André K. Eckhardt

Ruhr-Universität Bochum | RUB · Organic Chemistry

Carbohydrates (CH2O)n are the formal adducts of carbon (atoms) to water with a repeating unit that structurally resembles H-C̈-OH (hydroxymethylene). Although hydroxymethylene has been suggested as a building block for sugar formation, it is a reactive species that had escaped detection until recently. Here we demonstrate that formaldehyde reacts w...

With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant simplest α‐keto carboxylic acid – glyoxylic acid (HCOCOOH) – is still elusive. Here we report the formation of glyoxylic acid via a cosmic ray driven non‐equilibrium chemistry in polar interstellar ices of carbon monoxi...

Phosphoryl nitride (NPO) is a highly reactive intermediate, and its chemistry has only been explored under matrix isolation conditions so far. Here we report the synthesis of an anthracene (A) and phosphoryl azide based molecule (N3P(O)A) that acts as a molecular synthon of NPO. Experimentally, N3P(O)A dissociates thermally with a first-order kinet...

Phosphorus mononitride (PN) only has a fleeting existence on Earth, and molecular precursors for the release of this molecule under mild conditions in solution have remained elusive. Here we report the synthesis of an anthracene-based precursor—an anthracene moiety featuring an azidophosphine bridge across its central ring—that dissociates into din...

Simple imines and diimines are common building blocks in organic synthesis, but the compound class is spectroscopically not well characterized. Herein we report the formation of the simplest diimine, namely 1,2-diiminoethane, as well as spectroscopic characterization by cryogenic matrix isolation IR and UV/Vis spectroscopy. Three conformers of 1,2-...

Enols - tautomers of ketones or aldehydes - are anticipated to be ubiquitous in the interstellar medium and play a key role in the formation of complex organic molecules in deep space, but their fundamental formation mechanisms have remained largely elusive as of now. Here we present a combined experimental and computational study demonstrating the...

Sugars and sugar-related molecules are ubiquitous in carbonaceous meteorites and in star-forming regions, but the underlying mechanisms of their formation have remained largely elusive. Herein, we report an unconventional synthesis of the hemiacetal, (R/S)-1-methoxyethanol (CH3OCH(OH)CH3), through quantum tunneling mediated reactions in low-tempera...

Oxirenes-highly strained 4π Hückel antiaromatic organics-have been recognized as key reactive intermediates in the Wolff rearrangement and in interstellar environments. Predicting short lifetimes and tendency toward ring opening, oxirenes are one of the most mysterious classes of organic transients, with the isolation of oxirene (c-C2H2O) having re...

Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic...

Glycinal (HCOCH2NH2) and acetamide (CH3CONH2) are simple molecular building blocks of biomolecules in prebiotic chemistry, though their origin on early Earth and formation in interstellar media remain a mystery. These molecules are formed with their tautomers in low temperature interstellar model ices upon interaction with simulated galactic cosmic...

Simple unhindered aldimines tend to hydrolyze or oligomerize and are therefore spectroscopically not well characterized. Herein we report the formation and spectroscopic characterization of the simplest imino acid, namely glycine imine, by cryogenic matrix isolation IR and UV/Vis spectroscopy. Glycine imine forms after UV irradiation of 2‐azidoacet...

Simple unhindered aldimines tend to hydrolyze or oligomerize and are therefore spectroscopically not well characterized. Herein we report the formation and spectroscopic characterization of the simplest imino acid, namely glycine imine, by cryogenic matrix isolation IR and UV/Vis spectroscopy. Glycine imine forms after UV irradiation of 2-azidoacet...

Carbonyl-bearing complex organic molecules (COMs) in the interstellar medium (ISM) are of significant importance due to their role as potential precursors to biomolecules. Simple aldehydes and ketones like acetaldehyde, acetone, and propanal have been recognized as fundamental molecular building blocks and tracers of chemical processes involved in...

The search for methods to bind CO2 and use it synthetically as a C1-building block under mild conditions is an ongoing endeavor of great urgency. The formation of heterocyclic carbene-carbon dioxide adducts occurs rapidly when the carbene is generated in solution in the presence of CO2. Here we demonstrate the reversible formation of a complex of t...

The tetrahedral 1,2,3-triphospha-4-azatricyclo [1.1.0.02,4] butane (P3N) molecule-an isovalent species of phosphorus (P4)-was prepared in low-temperature (5 K) phosphine-nitrogen ices and was identified in the gas phase through isomer-selective, tunable, soft photoionization reflectron time-of-flight mass spectrometry. Theoretical calculations reve...

Cage-opening reactions of the highly strained tri-tert-butylphosphatetrahedrane (1), shown here to function as a synthon of (tri-tert-butylcyclopropenyl)phosphinidene, are described. Treatment of 1 with a base-stabilized silylene led to the corresponding phosphasilene, which was isolated in 72% yield as a red crystalline solid. Phosphinidene transf...

11-Azido-9,10-dihydro-9,10-phosphanoanthracene (N3PA) has been demonstrated recently as a transfer reagent for molecular phosphorus mononitride (PN) because it easily dissociates at room temperature into dinitrogen (N2), PN, and anthracene (A). Here we report further reactivity studies of the N3PA molecule including strain-promoted 1,3-dipolar cycl...

Phosphoryl nitride (NPO) is a highly reactive intermediate, and its chemistry has only been explored under matrix isolation conditions so far. Here we report the synthesis of an anthracene (A) and phosphoryl azide-based molecule (N3P(O)A) that acts as a molecular synthon of NPO. Experimentally, N3P(O)A dissociates thermally with a first order kinet...

Phosphoryl nitride (NPO) is a highly reactive intermediate, and its chemistry has only been explored under matrix isolation conditions so far. Here we report the synthesis of an anthracene (A) and phosphoryl azide-based molecule (N3P(O)A) that acts as a molecular synthon of NPO. Experimentally, N3P(O)A dissociates thermally with a first order kinet...

Polyhedral nitrogen containing molecules such as prismatic P3N3 - a hitherto elusive isovalent species of prismane (C6H6) - have attracted particular attention from the theoretical, physical, and synthetic chemistry communities. Here we report on the preparation of prismatic P3N3 [1,2,3-triaza-4,5,6-triphosphatetracyclo[2.2.0.02,6.03,5]hexane] by e...

The rotational spectra of the singly substituted carbon-13 isotopic species of six sulphur-terminated carbon chains have been detected between 5 and 40 GHz using a supersonic discharge jet source in combination with a cavity Fourier transform microwave spectrometer. These molecules are HC3HS, a closed-shell isomer of H2C3S, and five radicals: HCCS,...

Phosphorus mononitride (PN) only has a fleeting existence on Earth and molecular precursors for a mild release of the molecule to enable chemical synthesis in solution do not exist. Here we report the synthesis of an anthracene (A) based molecular precursor (N3PA) that dissociates into dinitrogen (N2), A and PN in solution with a first order half-l...

Phosphorus mononitride (PN) only has a fleeting existence on Earth and molecular precursors for a mild release of the molecule to enable chemical synthesis in solution do not exist. Here we report the synthesis of an anthracene (A) based molecular precursor (N3PA) that dissociates into dinitrogen (N2), A and PN in solution with a first order half-l...

Tri-tert-butylphosphatetrahedrane (1) is shown here to act as a synthon of isomeric tri-tert-butylphosphacyclobutadiene in the presence of a Lewis acid or transition-metal complex. When it is combined with a substoichiometric amount of triphenylborane, compound 1 forms a ladderane-type dimer of tri-tert-butylphosphacyclobutadiene in 72% isolated yi...

he formation of complex organic molecules by energetic electrons mimicking secondary electrons generated within trajectories of galactic cosmic rays was investigated in interstellar ice analog samples of carbon monoxide and water at 5 K. Simulating the transition from cold molecular clouds to star-forming regions, newly formed products sublimed dur...

The simplest α,β-unsaturated sulfinyl radical CH2[double bond, length as m-dash]C(H)SO˙ has been generated in the gas phase by high-vacuum flash pyrolysis (HVFP) of sulfoxide CH2[double bond, length as m-dash]C(H)S(O)CF3 at ca. 800 °C. Two planar cis and trans conformers of CH2[double bond, length as m-dash]C(H)SO˙ were isolated in cryogenic matrix...

We present the first formation of the previously elusive phosphine imide (HN[double bond, length as m-dash]PH3) along with its phosphinous amide (H2N–PH2) isomer via exposure of phosphine (PH3) and ammonia (NH3) ices to ionizing radiation

The species on the C3H2O potential energy surface have long been known to play a vital role in extraterrestrial chemistry. Here we report on the hitherto uncharacterized isomer ethynylhydroxycarbene (H-C≡C-C̈-OH, 1) generated by high-vacuum flash pyrolysis of ethynylglyoxylic acid ethyl ester and trapped in solid argon matrices at 3 and 20 K. Upon...

As sulfur containing organic molecules thioamides and their isomers are conceivable intermediates in prebiotic chemistry, e. g. , in the formation of amino acids and thiazoles and resemble viable candidates for detection in interstellar media. Here we report the characterization of parent thioformamide in the solid state via single crystal X‐ray di...

The identification of silicon–substituted, complex organics carrying multiple functional groups via classical infrared spectroscopy is challenging because the group frequencies of functional groups often overlap. Photoionization (PI) reflectron time‐of‐fight mass spectrometry (ReTOF‐MS) in combination with temperature programmed desorption (TPD) ho...

We present a comprehensive experimental study of a di-t-butyl-substituted cyclooctatetraene-based molecular balance to measure the effect of 16 different solvents on the equilibrium of folded versus unfolded isomers. In the folded 1,6-isomer, the two t-butyl groups are in close proximity (H···H distance ≈ 2.5 Å), but they are far apart in the unfol...

Significance Carbenes represent key reactive intermediates in molecular mass growth processes leading to carbonaceous nanostructures in the interstellar medium and in combustion systems. However, due to their short lifetimes and tendency for dimerization, carbenes represent one of the foremost obscured classes of reactive intermediates, with the pr...

Pyruvic acid represents a key molecule in prebiotic chemistry to form metabolites and amino acids. Without liquid water on the early Earth, endogenous formation of pyruvic acid is unlikely, and an exogenous delivery constitutes an appealing alternative. However, despite the detection of more than 200 molecules in space, pyruvic acid is elusive. Her...

Acetic acid (CH3COOH) is considered a key molecule in the formation of the simplest amino acid, glycine, and consequently peptides. It is ubiquitous in the interstellar medium and has been detected toward hot cores, in the coma of comets, and on the surface of the comet 67P/Churyumov-Gerasimenko by the Rosetta mission. Here we present the isomer-se...

Elusive [S, S, N, O] isomers including the perthiyl radical •SSNO are S/N hybrid species in the complex bioinorganic chemistry of signaling molecules H2S and •NO. By mixing thermally generated disulfur (S2) with •NO in the gas phase, •SSNO was generated and subsequently isolated in cryogenic Ar- and N2-matrices at 10.0 K and 15.0 K, respectively. U...

Although the chemistry of phosphorus and nitrogen has fascinated chemists for more than 350 years, the Hückel aromatic cyclotriphosphazene (P 3 N 3 , 2 ) molecule—a key molecular building block in phosphorus chemistry—has remained elusive. Here, we report a facile, versatile pathway producing cyclotriphosphazene and its Dewar benzene–type isomer (P...

Small molecules solely consisting of H, N, O, and S are highly relevant intermediates in atmospheric chemistry and biology. Even though several isomers of [HNO2S] have been computationally predicted, only the IR spectra for the two lowest-energy isomers HNSO2 and syn-syn HONSO have been previously reported. Herein, the photochemistry (193 nm laser)...

Endlich nachgewiesen: Das bisher unbekannte 1,1‐Ethendiol, das energetisch höher liegende Tautomer der Essigsäure, wurde synthetisiert und spektroskopisch nachgewiesen. Es ist leicht durch Decarboxylierung von Malonsäure herstellbar, einer Reaktion also, die oft implizit in synthetischen Schritten mit 1,3‐Dicarbonsäuren postuliert wurde. Abstract...

We present the first spectroscopic identification of hitherto unknown 1,1‐ethenediol, the enol tautomer of acetic acid. The title compound was generated in the gas phase through flash vacuum pyrolysis of malonic acid at 400 °C. The pyrolysis products were subsequently trapped in argon matrices at 10 K and characterized spectroscopically by means IR...

We present a novel concept for the in situ control of site-selectivity of catalytic acetylations of partially protected sugars based on light as external stimulus using oligopeptide catalysts equipped with an azobenzene moiety. The isomerizable azobenzene-peptide backbone defines the size and shape of the catalytic pocket while the π-methyl-L-histi...

Quantum mechanical tunneling (QMT) of heavy atoms like carbon or nitrogen for the longest time has been considered very unlikely, but recent evidence suggests that heavy-atom QMT does occur more frequently than assumed. Here we demonstrate that carbon vs. nitrogen heavy-atom QMT can even be competitive leading to two different products originating...

With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant simplest α‐keto carboxylic acid – glyoxylic acid (HCOCOOH) – is still elusive. Here we report the formation of glyoxylic acid via a cosmic ray driven non‐equilibrium chemistry in polar interstellar ices of carbon monoxi...

S-Nitrosothiols (RSNO) are exogenous and endogenous sources of nitric oxide in biological systems due to facile homolytic cleavage of the S–N bonds. By following the photolytic decomposition of prototypical RSNO (R = Me and Et) in Ne, Ar, and N2 matrices (< 10 K), elusive caged radical pairs (RPs) con-sisting of nitric oxide (NO•) and thiyl radical...

We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rearranges to its cis-conformer. Prolonged irradiation...

We report the spontaneous gas-phase formation of 1,3-dioxolane-4-ol, a mixed hemiacetal resulting from the addition of glycolaldehyde to formaldehyde. It was spectroscopically characterized by matching matrix IR spectra with coupled cluster computations. The formation of the hemiacetal must be surface-catalyzed owing to the very high computed react...

Arylsulfinyl radicals are key intermediates in sulfoxide chemistry. As the parent molecule, phenylsulfinyl radical PhSO• has been generated for the first time in the gas phase through high-vacuum flash pyrolysis (HVFP) of PhS(O)R (R = CF3 and Cl) at about 1000 K. Upon UV light irradiation (365 nm), PhSO• isomerizes to a novel oxathiyl radical PhOS•...

Carbene In ihrer Zuschrift auf S. 5346 charakterisieren P. R. Schreiner und A. K. Eckhardt das einfachste Aminocarben, Aminomethylen, in festem Ar mittels IR‐ und UV/Vis‐Spektroskopie.

Carbenes In their Communication on page 5248, P. R. Schreiner and A. K. Eckhardt report the spectroscopic characterization of the simplest amino carbene, aminomethylene, in solid Ar by matrix isolation IR and UV/Vis spectroscopy.

Disulfur dixoide, OSSO, has been proposed as the enigmatic "near-UV absorber" in the yellowish atmosphere of Venus. However, the fundamentally important spectroscopic properties and photochemistry of OSSO are scarcely documented. By either condensing gaseous SO or 266 laser photolysis of S2∙∙∙O2 complex in Ar or N2 at 15 K, syn-OSSO, anti-OSSO, and...

Although N-heterocyclic carbenes have been well-studied, the simplest aminocarbene, aminomethylene H-C̈-NH2, has not been spectroscopically identified yet. Here we report the gas phase prep-aration of aminomethylene by high-vacuum flash pyrolysis of cyclo-propylamine and subsequent trapping of the pyrolysate in an inert argon matrix at 12 K. Aminom...

Although N-heterocyclic carbenes have been well-studied, the simplest aminocarbene, aminomethylene H-C̈-NH2, has not been spectroscopically identified yet. Here we report the gas phase prep-aration of aminomethylene by high-vacuum flash pyrolysis of cyclo-propylamine and subsequent trapping of the pyrolysate in an inert argon matrix at 12 K. Aminom...

An emission spectrum of H2¹⁶O has been recorded, with Doppler-limited resolution, at 1943 K using Hot Gas Molecular Emission (HOTGAME) spectroscopy. The wavenumber range covered is 6600 to 7050 cm−1. This work reports the analysis and subsequent assignment of close to 3700 H2¹⁶O transitions out of a total of more than 6700 measured peaks. The analy...

Although frequently employed, heavy atom kinetic isotope effects (KIE) have not been reported for quantum mechanical tunneling reactions. Here we examine the secondary KIE through 13C substitution of the carbene atom in methylhydroxycarbene (H3C–C̈–OH) in its [1,2]H tunneling shift reaction to acetaldehyde (H3C–CHO). Our study employs matrix isolat...

When mixing SO with O2 in N2, Ne, or Ar, an end-on complex OS–OO forms in the gas phase and can subsequently be trapped at cryogenic temperatures (2.8–15.0 K). Upon infrared light irradiation, OS–OO converts to SO3 and SO2 + O with concomitant formation of a rare 1,2,3-dioxathiirane 2-oxide, i.e., cyclic OS(=O)O. Unexpectedly, the ring-closure of 1...

Two hitherto unreported sulfur-centered radicals—the trifluoromethyl sulfinyl radical and the trifluoromethyl oxathiyl radical, were generated in the gas phase and then trapped in solid noble gas matrices for characterization with IR and UV/Vis spectroscopy. Subsequent UV light irradiation resulted in an unprecedented isomerization from a sulfinyl...

Two hitherto unreported sulfur-centered radicals CF3SO* and CF3OS* were generated in the gas phase through high-vacuum flash pyrolyses of sulfoxide CF3S(O)X (X = CF3, Cl, PhO) precursors. The CF3OS* molecule is the first experimental example for constitutes an oxathiyl radical. It was isolated and characterized by combining matrix-isolation IR and...