Aromaticity Of Ring Research Articles

Indoloindolizines: The Complete Story of a Polycyclic Aromatic Scaffold from Theoretical Design to Organic Field-Effect Transistor Applications.

The development of stable and tunable polycyclic aromatic compounds (PACs) is crucial for the advancement of organic optoelectronics. Conventional PACs, such as acenes, often suffer from poor stability due to photooxidation and oligomerization, which are linked to their frontier molecular orbital energy levels. To address these limitations, we designed and synthesized a new class of π-expanded indoloindolizines by merging indole and indolizine moieties into a single polycyclic framework. We developed a scalable synthetic protocol to produce a wide range of π-expanded derivatives. The structural, electronic, and optical properties of these compounds were extensively characterized. We achieved precise modulation of the electronic structure by controlling the aromaticity of specific rings. Benzannulation at targeted positions allowed fine-tuning of the HOMO-LUMO gap, leading to distinct shifts in the optoelectronic properties. Single-crystal X-ray diffraction confirmed their molecular structures, while theoretical calculations provided insights into the observed experimental trends. These indoloindolizines exhibit vivid colors and fluorescence across the visible spectrum and enhanced stability against photooxidation. Reactivity studies demonstrated high regioselectivity in electrophilic substitutions, highlighting the indole-like behavior of these compounds and opening avenues for further functionalization. To showcase the practical utility of our design rules, we fabricated organic field-effect transistors (OFETs) using the newly developed indoloindolizines, which revealed remarkable performance with ambipolar charge transport properties. Overall, our work establishes indoloindolizines as a promising platform for the development of stable, tunable organic materials for optoelectronic applications. Through rational molecular design, we have provided a new pathway for molecular innovation in organic electronics.

Development of Benzimidazole Anticancer Leads for EGFR Inhibition by 3D-QSAR Based Virtual Screening, Molecular Docking, Molecular Simulation and Drug Likeness Study

Background: Breast cancer is the most common cancer in women. Tyrosine kinase inhibitors were developed to treat breast cancer. EGFR/ErbB1 inhibition has proved to be a promising target in breast carcinoma therapy. Drugs with benzimidazole nucleus have been approved by the FDA for cancer treatment. Objective: To design and develop benzimidazole anticancer small molecules for EGFR inhibition for the treatment of breast cancer. Methods: By 3D-QSAR-based virtual screening, molecular docking, molecular simulation and drug likeness study. Results: In this research, a 3D-QSAR pharmacophore was generated with four salient features. Namely H-bond acceptor (HBA), two ring aromatic (RA) and hydrophobic (HY) features. Its correlation- coefficient (r) is 0.8412, RMSD of 0 .96 and with 32.84 bits cost difference value. With virtual screening, 4 top hits were identified. Novel benzimidazole derivatives were designed (1a-ll) by using the features of hit molecules and the pharmacophore. The novel designed small molecules that were druggable as they passed the Lipinski and Veber rule. Novel ligands and EGFR protein interaction were good. 1a and 1i were found to be the best-designed molecules. They had -8.6 Kcal/mol and -8.4 Kcal/mol docking interaction energy, respectively, whereas Compound 4 (reference) scored -7.4 Kcal/mol. Both these molecules were stable inside the binding pocket of the EGFR protein. The molecular dynamic simulation study revealed that 1a attained equilibrium at 0.15nm. Conclusion: In silicon novel benzimidazole small molecules were designed and developed as EGFR inhibitors to treat breast cancer.

Dithienoarsinines: stable and planar π-extended arsabenzenes.

Stable planar dithienoarsinines were synthesized and structurally characterized. These compounds exhibit monomeric structures in the solution and solid states, avoiding dimerization, even in the absence of steric protection. They exhibited high global aromaticity with 14 or 22π-electron systems. In the solid state, intermolecular interactions through arsenic atoms were observed, and As⋯As interactions resulted in aggregation-induced emission enhancement properties with a significant bathochromic shift. The W(CO)5 complex displayed a significantly distorted coordination geometry owing to arsenic cooperative stacking and hydrogen interactions, resulting in a 1D alignment of the complex. Additionally, despite their aromatic nature, dithienoarsinines undergo reactions with alkynes or benzynes to form the corresponding [4 + 2] cycloadducts. Oxygen molecules oxidize the p-position of arsinine, leading to the formation of σ-dimerized compounds while retaining the aromaticity of the arsinine ring. In contrast, oxygen attacks the phosphorus atom in phosphinine, resulting in the formation of phosphinic acid with a loss of aromaticity.

In Search of Entangled Singlet Pure Diradicals.

Recent work has documented conjugate polycyclic hydrocarbons presenting unusual properties: accepting full on-bond electron pairing, they could be considered as closed-shell architectures, but their ground-state wave function is actually a pure diradical singlet, free of any ionic component, in contrast to diradicaloids. These so-called entangled molecules also differ from disjoint diradicals, which do not accept on-bond electron pairing, in that their singly occupied molecular orbitals (SOMOs) are spatially entangled rather than disjoint. The present work first extends the study to a broad series of architectures exhibiting the same properties, namely: they present two degenerate SOMOs in the topological Hückel Hamiltonian, and their pure diradical wave functions lead to symmetry-keeping geometries. These solutions are always of lower energy than the closed-shell solutions that break symmetry and destroy aromaticity of some six-membered rings. A topological criterion ensuring that a given conjugate hydrocarbon will behave as an entangled pure diradical is then formulated. Next, a second set of molecules is proposed, still exhibiting two degenerate Hückel SOMOs, but with smaller contrast between the energies of open-shell and closed-shell solutions. Conservation of six-membered rings aromaticity appears as the driving factor ruling the stability of diradical solutions.

Exploring and Regulating Heteroatom-Electronegativity-Associated with Ring Aromaticity and Excited State Intramolecular Proton Transfer Mechanism for Benzothiazole-Based Fluorophore.

A novel fluorophore 2-(2'-hydroxy-5'-benzaldehyde phenyl) benzothiazole (HBBT) with excited state intramolecular proton transfer (ESIPT) characteristics, showing good selectivity for Cu+/Cu2+ ions had been synthesized experimentally (Molecules 2022, 27, 7678). However, its ESIPT mechanism and fluorescent performance related to atomic substituents have not been investigated systematically. In this work, two HBBT derivatives, 2-(2'-hydroxy-5'-benzaldehyde phenyl)benzoimidazole (HBBI) and 2-(2'-hydroxy-5'-benzaldehyde phenyl)benzopyrrole (HBBP), were obtained by respectively using -NH and -CH2 groups in place of the sulfur atom in the thiazole ring. The absorption/emission spectra and ring aromaticity as well as ESIPT processes of HBBT and its derivatives were studied using density functional theory (DFT) and time-dependent DFT (TD-DFT). The simulated absorption and fluorescence wavelengths of HBBT agreed well with the corresponding values obtained in the experiment. According to the analyses of geometry structures, electron densities, and infrared vibration frequencies, the intramolecular hydrogen bond becomes stronger upon light excitation. The frontier molecular orbitals were analyzed via establishing potential energy curves, and the ESIPT behavior was described deeply. Obviously, the NH-substitution makes ring 4 more aromatic, while the CH2-substitution changes ring 4 from aromatic to antiaromatic. The ESIPT process helps to alleviate the excited state antiaromaticity. The greater the antiaromaticity of the S1 state normal form, the higher the barrier of ESIPT.

On the chemistry of sunlight-induced DNA lesions: A perspective on the alkaline chemical-induced reactivities of photo-damaged pyrimidine intra-strand dimers.

Photoexcitation of cellular as well as isolated DNAs upon exposure to the UV portion of sunlight or other UV sources can lead to the covalent dimerization of adjacent intra-strand stacked pyrimidine nucleobase rings (i.e., at 5'-Py-p-Py-3' sites). These modifications generate, in mammalian DNA as well as the DNA of all other forms of life, lesions such as cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs); and, in bacterial endospores, spore photoproducts (SPs). Importantly, the lesions formed in higher organisms can lead to disease states including cancer. While the formation, structure, and biological outcomes of pyrimidine dimer lesions have been the focus of much research, less has been known about their fundamental chemical properties until recently. Such an understanding of these lesions may lead to novel means to chemically identify and quantitate their presence in the genome. This review is intended to provide an overview of intra-strand pyrimidine dimer lesions derived from 5'-T-p-T sites with a focus on presenting what is currently known about their individual invitro alkaline chemical reactivities. Included here are descriptions of investigations of the DNA lesions CPD, 6-4PP, and SP, and, for comparison, the monomeric pyrimidine lesion 5,6-dihydo-2'-deoxyuridine (dHdU). Of interest, the alkaline hydrolyses of these various lesions are all found to be centered on the loss of aromaticity of a lesion Py ring (T) leading to a carbonyl "hot spot," the focal point of initial hydrolytic attack.

Simple and Effective Identification of Local 6π- and Global [4n + 2] Aromaticity of Macrocyclic Conjugated Hydrocarbons by 1H/13C Chemical Shifts and the Corresponding Ring Current Effect.

Structures, 1H/13C chemical shifts, and the ring current effects (spatial magnetic properties: through-space NMR shieldings [TSNMRSs]) of various π-conjugated macrocyclic hydrocarbons and the corresponding charged analogues have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus-independent chemical shift (NICS) characterization. The spatial magnetic properties (TSNMRS) are visualized as iso-chemical shielding surfaces (ICSSs) of various size and direction and together with especially the δ(1H)/ppm chemical shifts employed to unequivocally qualify and quantify local 6π-aromaticity of individual benzenoid building blocks and the global ([4n + 2], n > 1) aromaticity of the macrocyclic ring.

СИНТЕЗ ТА АНТИОКСИДАНТНА АКТИВНІСТЬ 2-МЕТИЛ-5-ХЛОРО-2,3-ДИГІДРОІМІДАЗО[2,1-b][1,3]ТІАЗОЛ-6-КАРБАЛЬДЕГІДУ

Imidazothiazoles annelated to the b face have been of particular interest to researchers in recent decades due to their powerful medical and biological potential. Antioxidant therapy of diseases associated with oxidative stress is one of the important areas of modern medicine. That is why this work is devoted to the synthesis of 2-methyl-5-chloro-2,3-dihydroimidazo[2,1-b][1,3]thiazole-6-carbaldehyde and the evaluation of its antioxidant potential. Synthetically available 2-methyl-2,3-dihydroimidazo[2,1-b][1,3]thiazol-5(6H)-one was used as a substrate. The presence of an activated methylene group in its structure makes it very attractive for further structural modification by pharmacoform groups and construction of biologically active compounds. It was found that 2-methylimidazothiazole undergoes a Vilsmeier-Haack reaction during heating with a DMF/POCl3 complex to form a 6-formyl-5-chloro derivative with a yield of 25%. The composition and structure of this chloraldehyde synthesized for the first time was unambiguously confirmed by a set of physicochemical analysis, including elemental analysis, chromato-mass, IR and NMR spectra. Specifically, IR spectrum contains an intense absorption band of valence vibrations of the С=О group at 1684 cm–1. The 1H NMR spectrum is characterized by a formyl group singlet at 9.72 ppm, and the signal of the corresponding carbon atom in the 13C NMR spectrum is recorded at 182.2 ppm. The fact of aromatization of the imidazole ring is confirmed by the shift of the signals of C5 and C6 atoms to the region of 139.4 ppm and 123.2 ppm, respectively. The antioxidant activity was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition method. Initially, it was experimentally confirmed that the rate of inhibition of radicals by the synthesized compound at a concentration of 5 mM is 54.1%. The next stage of the study showed that the IC50 data is 1.669 mM, vs IC50 = 0.097 mM for ascorbic acid. Therefore, 2-methyl-5-chloro-2,3-dihydroimidazo[2,1-b][1,3]thiazole-6-carbaldehyde is of interest for advanced pharmacological studies and design of promising synthetic antioxidants.

A Deep‐Red Emissive Sulfur‐Doped Double [7]Helicene Photosensitizer: Synthesis, Structure and Chiral Optical Properties

AbstractDoping of polycyclic conjugated hydrocarbons (PCHs) with sulfur atoms is becoming more and more important as a means of creating unique functional materials. Recently, thiophene‐containing multiple helicenes have garnered enormous attention due to their intriguing electronic and (chir)optical properties compared with carbohelicenes. However, the efficient synthesis of thiopyran‐containing multiple helicenes and the underlying sulfur doping mechanisms are rather unexplored. Herein, the synthesis and structural analysis of a thiopyran‐containing double [7]helicene 3 are reported. X‐ray crystallographic analysis reveals 3 and its dication with C2‐symmetric propeller‐shape structures and compact interactions in the solid state. 3 exhibits deep‐red to near‐infrared (NIR) fluorescence emission. Tunable aromaticity of the central benzene ring and thiopyran rings is found by chemical oxidation, which is further confirmed by nucleus‐independent chemical shift (NICS), anisotropy of the induced current density (ACID) and harmonic oscillator model of aromaticity (HOMA) analysis. Furthermore, the chiral and photosensitizing characters of 3 are investigated. The excellent deep‐red to NIR fluorescence, circularly polarized luminescence (CPL) and photosensitizing activities suggest that 3 can be used as an outstanding photosensitizer in photodynamic therapy (PDT) and bioimaging, especially paving the way for future CPL‐PDT and CPL‐bio‐probe applications.

A Deep-Red Emissive Sulfur-Doped Double [7]Helicene Photosensitizer: Synthesis, Structure and Chiral Optical Properties.

Doping of polycyclic conjugated hydrocarbons (PCHs) with sulfur atoms is becoming more and more important as a means of creating unique functional materials. Recently, thiophene-containing multiple helicenes have garnered enormous attention due to their intriguing electronic and (chir)optical properties compared with carbohelicenes. However, the efficient synthesis of thiopyran-containing multiple helicenes and the underlying sulfur doping mechanisms are rather unexplored. Herein, the synthesis and structural analysis of a thiopyran-containing double [7]helicene 3 are reported. X-ray crystallographic analysis reveals 3 and its dication with C2-symmetric propeller-shape structures and compact interactions in the solid state. 3 exhibits deep-red to near-infrared (NIR) fluorescence emission. Tunable aromaticity of the central benzene ring and thiopyran rings is found by chemical oxidation, which is further confirmed by nucleus-independent chemical shift (NICS), anisotropy of the induced current density (ACID) and harmonic oscillator model of aromaticity (HOMA) analysis. Furthermore, the chiral and photosensitizing characters of 3 are investigated. The excellent deep-red to NIR fluorescence, circularly polarized luminescence (CPL) and photosensitizing activities suggest that 3 can be used as an outstanding photosensitizer in photodynamic therapy (PDT) and bioimaging, especially paving the way for future CPL-PDT and CPL-bio-probe applications.

Rational Design of Cyclopentadiene-Based Super- and Hyperacids Based on Aromaticity.

The design and synthesis of neutral organic superacids have been of interest recently due to their vast applications in chemistry and material sciences, for example, olefinic polymerization, isolation of highly reactive short-lived cations, etc. Cyclopentadiene behaves as a mild organic acid, producing a stable conjugate base by gaining aromaticity and conjugation after deprotonation. To stabilize conjugate bases of organic acids to show superacidities and hyperacidities, we considered aromatic phenyl substituents with cyclopentadiene (mono-, di-, and triphenyl-substituted cyclopentadiene and their cyano derivatives). The MP2, DFT (B3LYP, M06-2X), and CBS-QB3 methods were used to calculate the gas-phase proton affinities of the parent cyclopentadiene, and the DFT methods were chosen for the substituted cyclopentadiene as they yield an experimental proton affinity of cyclopentadiene of 253.66 kcal/mol (Expt. 253.6 ± 1.3 kcal/mol). The stable trisubstituted cyclopentadiene derivative shows gas-phase enthalpies of deprotonation (ΔHacid) of 245 and 239 kcal/mol with DFT B3LYP and M06-2X methods, respectively, with values in the range of hyperacidity. Some of the tautomers of cyclopentadiene derivatives show hyperacidity, with proton affinity values of 205-240 kcal/mol. Triphenyl-substituted cyclopentadiene behaves as a moderate acid but transforms into a superacid after replacing the phenyl group with nitrobenzene, which is a stronger acid than H2SO4 (ΔHacid = 298 kcal/mol). The nucleus-independent chemical shift (NICS) shows the extent of conjugation in the derivatives of cyclopentadienyl anions after deprotonation, which affects the stabilities of conjugate bases, i.e., the acidities of the protonated species. The calculated harmonic oscillator model of aromaticity and NICS indices reveal that the stability of conjugate bases as well as their acidities increase with increasing aromaticity of cyclopentadiene rings after deprotonation in all molecules.

Regulating the fluorescence properties and ESIPT mechanism as well as ring aromaticity of benzothiazole-based derivatives by hetero nitrogen substitution: A TD-DFT study

The effects of hetero nitrogen substitution on photophysical properties and excited state intramolecular proton transfer (ESIPT) behaviors of 2-(2′‑hydroxy-5′-benzaldehyde phenyl) benzothiazole (HBBT) have been investigated at the B3LYP/6-311+G(d,p) level using density-functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The geometrical structures as well as absorption/emission spectra of all derivatives were obtained at the same level of theory. The enhancement of intramolecular hydrogen bonds (IHBs) in the excited state (S1) was obtained by analyzing the bond lengths and angles, infrared spectra (IR) and topological parameters. Potential energy curves (PECs) have been constructed, and the order of the ESIPT barrier is HBBT-3 < HBBT-4 < HBBT-34 < HBBT-2 < HBBT-1 < HBBT-12. Except for HBBT-2, the emission wavelengths of other HBBT derivatives have varying degrees of redshift compared to HBBT. The nitrogen substitution at position 3,4 is favorable to ESIPT process, and influences the photophysical features of HBBT significantly. ESIPT process will occur in the direction of relieve the antiaromaticity of S1 state.

Unlocking the Potential of Glutinol: Structural Diversification and Antifungal Activity against Phytopathogenic Fusarium Strains.

Unlike most common pentacyclic plant triterpenes, glutinol has a methyl group at position C-9 and a Δ5 double bond. At the same time, it lacks a methyl at C-10. These features significantly modify its chemical behavior compared to other triterpenes, particularly under oxidative conditions. Although the isolation of glutinol from various plant species has been documented, its chemistry remains largely unexplored. In this study, glutinol was isolated from the bark of Balfourodendron riedelianum as a starting material for top-down strategies of structural diversification, which included ring fusion, oxidation, aromatization, and ring cleavage reactions. Glutinol, together with a library of 22 derivatives, was evaluated for antifungal activity against three phytopathogenic Fusarium strains, F. solani, F. graminearum, and F. tucumaniae. Some of the derivatives displayed antifungal activity; in particular, compound 12, featuring a triazine ring, displayed the best fungicidal properties against F. solani and F. graminearum, while the ring B cleavage product 23 showed the best activity against F. tucumaniae. This study highlights the potential of glutinol as a scaffold for structural diversification, and these results may contribute to the design of novel fungicidal agents against phytopathogenic strains.

Probing the Limit of the Number of Saturated Atoms for Achieving Hyperconjugative Aromaticity.

Aromaticity is a fundamental concept in organic chemistry. Hyperconjugative aromaticity, also known as hyperconjugation-induced aromaticity, has evolved from its origin from main group substituents to transition metal analogues, establishing itself as an important category of aromaticity. Additionally, aromatic compounds comprising two sp3-carbon atoms have recently been reported both experimentally and computationally. However, what is the maximum number of sp3-hybridized atoms needed to maintain hyperconjugative aromaticity? Here, we report that hyperconjugative aromaticity can be achieved in hexa-substituted indoliums and octa-substituted pyrroliums, possessing three-five sp3-hybridized carbon/nitrogen atoms by means of density functional theory (DFT) calculations. The aromaticity was confirmed by using various aromaticity indices, i.e., NICS, MCI, and EDDB. Notably, the strong electron-donating ability and aurophilicity of Au(I) substituents play a pivotal role in maintaining the aromaticity and structural integrity. In addition, increasing the number of hyperconjugative centers will decrease the aromaticity in these five-membered rings. Our findings highlight the significance of transition metal substituents in hyperconjugative aromaticity and offer a novel approach for designing aromatic organometallics.

Interaction between aromaticity of rings and NMR chemical shifts of 1H and 13C in resonance-assisted hydrogen bond for 2-hydroxyl diaryl schiff bases

In this paper, forty-four schiff bases 2-OH-XArCH=NArY (2-OH-XBAY) compounds with different substituents were investigated by quantum mechanical calculations. The chemical shifts δH(OH) of H on OH and δC(CH=N) of C on CH=N in resonance-assisted hydrogen bond (RAHB) ring of compounds were determined, and the aromaticity of the rings of the compounds was evaluated using the para-delocalization index (PDI). The interaction between the aromaticity of the all rings in molecule and the chemical shift was studied. The results show: (1) Due to the electron transfer from the benzene ring A (at C of CH=N bond) to the quasi-aromatic ring Q (RAHB ring), the π-electron delocalization of ring Q increases, resulting in a decrease in the π-electron delocalization of ring A. (2) The π-electron delocalization effect of the ring Q has a greater influence on the chemical shift δH(OH) of H on OH, followed by the ring A. The benzene ring B (at N of CH=N bond) has only little effect on δH(OH). (3) Only the aromaticity of ring Q in 2-OH-XBAY can be characterized by δH(OH) and δC(CH=N). (4) Through the structure and orbital analysis of parent molecule 2-OH-BA, it can be considered that the H on OH participates in the π-electron circulation of the ring Q.

Molecular-strain induced phosphinidene reactivity of a phosphanorcaradiene

Phosphanorcaradienes are an appealing class of phosphorus compounds that can serve as synthons of transient phosphinidenes. However, the synthesis of such species is a formidable task owing to their intrinsic high reactivity. Herein we report straightforward synthesis, characterization and reactivity studies of a phosphanorcaradiene, in which one of the benzene rings in the flanking fluorenyl substituents is intramolecularly dearomatized through attachment to the phosphorus atom. It is facilely obtained by the reduction of phosphorus(III) dichloride precursor with potassium graphite. Despite being thermally robust, it acts as a synthetic equivalent of a transient phosphinidene. It reacts with trimethylphosphine and isonitrile to yield phosphanylidene-phosphorane and 1-phospha-3-azaallene, respectively. When it is treated with one and two molar equivalents of azide, iminophosphane and bis(imino)phosphane are isolated, respectively. Moreover, it is capable of activating ethylene and alkyne to afford [1 + 2] cycloaddition products, as well as oxidative cleavage of Si–H and N–H bonds to yield secondary phosphines. All the reactions proceed smoothly at room temperature without the presence of transition metals. The driving force for these reactions is most likely the high ring-constraint of the three-membered PC2 ring and recovery of the aromaticity of the benzene ring.

A comparative DFT study of monosubstituted silabenzene and benzene structures: Effects of Si atom incorporation in benzene ring

In the present study, monosubstituted structures with 16 substitutions in the ortho, meta, and para positions of silabenzene have been comprehensively compared with similar structures in benzene. This study aimed to investigate the effect of Si atom incorporation in the benzene ring. This comparison investigated the chemical properties, including structural geometries of molecules, molecular orbitals and reactivity, ring aromaticity, and excitation energy of each monosubstituted silabenzene and benzene structure. The density functional theory (DFT) at the B3LYP/6–311G++(d,p) level of theory was used to perform all relevant calculations. In addition to changes in ring geometry values and electron donating, the results showed that the Si atom incorporation in benzene ring and its monosubstituted derivatives in different positions caused a significant decrease in LUMO, chemical hardness, ring aromaticity, excitation energy, and a significant increase in HOMO, electrophilicity, nucleophilicity, and NMR chemical shift values. Among the positions of the substituents concerning the Si atom in the ring, the ortho and para positions exhibited the most optimal values. In contrast, the meta position displayed different values compared to the ortho and para positions. This difference is attributed to the electron-withdrawing effects of the substituents. Also, among substitutions, electron-donating substitutions especially -NH2 compared to electron-withdrawing substitutions especially -NO2 decreased HOMO, electrophilicity, excitation energy, and increased LUMO, chemical hardness, nucleophilicity, and ring aromaticity.

Insight into the Stability of Pentazolyl Derivatives based on Covalent Bond.

Pentazole is regarded as a unique inorganic molecule that possess organic heterocyclic structure. Therefore, the research on pentazolyl derivatives represents a cutting-edge direction in both contemporary inorganic chemistry and heterocyclic chemistry. Moreover, their synthesis is regarded as the most significant research topic in the field of energetic materials due to the great potential of pentazolyl derivatives to breakthrough the energy bottleneck of CHNO-based energetic materials. However, synthesizing pentazolyl derivatives is challenging. To provide a theoretical support for the synthesis, we conducted theoretical studies on six single-ring pentazolyl derivatives with different functional groups. The results suggest that derivatization reduces the bond strength and weakens the aromaticity of the pentazolate ring. Further analysis showed that derivatization mainly affects the π aromaticity of the pentazolate ring, and ultimately causing poor stability of the pentazolyl derivatives. Among the six derivatives investigated in this study, fluoro pentazole (cyclo-N5-F) and hydroxyl pentazole (cyclo-N5-OH) possess good aromaticity, which is similar to the reported cyclo-N5-NCHN(CH3)2. Further calculations show that the kinetic stability of cyclo-N5-OH is higher than that of cyclo-N5-F. These results collectively indicate that cyclo-N5-OH is a promising candidate for synthesizing single-ring pentazolyl derivatives.

On the mechanism of Siebold’s test for morphine

In this communication the reaction course of Siebold’s test for morphine is provided. The test is based on the interaction of the alkaloid in sulphuric acid with potassium perchlorate. Perchloric acid is the intermediate that gives rise the reactive species, ClO3+. A mixed perchlorate is formed by interaction with the phenolic group at C-3 in morphine. Protonation of this ester induces nucleophilic reaction at C-2 (Umpolung). A new perchlorate results with concomitant ketone formation at C-3 and elimination of chloric acid (first redox reaction). Enolization restores ring aromatization, and protonation of the perchlorate at C-2 produces a concerted push-pull mechanism, via three electron-shifts, that gives rise separation of chloric acid and formation of an ortho-quinone (second redox reaction).

Valuable insights into the structural, electronic, and aromaticity aspects of azulene and its monophospha-derivatives

Azulene-based conjugated systems have garnered considerable interest owing to their atypical structures. The incorporation of a phosphorous atom into the azulene framework offers an enticing prospect for the creation of unique organophosphorous π-conjugated compounds. No such phosphaazulene skeleton however has been reported to date. Here, density functional theory calculations were employed to examine the physicochemical properties and aromaticity of azulene and its monophospha-derivatives. The electronic, magnetic, and structural properties were taken into consideration. The reactivity of azulene and its monophospha-analogs including 1-phospha (1p), 2-phospha (2p), 4-phospha (3p), 5-phospha (4p), and 6-phosphaazulene (5p), was examined through local electrophilicity and local nucleophilicity indices. The stability and aromaticity of these compounds were determined using DFT calculations with the B3LYP/6–311 + G(d,p) method. The stability of monophosphaazulene derivatives is significantly influenced by the position of the phosphorus atom, as indicated by the energy calculations. The order of stability was found to be 1p > 2p > 5p > 3p > 4p. Aromaticity studies based on HOMA, ΔBl, FLUπ, SA, and NICS indices indicated that the incorporation of a phosphorus atom into the 5-membered ring decreased its aromaticity while simultaneously increasing the aromaticity of the 7-membered ring. However, replacing the carbon atom with phosphorus atom in the 7-membered ring reduced the aromaticity of both rings. Additionally, the ability of π-stacking, as determined by the LOLIPOP criterion, was reduced in the monophosphaazulene derivatives compared to azulene, except for compound 5p. The order of π-stacking ability was 5p > azulene > 2p > 1p > 4p > 3p. Overall, there was a good agreement between the various aromaticity indices, providing consistent results for both rings in azulene and monophosphaazulenes.