Ring Strain Research Articles

Expansion of Structure Property in Cascade Nazarov Cyclization and Cycloexpansion Reaction to Diverse Angular Tricycles and Total Synthesis of Nominal Madreporanone.

A cascade Nazarov cyclization/dicycloexpansions reaction was developed for the precise synthesis of the angularly fused M/5/N (M=5, 6; N=4-9, 13) tricyclic skeletons. The prioritized expansion of the first ring played a critical role in the transformations, due to the release of ring strain, and the nature of the substituents present on the substrate is another influencing factor. This pioneering cascade reaction features broad substrates scope (33 examples), short reaction time, exceptional yields (up to 95 %), and remarkable regioselectivities (>20 : 1). Exploiting the synthetic application of this cascade reaction, we successfully executed a succinct total synthesis of nominal madreporanone for the first time.

Bending deformation effects on the optoelectronic performance of flexible GaInP/GaAs/InGaAs triple junction solar cells

To achieve genuine carbon neutrality, PV-powered vehicles show promise for future automotive development. However, the impact of curved surfaces on flexible solar cell module performance remains uncertain. This study specifically focuses on newly-designed flexible GaInP/GaAs/InGaAs triple junction solar cells, which have the highest potential output efficiency. A computational model was developed to analyze the electrical performance of curved solar cells, and variations in short-circuit current (Isc) and open-circuit voltage (Voc) with bending angles were determined to closely match experimental data. The effects of incident light intensity, angle, and bending strain on solar cell performance were analyzed to explain the observed Isc and Voc trends. This method can be applied to other III-V group solar cells, providing theoretical support for accurately calculating the performance of curved solar cell modules.

Selective Methylation of Cyclic Ether Towards Highly Elastic Solid Electrolyte Interphase for Silicon-based Anodes.

Silicon (Si)-based anodes offer high theoretical capacity for lithium-ion batteries but suffer from severe volume changes and continuous solid electrolyte interphase (SEI) degradation. Here, we address these challenges by selective methylation of 1,3-dioxolane (DOL), thus shifting the unstable bulk polymerization to controlled interfacial reactions and resulting in a highly elastic SEI. Comparative studies of 2-methyl-1,3-dioxolane (2MDOL) and 4-methyl-1,3-dioxolane (4MDOL) reveal that 4MDOL, with its larger ring strain and more stable radical intermediates due to hyperconjugation effect, promotes the formation of high-molecular-weight polymeric species at the electrode-electrolyte interface. This elastic, polymer-rich SEI effectively accommodates volume changes of Si and inhibits continuous side reactions. Our designed electrolyte enables Si-based anode to achieve 85.4% capacity retention after 400 cycles at 0.5 C without additives, significantly outperforming conventional carbonate-based electrolytes. Full cells also demonstrate stable long-term cycling. This work provides new insights into molecular-level electrolyte design for high-performance Si anodes, offering a promising pathway toward next-generation lithium-ion batteries with enhanced energy density and longevity.

Selective Methylation of Cyclic Ether Towards Highly Elastic Solid Electrolyte Interphase for Silicon‐based Anodes

Silicon (Si)‐based anodes offer high theoretical capacity for lithium‐ion batteries but suffer from severe volume changes and continuous solid electrolyte interphase (SEI) degradation. Here, we address these challenges by selective methylation of 1,3‐dioxolane (DOL), thus shifting the unstable bulk polymerization to controlled interfacial reactions and resulting in a highly elastic SEI. Comparative studies of 2‐methyl‐1,3‐dioxolane (2MDOL) and 4‐methyl‐1,3‐dioxolane (4MDOL) reveal that 4MDOL, with its larger ring strain and more stable radical intermediates due to hyperconjugation effect, promotes the formation of high‐molecular‐weight polymeric species at the electrode‐electrolyte interface. This elastic, polymer‐rich SEI effectively accommodates volume changes of Si and inhibits continuous side reactions. Our designed electrolyte enables Si‐based anode to achieve 85.4% capacity retention after 400 cycles at 0.5 C without additives, significantly outperforming conventional carbonate‐based electrolytes. Full cells also demonstrate stable long‐term cycling. This work provides new insights into molecular‐level electrolyte design for high‐performance Si anodes, offering a promising pathway toward next‐generation lithium‐ion batteries with enhanced energy density and longevity.

Single‐Molecule Conductance of Staffanes

We report the first conductance measurements of [n]staffane oligomers in single‐molecule junctions. Our studies reveal two quantum transport characteristics unique to staffanes that emerge from their strained bicyclic structure. First, though staffanes are composed of weakly conjugated C‐C σ‐bonds, staffanes carry a shallower conductance decay value (β = 0.84 ± 0.02 n‐1) than alkane chain analogs (β = 0.96 ± 0.03 n‐1) when measured with the scanning tunneling microscopy break junction (STM‐BJ) technique. Staffanes are more conductive than other σ‐bonded organic backbones in the literature on a per atom basis. Density functional theory calculations suggest staffane backbones are effective conduits for charge transport because their significant bicyclic ring strain destabilizes the HOMO‐2 energy, aligning it more closely with the Fermi energy as oligomer order increases. Second, the monostaffane is significantly lower conducting than expected. DFT calculations suggest that short monostaffanes sterically enforce insulating gauche interelectrode orientations over syn orientations. Meanwhile, [2‐5]staffane wires may accommodate axial mechanical strain by “rod‐bending”. These findings show for the first time how bicyclic ring strain can enhance charge transmission in saturated molecular wires. These studies showcase the STM‐BJ technique as a valuable tool for uncovering the stereoelectronic proclivities of molecules at material interfaces.

Single-Molecule Conductance of Staffanes.

We report the first conductance measurements of [n]staffane oligomers in single-molecule junctions. Our studies reveal two quantum transport characteristics unique to staffanes that emerge from their strained bicyclic structure. First, though staffanes are composed of weakly conjugated C-C σ-bonds, staffanes carry a shallower conductance decay value (β = 0.84 ± 0.02 n-1) than alkane chain analogs (β = 0.96 ± 0.03 n-1) when measured with the scanning tunneling microscopy break junction (STM-BJ) technique. Staffanes aremore conductive than other σ-bonded organic backbones in the literature on a per atom basis. Density functional theory calculations suggest staffane backbones are effective conduits for charge transport because their significant bicyclic ring strain destabilizes the HOMO-2 energy, aligning it more closely with the Fermi energy as oligomer order increases. Second, the monostaffane is significantly lower conducting than expected. DFT calculations suggest that short monostaffanes sterically enforce insulating gauche interelectrode orientations over syn orientations. Meanwhile,[2-5]staffane wires may accommodate axial mechanical strain by "rod-bending". These findings show for the first time how bicyclic ring strain can enhance charge transmission in saturated molecular wires. These studies showcase the STM-BJ technique as a valuable tool for uncovering the stereoelectronic proclivities of molecules at material interfaces.

Bending and shear strengthening of timber beams using prestressed steel and composite bars – experimental and numerical studies

The paper describes a program of experimental and numerical tests aimed at determining the mechanical properties of beams made of laminated timber (BSH) and laminated veneer lumber (LVL) reinforced with pre-stressed bars made of basalt, glass, natural and steel fibers, basalt mats with roving and composite, polyethylene and natural yarn. The paper presents various types of reinforcements, the purpose of which was to obtain higher load-bearing capacity and stiffness in bending with shear than for unreinforced beams. The effectiveness of different reinforcement schemes was compared for seventeen beams subjected to experimental tests on a test stand, the modes of destruction were described, as well as mechanical properties, deformations and deflections for reinforced and unreinforced beams under multiply variable and long-term loading. Based on the experimental studies, a significant increase in the load-bearing capacity and stiffness of the reinforced beams subjected to simultaneous bending and shear was confirmed, and it was indicated that the reinforcements by pre-stressed bars (steel, with polymer reinforcement or natural fibers) and composite mats eliminated local defects and discontinuities in the wood, without affecting the quality and strength of the FRP-wood connection. The numerical results of the analysis of the beam models using the finite element method showed compliance with the experimental studies in terms of deflections, linear and angular strains for the reinforced and unreinforced beams

Allylic Epoxides Increase the Strain Energy of Cyclic Olefin Monomers for Ring-Opening Metathesis Polymerization.

Ring-opening metathesis polymerization (ROMP) is an effective method for synthesizing functional polymers, but since the technique typically relies on high ring strain cyclic olefins, the most common monomers are norbornene derivatives. The reliance on one class of monomer limits the obtainable properties of ROMP polymers. In this work, we investigate new bicyclic monomers synthesized via epoxidation of commercial dienes. DFT estimates of these monomers' ring strains suggests a significant increase in strain for cyclic olefins containing allylic epoxides. We found that the eight-membered (3,4-COO) and five-membered (CPO) cyclic olefins were particularly effective for ROMP. CPO was of especially intriguing due to its excellent polymerizability when compared to the limited reactivity of other five-membered rings. Unlike polynorbornenes, the resulting polymers of both monomers displayed glass transition temperatures well below room temperature. Interestingly, poly(3,4-COO) showed both high stereo- and regioregularity while poly(CPO) showed little regularity. Both polymers could be readily modified via post-polymerization ring-opening of the reactive allylic epoxides. With a high epoxide density in poly(CPO), CPO is an exciting new ROMP monomer that is easily synthesized, can be polymerized to high conversion at room temperature, and may be facilely modified to yield a wide range of functional materials.

Allylic Epoxides Increase the Strain Energy of Cyclic Olefin Monomers for Ring‐Opening Metathesis Polymerization

Ring‐opening metathesis polymerization (ROMP) is an effective method for synthesizing functional polymers, but since the technique typically relies on high ring strain cyclic olefins, the most common monomers are norbornene derivatives. The reliance on one class of monomer limits the obtainable properties of ROMP polymers. In this work, we investigate new bicyclic monomers synthesized via epoxidation of commercial dienes. DFT estimates of these monomers’ ring strains suggests a significant increase in strain for cyclic olefins containing allylic epoxides. We found that the eight‐membered (3,4‐COO) and five‐membered (CPO) cyclic olefins were particularly effective for ROMP. CPO was of especially intriguing due to its excellent polymerizability when compared to the limited reactivity of other five‐membered rings. Unlike polynorbornenes, the resulting polymers of both monomers displayed glass transition temperatures well below room temperature. Interestingly, poly(3,4‐COO) showed both high stereo‐ and regioregularity while poly(CPO) showed little regularity. Both polymers could be readily modified via post‐polymerization ring‐opening of the reactive allylic epoxides. With a high epoxide density in poly(CPO), CPO is an exciting new ROMP monomer that is easily synthesized, can be polymerized to high conversion at room temperature, and may be facilely modified to yield a wide range of functional materials.

Synthesis of silacycles via metal hydrogen atom transfer and radical-polar crossover mechanism

In this study, we have developed an efficient method for silacycle synthesis using metal hydride hydrogen atom transfer (MHAT) and radical-polar crossover (RPC) mechanism. Allylic silanols were synthesized via one-step condensation and then cyclized under mild conditions using N-fluoropyridinium tetrafluoroborate (Me3NFPY·BF4) as the oxidant under cobalt catalysis. This approach yielded five-, six-, and seven-membered silacycles with high selectivity, with the six-membered rings being the favored products. Density functional theory (DFT) calculations provided valuable insights into the reaction mechanisms and highlighted the role of ring strain in determining product selectivity. This study demonstrated the effectiveness of combining MHAT/RPC methodologies with silicon tethering, thus offering a robust platform for expanding the use of silicon-based strategies in synthetic chemistry.

From Cyclopropene to Housane Derivatives Via Intramolecular Cyclopropanation.

The synthesis of housanes derivatives from cyclopropenes is described. Under rhodium(II) catalysis, cyclopropenylvinyl carbinols can regioselectively generate a carbene intermediate which undergo an intramolecular cyclopropanation to form a housane, a skeleton with similar ring strain as the cyclopropene precursor. The procedure shows a remarkable broad scope and efficiency. Moreover, the method served to prepare man-made housane-containing terpene derivatives, which are not accessible by Nature.

Strain-Release-Driven Electrochemical Skeletal Rearrangement of Non-Biased Alkyl Cyclopropanes/butanes.

Capitalizing the inherent strain energy within molecules, strain-release-driven reactions have been widely employed in organic synthesis. Small cycloalkanes like cyclopropanes and cyclobutanes, with their moderate ring strain, typically require dense functionalization to induce bias or distal activation of (hetero)aromatic rings via single-electron oxidation for relieving the tension. In this study, we present a pioneering direct activation of alkyl cyclopropanes/butanes through electrochemical oxidation. This approach not only showcases the potential for ring-opening of cyclopropane/butane under electrochemical conditions but also streamlines the synthesis of diverse oxazolines and oxazines. The applicability of our method is exemplified by its broad substrate scopes. Notably, the products derived from cyclobutanes undergo a formal ring contraction to cyclopropanes, introducing an intriguing aspect to our discoveries. These discoveries mark a significant advancement in strain-release-driven skeletal rearrangement reactions of moderately strained rings, offering sustainable and efficient synthetic pathways for future endeavours.

Ligand-Controlled Enantioselective and Regiodivergent Construction of 1,2- and 1,3-Disubstituted Alicycles.

Three-dimensional alicyclic skeletons with multiple stereochemically defined chiral centers are highly valuable in modern drug discovery. Here, we reported a diverse approach to access 1,2- and 1,3-disubstituted chiral cycloalkanes by the strategy of NiH-catalyzed, transannular-directed alkene desymmetrization. The ring strain of the bridged bicyclic organonickel intermediate and the coordination effect of the ligand were identified as crucial factors in determining site selectivity by influencing the NiH migration step. This methodology demonstrates a broad substrate scope and displays good tolerance toward various functional groups, resulting in excellent outcomes in terms of the yield, regioselectivity, and enantioselectivity.

The origin of selectivity in the trimerization of 1,3-cyclopentadiene from an activation strain perspective.

Quantum chemical modeling (DFT-PBE0/cc-pVTZ) of the [4 + 2]-cycloaddition reaction of 1,3-cyclopentadiene (CPD) to (exo/endo)-dicyclopentadiene (DCPD) was carried out, resulting in 14 products-CPD trimers. According to calculations, exo-addition of CPD to the norbornene (NB) fragment of DCPD and trans-addition of CPD to the cyclopentene (CP) fragment of DCPD are kinetically preferred. Ring strain energies ERS were calculated for all trimers using the homodesmotic reaction approach. The least strained trimers are formed by exo-addition of CPD to the NB fragment of exo-DCPD, while the most strained ones are formed by endo-addition of CPD to the NB fragment of endo-DCPD. ERS values are in good agreement with thermodynamic stability of trimers. Analysis of activation energy using the activation strain model showed steric effects causing deformation of the DCPD molecule upon reaching the transition state to be the leading factor of the magnitude of the cycloaddition reaction activation barrier. Deformation of the DCPD molecule mostly occurs in two dihedral angles-the angle of escape of H atoms from the plane of the double bond involved in cycloaddition and the angle between the NB and CP fragments. The sum of deviations of these angles in the transition states (or products) structures is in good agreement with Gibbs activation energies of cycloaddition reactions of CPD to DCPD. Quantum chemical calculations were carried out using density functional theory in Gaussian 09 software. Hybrid exchange-correlation PBE0 functional was used with cc-pVTZ basis set.

High Molecular Weight Semicrystalline Substituted Polycyclohexene From Alternating Copolymerization of Butadiene and Methacrylate and Its Ambient Depolymerization.

Cyclohexene cannot be polymerized via ring-opening polymerization under any conditions due to its lack of ring strain. A hypothetical polycyclohexene would therefore have a strong thermodynamic driving force to depolymerize to monomer if a metathesis catalyst were provided while otherwise having thermal and hydrolytic stability under normal conditions because of its hydrocarbon backbone. We envisioned access to this otherwise unattainable family of polymers via the alternating polymerization of a diene and an alkene. Ethyl aluminum chloride was found to promote highly alternating polymerization of butadiene and methacrylate when radically initiated at room temperature, resulting in formal polycyclohexene structures. Ultrahigh molecular weight (up to 1750 kDa) polymers can be synthesized at the decagram scale in high monomer conversions. The resulting presumably atactic copolymers exhibited semicrystallinity, leading to high toughness. In the presence of a small amount of the Grubbs catalyst, the generated polycyclohexene can be fully depolymerized at ambient temperatures into pure constituent cyclohexene. The strategy of using orthogonal chemistry for the polymerization and depolymerization processes allows access to polymer structures with subambient ceiling temperatures without using ultralow temperature synthesis or relying on the monomer-polymer equilibrium.

A computational insight to an old concept: The Mills–Nixon effect

The Mills-Nixon (MN) effect in trisannelated benzenes (1–10) is analyzed by Wiberg bond order (WBO), bond lengths alteration (ΔBL), Nucleus Independent Chemical (NICS), Harmonic Oscillator Model of Aromaticity (HOMA), and Localized orbital locator (LOL) analyses in B3LYP/6–311++G (d,p) level of theory. Coulomb repulsion, antiaromatic instability, angle strain and ring strain were the significant factors in the MN effect creation in the studied structures. The obtained results showed that the aromaticity is decreased in the benzene ring is in the 8 > 9 > 3 > 1 > 7 > 2 > 6 > 5 > 10 > 4 order and the strongest MN effect is seen in structure 4.

Terpenoid Cyclophanes with Planar Chirality.

The strain-induced chirality of cyclophanes has attracted interest within the synthetic community. Herein, we report the synthesis of anilinocyclophanes derived from naturally occurring terpenes, such as citronellol, geraniol, and farnesol. The resulting cyclic oligoprenyl molecules exhibit considerable ring strain (up to 31 kcal/mol), as evident from their bent aniline planes, and possess chirality across the planes of an aryl ring and double bonds. Unexpected outcomes, such as the formation of isomerized neraniline, highlight the influence of ring strain on the stability and reactivity of terpenoid para-cyclophanes.

An Exopolysaccharide from the Cyanobacterium Arthrospira platensis May Utilize CH-π Bonding: A Review of the Isolation, Purification, and Chemical Structure of Calcium-Spirulan.

The CH-π bonding potential of a saccharide is determined primarily by the number of hydrogen atoms available for bonding and is reduced by side groups that interfere with the CH-π bond. Each hydrogen bond increases the total bond energy, while interfering hydroxyl groups and other side groups reduce the bond energy by repulsion. The disaccharide repeating units of Calcium-Spirulan (Ca-SP), a large exopolysaccharide sub fractionated from the supernatant of the cyanobacterium Arthrospira platensis, contain a unique monosaccharide that is completely devoid of hydroxyl groups and side groups on its entire beta surface, leaving five hydrogen atoms available for CH-π bonding in the planar conformation. While planar conformations of independent pyranose rings are rare-to-nonexistent, due to ring strain associated with that conformation, the binding site of a protein could provide the conformational energy needed to overcome that energy barrier. By enabling a planar conformation, a protein could also enable the sugar to form a novel 5-hydrogen CH-π bond configuration. One study of the anticoagulant property of Ca-SP shows that the molecule acts as an activator of Heparin Cofactor II (HC-II), boosting its anticoagulant kinetics by 104. In comparison, the longstanding anticoagulant drug Heparin boosts the HC-II kinetics by 103. The difference may be explained by this unique CH-π configuration. Here, we review current knowledge and experience on the isolation techniques, analytical methods, and chemical structures of Ca-SP. We emphasize a discussion of the CH-π bonding potential of this unique polysaccharide because it is a topic that has not yet been addressed. By introducing the topic of CH-π bonding to the cyanobacterial research community, this review may help to set the stage for further investigation of these unique molecules, their genetics, their biosynthetic pathways, their chemistry, and their biological functions.

Trends in the Reactivity of Pentacyclic Ether Derivatives on Silicon and Germanium Surfaces Revealed by Energy Decomposition Analysis for Extended Systems

We analyze the adsorption and ring‐opening reaction of pentacyclic chalcogen alkyls with chalcogen atoms ranging from oxygen to tellurium using computational analysis. Thus extends our previous investigation of THF on silicon towards germanium surface and towards the heavier chalcogen homologues. We found an increasing dative bond strength of the precursor state with the period of the chalcogen atom on both surfaces. Using energy decomposition analysis for extended systems (pEDA), differences in the trends between silicon and germanium were revealed. Following the dative bound state, subsequent ring‐opening reactions were found to proceed via a nucleophilic back‐side attack, similar to a molecular SN2 reaction. Reaction energies and barrier heights show a maximum for the sulfur derivative. This trend was found to correlate with the position of the transition state in the reaction and agrees with the molecular reactivity. The uniquely low barrier of THF can be attributed to its ring strain. Our findings shed light on the fundamental aspects of surface chemistry and the benefits of using quantitative bonding analysis in this field. It also paves the way for future explorations into the functionalization of semiconductor surfaces using higher‐period ether derivatives.

Stepwise Photochromism of Large Macrocycles Incorporating Two Negative Photochromic Units.

Macrocyclic photochromic molecules incorporating multiple photochromic units are known to exhibit cooperative and nonlinear photochromic reactions among distinct photochromic components. While extensive research has concentrated on positive photochromic molecules, this study presents a pioneering attempt in synthesizing macrocyclic photochromic molecules that integrate negative photochromic units. Binaphthyl-bridged phenoxyl imidazolyl radical complex, BN-PIC, exhibits unique negative photochromism in which the thermally stable colored isomer converts to the metastable colorless isomer via a short-lived biradical upon visible-light irradiation. Macrocyclic biphotochromic molecules incorporating two BN-PIC units were synthesized and the effects of ring strain on the photochromic properties including the photoconversion efficiencies and the rates of the thermal reverse reaction were investigated. The photokinetic study of these macrocyclic biphotochromic molecules demonstrated that the structural distortion of the ring caused by the isomerization of one photochromic unit significantly influenced the photoisomerization efficiency and the rate of the thermal reverse reaction of the other photochromic unit.