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Competing alternative pathways for formation of particular ion in mass spectra of substituted benzophenones
Exploration of the effect on acidity of alkyl groups bonded to trigonal and digonal carbon. Some results on the relative acidities of toluene and p-xylene, and acetylene and substitute acetylenes, as determined by ion cyclotron resonance (icr) spectroscopy, are described. Some limitations of the CNDO/2 calculation method are discussed.
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The impact resistance of flame retardant composites, especially thermoplastic molding: compounds containing over 60% hydrated mineral filler such as Al(OH)3 or Mg(OH)2 as improved by coating the filler with 1 to 20% of an elastomer. The composite will fail by crazing or shearing rather than by brittle fracture. A well bonded elastomeric interphase resulted by utilizing acidic substituted resins such as ethyl-hexyl acrylate-acrylic acid copolymers which bond to and are cross-linked by the basic filler particles. Further improvement in impact resistance was provided by incorporating 1 to 10% of a resin fiber reinforcement such as polyvinyl alcohol fibers that decompose to yield at least 30% water when heated to decomposition temperature.
The photocurrents of the substituted anthracenes, 1,5-diacetylanthracene (2), 1-acetylanthracene (3), 9-acetylanthracene (4), 1,5-dichloroanthracene (5), 1,5-diethylanthracene (6), 1,5-dimethoxyanthracene (7), 9-cyanoanthracene (8), and anthracene (1) were measured by using their surface type cells in nitrogen. The compounds of (1), (5), (6), (7), and (8) showed the photocurrent spectra which corresponded to the absorption spectra of their evaporated films. In the cases of (2) and (3), however, the anomalous photocurrent appeared in the threshold region of their absorption spectra. The appearance of the anomalous photocurrent was characteristic of anthracenes having the acetyl group at 1- and/or 5-position. The magnitude of the photocurrents of the 1,5-disubstituted anthracenes was similar to that of (1). The photocurrents of the monosubstituted anthracenes were smaller than that of (1). Among the monosubstituted anthracenes, the compound (4) showed no photocurrent under the same conditions. Contrary to the results obtained in the cases of phenazines, the photoconductivities of the anthracene derivatives became better in air.
Transition metal (i.e., Mn, Fe, Cr) and chalcogen (Se) substituents are introduced into single-crystalline NiPS 3 , and the evolution of the two emergent quasi-particle excitations characteristic to the XXZ correlated antiferromagnetism of NiPS 3 (i.e., spin orbit entangled exciton (SOX) and two-magnon scattering (2M )) are investigated as functions of substituent concentration through comprehensive room- and low-temperature photoluminescence (PL) and Raman spectroscopy studies. These findings are further correlated with the magnetic properties of the same set of compounds reported in prior studies. The work revealed that the SOX emission intensities and linewidths are mainly controlled by the magnetic anisotropy and spin orientations, and are strongly suppressed by the introduction of substituents. The suppression depends on the type of substituent, with Fe affecting the SOX emission more than Mn and Cr. The 2 M scattering is linked to short-range correlations and exhibits greater resiliency against metal atom substitution. While the 2M peak at low temperature gets suppressed and red-shifted in frequency with increasing concentrations of all the substituents, Fe induces the weakest suppression compared to all other substituents. Altogether, these findings revealed the introduction of substituents as a powerful route to control the emergent collective excitations in NiPS 3 and mixed-MPX 3 materials.
Here, we report the role of pendant amine basicity on the proton-coupled electron transfer (PCET) reactivity for the conversion of [Co III Cp(P Ph 2 N R 2 )(CH 3 CN)] 2+ complexes to [HCo III Cp(P Ph 2 N R 2 )] + , which is a key transformation involved in catalytic CO 2 conversion to formate and in H 2 evolution. Three complexes were studied, where the amine substituent (R) varies from benzyl, methoxyphenyl, or phenyl. In previous work on the benzyl system, we showed that the amine on the P Ph 2 N Bn 2 ligand serves as a kinetically accessible protonation site and enables three participating hydride formation mechanisms. In this work, a combination of electrochemical measurements and theoretical calculations were used to show that the electronic donation at the pendant amine influences the accessible PCET mechanism and proton transfer kinetics related to cobalt hydride formation under analogous reaction conditions. Notably, the amine with the most electron-donating substituent correlates to the lowest barrier for amine protonation, and specific cobalt hydride formation mechanisms can be shut off for the amine with the least electron-donating substituent. The mechanistic and kinetic changes upon modulation of the amine substituent have great implications for overall catalytic efficiency and selectivity, especially to generate the cobalt hydride intermediate involved in selective CO 2 reduction to formate. This work shows how to exploit kinetic basicity using ligand-cooperative design to facilitate PCET reactions involved in energy related transformations.
We report the ethenylation of 1,3- and 1,2-disubstituted benzenes using [(η 2 -C 2 H 4 ) 2 Rh(μ-OAc)] 2 as a catalyst precursor and Cu(OPiv) 2 as the oxidant. The regioselectivity of alkenylation for 1,3-disubstituted benzenes produces 3,5-disubstituted styrene products, while the alkenylation of 1,2-disubstituted benzenes produces 3,4- disubstituted styrene products. The rate of alkenylation is influenced by steric and electronic factors based on the substituents of the benzene unit. In all cases, 1,2-disubstituted benzenes react faster than 1,3-disubstituted benzenes, with a rate difference that is from 2 times up to >70 times more rapid for 1,2-disubstituted substrates. This is likely due to the difference in the number of accessible C−H bonds based on the steric protection of C−H bonds adjacent to functionality. Furthermore, the rate of alkenylation is influenced by the arene substituent electronics. The rates of alkenylation for 1,2-disubstituted benzenes follow the trend OMe > Me > CF 3 > Cl, while for 1,3-disubstituted benzenes the trend is CF 3 > Cl > Me > OMe. Using quantum mechanics DFT calculations, we found that the C−H activation step can occur by two different mechanisms. The electronic properties of substituents on the arene ring change the preferred C−H bond-breaking mechanism for 1,2-disubstituted and 1,3-disubstituted benzenes.
Molecular-level insights into reactive separations are crucial for the design of new conversion pathways of carbon dioxide (CO 2 ). This work explores a postulated pathway that directs CO 2 to undergo inverse-electron-demand Diels–Alder reactions to produce heterocycles using the CO 2 chemically fixed on water-lean solvent molecules. Density functional theory calculations are applied to evaluate the lowest unoccupied molecular orbital (LUMO) energies of three types of reactants (1,3-butadiene, 1,3-cyclohexadiene, and 1,2,4,5-tetrazine) with various functional substituents. These calculations also provide a data set (5.8k data) for developing a machine learning model to efficiently predict LUMO energies. A computational screening of LUMO energies for an additional 47k diene and tetrazine candidates is performed, and a list of candidates with lowered LUMO energies by electron-withdrawing substituents is provided. These candidates are further examined by their reaction energy barriers computed from the interatomic potential or density functional theory. Two major energy barriers are identified, one for the proton transfer within the water-lean solvent and the other for the CO 2 transfer from the solvent molecule to the reactant candidate (diene or tetrazine). The functional substituents have a more significant impact on the second barrier but a very slight one on the first barrier. This exploratory work demonstrates a new possibility for guiding experimental efforts toward the chemical conversion of fixated CO 2 to value-added compounds.
This study explores the performance and stability of ammonium and phosphonium-based polymeric ionic liquids (PILs) with methyl and butyl substituents in moisture-swing direct air capture of CO 2 . The polymers are synthesized with chloride counterions, followed by ion exchange to the bicarbonate ion, and tests for CO 2 capture capacity and stability under cyclic wet–dry conditions. The phosphonium polymer with methyl substituents [PVBT-MeP] demonstrates the highest CO 2 capture capacity at ≈510 µmol g⁻¹, attributed to minimal steric hindrance and stronger ion pairing with bicarbonate. However, oxidative degradation is detected by 31 P NMR spectroscopy after the moisture swing experiment, with the appearance of a phosphine oxide peak at 61.28 ppm, which indicates phosphorus oxidation as the primary degradation pathway. In contrast, the ammonium polymer with butyl substituents [PVBT-BuN] exhibits the highest stability, showing no degradation over five moisture swing cycles. Additional stability experiments in 0.5 m KHCO 3 solutions reveal no degradation for any PIL, suggesting that oxidative degradation is driven by dynamic acid-base reactions during the moisture swing cycles in the air. Furthermore, these findings reveal the potential of phosphonium-based PILs for moisture-swing direct air capture, achieving high capacity while highlighting the need for optimized stability through counterion and structural design.
Here, this study reports the synthesis and characterization of the first fluorinated coinage metal pyrazolates with SF 5 groups, specifically {[3-(SF 5 )Pz]M} 3 (M = Cu, Ag), and compares them to trifluoromethylated analogs. X-ray analysis reveals different pyrazolyl ligand orientations and metallophilic interactions, as well as supramolecular structures influenced by fluorinated substituents and metals. The {[3-(SF 5 )Pz]M} 3 complexes form face-to-face sandwich adducts with benzene. Photophysical investigations show that copper complexes exhibit long-lived phosphorescence, while silver analogs display fast fluorescence, with emission properties modulated by substituents, solvent environment, and intermolecular interactions. Computational studies confirm the experimental geometries and demonstrate that SF 5 substituents increase the π-acidity and enhance arene binding over the analogs featuring the smaller and less-electron-withdrawing CF 3 groups and provide insights into metallophilic interactions and photoluminescence. These newly uncovered SF 5 decorated materials, with enhanced π-acidity and arene-binding ability, are promising materials for molecular sensing and tunable luminescence.
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Polymer electrolytes enhance the safety of lithium-ion battery systems, but current state-of-the-art poly(ethylene oxide)-based polymer electrolytes fail to achieve the electrochemical properties necessary for practical applications. We probed the impact of substituent density on the electrolyte performance by introducing methyl substituents into the backbone of a series of poly(1,3-dioxolane) (PDXL)-based copolymers. The polymerization of 1,3-dioxolane (DXL) and 4-methyl-1,3-dioxolane (MeDXL) yielded a series of random copolymers that were amorphous above 10% MeDXL incorporation. The copolymers with 10 and 20% MeDXL incorporation exhibited higher efficacies than those of either PDXL or poly(ethylene oxide) (PEO), highlighting the use of methyl substituents to control the electrochemical properties of polymer electrolytes.
Starting from a simple scaffold hopping exercise based on our previous exploration of cysteine protease inhibitors against legumain, compound 6a was identified as a starting point for the development of a SARS-CoV-2 main protease (M Pro ) inhibitor. Compound 6a displayed submicromolar biochemical potency in the ultrasensitive assay developed by Drag and coworkers. Through an iterative structure−activity relationship campaign, we discovered an unexpected improvement in both biochemical and cellular potency through the incorporation of an ortho substituent within the P3 benzamide. X-ray crystallography revealed that incorporation of the ortho substituent caused a subtle but important binding enhancement of the P1 glutamate group within the M Pro S1 pocket. While incorporation of the ortho substituent improved the potency, the off-target selectivity against a panel of cysteine proteases and cell activity remained suboptimal. Further scanning of the P2 core revealed that incorporation of the 3.1.0 proline could address these issues and afford compound 22e, a highly potent and cellularly active M Pro inhibitor.
Developing multicharge and spin stabilization strategies is fundamental to enhancing the lifetime of functional organic materials, particularly for long-term energy storage in multiredox organic redox flow batteries. Current approaches are limited to the incorporation of electronic substituents to increase or decrease the overall electron density or bulky substituents to sterically shield reactive sites. With the aim to further expand the molecular toolbox for charge and spin stabilization, we introduce regioisomerism as a scaffold-diversifying design element that considers the collective and cumulative electronic and steric contributions from all of the substituents based on their relative regioisomeric arrangements. Through a systematic study of regioisomers of near-planar aromatic cyclic triindoles and nonplanar nonaromatic cyclic tetraindoles, we demonstrate that this regioisomeric engineering strategy significantly enhances the H-cell cycling stability in the above two new classes of 2e – catholytes, even when current strategies failed to stabilize the multicharged species. Density functional theory calculations reveal that the strategy operates by redistributing the charge and spin densities while highlighting the role of aromaticity in charge stabilization. The most stable 2e – catholyte candidate was paired with a viologen derivative anolyte to achieve a proof-of-concept all-organic flow battery with 1.26–1.49 V, 98% capacity retention, and only 0.0117% fade/h and 0.00563% fade/cycle over 400 cycles (192 h), which is the highest capacity retention ever reported over 400 cycles in a multielectron all-organic flow battery setup. We anticipate regioisomeric engineering to be a promising strategy complementary to conventional electronic and steric approaches for multicharge and spin stabilization in other functional organic materials.
Chiral ensembles can arise through supramolecular curvature that resolves geometric frustrations in the packing of bent, achiral molecular or colloidal building blocks. Here, we leverage orthogonal protection−deprotection click chemistry to create sequence-defined mesogenic heterodimers exhibiting emergent chirality. We compare the hierarchical self-assembly of the synthesized asymmetric, achiral heterodimers, which differ only in the position of a methyl substituent. Both dimers form chiral spherulites composed of nanocylinders. However, the detailed arrangement of nanocylinders depends on the position of the methyl substituent and the crystallization conditions. Despite the chemical similarity, in one dimer, two crystalline forms are optically active. They form conglomerates of dextrorotatory and levorotatory spherulites. The other dimer forms more highly anisotropic spherulites that mask circular birefringence arising from the misorientation of nanocylinders, while mapping of nanocylinder directors reveals a sense at the spherulite surface. We propose that differences in nanocylinder arrangements may arise from changes in nanocylinder curvature and dimensions dictated by the methyl substituent position, inducing chirality. These results demonstrate multiscale hierarchical assembly relevant to dense systems of tubular structures and highlight the role of sequence and molecular design in directing the bottom-up hierarchical self-assembly and chirality of mesogenic systems.
A series of heteroleptic copper(I) β-diketiminate triarylphosphine complexes is reported, having the general formula Cu(R 1 NacNac R2 )(PPh X 3 ), where R 1 NacNac R2 is a substituted β-diketiminate and PPh X 3 is a triphenylphosphine derivative. A total of five different R 1 NacNac R2 ligands and three different triarylphosphines are used to assemble the nine complexes. Here, the syntheses, X-ray crystal structures, cyclic voltammograms, and UV–vis absorption spectra of all compounds are described. Whereas most of the compounds are weakly luminescent or only luminesce at 77 K, the four complexes with the more sterically encumbered β-diketiminate ligands, with methyl or isopropyl substituents at the 2- and 6-positions of the N-phenyl rings, exhibit weak room-temperature photoluminescence with peaks between 519 and 566 nm and long excited-state lifetimes in the range of 15–70 μs. The sterically encumbering substituents in this subset have subtle effects on the UV–vis absorption maximum, which red shifts slightly as the steric bulk increases, as well as significant effects on the photoluminescence lifetime, which is observed to increase as the steric bulk is augmented. Substituents on the triarylphosphine also influence the excited-state dynamics in the bulky complexes, with the more electron-rich tris(4-methoxyphenyl)phosphine (PPh OMe 3 ) giving longer-excited-state lifetimes compared to triphenylphosphine (PPh 3 ) when the same R 1 NacNac R2 ligand is used.
The photochemical properties and reaction mechanisms of a series of hypervalent iodoazide compounds (R–IN3) were investigated, with substituents (−CH 3 , −H, −CF 3 ) tuning the electronic density of the phenyl ring. With the help of UV irradiation, ultrafast time-resolved spectroscopy, and density functional theory (DFT) calculations, we elucidated the mechanisms of azide radical (N 3 • ) release and its subsequent reactivity. UV–vis spectroscopy reveals that the photoconversion rates follow the trend CH3 > H > CF3, aligning with DFT-calculated ΔG values for ring-opening transitions. Homolytic cleavage of the I–N bond is identified as the dominant pathway for N3• generation upon UV irradiation, occurring within 400 fs. The released azide radicals react with the solvent molecules, while the iodo radical R–I C • fragments undergo a thermodynamically uphill lactone ring-opening (RO) reaction and subsequent hydrogen atom abstraction from the solvent to form carboxylic acids R–I–COOH, as validated by NMR and IR spectroscopy. The study also highlights the role of substituents in influencing reaction kinetics and intermediate stability, with electron-donating groups accelerating the release of the N 3 • species. This work bridges experimental observations with computational predictions, offering a foundation for future advancements in azide-based reactions and materials.