Fundamental Chemical Concepts Research Articles

Highly Solvating Electrolytes with Core‐Shell Solvation Structure for Lean‐Electrolyte Lithium‐Sulfur Batteries

The practical energy density of lithium‐sulfur batteries is limited by the low sulfur utilization at lean electrolyte conditions. The highly solvating electrolytes (HSEs) promise to address the issue at harsh conditions, but the conflicting challenges of long‐term stability of radical‐mediated sulfur redox reactions (SRR) and the poor stability with lithium metal anode (LMA) have dimmed the efforts. We now present a unique core‐shell solvation structured HSE formulated with classical ether‐based solvents and phosphoramide co‐solvent. The unique core‐shell solvation structure features confinement of the phosphoramide in the first solvation shell, which prohibits severe contact reactions with LMA and endows prolonged stability for [S3]•– radical, favoring a rapid radical‐mediated solution‐based SRR. The cell with the proposed electrolyte showing a high capacity of 864 mA h gsulfur−1 under high sulfur loading of 5.5 mgsulfur cm−2 and low E/S ratio of 4 µL mgsulfur−1. The strategy further enables steady cycling of a 2.71‐A h pouch cell with a high specific energy of 307 W h kg−1. Our work highlights the fundamental chemical concept of tuning the solvation structure to simultaneously tame the SRR and LMA stability for metal‐sulfur batteries wherein the electrode reactions are heavily coupled with electrolyte chemistry.

Highly Solvating Electrolytes with Core-Shell Solvation Structure for Lean-Electrolyte Lithium-Sulfur Batteries.

The practical energy density of lithium-sulfur batteries is limited by the low sulfur utilization at lean electrolyte conditions. The highly solvating electrolytes (HSEs) promise to address the issue at harsh conditions, but the conflicting challenges of long-term stability of radical-mediated sulfur redox reactions (SRR) and the poor stability with lithium metal anode (LMA) have dimmed the efforts. We now present a unique core-shell solvation structured HSE formulated with classical ether-based solvents and phosphoramide co-solvent. The unique core-shell solvation structure features confinement of the phosphoramide in the first solvation shell, which prohibits severe contact reactions with LMA and endows prolonged stability for [S3]•- radical, favoring a rapid radical-mediated solution-based SRR. The cell with the proposed electrolyte showing a high capacity of 864 mA h gsulfur-1 under high sulfur loading of 5.5 mgsulfur cm-2 and low E/S ratio of 4 µL mgsulfur-1. The strategy further enables steady cycling of a 2.71-A h pouch cell with a high specific energy of 307 W h kg-1. Our work highlights the fundamental chemical concept of tuning the solvation structure to simultaneously tame the SRR and LMA stability for metal-sulfur batteries wherein the electrode reactions are heavily coupled with electrolyte chemistry.

Inferring the existence of hydrogen bonds directly from statistical analysis of molecular dynamics trajectories.

As a demonstration of how fundamental chemical concepts can be gleaned from data using machine learning methods, we demonstrate the automated detection of hydrogen bonds by statistical analysis of molecular dynamics trajectories. In particular, we infer the existence and nature of electrostatically driven noncovalent interactions by examining the relative probability of supramolecular configurations with and without electrostatic interactions. Then, using Laplacian eigenmaps clustering, we identify hydrogen bonding motifs in hydrogen fluoride, water, and methanol. The hydrogen bonding motifs that we identify support traditional geometric criteria.

Electronegativity Effects on Conformational Stability Using Bent's Rule: From Simple Molecules to Acetylcholine

Hybridization and electronegativity are fundamental concepts in chemistry connected by Bent's rule. This rule explains many aspects of the structural chemistry and reactivity of organic and inorganic compounds. Over decades, the application of Bent's rule has expanded, demonstrating its wide-ranging utility in elucidating molecular stability due to the substitution of highly electronegative atoms. This study successfully leverages Bent's rule to explain conformational energy difference in acetylcholine case using density-functional calculations. We used butane (Group 2) and butanone (Group 3) families to model the head of ACh+ and substituted one of the carbons with highly electronegative atoms: B, C, N, and O. This enabled us to evaluate the effects of electronegativity, as well as the presence of carbonyl groups, on their conformational stability and s character. There were three highlighted results. First, our calculations result in the s character are consistent with Bent's rule. Second, the high conformational energy differences can be attributed to the changes of s character in C2–Z bond: linear in Group 2 and exponential in Group 3, indicating the strong contribution of the carbonyl group. Third, the key determining factor in ACh+ conformational stability is the carbonyl group, which also strongly contributes to the solute-solvent interactions. Therefore, our study can be further applied to other similar molecules, potentially leading to broader applications in chemistry, especially for understanding ACh+ stability for Alzheimer’s Disease treatment.

Can Aromaticity Be Evaluated Using Atomic Partitions Based on the Hilbert-Space?

Aromaticity is a fundamental concept in chemistry that explains the stability and reactivity of many compounds by identifying atoms within a molecule that form an aromatic ring. Reliable aromaticity indices focus on electron delocalization and depend on atomic partitions, which give rise to the concept of an atom-in-the-molecule (AIM). Real-space atomic partitions present two important drawbacks: a high computational cost and numerical errors, limiting some aromaticity measures to medium-sized molecules with rings up to 12 atoms. This restriction hinders the study of large conjugated systems like porphyrins and nanorings. On the other hand, traditional Hilbert-space schemes are free of the latter limitations but can be unreliable for the large basis sets required in modern computational chemistry. This paper explores AIMs based on three robust Hilbert-space partitions - meta-Löwdin, Natural Atomic Orbitals (NAO), and Intrinsic Atomic Orbitals (IAO) - which combine the advantages of real-space partitions without their disadvantages. These partitions can effectively replace real-space AIMs for evaluating the aromatic character. For the first time, we report multicenter index (MCI) and Iring values for large rings and introduce ESIpy, an open-source Python code for aromaticity analysis in large conjugated rings.

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.

Low-lying LUMO Boosts Conductance in Antiaromatic Dibenzopentalene Versus Aromatic Analogues.

Antiaromaticity is a fundamental concept in chemistry, but the study of molecular wires incorporating antiaromatic units is limited. Despite initial predictions, very few studies show that antiaromaticity has a beneficial effect on electron transport. Dibenzo[a,e]pentalene (DBP) is a stable structure that displays appreciable antiaromaticity within the five-membered rings of the pentalene core. We have investigated derivatives of DBP furnished with pyridyl (Py) and F4-pyridyl (PyF4) anchor groups, and compared the conductance with purely aromatic phenyl and anthracene analogues. We find that the low-bias conductance of DBP-Py is approximately 60 % larger than that of the anthracene analogue Anth-Py and 250 % larger compared to the phenyl derivative Ph-Py. This is due to a better alignment of the LUMO with the gold Fermi level, which we confirm by conductance-voltage spectroscopy where the conductance of DBP-Py shows the greatest voltage-dependence. The F4-pyridyl compounds, which have lower LUMO energies compared to the pyridyl analogues, did not, however, form detectable molecular junctions. The strongly electron-withdrawing fluorine atoms reduce the donor capability of the nitrogen lone-pair to the point where stable N-Au bonds no longer form.

Game-based learning in metaverse: Virtual chemistry classroom for chemical bonding for remote education

AbstractVirtual classrooms based on the metaverse or virtual reality are useful and effective for imparting basic chemistry concepts. Interactive and immersive environments can effectively teach fundamental chemistry concepts, such as chemical bonding and formulas, thereby making these otherwise abstract and intangible ideas more accessible and understandable. With the outbreak of Covid-19, e-learning platforms have also been developed for chemistry education. However, these platforms are unable to make learning chemistry interactive and enjoyable. Therefore, there is a need to motivate students to learn basic chemistry concepts in an immersive and interactive environment. In this paper, we propose an immersive virtual reality-based Virtual Chemistry Classroom for Chemical Bonding (VC3B) to facilitate the learning of chemical bonding and formulas through a game-based learning approach. It includes two different games for learning chemical bonding and formulas. In the first game, molecule construction, students reconstruct the structure of molecules by rearranging the atoms in order to learn about chemical bonding. In the second game, chemical formula, students compose the chemical formula of a given compound to help them memorize chemical formulas. The study, conducted on 90 middle school students, employed a randomized controlled study design, dividing participants into three groups. Each group learned about chemical bonding and formulas through three different mediums. After conducting the experiment, the students were given a questionnaire to evaluate the usability of VC3B. The results of the study were positive, with participants finding the VC3B to be more interactive than traditional book and online lecture methods. Participants were also motivated to learn and enhance their knowledge of chemistry.

Linking Waterbody Acidification and Aquatic Plant Metabolism: A Lesson Plan for Middle School Students

Ocean acidification, the lowering of seawater pH due to increased concentrations of carbon dioxide in the atmosphere, is an emerging environmental challenge associated with climate change. This publication is intended for Florida grade eight educators and other environmental educators of middle school students. We designed a lesson plan to reinforce fundamental concepts in acid-base chemistry, including the pH scale, and to introduce students to waterbody acidification, its negative effects on shell-forming organisms, and the potential role of aquatic plant metabolism (i.e., photosynthesis and respiration) in mitigating these effects. The goal of the lesson plan is to encourage students to link water chemistry and biological processes while learning about the challenges and potential solutions to acidification within a local context. This lesson plan will contribute to state learning standards while generating appreciation for the complexity of the natural environment.

An Analysis of Copper Enrichment on a Gold Electrocatalyst as a Method of Syngas Synthesis from CO2

This literary review examines the work of a distinguished research team from the University of Berkeley and the University of Toronto. The work in question was a key paper in the global search within the scientific community to find a solution to the excess of fossil fuels within the atmosphere. Specifically, this research team’s focus was the electrochemical reduction of carbon dioxide to hydrogen gas and carbon monoxide. This review offers a fundamental standpoint, honing in on a specific technique that is cutting-edge in terms of technology, research, and methodology, while also being broadly applicable. The technique includes the use of a gold (Au) electrode precisely coated with a copper (Cu) monolayer, which (altogether) serves as the electrocatalyst powering the reaction. Techniques like Raman spectroscopy and cyclic voltammetry, coupled with concepts such as Molecular Orbital Theory, helped to explain the inner workings of the carbon dioxide reduction reaction. This study demonstrated that changing the amount of Cu deposited onto a Au surface affected the produced hydrogen gas (H2) to carbon monoxide (CO) ratio. This review also considered the appropriateness of Raman spectroscopy, and whether or not it was the best technical choice given the context of this experiment. Altogether, this review uses fundamental concepts in chemistry to analyze a new method of reducing carbon dioxide, an electrochemical process that is growing increasingly relevant in today’s efforts to reduce fossil fuel emissions.

Chemical bonding misnomer in AeF- (Ae = Be-Ca) anions.

Chemical bonding is the fundamental concept in chemistry and multiple bonding holds a special position. Recent quantum chemical calculations predicted the presence of triple dative bonds in BeF- and MgF- and quadruple dative bonds in CaF- anions. The present quantum chemical calculations based on quantum theory of atoms in molecules (QTAIM), electron localization function (ELF) and adaptive density partitioning (AdNDP) analyses find no sign of multiple dative bonding in these anions. In fact, the bond is actually an electron-sharing covalent one, rather than dative. Charge distribution analysis and comparison with a neutral AeF molecule reveal no difference in bonding between the neutral AeF molecule and its anion.

Spin population determines whether antiaromaticity can increase or decrease radical stability.

Aromaticity, as a classical and fundamental concept in chemistry, can enhance thermodynamic stability. In sharp contrast, a previous study showed that antiaromaticity rather than aromaticity can enhance the radical stability of α-methyl heterocyclic compounds. Here, we demonstrate a similar antiaromaticity-promoted radical stability when the methyl group is replaced by five-membered (alkyl)(amino)cyclics (AACs). More interestingly, when an AAC is fused with an antiaromatic ring, the radical stability could be either reduced or enhanced, depending on the spin population. Specifically, when the spin density is populated on an incoming antiaromatic 1,4-dihydro-1,4-diborinine moiety, the radical stability is enhanced whereas when the spin density is maintained on the original five-membered ring, the radical stability is reduced. Our findings highlight the importance of spin density in tuning the radical stability, inviting experimental chemists' verification.

High-pressure stabilization of open-shell bromine fluorides.

Halogen fluorides are textbook examples of how fundamental chemical concepts, such as molecular orbital theory or the valence-shell electron-repulsion (VSEPR) model, can be used to understand the geometry and properties of compounds. However, it is still an open question whether these notions are applicable to matter subject to high pressure (>1 GPa). In an attempt to gain insight into this phenomenon, we present a computational study on the phase transitions and reactivity of bromine fluorides at pressures of up to 100 GPa (≈106 atm). We predict that at a moderately high pressure of 15 GPa, the bonding preference in the Br/F system should change considerably with BrF3 becoming thermodynamically unstable and two novel compounds emerging as stable species: BrF2 and BrF6. Calculations indicate that both these compounds contain radical molecules while being non-metallic. We propose a synthetic route for obtaining BrF2 which does not require the use of highly reactive elemental fluorine. Finally, we show how molecular orbital diagrams and the VSEPR model can be used to explain the properties of compressed bromine fluorides.

Ein Lernposter zum Aufbau von Reinstoffen

Pure chemical substances present a clearly defined area for teaching in which fundamental chemistry concepts can be treated didatically. However, the multitude of concepts involved can easily lead to misunderstandings. A graphical visualisation is presented that can help the students to understand the structure and the scope of the different concepts.

Phase-Dependence of Molecular Structures Arising from Weak London Dispersion Interactions.

ConspectusThe structures of molecules can be different in different phases. Intermolecular forces, even those of weak noncovalent interactions (WNCIs), can lead to a preference for quite different conformations in the solid, the gas, and the liquid phases. WNCIs can cause variations in bond lengths, angles, and torsional angles. Since structure is a fundamental concept in chemistry, the knowledge of structural changes with phase is important to understand the source and effects of distorting contributions from WNCIs but also as a predictive tool for the design and stabilization of new bonding situations.X-ray crystallography is ubiquitous and now mostly straightforward to perform, but facilities for the determination of accurate gas-phase structure determination are rare, and gas-phase work is laborious and time-consuming. There are currently about 1.25 million crystal structures and more than 12 500 experimental gas-phase structures, but the intersection of the two data sets that can tell us about the structural differences of the same molecule in different phases is surprisingly small.In this Account, we describe several cases of WNCI-dominated systems for which accurate experimental structure determinations exist for both the gas phase and the solid state and, in one case, also for solution. The examples include aryl-aryl, aryl-alkyl, and alkyl-alkyl interactions; systems with chalcogen and halogen bonding; and fluorine-based interactions in arylboranes. We work out the role of WNCIs in stabilizing large, strained, or sterically overloaded molecules. We will show how flexible molecules will fold under the action of WNCIs when isolated in the gas and how they fold or unfold when they are embedded in an environment of neighbors in crystals. We will show how they can vary in strength when the substitution patterns in aryl groups are changed by different halogens and how intramolecular WNCIs, such as those forming rings, change when such systems experience additional intermolecular WNCIs.Overall, we hope that this Account will give the reader an idea of the type and magnitude of structural changes that can be expected from a free molecule in the gas phase or a single molecule calculated by quantum chemistry compared with one embedded in a crystal. This should define the limits of comparability and provide some predictive concepts of the distortions and variations to be expected.

Experimental teaching of the Avogadro constant

Although Avogadro’s number is a fundamental concept in chemistry, it is often overlooked in secondary education textbooks in Greece. Students are taught about mol, the number Avogadro, the molar volumes, and the equation of the state of gases. However, in no case is a detailed examination held about the importance of this number and the connection of macroscopic and microscopic quantities through the Avogardo constant. Also, the references related to the topic fail to raise students’ awareness of the atomic and molecular structure and the procedure with which the matter becomes quantic. Furthermore, the experimental approach is non-existent. To address these shortcomings, this project proposes a new and straightforward experimental method for students to determine the value of Avogadro’s number. The carefully designed experimental procedure can be completed within one teaching hour, encouraging active student participation. More importantly, the proposed experimental setup does not require sophisticated instruments and poses no risks, making it feasible for students to conduct it themselves.

A Simple Method for Teaching Bragg’s Law in an Undergraduate Teaching Laboratory with the Use of Metal–Organic Frameworks

Metal–organic frameworks (MOFs) are a class of porous materials that are often crystalline with high surface area and structural tunability. In this laboratory experiment designed for inorganic chemistry students at the undergraduate level, students complete a two-step experiment where they will first (i) synthesize two isostructural zirconium-based MOFs, UiO-66 and UiO-67, and then (ii) isolate and characterize the materials using powder X-ray diffraction (PXRD). A simple solvothermal procedure was developed for the synthesis of UiO-66 and UiO-67 using the air/moisture-stable zirconyl chloride octahydrate as a starting reagent. Depending on the equipment available, the MOFs can be further characterized by nitrogen adsorption analysis for surface area determination using Brunauer–Emmett–Teller (BET) theory, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermogravimetric analysis (TGA), 1H nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM). Upon synthesizing the MOFs and collecting the characterization data, students analyze and describe their results by answering a series of questions included in the laboratory manual. This exercise will allow students to develop practical laboratory skills while expanding their knowledge on some fundamental concepts in inorganic chemistry, materials chemistry, MOFs, crystallography, and other characterization techniques as availability allows.

On how some fundamental chemical concepts are correlated by arithmetic, geometric and harmonic means

On how some fundamental chemical concepts are correlated by arithmetic, geometric and harmonic means

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.

Assessment of the performance of six indices in predicating the aromaticity of planar porphyrinoids.

Aromaticity is a fundamental chemical concept that has been widely used in explaining the reactivity, stability, structure, and magnetic properties of many molecules such as conjugated macrocycles, metal heterocyclic compounds, and certain metal clusters. Porphyrinoids (including porphyrin) are of particular interest in terms of diverse aromaticity. Various indices therefore have been used to predict the aromaticity of porphyrin-like macrocycles. However, the reliability of these indices for porphyinoids is always questionable. In order to assess the performance of the indices, we have selected six representative indices to predict the aromaticity of 35 porphyrinoids. The calculated values were then compared with the corresponding results obtained from experiments. Our studies suggest that the theoretical prediction by nucleus independent chemical shifts (NICS), topology of the induced magnetic field (TIMF), anisotropy of the induced current density (AICD), and gauge including magnetically induced current method (GIMIC) are essentially consistent with experimental evidence in all 35 cases and thus are preferred indices. Based on density functional theory, the performance of the NICS, TIMF, AICD, GIMIC, harmonic oscillator model of aromaticity (HOMA), and multicenter bond order (MCBO) indices were evaluated theoretically. Molecular geometries were optimized at the M06-2X/6-311G** level. NMR calculations using GIAO or CGST method were performed at the M06-2X/6-311G** level. The above calculations were carried out using Gaussian16 suite. The TIMF, GIMIC, HOMA, and MCBO indices were obtained using the Multiwfn program. The AICD outputs were visualized using the POV-Ray software.