Ring Atoms Research Articles

β-Pyrrole functionalized push-pull BODIPYs: Synthesis, photophysical, electrochemical, thermal and computational studies

A series of [Formula: see text]-pyrrole functionalized push-pull BODIPYs BDP 1-06 were designed and synthesized via Palladium-catalyzed Suzuki cross-coupling reaction and by increasing the oxidation state of the sulfur atom in the thiazine ring. The effect of various donor entities on the photophysical, electrochemical, thermal, and computational studies of the BODIPY was investigated. The absorption spectra of the push-pull BODIPY BDP 2 show a red shift compared to the rest of the BDPs, due to strong donor-acceptor interaction. The phenothiazine-5,5-dioxide functionalized BODIPY BDP 6 exhibit a blue shift in the UV-vis region compared to the phenothiazine substituted BODIPY BDP 5 due to the weak donor ability of the phenothiazine-5,5-dioxide unit. The electrochemical studies were performed for the push-pull BODIPYs BDP 1–6 to analyze the effect of different donor groups on the redox properties of the BODIPY. The thermogravimetric analysis of the BODIPYs BDP 1–6 shows that BDP 2 exhibits excellent thermal stability compared to BDP 1, 3, 4, 5, and 6. The theoretical studies reveal that the phenothiazine-5,5-dioxide substituted BODIPY BDP 6 exhibits a large HOMO–LUMO gap compared to phenothiazine functionalized BODIPY BDP 5 due to the low donor ability of the phenothiazine-5,5-dioxide unit. The theoretical calculations were consistent with the experimental observations.

Insights into persulfate activation by FeO for phenol removal: The production and effect of Fe(IV)

This study presents new findings on persulfate (PDS) activation by iron(II) oxide (FeO). PDS was activated through both homogeneous and heterogeneous approaches, while the latter played a dominant role. The species responsible for phenol oxidation were identified as SO4−, OH, and high-valent Fe(IV). A new possible formation pathway of aqueous Fe(IV) is proposed, involving electron transfer between SO4−/OH and Fe(III)–OH complex. Density functional theory calculations support that Fe(IV) is apt to attack phenol by electrophilic addition on the benzene ring and hydrogen atom abstraction on the phenolic hydroxyl group. Phenol removal was accelerated at a higher catalyst dosage or PDS concentration but inhibited at higher pH. The coexistence of inorganic anions (e.g., PO43−, SO42−, NO3−, and Cl−) and fulvic acid have different effects on this system. Phenol degradation mainly occurred through hydroxylation and eventual ring-opening. In addition, the FeO/PDS system has not only achieved a high removal effect on other phenolic compounds but has also exhibited high performance in actual water. Thus, this system is anticipated to be a promising treatment technique for phenolic-polluted water.

Effect of Phosphorus Substitution in the Cyclopentadienyl Ring of Ferrocene: Combined Mössbauer Spectroscopy and DFT Studies

A series of phosphaferrocenes with different numbers of phosphorus atoms and phenyl groups in the cyclopentadienyl ring were successfully synthesized and studied by Mössbauer spectroscopy. Revealed Mössbauer hyperfine parameters are in line with density functional theory (DFT) calculations. It was found that substitution of CH-units by phosphorus atoms in the cyclopentadienyl ring affects the population of the molecular orbitals related to iron. These changes influence on Mössbauer hyperfine parameters, especially on the quadrupole splitting values. Intermolecular vibrations were analyzed in terms of the Debye model of solids based on the temperature dependence of Mössbauer absorption. The characteristic lattice Debye temperatures and the intermolecular force constants were calculated for each studied sample.

Silver Nanoparticle-Embedded Conductive Hydrogels for Electrochemical Sensing of Hydroquinone.

In this work, a conductive hydrogel was successfully synthesized, taking advantage of the high number density of active amino and hydroxyl groups in carboxymethyl chitosan and sodium carboxymethyl cellulose. These biopolymers were effectively coupled via hydrogen bonding with the nitrogen atoms of the heterocyclic rings of conductive polypyrrole. The inclusion of another biobased polymer, sodium lignosulfonate (LS), was effective to achieve highly efficient adsorption and in-situ reduction of silver ions, leading to silver nanoparticles that were embedded in the hydrogel network and used to further improve the electro-catalytic efficiency of the system. Doping of the system in the pre-gelled state led to hydrogels that could be easily attached to the electrodes. The as-prepared silver nanoparticle-embedded conductive hydrogel electrode exhibited excellent electro-catalytic activity towards hydroquinone (HQ) present in a buffer solution. At the optimum conditions, the oxidation current density peak of HQ was linear over the 0.1-100 μM concentration range, with a detection limit as low as 0.12 μM (signal-to-noise of 3). The relative standard deviation of the anodic peak current intensity was 1.37% for eight different electrodes. After one week of storage in a 0.1 M Tris-HCl buffer solution at 4 °C, the anodic peak current intensity was 93.4% of the initial current intensity. In addition, this sensor showed no interference activity, while the addition of 30 μM CC, RS, or 1 mM of different inorganic ions does not have a significant impact on the test results, enabling HQ quantification in actual water samples.

Deciphering Structural and Dynamical Properties of Hydrated Cobalt Porphyrins via Ab Initio Quantum Mechanical Charge Field Molecular Dynamics Simulation.

The present study successfully implemented the ab initio quantum mechanical charge field molecular dynamics (QMCF MD) formalism for the investigation of structural and dynamical properties of hydrated cobalt-porphyrin complexes. Considering the significance of cobalt ions in biological systems (for instance, vitamin B12), which reportedly incorporate cobalt ions in a d6, low spin, +3 state chelated in the corrin ring, an analog of porphyrin, the current study is focused on cobalt in the oxidation states +2 and +3 bound to the parent porphyrin lead structures embedded in an aqueous solution. These cobalt-porphyrin complexes were investigated in terms of their structural and dynamical properties at the quantum chemical level. The structural attributes of these hydrated complexes revealed the contrasting features of the water binding to these solutes, including a detailed evaluation of the associated dynamics. The study also yielded notable findings in regard to the respective electronic configurations vs coordination, which suggested that Co(II)-POR possesses a 5-fold square pyramidal coordination geometry in an aqueous solution containing the metal ion coordinating to four nitrogen atoms of the porphyrin ring and one axial water as the fifth ligand. On the other hand, high-spin Co(III)-POR was hypothesized to be more stable due to the smaller size-to-charge ratio of the cobalt ion, but the high-spin complex demonstrated unstable structural and dynamical behavior. However, the corresponding properties of the hydrated Co(III)LS-POR revealed a stable structure in an aqueous solution, thus suggesting the Co(III) ion to be in a low-spin state when bound to the porphyrin ring. Moreover, the structural and dynamical data were augmented by computing the free energy of water binding to the cobalt ions and the solvent-accessible surface area, which provide further information on thermochemical properties of the metal-water interaction and the hydrogen bonding potential of the porphyrin ring in these hydrated systems.

Insights into the synergistic effects of safranine in an acidic copper bath on through-hole void-free filling for high-quality electronics interconnection

In this work, we develop a novel safranine (SA)-based acidic sulfate copper electronic plating process for through-hole copper void-free filling for high-quality electronics interconnection, and both the molecule actions and synergistic effects of safranine (SA) are carefully explored. Cyclic voltammetry experiments at rotating rates of 200 r/min and 1200 r/min demonstrate that SA itself can accelerate the electro-reduction of copper ion, heighten the inhibiting effect of polyethylene glycol (PEG) and acceleration effect of bis-(3-sulfopropyl) disulfide (SPS). The addition of SA to the virgin make-up solution (VMS) containing PEG and SPS makes the relative electric charge (∆Q) between the low and high rotating rates be increased from 1.27 ± 0.04–22.53% ± 0.05, indicating the higher copper electronic plating amount at the center than that at the mouth of through-hole. In situ Fourier transform infrared spectroscopy together with theoretical calculations further illustrate that the molecule SA is adsorbed on the copper surface through the N atom in the aromatic ring, PEG and SPS can heighten the adsorption of SA on the Cu surface, and both PEG and SPS both synergistically influence with SA to achieve the void-free copper filling of through-hole.

Dynamic and Static Nature of XH-∗-π and YX-∗-π (X = F, Cl, Br, and I; Y = X and F) in the Distorted π-System of Corannulene Elucidated with QTAIM Dual Functional Analysis.

The dynamic and static nature of the XH-∗-π and YX-∗-π (X = F, Cl, Br, and I; Y = X and F) interactions in the distorted π-system of corannulene (π(C20H10)) is elucidated with a QTAIM dual functional analysis (QTAIM-DFA), where asterisks emphasize the presence of bond critical points (BCPs) on the interactions. The static and dynamic nature originates from the data of the fully optimized and perturbed structures, respectively, in QTAIM-DFA. On the convex side, H in F-H-∗-π(C20H10) and each X in Y-X-∗-π(C20H10) join to C of the central five-membered ring in π(C20H10) through a bond path (BP), while each H in X-H-∗-π(C20H10) does so to the midpoint of C=C in the central five-membered ring for X = Cl, Br, or I. On the concave side, each X in F-X-∗-π(C20H10) also joins to C of the central five-membered ring with a BP for X = H, Cl, Br, and I; however, the interactions in other adducts are more complex than those on the convex side. Both H and X in X-H-∗-π(C20H10) (X = Cl and Br) and both Fs in F-F-∗-π(C20H10) connect to the three C atoms in each central five-membered ring (with three BPs). Two, three, and five BPs were detected for the Cl-Cl, I-H, Br-Br, and I-I adducts, where some BPs do not stay on the central five-membered ring in π(C20H10). The interactions are predicted to have a vdW to CT-MC nature. The interactions on the concave side seem weaker than those on the convex side for X-H-∗-π(C20H10), whereas the inverse trend is observed for Y-X-∗-π(C20H10) as a whole. The nature of the interactions in the π(C20H10) adducts of the convex and concave sides is examined in more detail, employing the adducts with X-H and F-X placed on their molecular axis together with the π(C24H12) and π(C6H6) adducts.

Isomer-Specific Heavy-Atom Tunneling in the Ring Expansion of Fluorenylazirines.

The photolysis of 2-azidofluorene in solid argon at 3 K results in the formation of 2-fluorenylnitrene. The nitrene undergoes subsequent rearrangements to two isomeric didehydroazepines (ketenimines) which differ in the position of the N atom in the seven-membered ring. The rearrangement of the nitrene to the didehydroazepines proceeds in a two-step process. The first step is a photochemical rearrangement to form the corresponding isomeric benzazirines A and B. The second step is the opening of the three-membered rings of A and B to form the isomeric didehydroazepines. While benzazirine A could easily be detected, isomer B was not observed, despite the corresponding didehydroazepine being formed in the matrix. Further experiments revealed that A rearranges to the didehydroazepine via heavy-atom tunneling. Semiquantitative estimations based on DFT calculations confirm that A should undergo a tunneling rearrangement with tunneling rates on the order of the experimentally observed rates. In contrast, estimations for B suggest that for this isomer the tunneling rates should be much larger, resulting in lifetimes too short to be observable under the conditions of matrix isolation. These experiments demonstrate the influence of position isomerism on quantum tunneling rates.

Preparation of Laterally Chloro-Substituted Schiff Base Ester Liquid Crystals: Mesomorphic and Optical Properties

A new class of Schiff base/ester compounds: ICln, 4-((2′-chlorophenylimino)methyl)phenyl-4″-alkoxy benzoates, were synthesized and their mesophase characteristics and thermal behavior were evaluated. Differential scanning calorimetry (DSC) was used to study mesophase transitions, and polarized optical microscopy was carried out to identify the phases (POM). The results show that all compounds are monomorphic, and enantiotropic nematic (N) phases were seen at all side chains. It was found that lateral Cl atoms in the terminal benzene ring influence both conformation and mesomorphic properties. Comparisons between the present investigated lateral Cl derivatives and their laterally neat, as well as their isomeric, compounds have been briefly discussed. Results revealed that the insertion of lateral Cl substituent in the molecular structure impacts the type and stability of the formed mesophases. The exchanges of the ester-connecting moiety improve their thermal nematic stability than their previously prepared structurally isomeric derivatives. These compounds exhibit a broad absorption in the UV-Visible region, including a peak in UV region and a tail around 550 nm, and there were observed to be absorption tail increases and energy band gap decreases with the increase of the alkoxy side chain length. The photoluminescence (PL) intensity was noted to be quenched for the bulky alkoxy group ascribed to non-radiative recombination through the defect states. Moreover, time resolved fluorescence decay spectra reveal that both the radiative and non-radiative recombination lifetime increases with the increase of alkoxy side chain length.

Synthesis, characterization and pharmacological studies of cobalt(II), nickel (II) and copper (II) complexes of thiazole schiff bases

Many Schiff bases prepared from 2-hydrazinobenzothiazole and isatin have been used to produce Co (II) complexes of the form [ML2]Cl2. Nitrogen from azomethine, oxygen from lactonyl, and nitrogen atoms of the thiazole ring contribute to coordinating the metallic ion. Complexes made entirely of metal have geometrical octahedrons, according to analytical, magnetic studies and spectroscopic (Infrared, Ultraviolet-Visible, ESR, FAB-mass) investigations. The conductivity measurements show the electrolytic behaviour of the metal complexes. The redox behaviour of the metal complexes is investigated using cyclic voltammetry. The antibacterial and antifungal activities of the Schiff bases and their metal complexes were examined using the Minimum Inhibitory Concentration method against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and S. typhi. Investigations into DNA cleavage were conducted using the agarose gel electrophoresis technique, and significant DNA cleavage was found.

Fluorinated 2-Phenylethylammonium Spacer Cations for Improved Stability of Ruddlesden–Popper Pb/Sn Halide Perovskites: Insight from First-Principles Calculations

Improving the stability of hybrid halide perovskite solar cells is essential for their commercialization in emerging cutting-edge technology. Here, we report the results of state-of-the-art first-principles calculations to achieve and understand enhancement in the stability of Ruddlesden–Popper (RP) lead/tin halide perovskites with fluorinated 2-phenylethylammonium (PEA) spacer cations. It is found that the substitution of up to five F atoms in the phenyl ring makes C slightly positively charged due to ∼0.5e charge transfer to electronegative F. This leads to the formation of electric dipoles in the spacer cation region and polarization of the charge density. This improves the formation energy and enhances the stability of the layers. The charge transfer makes some of the C 2p orbitals partly empty so that they hybridize with F 2p orbitals near the conduction band minimum. This is interesting for the charge transport perpendicular to the layers. Our study further shows that changing the metal cations Pb with Sn does not affect the orientation of the cation molecules in the pure as well as chemically tuned RP layers whereas changing the halide ions I with Br has an impact on the orientation of the organic molecules. The calculated structures of the layers agree well with the available experimental results and suggest structures of some unexplored layers that would be interesting to fabricate. The calculated electronic structure and optical properties show that the absorption coefficient is high (∼105 cm–1) for the layers having heavily fluorinated spacer cations. Furthermore, we find higher stability and a desirable lower direct band gap for Sn-based green perovskite layers compared to the Pb counterparts. Our results provide computational insight into the surface engineering of RP perovskites for further developments in this fast-growing area.

Covalent Furan‐Benzimidazole‐Linked Polymer Hollow Fiber Membrane for Clean and Efficient Photosynthesis of Hydrogen Peroxide

AbstractPhotocatalytic H2O2 production by conversion of O2 in aqueous solution is often challenged by the use of sacrificial agents, the separation of powdery photocatalysts, solution, and contaminants, and low activity of photocatalyst. Herein, a membrane of covalent furan‐benzimidazole‐linked polymer (Furan‐BILP) with both O‐ and N‐containing heterocycles bonded via OCCN is reported for the first time as a photocatalyst to harvest clean H2O2 in pure water with high‐performance. A coordination‐polymer hard template strategy is developed to produce Furan‐BILP hollow microfibers that can be further assembled into membranes with desired sizes. The resultant Furan‐BILP membrane directly delivers clean H2O2 solution as the product with a high H2O2 production rate of 2200 µmol g−1 h−1 in pure water. Density functional theory calculations and experiment results indicate that the C atom from Furan ring on the linkage binds to the adsorbed OOH*, the H atom of OOH* forms a hydrogen bond with the N atom in the benzimidazole ring, thus the intermediate six‐membered ring structure stabilizes the OOH* and favors 2e‐ORR. The strategy using both molecular engineering to tune the electronic structure and macrostructural engineering to shape the morphology may be applied to design other coordination organic polymer photocatalysts with further improved performance.

Mitigating a Bioactivation Liability with an Azetidine-Based Inhibitor of Diacylglycerol Acyltransferase 2 (DGAT2) En Route to the Discovery of the Clinical Candidate Ervogastat.

We recently disclosed SAR studies on systemically acting, amide-based inhibitors of diacylglycerol acyltransferase 2 (DGAT2) that addressed metabolic liabilities with the liver-targeted DGAT2 inhibitor PF-06427878. Despite strategic placement of a nitrogen atom in the dialkoxyaromatic ring in PF-06427878 to evade oxidative O-dearylation, metabolic intrinsic clearance remained high due to extensive piperidine ring oxidation as exemplified with compound 1. Piperidine ring modifications through alternate N-linked heterocyclic ring/spacer combination led to azetidine 2 that demonstrated lower intrinsic clearance. However, 2 underwent a facile cytochrome P450 (CYP)-mediated α-carbon oxidation followed by azetidine ring scission, resulting in the formation of ketone (M2) and aldehyde (M6) as stable metabolites in NADPH-supplemented human liver microsomes. Inclusion of GSH or semicarbazide in microsomal incubations led to the formation of Cys-Gly-thiazolidine (M3), Cys-thiazolidine (M5), and semicarbazone (M7) conjugates, which were derived from reaction of the nucleophilic trapping agents with aldehyde M6. Metabolites M2 and M5 were biosynthesized from NADPH- and l-cysteine-fortified human liver microsomal incubations with 2, and proposed metabolite structures were verified using one- and two-dimensional NMR spectroscopy. Replacement of the azetidine substituent with a pyridine ring furnished 8, which mitigated the formation of the electrophilic aldehyde metabolite, and was a more potent DGAT2 inhibitor than 2. Further structural refinements in 8, specifically introducing amide bond substituents with greater metabolic stability, led to the discovery of PF-06865571 (ervogastat) that is currently in phase 2 clinical trials for the treatment of nonalcoholic steatohepatitis.

DFT simulation of the Raman spectrum of single layer graphene

Raman spectroscopy is one of the most suitable tools for studying few-layer graphene. The position of the G band and the defect-induced D and D' bands in the spectra of perfect single-layer graphene with sp2-hybridized carbon atoms and hydrogenated graphene with 27.7% sp3-hybridized carbon atoms are simulated using the Density Functional Theory (DFT) method with Perdew-Burke-Ernzerhof (PBE) functional. In the case of perfect graphene, the Raman G band is predicted at 1612 cm-1. In the case of the hydrogenated structure, a new feature appears. Namely, along with the G band, now shifted to 1591 cm-1, an additional feature, located at 1703 cm-1, is clearly seen. The latter is due to oscillations, involving six atomic benzene rings, containing two sp3-hybridized C atoms. According to our results, the presence of defects, related to sp3 hybridized carbon, gives rise to the appearance of the defect D' band in the Raman spectrum of defective graphene. This study shows that it is possible to simulate Raman spectra using the DFT method, with the results qualitatively matching the experimental data.

Origin of structure and stability of M@C18 (M = Cu, Ag, and Au) complexes with D9h point group.

Theoretical predictions and recent experimental studies lead to the discovery of an exciting new member of the carbon allotrope family polyynic cyclo[18]carbon (C18 ). Present investigation aims to probe the structure, stability, and properties of coinage metal (M)@C18 complexes using density functional theory (DFT) calculations. The DFT results unequivocally show that even Cu@C18 , Ag@C18 , and Au@C18 complexes substantially preserve the ground state polyynic structure of C18 . It is also worth to mention that only Au@C18 is a stable D9h structure, however the symmetry is distorted in the case of Cu@C18 and Ag@C18 . Due to computational limitations, in this investigation the M@C18 complexes were scrutinized using the C2v sub abelian group of D9h . The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of D9h conformers are a singlet a1 and two same value singlets a1 ⊕ b1 generated from doublet e, respectively. The non-covalent interaction index (NCI), quantum theory of atoms in molecule (QTAIM), and energy decomposition analysis (EDA) vividly explains the interaction between a coinage metal atom and C18 ring. It is found from the results that the stability of Cu@C18 Ag@C18 , and Au@C18 is governed by the attractive electrostatic, orbital and dispersion interaction.

Quantum-chemical study of the structure of amidinyltetramethoxycarbonylcyclopentadiene and its Hg(II) and Tl(I) complexes

DFT CAM-B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p)/SDD calculations showed that the polydentate amidinyltetramethoxycarbonylcyclopentadienyl ligand and its Hg(II) and Tl(I) complexes are the most stable in the form of ylide isomers, in which the hydrogen or metal atom is bonded to the terminal nitrogen atom of the amidinium fragment and in the case of metal complexes, it is additionally coordinated by the π -system of the cyclopentadiene ring. Alternative isomers in which hydrogen or metal atoms are bonded to carbon atoms of the cyclopentadiene ring or to carbonyl oxygen atoms of methoxycarbonyl substituents are energetically less stable at Δ E ZPE = 4.1-15.1 kcal/mol.

Photoinduced Long-Distance Hydrogen-Atom Transfer in Molecules with a 7-Hydroxyquinoline Frame and a Carbaldehyde or Aldoxime Group as the Intramolecular Hydrogen Transporting Crane.

The photochemical properties of monomeric 7-hydroxyquinoline substituted at position 8 with carbaldehyde or aldoxime groups were studied for the molecules isolated in solid Ar low-temperature matrices (at 10 K). It was experimentally demonstrated that upon UV excitation, both carbaldehyde and aldoxime groups act as intramolecular cranes transmitting hydrogen atoms from the hydroxyl group to the remote nitrogen atom of the quinoline ring. Furthermore, in the case of 7-hydroxyquinoline-8-aldoxime (and its derivatives), the second photochemical channel was activated upon UV (λ > 360 nm) excitation. This process involves syn-anti isomerization around the double C═N bond in the aldoxime group. The structures of the reactant hydroxy tautomeric form and the photoproduced isomers of the studied molecules were unequivocally determined by means of IR spectroscopy combined with theoretical predictions of the IR spectra of the candidate structures.

In Silico Optimization of Frizzled-8 Receptor Inhibition Activity of Carbamazepine: Designing New Anti-Cancer Agent.

Frizzled-8 (FZD8) receptor is a therapeutic target for cancer treatment and recent research has shown that carbamazepine (CBZ) can inhibit this receptor. In this work, it has been tried to optimize CBZ to enhance its binding capacity to the N6W binding site of FZD8 by using structure-based drug design methods. CBZ and its 83 derivatives were docked to the N6W binding site of FZD8. Docking results show that two compounds 79 and 82 have the smallest binding energies and are fitted to the N6W binding site. Compounds C79 and C82 have been synthesized by replacing a hydrogen atom of the seven-membered ring in CBZ with benzoate and nicotinate groups, respectively. In addition, docking results show that a trifluoromethyl on one of the phenyl rings is favorable for improving the FZD8 inhibition activity of the molecule. Both molecules C79 and C82 were subjected to molecular dynamics (MD) simulation. MD results show that FZD8-C82 complex is stable and this compound binds to the N6W binding site more strongly than compounds C79 and CBZ.

Study of the reaction mechanism based on the formation of the first carbocyclic ring from propargyl and diacetylene

The formation of the first carbon ring is a crucial rate-controlling step in developing polycyclic aromatic hydrocarbons (PAHs). It is vital to investigate the mechanism of the creation of the first carbon ring to inhibit the formation of PAHs. To explore the growth process of the first carbocyclic ring, this work used the average localized ionization energy (ALIE) and electrostatic potential (ESP) to predict the reaction sites. Moreover, the reaction paths and chemical kinetic parameters for the generation of the first carbocyclic ring from propargyl (C3H3) + diacetylene (C4H2) are calculated based on the density functional theory (DFT) method and transition state theory (TST). The results showed that the addition reaction of C3H3 +C4H2 can form five-, six- and seven-membered ring molecules, in which the five-membered ring formation is fastest and the six-membered ring formation is slowest. During the formation of the first carbon ring, the activation energy required for the H transfer and cyclization reactions is large, and the reaction rate is slow, which determines the formation rate of the first carbon ring. The rate of H-transfer reaction on each carbon ring depends on the number of C atoms of the carbon ring, with the five-membered ring being the fastest and the six-membered ring the slowest. This paper improves the reaction kinetics and thermodynamic data of the first carbon ring formation during the combustion of hydrocarbon fuels, which offers a powerful theoretical basis for predicting the generation of PAHs.

Phosphole aromaticity enhancement by electron pumping through Schleyer hyperconjugative aromaticity: A comprehensive DFT study

Combination of aromaticity and hyperconjugation as two fundamental concepts in organic chemistry results hyperconjugative aromaticity. Due to trigonal pyramidal P (III) atom in phosphole ring, it is only slightly more aromatic than cyclopentadiene. In the present work, the hyperconjugative aromaticity of phosphole derivatives, bearing an electron donating group, have been studied at the DFT-B3LYP/6–311++G(d, p) level of theory using various aromaticity indices such as geometric, magnetic, electronic and energetic criteria. Our DFT calculations reveal that an electropositive substituent can enhance phosphole aromaticity through Schleyer hyperconjugative aromaticity. This hyperconjugative electron donation by the substituents results in a partially anionic phosphole ring. Among the electropositive groups, silyl and germanium substituents have the best performance. The excellent correlations are observed between all aromaticity indices. Our findings could help chemists to design novel hyperconjugative aromatic phospholes.