Gas-Phase Synthesis of Coronene through Stepwise Directed Ring Annulation

Abstract

Molecular beam experiments together with electronic structure calculations provide the first evidence of a complex network of elementary gas-phase reactions culminating in the bottom-up preparation of the 24π aromatic coronene (C24H12) moleculea representative peri-fused polycyclic aromatic hydrocarbon (PAH) central to the complex chemistry of combustion systems and circumstellar envelopes of carbon stars. The gas-phase synthesis of coronene proceeds via aryl radical-mediated ring annulations through benzo­[e]­pyrene (C20H12) and benzo­[ghi]­perylene (C22H12) involving armchair-, zigzag-, and arm-zig-edged aromatic intermediates, highlighting the chemical diversity of molecular mass growth processes to polycyclic aromatic hydrocarbons. The isomer-selective identification of five- to six-ringed aromatics culminating with the detection of coronene is accomplished through photoionization and is based upon photoionization efficiency curves along with photoion mass-selected threshold photoelectron spectra, providing a versatile concept of molecular mass growth processes via aromatic and resonantly stabilized free radical intermediates to two-dimensional carbonaceous nanostructures.

Unconventional gas-phase synthesis of biphenyl and its atropisomeric methyl-substituted derivatives

“…These patterns classify this reaction sequence as a low-temperature framework for the formation of (un)substituted biphenyls and PAHs as building blocks in molecular mass growth processes to carbonaceous nanostructures. Prototypes of successive reactions, of which the fundamental mechanisms have previously been explored, 73–78 are featured in Fig. 8 eventually leading to the formation of coronene (C 24 H 12 )—a fundamental molecular building block in two-dimensional carbonaceous nanostructures— via hydrogen abstraction–acetylene addition (HACA), hydrogen abstraction–vinylacetylene addition (HAVA), and radical–radical reactions (RRR).…”

Conformer-Specific Photoelectron Spectroscopy of Carbonic Acid: H2CO3

“…Multiplexed photoionization , and photoelectron spectroscopic − methods offer high sensitivity (<1 ppb), multiplicity (detection of various species at the same time), and high selectivity because constitutional isomers and diastereomers including conformers often have different ionization energies (AIEs) and vibronic structures. Thus, photoionization tools are ideally suited as a detection tool in terrestrial astrochemistry experiments to sample from complex reactive environments and probe the entire chemistry at conditions relevant to the interstellar medium.…”