Isomeric Products Research Articles

Mechanistic Insights Into the Methoxycarbonylation of Technical Grade Oleochemicals: Catalytical and Structural Analysis of Conjugated Fatty Acid Methyl Esters

ABSTRACTThis study examines the valorization of vegetable oils through Pd‐catalyzed methoxycarbonylation. It investigates the inhibitory effects of polyunsaturated fatty acid methyl esters (PU‐FAME) on catalyst activity, which are frequently reported in academic literature. A particular focus lies on the isomerization of polyunsaturated FAME into conjugated species. In light of the formation of a stable Pd‐allyl complex with polyunsaturated compounds, an investigation of the isomerization products was conducted. NMR and GC analyses demonstrated that isomerization results in the conjugation of double bonds and their relocation toward the ω‐end of the carbon chain. The isomerization results in a thermodynamic distribution of isomerization products for mono‐ and polyunsaturated FAME. The formation of conjugated substrates was confirmed by structural analysis, and oxidative cleavage techniques were employed to determine the precise distribution of double bond positions. The findings offer insight into how conjugated PU‐FAME inhibit methoxycarbonylation, thereby limiting the valorization of vegetable oils.Practical Applications: This study provides further insights into the homogeneous catalyzed formation of conjugated methyl linoleate using a palladium catalyst. Combining different analytic techniques and chemical modification provides a novel approach for determining double bond positions in fatty acids. Furthermore, these findings may facilitate the design of new catalysts for the methoxycarbonylation process, thereby preventing the formation of conjugated intermediates. This could result in an efficient conversion of technical‐grade oils. Additionally, the production of a diverse range of isomers for subsequent functionalization is demonstrated.

Erratum to: Isomer production studied with simultaneous decay curve analysis for alpha-particle induced reactions on natural platinum up to 29 MeV

Erratum to: Isomer production studied with simultaneous decay curve analysis for alpha-particle induced reactions on natural platinum up to 29 MeV

Donor/Acceptor Ligands Based on an o-Terphenyl Motif to Achieve Thermally Activated Delayed Fluorescence in Zn(II) Complexes.

The photophysical properties of six new luminescent tetrahedral Zn(II) complexes are presented that survey two electronic donor moieties (phenolate and carbazolate) and three electronic acceptors (pyridine, pyrimidine, and pyrazine). A unique ligand based on an o-terphenyl motif forms an eight-membered chelate, which enhances through-space charge-transfer (CT) interactions by limiting through-bond conjugation between the donor and acceptor. A single isomeric product was obtained in yields up to 90%. Single-crystal X-ray diffraction structures of Zn complexes incorporating either donor show complementary interligand π-π interactions. All of the Zn complexes display long-lived luminescence in the solid state consistent with emission involving the triplet state. The phenolate-based complexes show evidence of CT emission in the solid state only with the strongest (pyrazinyl) acceptor. In contrast, all carbazolate-based complexes show evidence of thermally activated delayed fluorescence (TADF) in the solid and solution state, with photoluminescent quantum yields of up to 39%. These ligands represent a new family of Zn coordination compounds demonstrating TADF/phosphorescent properties that expand upon and elucidate design principles in the pursuit of photoactive earth-abundant metal complexes.

Single-isomer bis(pyrrolidino)fullerenes as electron-transporting materials for tin halide perovskite solar cells.

Although fullerene bisadducts are promising electron-transporting materials for tin halide perovskite solar cells, they are generally synthesized as a mixture of isomeric products that require a complicated separation process. Here, we introduce a phenylene-bridged bis(pyrrolidino)fullerene, Bis-PC, which forms only a single isomer due to geometrical restriction. When used in a tin perovskite solar cell with a PEA0.15FA0.85SnI3 (PEA: phenylethylammonium and FA: formamidinium) light absorption layer, the resulting open-circuit voltage (V OC) was 0.78 V, a value higher than that of fullerene monoadducts and comparable to that of the commonly used indene-C60 bisadduct (ICBA). The performance could be further improved by the composition engineering of perovskite, where the PEA0.15(FA0.87MA0.13)0.85SnI3 based device (MA: methylammonium) exhibited a photoelectric conversion efficiency of 12.3% with a V OC of 0.86 V. The device with single-isomer Bis-PC shows superior stability to that with mixed-isomer ICBA, retaining its initial performance after 3000 h storage under an inert atmosphere.

DFT Calculations of 1H and 13C NMR Chemical Shifts of Hydroxy Secondary Oxidation Products of Geometric Isomers of Conjugated Linoleic Acid Methyl Esters: Structures in Solution and Revision of NMR Assignments.

Detailed DFT studies of 1H and 13C NMR chemical shifts of hydroxy secondary oxidation products of various geometric isomers of conjugated linolenic acids methyl esters are presented. Several low energy conformers were identified for model compounds of the central dienenol OH moiety, which were found to be practically independent on the various functionals and basis sets used. This greatly facilitated the minimization process of the geometric isomers of conjugated linolenic acids methyl esters. Several regularities of the literature experimental 1H and 13C chemical shifts were reproduced very accurately with the computational chemical shifts of the Gibbs low energy DFT optimized conformers, after a Boltzmann analysis. δ(13C) and δ(1H) of the methine CH-OH group are highly diagnostic for the trans/trans and cis/trans geometric isomerism of the adjacent double bond. δ(13C) of the -CH2- group adjacent to the terminal double bond of the conjugated system strongly depend on the cis/trans geometric isomerism of this bond and, thus, could be of importance in structural analysis. Ambiguities in the reported literature resonance assignments of olefinic carbons had been resolved. Computational δ(1H) and δ(13C) can be utilized for the identification of geometric isomerism and structural and conformational elucidation of hydroxy derivatives of conjugated linoleic acids and their ester derivatives.

Complete Epoxy Phosphonate Conversion to Dimethyl (1E)-3-Hydroxyprop-1-Enylphosphonate with Photobiocatalysts’ Assistance

Phosphonates derivatives are compounds of interests and are applied as drugs of, e.g., antibacterial antiviral activities, connected with their inhibitory activity towards different enzymes, which is related to the configuration of particular compound isomers. The biological synthesis of such molecules is the method of choice and can be carried out using enzymes or whole cells from organisms. Photobiocatalysts employed in the bioconversion of epoxymethyl dimethyl phosphonate are able to convert this substrate into a pure geometric isomer of the unsaturated product, dimethyl (1E)-3-hydroxyprop-1-enylphosphonate, which is a rare and expensive compound of high added value. Six different strains were screened towards dimethyl epoxy phosphonate and in the case of Synechococcus bigranulatus, over 99% conversion was achieved. The product structure was confirmed with Mass Spectroscopy (MS); 1H, 13C, 31P, and 2D Nuclear Magnetic Resonance (NMR); and Infrared Spectroscopy (IR).

Migratory Aryl Cross-Coupling.

A fundamental property of cross-coupling reactions is regiospecificity, meaning that the site of bond formation is determined by the leaving group's location on the electrophile. Typically, achieving a different substitution pattern requires the synthesis of a new, corresponding starting-material isomer. As an alternative, we proposed the development of cross-coupling variants that would afford access to multiple structural isomers from the same coupling partners. Here, we first demonstrate that a bulky palladium catalyst can facilitate the efficient, reversible transposition of aryl halides by temporarily forming metal aryne species. Despite the nearly thermoneutral equilibrium governing this process, combining it with the gradual addition of a suitable nucleophile results in dynamic kinetic resolution of the isomeric intermediates and high yields of unconventional product isomers. The method accommodates a range of oxygen- and nitrogen-centered nucleophiles and tolerates numerous common functional groups. A Curtin-Hammett kinetic scheme is supported by computational and experimental data, providing a general mechanistic framework for extending this migratory cross-coupling concept.

Chemical Composition of Secondary Organic Aerosol Formed from the Oxidation of Semivolatile Isoprene Epoxydiol Isomerization Products.

3-Methylenebutane-1,2,4-triol and 3-methyltetrahydrofuran-2,4-diols, previously designated "C5-alkene triols", were recently confirmed as in-particle isomerization products of isoprene-derived β-IEPOX isomers that are formed upon acid-driven uptake and partition back into the gas phase. In chamber experiments, we have systematically explored their gas phase oxidation by hydroxyl radical (•OH) as a potential source of secondary organic aerosol (SOA). •OH-initiated oxidation of both compounds in the presence of ammonium bisulfate aerosol resulted in substantial aerosol volume growth. Compositions of low-volatility products in both the gas and particulate phases were established by high-resolution mass spectrometry measurements. Under conditions mimicking the Southeast USA (50% relative humidity, bulk seed aerosol pH 1.4), we estimate the SOA yield from •OH-initiated oxidation of 3-methylenebutane-1,2,4-triol to be 93.1%, equating to 1.95 ± 0.81 Tg C Yr-1, and from 3-methyltetrahydrofuran-2,4-diol oxidation to be 26.7%, equating to 1.76 ± 1.26 Tg C Yr-1. Previously unreported isoprene-derived oxidation products, 2,3-dihydroxy-2-(hydroxymethyl)propanal, 1,3,4-trihydroxybutan-2-one, and four organosulfates have been confirmed in ambient SOA, and aid in understanding isoprene oxidation pathways in HO2• dominated environments as NOx levels continue to decline in the US. This work underlines the need for inclusion of partitioning of in-particle formed semivolatile products and their atmospheric oxidation pathways in atmospheric models.

Cp2TiCl2-Catalyzed Interaction of Methylenecycloalkane with BF3·THF

The Cp2TiCl2-catalyzed interaction of methylenecycloalkanes with BF3·THF in tetrahydrofuran was carried out for the first time with the formation of target 1-fluoro-1-boraspirocarbocycles and also isomerization products of a starting monomer (1-methylcycloalk-1-enes). The structure of reaction products was elucidated using one- (1H, 13C Dept, 11B, 19F) and two-dimensional (COSY, HSQC, HMBC) NMR spectroscopy, mass spectrometry combined with quantum-chemical calculations of 13C NMR chemical shifts.

Blue‐Emitting Iridium(III) Carbene Phosphors with Suppressed Efficiency Roll‐Off and Enhanced Durability of Hyper‐OLED Devices

AbstractOLED technology has been long hampered by the slow progress of efficient and durable blue phosphors. To circumvent this issue, a novel imidazo[4,5‐b]pyrazin‐2‐ylidene chelate with both the bulky tert‐butyl and 2,6‐dimethylphenyl appendages is rationally employed in synthesizing Ir(III) carbene phosphors f‐ct8c and f‐ct8d. Installation of bulky groups at the proper location not only reduces the anticipated product isomers to two, but also improves the photophysical efficiency of these Ir(III) emitters. Notably, these emitters exhibited blue photoluminescence with excellent quantum yields and short radiative lifetimes. One device with assistant sensitizer f‐ct8c at 10 wt% and terminal emitter ν‐DABNA at 1 wt% has successfully achieved a remarkable EQEmax of 30.5%, CIExy chromaticity of (0.129, 0.079), confirming the generation of exceptional blue hyperphosphorescence. Moreover, the same emitter f‐ct8c co‐doped in exciplex co‐host of SiCzCz: SiTrzCz2 afforded EQEmax of 28.4% and EQE of 23.6% at practical luminance of 1000 cd m‒2, respectively, together with max. luminance exceeding 27000 cd m‒2. A long operational lifetime LT50 of 309 h is obtained for f‐ct8d at an initial brightness of 500 cd m‒2, affirming the improved efficiency and stability of the molecular designs.

Fine-Tuning the Function of Farnesene Synthases for Selective Synthesis of Farnesene Stereoisomers.

Farnesene synthase from Artemisia annua (AaFS) catalyzes the reaction from farnesyl pyrophosphate (FPP) to give the sesquiterpene β-farnesene, a key building block for the biosynthesis of vitamin E. However, an insufficient yield of β-farnesene precludes its industrialization. Understanding the mechanism would be essential for attaining β-farnesene in high yield. Guided by structure-based enzyme engineering, we designed several potent variants, among which L326I increased the β-farnesene yield from 450.65 to 3877.42 mg/L. Furthermore, we found that the function of β-farnesene synthase AaFS can be modulated at two positions; W299 is responsible for tuning the enzyme's function to give its isomeric product α-farnesene and Y402 is the key residue for diverting from the linear farnesene products to the monocyclic α-bisabolol product. These findings provide valuable insights into the catalytic mechanism and functional modulation of farnesene synthases and set the basis for rational engineering of farnesene synthases for selective biosynthesis of diverse sesquiterpene natural products.

High-yield production of lactide isomers from depolymerization of polylactic acid in supercritical carbon dioxide

Chemical depolymerization of polylactic acid (PLA) was demonstrated in supercritical carbon dioxide medium. No catalyst, organic solvent or water was employed in the reaction. The primary feedstocks used in ring opening polymerization of PLA, lactide isomers, were produced with high yield. More specifically, lactides were produced as the sole nongaseous products with a 93 % yield based on the initial polymer mass at 200 °C and 310 bar in 120 min. The influences of the reaction temperature, time, and pressure on PLA depolymerization products were investigated. While the lactide yield and distribution were highly influenced by the reaction temperature and time, further improvement was attained with an increase in the pressure. The results demonstrate that supercritical CO2 can be applied as a promising reaction medium for PLA degradation, providing a high-yield production of its feedstock. The process can enable green depolymerization of polylactic acid and promote its circular economy with a closed loop production.

Experimental test of neutron intensity monitor with isomer production reaction for p-Li neutron source for boron neutron capture therapy

IntroductionBoron Neutron Capture Therapy (BNCT) is a promising cancer therapy. At present, development of accelerator based neutron source (ABNS) is underway to be utilized as a neutron source instead of nuclear reactor. However, it is known that the neutron field formed with accelerators have different characteristics depending on kinds of accelerators. We thus have to characterize the field before practical use.MethodIn the authors’ group, various neutronics characterization devices have been developed for our p-Li based BNCT machine named CSePT. In this paper, three neutron intensity monitor foils with an isomer production reaction for several tens to 800 keV of the p-Li neutrons were proposed, i.e., 107Ag, 115In and 189Os.Result and DiscussionFrom the experimental test results, two activation foils of 107Ag and 115In were confirmed to be a possible candidate as the monitor. However, the isomer production cross sections of them should be examined for practical use.

Skeletal Isomerization of Ergosterol-5,8-Peroxide Leading to the Discovery of Unprecedented Ergostanes and Collective Syntheses of 5,6-Epoxysterols and (+)-Sarocladione.

Skeletal isomerization of ergosterol peroxide, a primary oxidation product of ergosterol, was investigated under thermal and iron(II)-mediated conditions. Thermal isomerization resulted in not only the isolation of the predicted 7-hydroxy-5,6-epoxides but also the discovery of the unprecedented 7/9/5-ring-fused ergostane for the first time. The iron(II)-mediated isomerization proceeded at ambient temperature, resulting in the formation of the expected 5,6-epoxysterols and a ring-opened bicyclic diketone. The diketone was further converted into novel ergostane under thermal conditions and into (+)-sarocladione under acidic conditions. All transformations from ergosterol to sarocladione, including the isolation of the unstable diketone intermediate, were achieved at ambient temperature, confirming the biosynthetic pathway of sarocladione. Several mushroom ingredients with a 5,6-epoxy group were synthesized stereoselectively from the isomerization products, leading to the confirmation or revision of the structures of natural products. The β-amyloid aggregation inhibitory activity of synthetic sterols was evaluated for the first time to gain insights into the potential for dementia prevention. This study is valuable both for supplying rare sterols found in mushrooms for biological studies and for shedding light on the oxidative metabolic pathways of ergosterol.

Mechanism for Site-Selective Hydroboration of C70 Fullerene with Borane by DFT-D3 Study.

We studied the hydroboration of the C70 fullerene using both B3LYP-D3(BJ)/6-311G(d,p) and M06-2X-D3/6-311G(d,p) levels of theory, incorporating the empirical dispersion interaction, and Fukui index calculations. Potential energy surfaces (PESs) and Gibbs free energy surfaces (GFESs) were calculated for the pathways from four BH3 adducts (located at the AB, CC, D, and E sites) on the C70 to eight products formed by the 1,2-addition of BH3 across the four [6,6]-ring fused bonds (AB, CC, DE, and EE) and across the two [5,6]-ring fused bonds (AA and DD). These pathways are two-step consecutive reactions. We denoted the positions on the fullerene cage as A through E, from the pole to the equator, based on the D5h symmetry of the C70 fullerene. In the first step reaction, the product ratios for the four adduct intermediates should be as the primary intermediate BH3(D), the secondary intermediate BH3(AB), the tertiary intermediate BH3(CC), and the minor intermediate BH3(E), based on the Fukui indices. In addition, in the second step reaction, transition states (TSs) from four adduct intermediates to eight product isomers, namely, BH2(A)H (B) to BH2(E)H (E), were obtained using the QST2 method. The calculated reaction coordinates showed exothermic reactions for all bonds except the EE bond. We also confirmed the transition states by frequency calculations and intrinsic reaction coordinate (IRC) analyses. The PESs and GFESs suggest spontaneous processes for the four isomers, of which the primary products are BH2(A)H (B) and its isomer BH2(B)H (A), the secondary product is BH2(C)H (C), and the tertiary product is BH2(D)H (D), all formed through adduct intermediates. Therefore, through the hydroboration reaction of C70, we could predict and design the site selectivity of C70 by controlling the energy barrier of the transition state in the second step of the reaction. This implies that we could selectively synthesize mainly BH2(B)H (A) isomers across the AB-[6,6]-ring fused bond and also design BH2(D)H(D) isomers across the DD-[5,6]-ring fused bond. Also, the calculations of formation rate constants can well simulate the experimental ratio of two C70H2 isomers by the hydrolysis of BH2(A)H(B), BH2(B)H(A), and BH2(C)H(C) products at room temperature.

Solvent-Mediated Rate Deceleration of Diels–Alder Reactions for Enhanced Selectivity: Quantum Mechanical Insights

Solvents can have a tremendous influence on the rate and selectivity of chemical reactions, but their effects are not always well accounted for. In the present work, density functional theory computations are used to investigate the influence of solvent on the Diels–Alder reactions of 9-methylanthracene with (5-oxo-2H-furan-2-yl) acetate and different anhydrides considering the overall reaction rates as well as selectivity between possible isomeric products. Crucially, we find that overall reaction rates are higher in non-polar toluene, whereas selectivity is enhanced in the polar solvent acetone. In the case of (5-oxo-2H-furan-2-yl) acetate, the difference in the reaction barriers is enhanced by 2.4 kJ/mol in acetone as compared to the gas phase, halving the yield of the side product. Similar results are found for the reaction of 9-methylanthracene with chloro-maleic anhydride and cyano-maleic anhydride, highlighting the generality of the trends observed. After presenting the energetics, a detailed discussion of the reactivity is given using electrostatic potentials, frontier orbitals, reactivity indices and Fukui functions. In summary, this study highlights the importance of solvent in influencing reaction rates and illustrates the possibility of studying its effects computationally.

Development and workflow of a separation process for optimum design: A case of phenylenediamine

AbstractAn industrial project based upon the multi‐scale objective‐oriented process development (MOPD) method for developing an optimum process for separating phenylenediamine (PDA) isomers was executed. This article reports the first four (4) steps of that project. In the first step, the solution for this separation problem was conceptualized. It is a distillation‐crystallization‐hybrid process. The second step is to validate the concept experimentally from the thermodynamic point of view followed by kinetic considerations. It was found that a 2‐stage crystallization is required to purify the main product isomers to the desirable specification that is higher than 99.5 mol%. A heat and material balance model was then constructed for analyzing and optimizing various design variables, also used to understand the operability of the process. Finally, with proper HAZOP analysis and detailed engineering, the pilot unit was designed. Throughout the project, all exercises and efforts are well focused with clear objectives, hence there are minimum detours on the execution; furthermore, the clear objectives enhanced the communications among various disciplines tremendously. It is a valuable asset for senior management in the allocation of resources and budgets.

Understanding Selectivity in Product Distributions from Laser Ablation of Organic Liquids.

Pulsed laser ablation in organic solvents is widely used to produce oxide-free metal and metal carbide nanoparticles, often with carbon coatings resulting from laser-induced reactions in the organic solvent. To gain insight into how the molecular structure of the solvent affects these reaction pathways, this work investigates ablation of the C6H14 isomers n-hexane, 2-methylpentane, and 3-methylpentane through characterization of the gas and liquid products with mass spectrometry. Ablation of each C6H14 isomer produces a distinct distribution of product molecular weights and isomers. 2-methylpentane preferentially produces C3 and C9, whereas 3-methylpentane produces C2, C4, C8, and C10 products. These preferential product distributions, along with the lack of such selectivity in n-hexane, arise from differences in the most favorable C-C bond scission pathways in each C6H14 isomer. Moreover, the particular isomers of C8H18, C9H20, C10H22, and C12H26 produced by ablation of each C6H14 isomer indicate that the vast majority of reaction pathways involve addition reactions between a fragment radical and parent C6H14 or between two C6H14 molecules, without molecular rearrangement. This propensity toward direct addition suggests that the chemical reactions induced by ultrashort pulsed laser ablation proceed on faster time scales than those of radical rearrangements.

Alkynes to (Free) Carbenes to Polycyclic Cyclopropanes.

Carbenes and carbenoids are commonly employed for the synthesis of cyclopropane-containing compounds. Here we report the metal-free, intramolecular cyclopropanation of tethered alkenes by free carbenes derived from alkynes to construct structurally unique multicyclic cyclopropanes with perfect atom economy. The nature of the tether influences both the rate of carbene formation and subsequent competing reaction events. Some of the substrates lead to metastable cyclopropane intermediates that further fragment to furnish interesting isomeric products by mechanistically novel processes. A removable siloxane tether can be utilized to achieve formal intermolecular cyclopropanations and to access cyclopropanol derivatives.

Isomer production studied with simultaneous decay curve analysis for alpha-particle induced reactions on natural platinum up to 29 MeV

Isomer production studied with simultaneous decay curve analysis for alpha-particle induced reactions on natural platinum up to 29 MeV