Binding the Power of Cycloaddition and Cross-Coupling in a Single Mechanism: An Unexpected Bending Journey to Radical Chemistry of Butadiynyl with Conjugated Dienes.

What if an experiment could combine the power of cycloaddition and cross-coupling with the formation of an aromatic molecule in a single collision? Crossed molecular beam experiments augmented with electronic structure and statistical calculations provided compelling evidence on a novel radical route involving 1,3-butadiynyl (HCCCC; X∑) radicals synthesizing (substituted) arylacetylenes in the gas phase upon reactions with 1,3-butadiene (CHCHCHCH; XA) and 2-methyl-1,3-butadiene (isoprene; CHC(CH)CHCH; XA'). This elegant mechanism merges two previously disconnected concepts of cross-coupling and cycloaddition-aromatization in a single collision event via the formation of two new C(sp)-C(sp) bonds and bending the 180° moiety of the linear 1,3-butadiynyl radical out of the ordinary by 60° to 120°. In addition to its importance to fundamental organic chemistry, this unconventional mechanism links two previously separated routes of gas-phase molecular mass growth processes of polyacetylenes and polycyclic aromatic hydrocarbons (PAHs), respectively, in low-temperature environments such as in cold molecular clouds like the Taurus Molecular Cloud (TMC-1) and in hydrocarbon-rich atmospheres of planets and their moons such as Titan, which revises the established understanding of low-temperature molecular mass growth processes in the Universe.

Untangling the Efficient Boron-Initialized Hydroxyl-Terminated Polybutadiene Combustion for High Energetic Solid Propulsion Systems.

Highly energetic boron (B) particles embedded in hydroxyl-terminated polybutadiene (HTPB) thermosetting polymers represent stable solid-state fuel. Laser-heating of levitated B/HTPB and pure HTPB particles in a controlled atmosphere revealed spontaneous ignition of B/HTPB in air, allowing for examination of the exclusive roles of boron. These ignition events are probed via simultaneous spectroscopic diagnostics: Raman and infrared spectroscopy, temporally resolved high-speed optical and infrared cameras, and ultraviolet-visible (UV-vis) spectroscopy.

Low-temperature gas-phase formation of cyclopentadiene and its role in the formation of aromatics in the interstellar medium.

The cyclopentadiene (CH) molecule has emerged as a molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures such as corannulene (CH), nanobowls (CH), and fullerenes (C) in deep space. However, the underlying elementary gas-phase processes synthesizing cyclopentadiene from acyclic hydrocarbon precursors have remained elusive. Here, by merging crossed molecular beam experiments with rate coefficient calculations and comprehensive astrochemical modeling, we afford persuasive testimony on an unconventional low-temperature cyclization pathway to cyclopentadiene from acyclic precursors through the reaction of the simplest diatomic organic radical-methylidyne (CH)-with 1,3-butadiene (CH) representing main route to cyclopentadiene observed in TaurusMolecular Cloud.

Theoretical Study of the Subsequent Decomposition Mechanisms of 1,1-Diamino-2,2-dinitroethene (FOX-7).

This computational study focuses on the mechanism of the consecutive decomposition of FOX-7 and compares the results with recent experimental study [J. Phys. Chem.

Interstellar formation of lactaldehyde, a key intermediate in the methylglyoxal pathway.

Aldehydes are ubiquitous in star-forming regions and carbonaceous chondrites, serving as essential intermediates in metabolic pathways and molecular mass growth processes to vital biomolecules necessary for the origins of life. However, their interstellar formation mechanisms have remained largely elusive. Here, we unveil the formation of lactaldehyde (CHCH(OH)CHO) by barrierless recombination of formyl (HĊO) and 1-hydroxyethyl (CHĊHOH) radicals in interstellar ice analogs composed of carbon monoxide (CO) and ethanol (CHCHOH).

Gas-phase preparation of silylacetylene (SiHCCH) through a counterintuitive ethynyl radical (CH) insertion.

Elementary reaction mechanisms constitute a fundamental infrastructure for chemical processes as a whole. However, while these mechanisms are well understood for second-period elements, involving those of the third period and beyond can introduce unorthodox reactivity. Combining crossed molecular beam experiments with electronic structure calculations and molecular dynamics simulations, we provide compelling evidence on an exotic insertion of an unsaturated sigma doublet radical into a silicon-hydrogen bond as observed in the barrierless gas-phase reaction of the D1-ethynyl radical (CD) with silane (SiH).

Experimental and theoretical study of the Sn-O bond formation between atomic tin and molecular oxygen.

The merging of the electronic structure calculations and crossed beam experiments expose the reaction dynamics in the tin (Sn, P) - molecular oxygen (O, XΣ-g) system yielding tin monoxide (SnO, XΣ) along with ground state atomic oxygen O(P). The reaction can be initiated on the triplet and singlet surfaces addition of tin to the oxygen atom leading to linear, bent, and/or triangular reaction intermediates. On both the triplet and singlet surfaces, formation of the tin dioxide structure is required prior to unimolecular decomposition to SnO(XΣ) and O(P).

Interstellar Formation of Nitrogen Heteroaromatics [Indole, CHN; Pyrrole, CHN; Aniline, CHNH]: Key Precursors to Amino Acids and Nucleobases.

Nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) are not only fundamental building blocks in the prebiotic synthesis of vital biomolecules such as amino acids and nucleobases of DNA and RNA but also a potential source of the prominent unidentified 6.2 μm interstellar absorption band. Although NPAHs have been detected in meteorites and are believed to be ubiquitous in the universe, their formation mechanisms in deep space have remained largely elusive.

Formation of Paraldehyde (CHO) in Interstellar Analog Ices of Acetaldehyde Exposed to Ionizing Radiation.

Acetaldehyde (CHCHO) plays a crucial role in the synthesis of prebiotic molecules such as amino acids, sugars, and sugar-related compounds, and in the progress of chain reaction polymerization in deep space. Here, we report the first formation of the cyclic acetaldehyde trimer - paraldehyde (CHO) - in low-temperature interstellar analog ices exposed to energetic irradiation as proxies of galactic cosmic rays (GCRs). Utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry and isotopic substitution experiments, paraldehyde was identified in the gas phase during the temperature-programmed desorption of the irradiated acetaldehyde ices based on the calculated adiabatic ionization energies and isomer-specific dissociative fragmentation patterns upon photoionization.

Formation of methylglyoxal (CHC(O)CHO) in interstellar analog ices - a key intermediate in cellular metabolism.

Ketoaldehydes are key intermediates in biochemical processes including carbohydrate, lipid, and amino acid metabolism. Despite their crucial role in the interstellar synthesis of essential biomolecules necessary for the Origins of Life, their formation mechanisms have largely remained elusive. Here, we report the first bottom-up formation of methylglyoxal (CHC(O)CHO)-the simplest ketoaldehyde-through the barrierless recombination of the formyl (HĊO) radical with the acetyl (CHĊO) radical in low-temperature interstellar ice analogs upon exposure to energetic irradiation as proxies of galactic cosmic rays.

Fulvenallenyl Radical (CH)-Mediated Gas-Phase Synthesis of Bicyclic Aromatic CH Isomers: Can Fulvenallenyl Efficiently React with Closed-Shell Hydrocarbons?

To understand the reactivity of resonantly stabilized radicals, often found in relevant concentrations in gaseous environments, it is important to determine their main reaction pathways. Here, it is investigated whether the fulvenallenyl radical (CH) reacts preferentially with closed-shell molecules or radicals. Electronic structure calculations on the CH potential energy surface accessed by the reactions of CH with methylacetylene (CHCCH) and allene (HCCCH) were combined with RRKM-ME calculations of temperature- and pressure-dependent rate constants using the automated EStokTP software suite and kinetic modeling to assess the reactivity of CH with closed-shell unsaturated hydrocarbons.

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

The biphenyl molecule (CH) acts as a fundamental molecular backbone in the stereoselective synthesis of organic materials due to its inherent twist angle causing atropisomerism in substituted derivatives and in molecular mass growth processes in circumstellar environments and combustion systems. Here, we reveal an unconventional low-temperature phenylethynyl addition-cyclization-aromatization mechanism for the gas-phase preparation of biphenyl (CH) along with -, -, and -substituted methylbiphenyl (CH) derivatives through crossed molecular beams and computational studies providing compelling evidence on their formation bimolecular gas-phase reactions of phenylethynyl radicals (CHCC, XA) with 1,3-butadiene- (CD), isoprene (CHC(CH)CHCH), and 1,3-pentadiene (CHCHCHCHCH). The dynamics involve de-facto barrierless phenylethynyl radical additions submerged barriers followed by facile cyclization and hydrogen shift prior to hydrogen atom emission and aromatization to racemic mixtures (, ) of biphenyls in overall exoergic reactions.

Ionizing radiation exposure on Arrokoth shapes a sugar world.

The Kuiper Belt object (KBO) Arrokoth, the farthest object in the Solar System ever visited by a spacecraft, possesses a distinctive reddish surface and is characterized by pronounced spectroscopic features associated with methanol. However, the fundamental processes by which methanol ices are converted into reddish, complex organic molecules on Arrokoth's surface have remained elusive. Here, we combine laboratory simulation experiments with a spectroscopic characterization of methanol ices exposed to proxies of galactic cosmic rays (GCRs).

Exploring the chemical dynamics of phenanthrene (CH) formation the bimolecular gas-phase reaction of the phenylethynyl radical (CHCC) with benzene (CH).

The exploration of the fundamental formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) is crucial for the understanding of molecular mass growth processes leading to two- and three-dimensional carbonaceous nanostructures (nanosheets, graphenes, nanotubes, buckyballs) in extraterrestrial environments (circumstellar envelopes, planetary nebulae, molecular clouds) and combustion systems. While key studies have been conducted exploiting traditional, high-temperature mechanisms such as the hydrogen abstraction-acetylene addition (HACA) and phenyl addition-dehydrocyclization (PAC) pathways, the complexity of extreme environments highlights the necessity of investigating chemically diverse mass growth reaction mechanisms leading to PAHs. Employing the crossed molecular beams technique coupled with electronic structure calculations, we report on the gas-phase synthesis of phenanthrene (CH)-a three-ring, 14π benzenoid PAH- a phenylethynyl addition-cyclization-aromatization mechanism, featuring bimolecular reactions of the phenylethynyl radical (CHCC, XA) with benzene (CH) under single collision conditions.

Stress-Alteration Enhancement of the Reactivity of Aluminum Nanoparticles in the Catalytic Decomposition of -Tetrahydrodicyclopentadiene (JP-10).

High-energy-density aluminum nanoparticles (AlNPs) upon thermal annealing followed by superquenching result in elevated stress levels in the metallic core and reduced surface energy at the core-shell interface. Isomer-selective vacuum ultraviolet-based photoionization mass spectrometry coupled to a high-temperature chemical microreactor reveals that these stress-altered AlNPs (SA-AlNPs) exhibit distinctive temperature-dependent reactivities toward catalytic decomposition of the hydrocarbon jet fuel -tetrahydrodicyclopentadiene (JP-10, CH) compared to untreated AlNPs (UN-AlNPs). SA-AlNPs show a delayed initiation of the decomposition for JP-10 by 200 K relative to the UN-AlNPs; however, the full decomposition is achieved at a 100 K lower temperature.

Gas-Phase Preparation of the 14π Hückel Polycyclic Aromatic Anthracene and Phenanthrene Isomers (CH) via the Propargyl Addition-BenzAnnulation (PABA) Mechanism.

Polycyclic aromatic hydrocarbons (PAHs) imply the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles, commonly referred to as soot particles in combustion systems and interstellar grains in deep space. Whereas gas phase formation pathways to the simplest PAH - naphthalene (CH) - are beginning to emerge, reaction pathways leading to the synthesis of the 14π Hückel aromatic PAHs anthracene and phenanthrene (CH) are still incomplete. Here, by utilizing a chemical microreactor in conjunction with vacuum ultraviolet (VUV) photoionization (PI) of the products followed by detection of the ions in a reflectron time-of-flight mass spectrometer (ReTOF-MS), the reaction between the 1'- and 2'-methylnaphthyl radicals (CH⋅) with the propargyl radical (CH⋅) accesses anthracene (CH) and phenanthrene (CH) via the Propargyl Addition-BenzAnnulation (PABA) mechanism in conjunction with a hydrogen assisted isomerization.

Methanetriol─Formation of an Impossible Molecule.

Orthocarboxylic acids─organic molecules carrying three hydroxyl groups at the same carbon atom─have been distinguished as vital reactive intermediates by the atmospheric science and physical (organic) chemistry communities as transients in the atmospheric aerosol cycle. Predicted short lifetimes and their tendency to dehydrate to a carboxylic acid, free orthocarboxylic acids, signify one of the most elusive classes of organic reactive intermediates, with even the simplest representative methanetriol (CH(OH))─historically known as orthoformic acid─not previously been detected experimentally. Here, we report the first synthesis of the previously elusive methanetriol molecule in low-temperature mixed methanol (CHOH) and molecular oxygen (O) ices subjected to energetic irradiation.

Initial decomposition pathways of 1,1-diamino-2,2-dinitroethylene (α-FOX-7) in the condensed phase.

The initial decomposition pathways of α-FOX-7 in the condensed phase (crystal) were investigated density functional theory. Calculations were carried out using three FOX-7 systems with increasing complexity from 1-layer (sheet) 2-layer (surface) to 3-layer (bulk). The encapsulated environment of the central α-FOX-7 molecule, where decomposition takes place, is reconstructed by neighbouring molecules following a crystal structure.

Interstellar formation of glyceric acid [HOCHCH(OH)COOH]-The simplest sugar acid.

Glyceric acid [HOCHCH(OH)COOH]-the simplest sugar acid-represents a key molecule in biochemical processes vital for metabolism in living organisms such as glycolysis. Although critically linked to the origins of life and identified in carbonaceous meteorites with abundances comparable to amino acids, the underlying mechanisms of its formation have remained elusive. Here, we report the very first abiotic synthesis of racemic glyceric acid via the barrierless radical-radical reaction of the hydroxycarbonyl radical (HOĊO) with 1,2-dihydroxyethyl (HOĊHCHOH) radical in low-temperature carbon dioxide (CO) and ethylene glycol (HOCHCHOH) ices.

Efficient Oxidative Decomposition of Jet-Fuel -Tetrahydrodicyclopentadiene (JP-10) by Aluminum Nanoparticles in a Catalytic Microreactor: An Online Vacuum Ultraviolet Photoionization Study.

The oxidation of gas-phase -tetrahydrodicyclopentadiene (JP-10, CH) over aluminum nanoparticles (AlNP) has been explored between a temperature range of 300 and 1250 K with a novel chemical microreactor. The results are compared with those obtained from chemical microreactor studies of helium-seeded JP-10 and of helium-oxygen-seeded JP-10 without AlNP to gauge the effects of molecular oxygen and AlNP, respectively. Vacuum ultraviolet (VUV) photoionization mass spectrometry reveals that oxidative decomposition of JP-10 in the presence of AlNP is lowered by 350 and 200 K with and without AlNP, respectively, in comparison with pyrolysis of the fuel.

Elucidating the chemical dynamics of the elementary reactions of the 1-propynyl radical (CHCC; XA) with 2-methylpropene ((CH)CCH; XA).

Exploiting the crossed molecular beam technique, we studied the reaction of the 1-propynyl radical (CHCC; XA) with 2-methylpropene (isobutylene; (CH)CCH; XA) at a collision energy of 38 ± 3 kJ mol. The experimental results along with and statistical calculations revealed that the reaction has no entrance barrier and proceeds indirect scattering dynamics involving CH intermediates with lifetimes longer than their rotation period(s). The reaction is initiated by the addition of the 1-propynyl radical with its radical center to the π-electron density at the C1 and/or C2 position in 2-methylpropene.

Hypergolic ionic liquids: to be or not to be?

Hypergolic ionic liquids (HIL) - ionic liquids which ignite spontaneously upon contact with an oxidizer - emerged as green space propellants. Exploiting the previously marked hypergolic [EMIM][CBH] - WFNA (1-ethyl-3-methylimidazolium cyanoborohydride - white fuming nitric acid) system as a benchmark, through the utilization of a novel chirped-pulse droplet-merging technique in an ultrasonic levitation environment and electronic structure calculations, this work deeply questions the hypergolicity of the [EMIM][CBH]-WFNA system. Molecular oxygen is critically required for the [EMIM][CBH]-WFNA system to ignite spontaneously.