoparticles.

Theoretical study of the reaction mechanism and kinetics of the phenyl + propargyl association

Potential energy surface for the phenyl + propargyl radical recombination reaction has been studied at the CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G** level of theory for the closed-shell singlet species and at the triplet-singlet gap CASPT2/cc-pVTZ-CCSD(T)-F12/cc-pVTZ-f12//CASSCF/cc-pVTZ level of theory for the diradical species. High-pressure limit rate constants for the barrierless channels were evaluated with variable reaction coordinate transition state theory (VRC-TST). Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations have been performed to assess temperature- and pressure-dependent phenomenological rate constants and product branching ratios. The entrance channels of the radical association reaction produce 3-phenyl-1-propyne and phenylallene which can further dissociate/isomerize into a variety of unimolecular and bimolecular products. Theoretical evidence is presented that, at combustion relevant conditions, the phenyl + propargyl recombination provides a feasible mechanism for the addition of a second five-member ring to the first six-member aromatic ring producing the prototype two-ring species indene and indenyl. Rate expressions for all important reaction channels in a broad range of temperatures and pressures have been generated for kinetic modeling.

Molecular mass growth through ring expansion in polycyclic aromatic hydrocarbons via radical-radical reactions

Polycyclic aromatic hydrocarbons (PAHs) represent key molecular building blocks leading to carbonaceous nanoparticles identified in combustion systems and extraterrestrial environments. However, the understanding of their formation and growth in these high temperature environments has remained elusive. We present a mechanism through laboratory experiments and computations revealing how the prototype PAH—naphthalene—can be efficiently formed via a rapid 1-indenyl radical—methyl radical reaction. This versatile route converts five- to six-membered rings and provides a detailed view of high temperature mass growth processes that can eventually lead to graphene-type PAHs and two-dimensional nanostructures providing a radical new view about the transformations of carbon in our universe.

Polycyclic aromatic hydrocarbons (PAHs) represent key molecular building blocks in extraterrestrial environments but the understanding of their formation and growth in this environment has remained elusive. Here the authors reveal how naphthalene can be efficiently formed via rapid radical–radical reactions.