Benzene Isomers Research Articles

Revisiting Butafulvene formation by Thermal Dimerization of Fluorene-Based Dialkynes - Effects of Aromatic Substitutents.

Butafulvenes, together with pentafulvenes and [3]radialenes, form a series of constitutional benzene isomers in which aromaticity changes significantly and can be strongly substituent dependent. Butafulvene, as a member of this series, is frequently proposed to be antiaromatic. Based on butafulvenes Hopf, Zimmerman and coworkers first time described, derivatives thereof were synthesized and the effects of substituents on both the stability of the intermediate isobenzenes and on their optoelectronic and (anti)aromatic properties are discussed.

Forging 1,1'-Bicyclopropenyls by Synergistic Au/Ag Dual-Catalyzed Cyclopropenyl Cross-Coupling.

1,1'-Bicyclopropenyl is a constitutional isomer of benzene comprising two coupled cyclopropene units with the endocyclic double bonds in conjugation. Due to the intrinsic high strain energy, it remains a long-standing challenge to prepare 1,1'-bicyclopropenyl derivatives, particularly multisubstituted, nonsymmetrical ones, in an efficient and modular manner. Herein a straightforward Au/Ag bimetallic-catalyzed cyclopropenyl cross-coupling has been developed, providing a robust and versatile strategy for the rapid assembly of symmetrical and unsymmetrical 1,1'-bicyclopropenyl derivatives from cyclopropenyl benziodoxoles (CpBXs) and terminal cyclopropenes. Advantages of this strategy include tolerance to a wide range of synthetically useful functional groups, mild reaction conditions, and a simple catalytic system. The obtained 1,1'-bicyclopropenyl derivatives were shown to be valuable synthetic intermediates through selective downstream manipulations.

Successively Controlling Nanoscale Wrinkles of Ultrathin 2D Metal-Organic Frameworks Nanosheets.

The wrinkles are pervasive in ultrathin two-dimensional (2D) materials, but the regulation of wrinkles is rarely explored systematically. Here, we employed a series of carboxylic acids (from formic acid to octanoic acid) to control the wrinkles of Zr-BTB (BTB=1, 3, 5-(4-carboxylphenyl)-benzene) metal-organic framework (MOF) nanosheet. The wrinkles at the micrometer scale were observed with transmission electron microscopy. Furthermore, high-angle annular dark-field (HAADF) images showed lattice distortion in many nanoscale regions, which was precisely matched to the nano-wrinkles. With the changes of hydrophilicity/hydrophobicity, MOF-MOF and MOF-solvent interactions were possibly synergistically regulated and wrinkles with different sizes were obtained, which was supported by HAADF, molecular dynamics, and density functional theory calculation. Different wrinkle sizes resulted in different pore sizes between the Zr-BTB nanosheet interlayers, providing highly-oriented thin films and the successive optimization of kinetic diffusion pathways, proved by grazing-incidence wide-angle X-ray scattering and nitrogen adsorption. The most suitable wrinkle pore from Zr-BTB-C4 exhibited highly efficient chromatographic separation of the substituted benzene isomers. Our work provides a rational route for the modulation of nanoscale wrinkles and their stacked pores of MOF nanosheets and improves the separation abilities of MOFs.

Cascade Photoreaction in Crystals: A Phase Change Caused by a Dewar Benzene Quantum Chain Triggers a Topochemical [2 + 2] Photodimerization.

Crystals undergoing tandem reactions where the first transformation enables the second one are rare. Using photoreactive Dewar benzene 3,4,5,6-tetramethyl-1,2-dicarboxylic diacid (DB) as a hydrogen-bonding template for the [2π+2π] photodimerization of trans-4,4'-bipyridyl-ethenes (BPE), we obtained crystals DB-BPE-NT with a DB:BPE = 2:1 stoichiometry with double bonds at a nonreactive distance of 5.957 Å. Exposure to UV light resulted in valence bond isomerization to Hückel benzene 3,4,5,6-tetramethyl-1,2-dicarboxylic acid (HB) by a quantum chain reaction that triggered the sought-after topochemical [2π+2π] photodimerization reaction. Notably, crystals HB:BPE-T with the Hückel benzene isomer and BPE adopted a 2:2 stoichiometry and displayed an efficient topochemically templated photodimerization reaction.

Boron-Nitrogen-Containing Benzene Valence Isomers.

Benzene is one of the most ubiquitous structural motifs in chemistry. The valence isomers of benzene have also attracted synthetic chemists' attention due to their unique structures, bonding, and reactivity. We have been investigating boron-nitrogen-containing benzene valence isomers via photoisomerization of 1,2-azaborines. In this contribution, we summarize recent developments of these highly strained BN-heterocyclic compounds including their synthesis, characterization, proposed mechanism of formation, and their potential applications.

Cascading in-situ grown UiO-66 and alternative calix[n]arenes for high-resolution isomer separation

High-resolution separation of numerous isomers is highly desirable for their high-quality analysis, yet challenging, which puts forward high requirements on the precise design of stationary phase. Herein, flexible 4-tert-butylcalix[n]arenes (TBCx[n]s) with different cavities have been intelligently integrated with in-situ grown UiO-66 coatings, to investigate their separation efficiencies for alkane and substituted benzene isomers. The modifications of UiO-66 with TBCx[n]s have made up for the deficiency of UiO-66 on the separation of ethylbenzene and styrene. The effects of TBCx[n]s on the separation performance of UiO-66@TBCx[n]s have demonstrated distinct regularities, i.e., the effects of TBCx[6] are superior to those of TBCx[8], while the TBCx[4] is the least effective. The baseline separation of all analytes has been achieved by the UiO-66@TBCx[6] column with enhanced selectivity and improved separation resolution (Rs). For the six groups of isomers that are most difficult to separate, the corresponding selectivity and Rs are greater than 1.09 and 5.48, respectively, confirming the outstanding separation performance of the UiO-66@TBCx[6] column and the feasibility of integrating soft supramolecule and rigid MOF.

Optimizing COF crystallinity for high-resolution GC separation

This research explores the influence of crystallinity on gas chromatographic (GC) separation using covalent organic frameworks (COFs) as stationary phases. Three COF materials (CTF-DCBs) with varying crystallinity were synthesized and characterized. CTF-DCB-1, with superior crystallinity, demonstrated high-selectivity GC separation of benzene isomers as well as styrene/phenylacetylene mixtures, while CTF-DCB-2 and CTF-DCB-3 exhibited lower crystallinity and worse separation performance. Thermodynamic and kinetic tests showed that CTF-DCB-1 had the worst thermodynamic adsorption but low diffusion mass transfer resistance, which resulted in the best separation. Therefore, optimizing the crystallinity of COFs is necessary for balancing the kinetic diffusion and thermodynamic interactions towards the analytes, achieving high-performance GC stationary phases.

Novel electrochemical ZnO/MnO2/rGO nanocomposite-based catalyst for simultaneous determination of hydroquinone and pyrocatechol.

An innovative electrochemical sensing method is introduced for dihydroxy benzene (DHB) isomers, specifically hydroquinone (HQ) and pyrocatechol (PCC), employing a zinc-oxide/manganese-oxide/reduced-graphene-oxide (ZnO/MnO2/rGO) nanocomposite (NC) as an electrode modifier material. Comprehensive characterization confirmed well-dispersed ZnO/MnO2 nanoparticles on rGO sheets. Electrochemical analysis revealed the ZnO/MnO2/rGO-NC-based modified electrode possesses low electrical resistance (126.2 Ω), high electrocatalytic activity, and rapid electron transport, attributed to the synergies between ZnO, MnO2 and rGO. The modified electrode demonstrated exceptional electrochemical performance in terms of selectivity for the simultaneous detection of HQ and PCC. Differential pulse voltammetry studies validated the proposed sensor's ability to detect HQ and PCC within linear response ranges of 0.01-115 μM and 0.03-60.53 μM, with detection limits of 0.0055 µM and 0.0053 µM, respectively. Practical validation using diverse water samples showcased excellent percent recovery of HQ and PCC using the ZnO/MnO2/rGO-based electrochemical sensor, underscoring the sensor's potential for real-world applications in environmental monitoring.

3,4-Dimethylenecyclobutene: A Building Block for Design of Macrocycles with Excited State Aromatic Low-Lying High-Spin States.

3,4-Dimethylenecyclobutene (DMCB) is an unusual isomer of benzene. Motivated by recent synthetic progress to substituted derivatives of this scaffold, we carried out a theoretical and computational analysis with a particular focus on the extent of (anti)aromatic character in the lowest excited states of different multiplicities. We found that the parent DMCB is non-aromatic in its singlet ground state (S0), lowest triplet state (T1), and lowest singlet excited state (S1), while it is aromatic in its lowest quintet state (Q1) as this state is represented by a triplet multiplicity cyclobutadiene (CBD) ring and two uncoupled same-spin methylene radicals. Interestingly, the Q1 state, despite having four unpaired electrons, is placed merely 4.8 eV above S0, and there is a corresponding singlet tetraradical 0.16 eV above. The DMCB is potentially a highly useful structural motif for the design of larger molecular entities with interesting optoelectronic properties. Here, we designed macrocycles composed of fused DMCB units, and according to our computations, two of these have low-lying nonet states (i. e., octaradical states) at energies merely 2.40 and 0.37 eV above their S0 states as a result of local Hückel- and Baird-aromatic character of individual 6π- and 4π-electron monocycles.

Design and synthesis of active site rich cobalt tin sulfide nano cubes: An effective electrochemical sensing interface to monitor environmentally hazardous phenolic isomers

In the present study, we synthesized Cobalt Tin Sulfide Nano Cubes (CoSnS2) using a simple sol–gel method, and the structural and morphological characterizations were performed to confirm the effectiveness and feasibility of the approach without any impurities. Further, to serve as an electrochemical interface for sensing dihydroxy benzene isomers (DHBIs), CoSnS2 nanoparticles were drop cast on the surface of the glassy carbon electrode (GCE). From the electrochemical characterizations, CoSnS2/GCE shows improved electrochemical performance than bare GCE, and can selectively detect DHBIs. The limits of detection (LODs) calculated for individual determination of catechol (CC) and hydroquinone (HQ) at CoSnS2/GCE was 10.21 nM (5.0–135.0 µM) and 12.56 nM (5.0–135.0 µM), respectively. Also, possible interference does notgreatly affect the analytical performance ofthe modified electrode.Overall, we investigated the simple synthesis of transitional-metal sulfides (TMSs) and their electrochemical sensing applications to chemicals that are dangerous to the environment. We anticipate that the easy approach proposed herein will be very attractive for producing and commercializingelectrochemical sensing devices in the future.

Characteristics of novel cycloaliphatic epoxides based on UV-induced cationic ring-opening polymerization for plastic coatings

Cationic ring-opening polymerization (CROP)-capable cycloaliphatic epoxide monomers bearing a benzyl ether group (CE-BEs) were developed as glass-replacement plastic coatings for lightweight automobiles. Three different monomers of bis(((7-oxabicyclo[4,1,0]heptan-3-yl)methoxy)methyl)benzene isomers were synthesized to provide the cycloaliphatic epoxide functional groups. 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FT-IR) spectroscopic analyses confirmed that the monomers were successfully synthesized. The shear viscosity and real-time crosslinking behavior of the CROP coatings were investigated using a rheometer. In particular, the release of thermal energy via CROP under UV irradiation was monitored using differential scanning photocalorimetry. The reaction conversion of cycloaliphatic epoxides by CROP before and after UV irradiation was verified using FT-IR spectroscopy. The transparency of the CROP coating films cured on a polycarbonate substrate was measured using an ultraviolet–visible spectrophotometer, and their adhesion was confirmed using cross-cut tests. For characterization of the surface mechanical properties, a nanoindentation tester and a nanoscratch tester were used in conjunction with an atomic force microscope to evaluate the surface hardness and scratch resistance, respectively. In addition, the thermomechanical properties of the cured CROP coating films were investigated using a rigid-body pendulum tester operated in dynamic physical mode. The ternary coating systems with CE-BEs were found to exhibit high photoreactivity, a dense crosslinking density, a transparent appearance, and enhanced adhesion and mechanical properties, making it suitable for glass-replacement plastic coatings.

Heavy-atom tunnelling in benzene isomers: how many tricyclic species are truly stable?

The variety of possible benzene isomers may provide a fundamental basis for understanding structural and reactivity patterns in organic chemistry. However, the vast majority of these isomers remain unsynthesized, while most of the experimentally known species are only moderately stable. Consequently, there is a high probability that the theoretically proposed isomers would also be barely metastable, a factor that must be taken into account if their creation in the laboratory is sought. In this work, we studied the kinetic stability of all 73 hypothetical tricyclic benzene isomers, especially focusing on their nuclear quantum effects. With this in mind, we evaluated which species are theoretically possible to synthesize, detect, and isolate. Our computations predict that 26% of the previously deemed stable molecules are completely unsynthesizable due to their intrinsic quantum tunnelling instability pushing for their unimolecular decomposition even close to the absolute zero. Five more systems would be detectable, but they will slowly and inevitably degrade, while seven more supposedly stable systems will break apart in barrierless mechanisms.

Scandia-doped zirconia for the electrochemical detection of hazardous dihydroxybenzene (DHB) isomers in water.

In this paper, modified yttria- and scandia-doped zirconium oxide were exploited for the development of an effective electrochemical sensor for the simultaneous detection of dihydroxy benzene (DHB) isomers, i.e. hydroquinone...

Phononic crystal sensor-demultiplexer for detection of benzene isomers

We have proposed a phononic crystal demultiplexer to distinguish three benzene isomers (p-xylene, m-xylene and o-xylene) from each other. It is obvious that the benzene series are so harmful materials for human body health; so, the proposed sensor could be applicable. The sensor structure consists of periodic tungsten rods in an aluminum host. In order to achieve the sensing purposes, the final phononic structure includes two parallel cavities which target materials are embedded in them. These parallel cavities act as quasi-Mach-Zehnder structure and have been used as acoustic wave resonators. In order to design the demultiplexer part of the structure, each branch was separately designed, then designed branches were assembled together in the form of a demultiplexer. Consequently, the peak frequencies of 189.5 kHz, 192 kHz, and 193 kHz for the mentioned isomers of benzene could be detected from relevant demultiplexer outputs. In this study, the finite element numerical method is used to analyze the acoustic wave propagation through the structure.

Benzene isomer takes the strain

Benzene isomer takes the strain

Zwitterionic polymer-terminated porous silica stationary phases for highly selective separation in hydrophilic interaction chromatography

We described two novel zwitterionic polymer-terminated porous silica stationary phases containing the same pyridinium cation and anions of different side chains (carboxylate and phosphonate groups) for use in hydrophilic interaction liquid chromatography (HILIC). These two novel columns were prepared by polymerizing 4-vinylpyridine and grafting it onto a silica surface, followed by quaternization reaction with 3-bromopropionic acid (Sil-VPC24) and (3-bromopropyl) phosphonic acid (Sil-VPP24), which possess positively charged pyridinium groups, and negatively charged carboxylate and phosphonate groups, respectively. The products obtained were verified through relevant characterization techniques such as elemental analysis, Fourier-transform infrared spectroscopy, thermogravimetric analysis, Zeta potential analysis, and Brunauer–Emmett–Teller analysis. The retention properties and mechanisms of different types of compounds (neutral, cationic, and anionic) on the two zwitterionic-modified silica stationary phases were studied by varying the buffer salt concentration and pH of the eluent. The separation of phenol and aromatic acids, disubstituted benzene isomers, sulfonamide drugs, as well as nucleosides/nucleobases were investigated on the two packed novel columns and a commercial zwitterionic column in identical HILIC mode, ensuring a thorough comparison between both novel columns and with a commercial standard. The results illustrated that various compounds could be separated up to various efficiencies based on the mechanism of hydrophilic interaction-based retention between the solutes and the two zwitterionic polymer stationary phases. The Sil-VPP24 column demonstrated the best separation performance out of the three, as well as flexible selectivity and excellent resolution. Both novel columns exhibited excellent stability and chromatographic repeatability for the separation of seven nucleosides and bases.

Synergetic effects of a poly-tartrazine/CTAB modified carbon paste electrode sensor towards simultaneous and interference-free determination of benzenediol isomers

Simultaneous and selective detection of dihydroxy benzene isomers by the synergistic effect of CTAB and tartrazine on a carbon paste electrode (poly-TZ/CTAB/MCPE) sensor by CV and DPV techniques.

Synthesis and characterization of potential impurities of ezetimibe

AbstractEzetimibe is an azetidinone derivative and a substituted β‐lactam, it is a hypolipidemic agent, and a drug substance that lowers the cholesterol levels in our body. The present work describes the origin, synthesis, and characterization of three impurities of ezetimibe, which are also positional isomers and/or related substances of ezetimibe. viz: o‐Fluoro benzene isomer, m‐Fluoro aniline analog, and des‐fluoro aniline analogs of ezetimibe.

High separation performance of carbon dioxide-based poly(ether-carbonate) copolymer for gas chromatographic analyses

This work presents the investigation of a novel CO2-based poly(ether-carbonate) copolymer, namely poly(propylene ether-carbonate)diol (PPCD), for gas chromatographic (GC) analyses. The PPCD column exhibited column efficiency of 4000 plates/m determined by naphthalene at 120 ℃ with the retention factor 6.23. Its separation performance was investigated by adopting a wide variety of analytes and isomers, including the isomer mixtures of alkanes, substituted benzene isomers with diverse groups, phenols and anilines, and the mixtures of organic solvents of high volatility, aliphatic amines and N-heterocycles. As a result, the PPCD column displayed distinctly higher resolving capability than the commercial columns described herein and achieved high column inertness towards acidic/basic analytes without involving any deactivation procedure. Additionally, it displayed excellent separation repeatability and reproducibility with the relative standard deviation (RSD) values less than 0.01% for within-day and in the range of 0.26% – 0.36% for between-day and 3.0% – 4.1% for between-column (n = 4). Further, the PPCD column (30 m) was used to GC–MS analysis of the lemongrass essential oil and resolved more components well than the indicated commercial columns, evidencing its outstanding separation performance for analyses of complex samples. Up to date, the CO2-based poly(ether-carbonate) copolymers are not reported in the field of chromatography. This work demonstrates their promising future as a new type of selective and inert stationary phases for practical GC analyses.

Palladium-catalysed construction of butafulvenes.

Butafulvene is a constitutional isomer of benzene, comprising a cyclobutene skeleton bearing two exocyclic conjugated methylene units. As a result of the intrinsic high strain energy and anti-aromaticity, the preparation of butafulvene compounds has been a fundamental issue for the development of butafulvene chemistry. Here an efficient palladium-catalysed coupling protocol involving propargylic compounds has been developed, providing a solid and versatile strategy for the rapid assembly of symmetric butafulvene derivatives. Based on mechanistic studies, two complementary mechanisms, both involving palladium catalysis, have been confirmed. With the mechanism unveiled, the synthesis of non-symmetric butafulvenes has also been achieved. Advantages of this strategy include tolerance to a wide range of propargylic molecules, mild reaction conditions, simple catalytic systems and easy scalability. The synthetic potential of the products as platform molecules for cyclobutene derivatives has also been demonstrated.