C-H Bond Research Articles

A computational characterization of the reaction mechanisms for the reactions N(2D) + CH3CN and HC3N and implications for the nitrogen-rich organic chemistry of Titan

The reactions of atomic nitrogen in its first electronically excited state, N(2D), with acetonitrile (CH3CN) and cyanoacetylene (HC3N) have been investigated by performing electronic structure calculations of the doublet potential energy surfaces and RRKM estimates of the product branching fractions. According to our results, the insertion of N(2D) into one of the sigma CH bonds of acetonitrile leading to the formation of cyanomethanimine (also known as iminoacetonitrile) and the N(2D) addition to the CC triple bond of cyanoacetylene leading to the formation of dicyanocarbene are the main reaction pathways under the conditions typical of the upper atmosphere of Titan, the massive moon of Saturn. Other molecular products originating from other reaction pathways only give a minor contribution.Implications for the atmospheric chemistry of Titan, as well as implications in prebiotic chemistry and in the chemistry of the interstellar medium, are also noted.

Catalysis & inhibition issues associated with Monoamine Oxidase (MAO). How unusually low α-C-H bond dissociation energies may open the door to single electron transfer

CH Bond dissociation energies for a unique selection of tertiary amines that are known substrates or inhibitors of monoamine oxidase have been calculated using density functional theory. These amines are unusual because they are the only tertiary amines that exhibit MAO substrate or inhibitor behavior. The unique structural feature common to these specific compounds is an sp3-hybridized CH2 moiety, which is α-both to nitrogen and an C=C or CC. The stabilization afforded the resulting radicals by extended delocalization dramatically lowers both the CH bond strength of the substrate (R-H → R· + H·) and pKa of the corresponding radical cation (RH·+ → R· + H+). This interplay of structure and thermodynamics may provide the driving force for an electron transfer mechanism for MAO catalysis and inhibition.

Pure Polycyclic Aromatic Hydrocarbon Isomerides with Delayed Fluorescence and Anti-Kasha Emission: High-Efficiency Non-Doped Fluorescence OLEDs.

Pure polycyclic aromatic hydrocarbons (PAHs) consisting solely of carbon-hydrogen or carbon-carbon bonds offer great potential for constructing durable and cost-effective emitters in organic electroluminescence devices. However, achieving versatile fluorescence characteristics in pure PAHs remains a considerable challenge, particularly without the inclusion of heteroatoms. Herein, an efficient approach is presented that involves incorporating non-six-membered rings into classical pyrene isomerides, enabling simultaneous achievement of full-color emission, delayed fluorescence, and anti-Kasha emission. Theoretical calculations reveal that the intensity and distribution of aromaticity/anti-aromaticity in both ground and excited states play a crucial role in determining the excited levels and fluorescence yields. Transient fluorescence measurements confirm the existence of thermally activated delayed fluorescence in pure PAHs. By utilizing these PAHs as emitting layers, electroluminescent spectra covering the entire visible region along with a maximum external quantum efficiency of 9.1% can be achieved, leading to the most exceptional results among non-doped pure hydrocarbon-based devices.

Computational Analysis of Some More Rectangular Tessellations of Kekulenes and Their Molecular Characterizations.

Cycloarene molecules are benzene-ring-based polycyclic aromatic hydrocarbons that have been fused in a circular manner and are surrounded by carbon-hydrogen bonds that point inward. Due to their magnetic, geometric, and electronic characteristics and superaromaticity, these polycyclic aromatics have received attention in a number of studies. The kekulene molecule is a cyclically organized benzene ring in the shape of a doughnut and is the very first example of such a conjugated macrocyclic compound. Due to its structural characteristics and molecular characterizations, it serves as a great model for theoretical research involving the investigation of π electron conjugation circuits. Therefore, in order to unravel their novel electrical and molecular characteristics and foresee potential applications, the characterization of such components is crucial. In our current research, we describe two unique series of enormous polycyclic molecules made from the extensively studied base kekulene molecule, utilizing the essential graph-theoretical tools to identify their structural characterization via topological quantities. Rectangular kekulene Type-I and rectangular kekulene Type-II structures were obtained from base kekulene molecules arranged in a rectangular fashion. We also employ two subcases for each Type and, for all of these, we derived ten topological indices. We can investigate the physiochemical characteristics of rectangular kekulenes using these topological indices.

Regioselective benzylation of imidazo[1,5-a]pyridines and indoles via iodine catalyzed reaction using alcohols - An approach to crystal structure prediction, DFT studies and Hirshfeld surface analysis

Iodine catalysed, regioselective C-1 benzylation of imidazo[1,5-a] pyridines and C-3 benzylation of indoles with diphenylmethanol has been developed. This new protocol provides an efficient protocol in the synthesis of the benzylation methodology as it targets exclusively CH bonds, even in presence of reactive NH bonds and variety of benzyl substituted indoles and imidazo[1,5-a] pyridines are synthesized with broad range of functionalities leads to the elegant formation of new CC bond under metal free conditions. This report represents a mild protocol for the synthesis of tris(heteroaryl/aryl) methanes from solid bench stable diarylmethanols. The products formed are interesting for their potential biological applications. The crystal structure of the compound 3k was determined by single crystal X-ray diffraction studies. The compound crystallized in triclinic crystal system with P-1 space group. The molecular structure is stabilized by short intermolecular interactions and intramolecular CH⋯N hydrogen bond interactions. The crystal structure also exhibits intermolecular CH⋯π, CCl⋯π and π⋯π stacking interactions. The intermolecular interactions are quantified through Hirshfeld surface analysis using fingerprint plots. The surface properties were analysed using 3D Hirshfeld surfaces. Further, the density functional theory calculations were carried to calculate the electronic properties of the molecule. The HOMO-LUMO energy gap is found to be 4.0981 eV. Finally, the chemically active sites on the molecule are identified by analysing the molecular electrostatic potential map.

Structure characterization and antioxidant activity of abalone visceral peptides-selenium in vitro

Peptide-selenium chelate is widely regarded as one of the best selenium supplements for relieving selenium deficiency. In this study, abalone visceral peptides (AVP) was used to prepare a new type of peptides-selenium chelate to develop an organic selenium supplement with antioxidant activity. AVP prepared by alcalase exhibited the highest selenium-chelating ability. UV–visible spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy and other structural analysis showed that selenium was mainly bound to the functional groups of –NH, –OH, –CH, CC, CO, and CN bonds on AVP. The formation of AVP-selenium chelate enhanced thermal stability and generated a new crystal structure. The ABTS•+ and •OH scavenging activities of AVP-selenium chelate were increased after in vitro digestion than that of AVP. Conclusively, this study analyzed the chelating mechanism of AVP and selenium from a structural perspective, which would provide a theoretical basis for the development of new selenium supplements.

One-pot Syntheses of Benzo- and Benzofuran-fused Iridaoxabenzenes via CH Bond Activations of Alkyl-bridged Diphenol Derivatives.

One-pot syntheses of new π-extended metallaaromatic compounds have been developed by utilizing Ir-mediated CH bond activation of ethylene- or ethylidene-bridged diphenol derivatives. Depending on the bridging alkyl groups, two types of iridaoxabenzenes, both of which are doubly fused with benzo and benzofuran units, have been obtained. Studies on their structures and electronic characters indicate that both complexes have an aromatic character on the iridaoxacycles, and their π-conjugated systems are fully delocalized over the whole molecular skeletons. These novel metallaaromatic complexes exhibited some reactivities which are distinct from those reported for the non-fused metallaaromatic compounds.

Isolation, identification, and synergistic mechanism of a novel antimicrobial peptide and phenolic compound from fermented walnut meal and their application in Rosa roxbughii Tratt spoilage fungus

This study aimed to identify an antimicrobial peptide and phenolic compound combination derived from fermented walnut meal against Penicillium. victoriae, a fungus responsible for Rosa. roxbughii Tratt spoilage, and ultimately investigate their synergistic mechanism. YVVPW and salicylic acid (SA) had the highest antifungal activity among identified 4 antimicrobial peptides, including FGGDSTHP, ALGGGY, YVVPW, and PLLRW, and 15 phenolic compounds, respectively. Molecular docking verified that YVVPW bound to regulatory subunit via hydrogen-bond, hydrophobic, and π-π conjugate interactions. YVVPW and SA exhibited synergistic effects with average minimal inhibitory concentration decreasing by 85.44 ± 8.04%. Fluorescence spectroscopy demonstrated quenching of intrinsic Trp and Tyr fluorescence by interaction. FTIR and molecular docking results revealed formation of 3 hydrogen bonds via OH, CO, NH, and CH bonds in YVVPW + SA, with π-π stacking occurring between the benzene ring and five-membered ring. These reinforce potential application of this combination as an effective fungistatic combination in fruit preservation.

(Invited) Identification of a Self-Photosensitizing Hydrogen Atom Transfer Organocatalyst System

The carbon-hydrogen (C-H) bond is a fundamental chemical bond that constitutes organic molecules, and its direct conversion leads to highly efficient molecular synthesis. In recent years, the hydrogen atom transfer (HAT) catalysis using the energy of visible light, has been attracting attention. However, existing methods require the use of photoredox catalysts such as organic molecules with complex structures and expensive metal complexes. In this study, we developed an organocatalytic system that mimics the electron transfer process of enzymes in vivo and promotes functionalization of stable C-H bond without photoredox catalyst. We designed a thiophosphoric acid catalyst that contains both a redox-active binaphthyl moiety and a sulfur atom. We found that this catalyst forms charge-transfer complexes with electron-deficient heteroaromatics and catalytically produces thyil radical via multi-step electron transfer under visible light irradiation.Based on the above design, we decided to investigate the formation of active HAT catalytic species in the absence of photoredox catalysis by the Minisci-type reaction using aldehydes and N-heteroaromatic rings. The results of the study confirmed that 29% of the product was obtained when using binaphtyl thiophosphoric acid (TPA) catalyst, as expected. Yield improved to 80% when an electron-donating group was introduced to the binaphthyl skeleton to enhance the donor-acceptor interaction. Changing the binaphthyl skeleton and thiophosphoric acid moieties markedly reduced reactivity, indicating that the presence of a sulfur atom in addition to a rigid binaphthyl skeleton is essential for the efficient reaction progress. With this optimized condition, alkylation of N-heteroaromatic rings by C-H bond activation of alcohols was found to proceed. Dehydrogenation of alcohols and benzylation of imines were also successfully achieved by using N-heteroaromatic catalyst. The mechanism of the electron transfer process has been confirmed by spectroscopic and computational methods, and will be presented in detail in the lecture. Figure 1

Actionable insights into hazard mitigation of typical 3D printing waste via pyrolysis

3D printing waste (3DPW) contains hazardous substances, such as photosensitizers and pigments, and may cause environmental pollution when improperly disposed of. Pyrolysis treatment can reduce hazards and turn waste into useful resources. This study coupled thermogravimetric (TG), TG-Fourier transform infrared spectroscopy-gas chromatography/mass spectrometry, and rapid pyrolysis gas chromatography/mass spectrometry analysis to evaluate the pyrolytic reaction mechanisms, products, and possible decomposition pathways of the three typical 3DPW of photosensitive resin waste (PRW), polyamide waste (PAW), and polycaprolactone waste (PCLW). The main degradation stages of the typical 3DPW occurred at 320–580 °C. The most appropriate reaction mechanisms of PRW, PAW and PCLW were D1, A1.2 and A1.5, respectively. The main pyrolysis processes were the decomposition of the complex organic polymers of PRW, the breaking of the NH–CH2 bond and dehydration of –CO–NH– of PAW, and the breaking and reorganization of the molecular chains of PCLW, mainly resulting in toluene (C7H8), undecylenitrile (C11H21N), tetrahydrofuran (C4H8O), respectively. Unlike the slow pyrolysis, the rapid pyrolysis produced volatiles consisting mainly of phenol, 4,4'-(1-methylethylidene)bis- (C15H16O2) for PRW; 1,10-dicyanodecane (C12H20N2) for PAW; and ɛ-caprolactone (C6H10O2) for PCLW. These pyrolysis products hold great potential for applications. The findings of the study offer actionable insights into the hazard reduction and resource recovery of 3D printing waste.

Theoretical determination of the standard enthalpies of formation of alkyl radicals using the concept of a complete set of homodesmotic reactions

The complete sets of homodesmotic reactions (HDR) for 107 acyclic alkyl free radicals С4-С9 of normal and branched structure were constructed using the graph-theoretic representation and analysis of a tested compound. The absolute enthalpies of the studied compounds and HDR reference structures were calculated using the M062X/cc-pVTZ level of theory. Based on these data, the thermal effects of HDRs were calculated and then applied to determine the standard enthalpies of formation of the studied radicals using the known enthalpies of formation of reference structures. The dissociation energies of BDE C–H and C–CH3 bonds were also calculated. The effect of radical structure on the BDE value is discussed, and a new effect of stabilization of the radical center in the skewed conformation of free radical is established; this effect has not been previously described in the scientific literature.

Influence of plasma parameters on low-k SiCOH film grown by plasma-enhanced chemical vapor deposition using dimethyldimethoxysilane

Here, we report the influence of the electron density and the electron temperature on the reduction of dielectric constant in the SiCOH thin film using dimethyldimethoxysilane (DMDMS) as a function of pressure. The measured electron density and electron temperature decreased as increasing the pressure. The decrease in the measured electron density with increasing pressure can be attributed to local electron kinetics. Moreover, the decreasing electron temperature is caused by increased inelastic collisions between electrons and neutral species in the chamber. It is identified that CH3 radicals are less dissociated from DMDMS molecular at higher pressure by a quadrupole mass spectroscopy. As increasing pressure, the increase of the Si–CH3 bonds in SiCOH thin films is confirmed by Fourier transform infrared spectroscopy. As a result, the dielectric constant and refractive index of the SiCOH films are reduced at low electron density and electron temperature.

Excitation of NH Stretching Modes in Aromatic Molecules: o-Toluidine and α-Methylbenzylamine.

Selectively excited o-toluidine and α-methylbenzylamine have been studied with quasi-classical trajectory procedures to determine the extent and timescales of intramolecular energy flow. The initial excitation is in the stretching mode of the para-CH bond, and its flow is initiated by interaction with an argon atom. Energy flow to the NH stretching mode is the dominant relaxation pathway, and its effectiveness is enhanced strongly by the methyl-NH interaction. Energy flow characteristics in both molecules are similar, but the flow is more effective in o-toluidine than in α-methylbenzylamine because the methyl group bonded to the benzene ring exerts stronger perturbation on the energy-flow pathway than the group bonded to the side chain. The relaxation of the initially excited CH completes on a timescale of several picoseconds, but the main part of energy flow to the NH occurs on a subpicosecond scale. In o-toluidine, carbon-carbon overtone modes lead to ring-CC bonds gaining and transporting more energy than high-frequency CH bonds, but they all gain far less energy than the NH stretching mode.

Preparation of long-flame coal flotation collector from waste cooking oil

There is currently a need to develop efficient and environmentally friendly (green) collectors to improve the poor flotation performance of long-flame coal (LFC) due to its vast porosity and high oxidation degree. Herewith, this study introduces ozone (O3) and ultraviolet (UV) oxidation methods to modify waste cooking oil collector (WCOC) and analyzes their effects on the LFC flotation performance. Furthermore, the separation efficiency (SE) of WCOC, O3-WCOC, UV-WCOC and common collectors (diesel, kerosene, DEP) were compared. Fourier Transform Infrared Spectroscopy (FTIR) and Gas chromatography-mass spectrometry (GC–MS) were used to observe the effects of O3 and UV oxidation on WCOC functional groups and chemical composition. The functional groups and wettability changes of LFC treated via common collectors, including WCOC, O3-WCOC and UV-WCOC adsorption were analyzed. Results revealed that a shorter O3 oxidation time resulted in better flotation performance and higher SE compared to UV oxidation. After O3 (5 min) and UV (9 h) oxidations, CH bonds in WCOC were oxidized and the content of oxygen-containing functional groups (particularly –OH) increased to 4.25% and 4.93% from 0.79%, respectively. Compared to common collectors, O3-WCOC and UV-WCOC demonstrated better reactions with oxygen-containing functional groups (especially O = CO and CO) on the LFC surface. This phenomenon led to a substantial increase in contact angle. This novel oxidation method could potentially be applied in wastewater treatment, mineral processing, and other fields.

Tuning the reactivity of Ni/MoS2 membrane for efficient methane pyrolysis and hydrogen production: A multi-scale study

This study investigates the performance of a Ni-coated MoS2 membrane for catalysis and separation in the methane pyrolysis process. Bifunctional membranes provide a low-energy and low-emission hydrogen generation and purification production process. To elucidate the reaction mechanism of the prepared membrane, a combined experimental and computational approach was employed using ReaxFF molecular dynamics simulations. The results demonstrate excellent catalytic and separation performance of the membrane, which was achieved through the increased specific surface area and reduced pore size of the MoS2 flower cluster. The Ni coating of MoS2 was found to attract methane, and transfer electrons to destabilize the CH bond, thus enhancing methane deep crack. In addition, the prepared membrane successfully blocked methane through Mo-edge defects, while promoting methane pyrolysis and driving H proton transportation for the H2 formation. The permeation test verified the excellent CH4/H2 separation performance of the ZSM-5 membrane coated with Ni and MoS2. This work provides theoretical and experimental guidance for the development of bifunctional membranes for methane pyrolysis to hydrogen generation, which has potential to reduce energy cost and greenhouse gas emissions.

Mo-modified Pt/CeO2 nanorods with high propane catalytic combustion activity: Comparison of phosphoric, sulphuric and molybdic acid modifications

Catalytic combustion is the most commonly used reaction to purify VOCs. The activation and dissociation of the CH bond over the catalyst becomes a key factor in controlling the rate of the reaction. To identify the factors promoting CH bond decomposition and the roles played by the acidity of the catalyst in propane catalytic combustion, molybdic acid, phosphoric acid, and sulfuric acid were used to acidify CeO2 nanorods, and Pt was then loaded onto the nanorods. The Mo acid modified Pt/CeO2 catalyst purified more than 90% of propane at a high space velocity of 150,000 mL/(g·h) and 300 °C, which is a significant improvement over the Pt/CeO2 catalyst. XRD patterns and TEM images showed that the crystal structure and morphology of CeO2 were not damaged by acid modification. XPS, in situ CO-DRIFTs, NH3-TPD, H2-TPR and other characterization methods were used on Mo acid modified catalysts to explore the reasons for the improved catalytic performance. The results showed that Pt2+ and Pt4+ coexist on 1% Pt/CeO2-18Mo catalyst, and there are more acidic sites, redox sites and adsorbed oxygen. The reaction order test showed the reaction order of molybdic acid modified catalyst to oxygen is -0.4, which is higher than other catalysts, meaning that oxygen is difficult to inhibit the reaction on the catalyst surface. Finally, in situ DRIFTs proved that 1% Pt/CeO2-18Mo catalyst had strong propane adsorption and activation capacity. This catalyst provides new insight into how VOCs can be eliminated more efficiently, green and economically.

Detailed kinetic mechanism of polyoxymethylene dimethyl ether 3 (PODE3). Part I: Ab initio thermochemistry and kinetic predictions for key reactions

In recent years, polyoxymethylene dimethyl ether 3 (PODE3) has emerged as a promising fuel additive to mitigate soot emissions in diesel engines, garnering significant research attention. Several detailed kinetic mechanisms of PODE3 have been developed to investigate its reaction pathways and to simulate its combustion process. Typically, these mechanisms employ analogy methods based on rate constants derived primarily from PODE1 sub-mechanisms. However, in this study, we present, for the first time, high-level ab initio quantum chemical calculations directly on PODE3 itself. (1) The bond dissociation energies (BDEs) of all CH and CO bonds in dimethyl ether (DME) and PODEn (n = 1–5) were calculated using combined compound methods (CBS-APNO/G3/G4). (2) The obtained BDE results were then utilized to investigate the unimolecular decomposition reactions of PODE3, demonstrating good agreement with previous Molecular Dynamics simulation results. (3) The rate constants of hydrogen abstraction reactions of PODE3 by H˙,C˙H3,CH3O˙,O˙H,HO˙2,O2 were calculated with all possible pre-reaction or post-reaction complexes identified. The rate constants of the H-atom abstraction reactions were found to primarily depend on the energy barriers following the order: O˙H>CH3O˙>H˙>C˙H3>HO˙2>O2. However, the abstraction by H˙ can dominate as temperature increases. (4) The rate constants of β-scission and isomerization reactions of PODE3 radicals were also computed. The calculated β-scission reaction rates supported the suitability of the rate analogy for PODEn, employing the long-chain PODE3. The energy barriers of the isomerization reactions with long chain transition states were comparable to the energy barrier of the β-scission reactions and are much lower than that in the case of PODE1 radicals. (5) The thermochemistry properties of all involved species, including PODE4–5 and their radicals, were calculated with the combined compound methods (CBS-APNO/G3/G4) for further combustion modeling. Considering PODE3′s nature as a long-chain PODEn, the rate constants computed for PODE3 can serve as a solid foundation for developing detailed mechanisms for PODE4–5.

Comparative study of temperature-programmed pyrolysis and two-step fast pyrolysis of oily sludge

Oily sludge (OS) is the main waste produced in the process of crude oil extraction, transportation, and refining. As a promising technology of OS treatment, pyrolysis can reduce pollutant emissions and fully recover resources. In this study, the pyrolysis characteristics and product quality of temperature-programmed pyrolysis (TPP) and two-step fast pyrolysis (TSFP) were investigated. For the TG analysis, the faster heating rate could promote the pyrolysis of OS and increase its weight loss rate. In TPP, the higher final pyrolysis temperature provided more energy, which made the CH bond and CC bond break, increased the gas yield and oil yield, and also increased the hydrogen component in the gas, but reduced the char yield. However, the lower final pyrolysis temperature could improve the calorific value of oil. In TSFP, the oil yield was mainly affected by the first step pyrolysis temperature (T1), and the oil yield was 30.9 % at T1 of 500 ℃. The gas yield was both affected by T1 and the second step pyrolysis temperature (T2), and the gas yield could reach a maximum of 32.5 % at 550 ℃ (T1) × 800 ℃ (T2), which was 46.9 % higher than that of TPP (700 ℃, 22.1 %). This was due to the fact that as the T2 rose, the macromolecular components broke down, promoting the generation of gas. In TSFP, the hydrogen component in the gas was the most at 500 ℃ (T1) × 800 ℃ (T2). Compared with TPP, the total calorific value of the available products (oil and hydrogen) could be increased by TSFP, which increased the energy utilization efficiency. This study is expected to provide a theoretical basis for the industrial application of TSFP.

Transition metal-free visible light photoredox-catalyzed remote C(sp3)-H borylation enabled by 1,5-hydrogen atom transfer.

The borylation of unreactive carbon-hydrogen bonds is a valuable method for transforming feedstock chemicals into versatile building blocks. Here, we describe a transition metal-free method for the photoredox-catalyzed borylation of unactivated C(sp3)-H bond, initiated by 1,5-hydrogen atom transfer (HAT). The remote borylation was directed by 1,5-HAT of the amidyl radical, which was generated by photocatalytic reduction of hydroxamic acid derivatives. The method accommodates substrates with primary, secondary and tertiary C(sp3)-H bonds, yielding moderate to good product yields (up to 92%) with tolerance for various functional groups. Mechanistic studies, including radical clock experiments and DFT calculations, provided detailed insight into the 1,5-HAT borylation process.

Are Si–C bonds formed in the environment and/or in technical microbiological systems?

Organosiloxanes are industrially produced worldwide in millions of tons per annum and are widely used by industry, professionals, and consumers. Some of these compounds are PBT (persistent, biaccumulative and toxic) or vPvB (very persistent and very bioaccumulative). If organosiloxanes react at all in the environment, Si–O bonds are hydrolyzed or Si–C bonds are oxidatively cleaved, to result finally in silica and carbon dioxide. In strong contrast and very unexpectedly, recently formation of new Si–CH3 bonds from siloxanes and methane by the action of microorganisms under mild ambient conditions was proposed (in landfills or digesters) and even reported (in a biotrickling filter, 30 °C). This is very surprising in view of the harsh conditions required in industrial Si–CH3 synthesis. Here, we scrutinized the pertinent papers, with the result that evidence put forward for Si–C bond formation from siloxanes and methane in technical microbiological systems is invalid, suggesting such reactions will not occur in the environment where they are even less favored by conditions. The claim of such reactions followed from erroneous calculations and misinterpretation of experimental results. We propose an alternative explanation of the experimental observations, i.e., the putative observation of such reactions was presumably due to confusion of two compounds, hexamethyldisiloxane and dimethylsilanediol, that elute at similar retention times from standard GC columns.