Methyl-substituted Derivatives Research Articles

Excited State Dynamics of Geometrical Evolution of α-Substituted Dibenzoylmethanatoboron Difluoride Complex with Aggregation-Induced Emission Property.

Organic molecules with an aggregation-induced emission (AIE) property have been attracting much attention from the viewpoint of application to solid state emissive materials. For the AIE mechanism, quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model with the contribution of the conical intersection (CI) and deduced the importance of the restricted access to a conical intersection (RACI) in the potential energy surface (PES). Although these theoretical studies have contributed to the elucidation of AIE phenomena, direct detection of the reaction dynamics is indispensable to clarify the actual PES and the deactivation mechanism. Along this line, we investigated excited state dynamics of the AIE molecule with dibenzoylmethanatoboron difluoride complexes using time-resolved absorption spectroscopies in both visible and infrared (IR) regions. While the reference system of 1,3-bis(4-methoxyphenyl)methanatoboron difluoride (2aBF2) showed strong emission in solution, the methyl-substituted derivative at the α-position of the dioxaborine ring (2amBF2) led to the very weak fluorescence in solution but strong emission in the solid state. Time-resolved visible absorption measurements revealed a peak shift and broadening of the stimulated emission in the solution of 2amBF2, owing to the rapid change of the molecular geometry. With the temporal evolution of time-resolved IR absorption signals and density functional theory (DFT) calculation of these systems, it was deduced that 2amBF2 has two stable geometries, namely, planar and bending, in the S1 state and the bending geometry in the S1 state led to rapid conversion to the S0 state. These results support the RACI model in the aggregated states, leading to the AIE properties.

A new conjugated tripoid N4 system containing furazan and triazolofurazan cores linked by a nitrogen bridge

Two thermostable representatives of methyl-substituted triazolofurazan derivatives with zwitterionic N+N– bonds were obtained via the thermal cyclization of N,N’-bis(azidofurazanyl)-N-methyltriazene. 5-(N-Azidofurazanyl-N-methylamino)triazolofurazan was the product of known intramolecular reaction of neighboring azido and azo groups. Its isomer with methyl group in the triazolofurazan core was formed in the course of new cyclization of azido and triazene groups representing an original NN bond formation reaction giving an unusual zwitterionic heterocyclic system.

Hydroconversion of lignin-derived platform compound guaiacol to fuel additives and value-added chemicals over alumina-supported Ni catalysts

Hydroconversion of guaiacol (GUA) over γ-Al2O3 and phosphatized-γ-Al2O3 (γ-Al2O3(P)) supported Ni catalysts was initiated by Lewis-sites and active Ni sites. Conversion proceeded via transmethylation and hydrodemethylation/hydrodemethoxylation as major and minor pathways, respectively, resulting in mainly catechol and methylcatechols, and via series of consecutive hydrodehydroxylation (HDHY) and ring hydrogenation (HYD) reactions leading to partially and fully deoxygenated, saturated, and unsaturated products. High Ni-loading and high H2 pressure promoted the formation of cyclohexane and methyl-substituted cyclohexanes; however, above 300 °C the hydrogenation–dehydrogenation equilibrium favored the formation of benzene and methyl-substituted benzenes. Ni/γ-Al2O3(P) showed suppressed HYD/HDHY activity resulting in pronounced formation of catechol and/or phenol and their methyl-substituted derivatives. Surface phenolate species were substantiated as surface intermediates of hydrodeoxygenation. Phosphatizing reduced the concentration of both basic OH and Lewis acid (Al+) – Lewis base (O–) pair surface sites of the γ-Al2O3 support and, thereby, suppressed phenolate formation and hydrodeoxgenation.

Unconventional gas-phase synthesis of biphenyl and its atropisomeric methyl-substituted derivatives.

The biphenyl molecule (C12H10) acts as a fundamental molecular backbone in the stereoselective synthesis of organic materials due to its inherent twist angle causing atropisomerism in substituted derivatives and in molecular mass growth processes in circumstellar environments and combustion systems. Here, we reveal an unconventional low-temperature phenylethynyl addition-cyclization-aromatization mechanism for the gas-phase preparation of biphenyl (C12H10) along with ortho-, meta-, and para-substituted methylbiphenyl (C13H12) derivatives through crossed molecular beams and computational studies providing compelling evidence on their formation via bimolecular gas-phase reactions of phenylethynyl radicals (C6H5CC, X2A1) with 1,3-butadiene-d6 (C4D6), isoprene (CH2C(CH3)CHCH2), and 1,3-pentadiene (CH2CHCHCHCH3). The dynamics involve de-facto barrierless phenylethynyl radical additions via submerged barriers followed by facile cyclization and hydrogen shift prior to hydrogen atom emission and aromatization to racemic mixtures (ortho, meta) of biphenyls in overall exoergic reactions. These findings not only challenge our current perception of biphenyls as high temperature markers in combustion systems and astrophysical environments, but also identify biphenyls as fundamental building blocks of complex polycyclic aromatic hydrocarbons (PAHs) such as coronene (C24H12) eventually leading to carbonaceous nanoparticles (soot, grains) in combustion systems and in deep space thus affording critical insight into the low-temperature hydrocarbon chemistry in our universe.

Methyl-Substituted Derivatives of Furazanoazepines: Synthesis, Structure, Enthalpy of Formation, and Ballistic Efficiency

Methyl-Substituted Derivatives of Furazanoazepines: Synthesis, Structure, Enthalpy of Formation, and Ballistic Efficiency

Synthesis and Biological Evaluation of Substituted Fused Dipyranoquinolinones

New methyl-substituted, and diphenyl-substituted fused dipyranoquinolinones are prepared in excellent yields via the triple bond activation and 6-endo-dig cyclization of propargyloxycoumarin derivatives by gold nanoparticles supported on TiO2 in chlorobenzene under microwave irradiation. In the absence of gold nanoparticles, the methyl-substituted propargyloxycoumarin derivatives resulted in fused furopyranoquinolinones through Claisen rearrangement and 5-exo-dig cyclization. The intermediate propargyloxy-fused pyridocoumarins are prepared by propargylation of the corresponding hydroxy-fused pyridocoumarins. The methyl-substituted derivatives of the latter are synthesized in excellent yield by the three-component reaction of amino hydroxycoumarin with n-butyl vinyl ether under iodine catalysis. The diphenyl-substituted derivatives of hydroxy-fused pyridocoumarins are obtained, also, by the three-component reaction of amino hydroxycoumarin with benzaldehyde and phenyl acetylene catalyzed by iron (III) chloride. Preliminary biological tests of the title compounds indicated lipoxygenase (LOX) (EC 1.13.11.12) inhibitory activity (60–100 μM), whereas compound 28a, with IC50 = 10 μM, was found to be a potent LOX inhibitor and a possible lead compound. Only compounds 10b and 28b significantly inhibited lipid peroxidation.

Synthesis, Structures, and Redox Behavior of Methyl-Substituted Derivatives of Thiophene-Inserted [3]Dendralene with Redox-Active 1,3-Dithiol-2-ylidene Units

Abstract Several derivatives of 1,3-dithiole[3]dendralene with one thiophene spacer (1) were newly prepared. X-ray structure analysis of the hexamethyl-1 (1Aa) revealed that 1Aa adopts a structure with significant distortion between the central 1,3-dithiole (DT) ring and the thiophene ring. Cyclic voltammograms of all the derivatives were composed of three pairs of one-electron redox waves in correspondence with the presence of three redox-active DT rings. The results of cyclic voltammetry and spectroelectrochemistry indicated that a positive charge in 1Aa•+ is mainly delocalized on the vinyl-extended tetrathiafulvalene (TTF) moiety, while two positive charges in 1Aa2+ are mainly distributed on the thiophene-inserted TTF moiety. X-ray structure analysis revealed that two-electron oxidation of 1Aa with (4-BrC6H4)3N•+SbCl6− gradually facilitated the formation of a dicationic species of its chlorinated product.

Synthesis and study of fluorine-functionalized ZnTPPs

Five fluorinated zinc tetraphenyl porphyrins derivatives, fluorinated either on all ortho positions of the meso phenyl rings (Zn(II)-5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrin) or in [Formula: see text]-positions with two, four, six or eight fluorine groups (2,3-difluoro-5,10,15,20-tetraphenylporphyrin, 7, 8,17,18-tetrafluoro-5,10,15,20-tetraphenylporphyrin, 7,8,12,13,17,18-hexafluoro-5,10,15,20-tetraphenyl- porphyrin and 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenylporphyrin, respectively), were studied to probe the effect of fluorine in on-surface synthesis approaches. Additionally, bulkier substituents have been used in 7,8,17,18-tetrabromo-5,10,15,20-tetraphenylporphyrin and 7,8,17,18-tetramethyl-5,10,15,20-tetraphenylporphyrin, for a direct comparison with the corresponding fluorinated compounds. Reported are the synthesis and electronic structure characterization of the compounds, using UV-vis absorption and fluorescence spectroscopies as well as electronic structure calculations of the ground state molecular properties. Steric and electronic effects of fluorination are explored. For all molecules studied, substitution with fluorine maintains a planar tetrapyrrole macrocycle and shifts in the absorption spectra were consistent with calculated changes in the HOMOs and LUMOs energies of the molecules. In contrast, the bromo and methyl-substituted derivatives exhibit chemical instability and spectral shifts, compared to parent compound ZnTPP, consistent with structural distortions and accounted for calculations. The site-specific effects of fluorination on the electronic structure are discussed in detail.

Influence of Hydroxyl Group Position and Substitution Pattern of Hydroxybenzoic Acid on the Formation of Molecular Salts with the Antifolate Pyrimethamine

A series of molecular salts of the antimalarial drug pyrimethamine (PYR) with salicylic acid (SA) and its methyl-substituted derivatives 3-methylsalicylic acid (3Me-SA), 4-methylsalicylic acid (4Me-SA), and 5-methylsalicylic acid (5Me-SA) was obtained. Additionally, cocrystallization of PYR with the structural analogues of SA 3-hydroxybenzoic acid (3OH-BA) and 4-hydroxybenzoic acid (4OH-BA) led in the case of 3OH-BA to the formation of a molecular salt, while cocrystallization with 4OH-BA did not lead to the formation of an associate of any kind. In all obtained crystal structures, the carboxylate anion interacts with the protonated at N1 pyrimethamine moiety in a linear fashion through a pair of parallel N–H···O hydrogen bonds forming a cyclic hydrogen-bonded motif. In the crystal structure of PYR-SA as well as in the structures involving methylated derivatives of SA (3Me-SA, 4Me-SA, and 5-Me-SA), a typical PYR-PYR association via a pair of N–H···N bonds between the N(4)H2 amino group of one molecule and the N3 unsubstituted amino atom of the second PYR molecule is observed, a motif that is characteristic of two known PYR polymorphs. On the other hand, in the structure of PYR-3OH-BA, the PYR-PYR connection is realized via a pair of N–H···N bonds between the N(2)H2 amino group of one molecule and the N3 unsubstituted amino atom of the second PYR molecule. In all of the structures, chlorine atoms are involved in C–H···Cl interactions with either the acid molecule or another PYR moiety, while in the structure of PYR-3Me-SA molecules are additionally connected through halogen Cl···Cl interactions. All of the obtained structures were thoroughly characterized by single-crystal X-ray analyses, Hirshfeld analyses, DFT calculations, and thermal analyses (TGA and DSC).

Ultraviolet Excitation Dynamics of Nitrobenzenes

Time-resolved photoelectron imaging was used to investigate nonadiabatic processes operating in the excited electronic states of nitrobenzene and three methyl-substituted derivatives: 3,5-, 2,6-, and 2,4-dimethylnitrobenzene. The primary goal was evaluating the dynamical impact of the torsional angle between the NO2 group and the benzene ring plane-something previously implicated in mediating the propensity for branching into different photodissociation pathways (NO vs NO2 elimination). Targeted, photoinitiated release of NO radicals is of interest for clinical medicine applications, and there is a need to establish basic structure-dynamics-function principles in systematically varied model systems following photoexcitation. Within our 200 ps experimental detection window, we observed no significant differences in the excited-state lifetimes exhibited by all species under study using a 267 nm pump and ionization with an intense 400 nm probe. In agreement with previous theoretical predictions, this suggests that the initial energy redistribution dynamics within the singlet and triplet manifolds are driven by motions localized predominantly on the NO2 group. Our findings also imply that both NO and NO2 elimination occur from a vibrationally hot ground state on extended (nanosecond) timescales, and any variations in NO vs NO2 branching upon site-selective methylation are due to steric effects influencing isomerization prior to dissociation.

Computational estimation on the propulsion performance of polycyclic hydrocarbons

Polycyclic hydrocarbons have great potential as advanced high-energy-density (HED) fuels, and their physicochemical and propulsion properties are highly important for propulsion purposes. In this work, the fuel properties including density, melting point, boiling point, critical temperature/pressure, enthalpy of vaporization, enthalpy of fusion, enthalpy of combustion and specific impulse of three families of polycyclic hydrocarbons (a, cyclopropyl and methyl-substituted derivatives of tri-, tetra- and penta-cyclic hydrocarbons; b, [n]prismanes; and c, homocubanes) were evaluated by combining the group contribution and quantum chemical methods. The applied method properly predicts the physicochemical properties of polycyclic hydrocarbons, which are highly dependent on their molecule structures. For category (a), the hydrocarbons with low H/C ratio generally have higher density, volumetric specific impulse and volumetric combustion heat. Importantly, for all three families of polycyclic hydrocarbons, introducing additional strained rings (cyclopropyl ring or cyclobutyl ring) in molecules remarkably improves their density and specific impulse, which are highly appropriate for volume-limited aerospace vehicles to extend the flight range and increase the payload. The study on the relationship between the propulsion performance and structure characteristics of these hydrocarbons will give the general rule for the rational design of HED fuels.

Equilibrium Structure in the Presence of Methyl Internal Rotation: Microwave Spectroscopy and Quantum Chemistry Study of the Two Conformers of 2-Acetylfuran.

For 2-acetylfuran, quantum chemistry predicted and proton magnetic resonance study reported two conformers, anti and syn, differing in the position of the carbonyl group with respect to the O1-C2 bond of the furan ring. The microwave spectrum of the title molecule was recorded in the frequency range from 2 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer, confirming the presence of both conformers. Spectroscopic parameters such as the rotational and centrifugal distortion constants could be determined with high precision. The spectra of all 13C- and 18O-isotopologues of the energetically more favorable anti-conformer could be assigned, allowing the experimental determination of bond lengths and bond angles from the heavy atom substitution rs and the semi-experimental equilibrium reSE structures. Splittings arising from the internal rotation of the acetyl methyl group could be resolved for both conformers as well as for all assigned isotopologues, from which the barrier to methyl internal rotation was determined. The torsional barrier is largely invariant at around 319 cm-1 in the parent species of anti-2-acetylfuran and its isotopologues, showing that though isotopic substitution greatly influences the rotational properties of the molecule and causes a different microwave spectrum, its effect on the methyl torsion is negligible. On the other hand, conformational effects play a decisive role, as the torsional barrier of 239.780(13) cm-1 found for syn-2-acetylfuran differs significantly from the value for anti-2-acetylfuran. The results are compared and discussed with other methyl-substituted furan derivatives and acetyl group containing ketones for a better understanding of different effects influencing molecular geometry parameters and methyl internal rotations.

Invariant and Variable Supramolecular Self-Assembly in 6-Substituted Uracil Derivatives: Insights from X-ray Structures and Quantum Chemical Study

In this study, three new 6-(arylthio)uracil derivatives, namely, 6-(phenylthio)pyrimidine-2,4(1H,3H)-dione (1), C10H8N2O2S; 6-(p-tolylthio)pyrimidine-2,4(1H,3H)-dione (2), C11H10N2O2S; and 6-(3,5-dimethylphenylthio)pyrimidine-2,4(1H,3H)-dione (3), C12H12N2O2S, have been synthesized. Single-crystal structures of these compounds reveal an invariant molecular tape contains alternate R22(8) synthons formed by N–H···O hydrogen bonds in 1 and 3. This alternate hydrogen-bonded pattern disappeared in 2; instead, a new synthon is generated. The lattice energy calculation suggests that the methyl-substituted derivatives (2 and 3) have high stabilization energy than compound 1. The electrostatic potential map reveals the difference in the accepting tendency of the carbonyl oxygen. The Hirshfeld surface and 2D-fingerprint plots analyses demonstrate that the major intermolecular interactions come from H···O contacts in 1, and these contacts were reduced due to the presence of methyl substitutions in 2 and 3. This reduction is compensated by the increase of the same amount of H···H contacts in these structures. Further, the PIXEL energy and DFT calculations at the M06-2X-D3/cc-pVTZ level of theory were used to characterize the dimeric topology formed in structures of 1–3. The intermolecular interaction energies of dimers calculated by the PIXEL method were compared with the B97D3/def2-TZVP level of approximation. Although these molecules’ crystal packing is somewhat different, the energy frameworks show similarities on the respective crystal structure’s shortest axis. Furthermore, the nature and strength of various noncovalent interactions such as N–H···O, C–H···O/S/π, π···π, and a chalcogen bond of type C–S···O═C were evaluated using the Bader’s quantum theory of atoms-in-molecules framework.

Mesomorphic, optical, dielectric, and electro-optic properties of azo-ester materials: Effect of lateral methyl and terminal substituents

The effect of introducing a lateral methyl substituent and the two different alkoxy terminal groups on the mesophase behavior of three-benzene-ring molecular core of azo-ester compounds bearing 2-methylbutoxy unit on the opposite terminal side (C1–C6) were explored. Their structures were confirmed by several spectroscopic techniques (Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy). The mesomorphic properties of these compounds were studied by differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering. Except for the un-substituted terminals (C1 and C4), all other derivatives are liquid crystalline, exhibiting enantiotropic nematic liquid crystal phase. The alteration of the alkoxy chain length from methoxy to butoxy at the phenyl ester terminal group (ring A) for each set of laterally-neat and laterally methyl-substituted mesogens decreases the nematic temperature range. A decrease in the mesophase temperature range is also observed when a lateral methyl substituent is incorporated into phenylazo ring of the mesogenic core (ring C). Optical study demonstrated that their absorption spectra are identical in shape due to the structural similarities of the mesogenic core. The corresponding fluorescence spectra exhibited blue-emission with the laterally methyl substituted compounds having a relatively higher fluorescence intensity compared to that of its laterally un-substituted analogues. Furthermore, the laterally methyl-substituted derivatives were subjected to the planar alignment and their dielectric and electro-optic properties were investigated. The nematic phase of the aligned samples shows antiferroelectric switching behavior with spontaneous polarization, Ps ~ 5 μC/cm2.

The discovery of new phloroglucinol glycosides from Agrimonia pilosa and the mechanism of oxidative dearomatization of the methyl-substituted phloroglucinol derivatives.

Six methyl-substituted phloroglucinol glycosides (1–6) were isolated from Agrimonia pilosa, including four new compounds (1–3, 6). The aglycones (1a–4a) of 1–4 and their corresponding oxidized products (1c–4c) were also obtained from A. pilosa. The structures were determined by a series of spectroscopic analyses and chiral separation. Notably, the structures of aglycones 1a–4a were unstable and prone to oxidation spontaneously, to yield the dearomatized structures 1c–4c. The mechanism of oxidative dearomatization was disclosed as a free-radical chain reaction with 3O2 by the techniques of HPLC-HR-MS2, EPR spectra and DFT-calculation, and hydroperoxide was defined as the intermediate.

Clarification of the Complexation Behaviour of 2,6-di-<i>O</i>-Methylated <i>β</i>-Cyclodextrin and Vitamin E and Radical Scavenging Ability of the Complex in Aqueous Solution

The precise understanding of the behaviour of vitamin E (α-tocopherol; Toc) complexed with cyclodextrin (CD) additives in aqueous solution is a fundamental issue for further development of their aqua-related biological applications. In this study, the solubilisation and complexation behaviours of Toc with methyl-substituted CD derivatives and the radical scavenging ability of the resulting complexes were precisely investigated in water media. Several problems were encountered upon pre-dissolving Toc in an organic solvent prior to the addition to the water media, such as enhancement of the dispersibility and decrease in the complexation capacity. Additionally, dispersions were obtained in some cases when mixing CD and Toc even in the absence of an organic solvent; therefore, to perform the measurements, a transparent solution was prepared via filtration with a nanopore filter. Consequently, unexpectedly, the addition of certain CD methylated derivatives did not always enhance the solubility of Toc significantly. However, 2,6-di-O-methylated β-CD (2,6-DMCD) formed a water-soluble inclusion complex with Toc, effectively enhancing its solubility. A phase solubility study indicated the formation of 1:2 or 1:3 Toc/CD inclusion complexes, and the interaction of 2,6-DMCD with both the chromanol head and the phytol chain of Toc was revealed by 2D ROESY nuclear magnetic resonance analysis. The interaction between 2,6-DMCD and the chromanol head was also confirmed for a 2,6-DMCD-2,2,5,7,8-pentamethyl-6-chromanol inclusion complex. Additionally, a rapid scavenging effect for molecularly dissolved Toc was demonstrated even in a system comprising a chromanol head directly encapsulated by CD. Hence, this work elucidated the precise complexation and radical scavenging ability of 2,6-DMCD-Toc in an aqueous solution, which paves the way for its biological applications.

Thermodynamic properties of 1,3,3-trimethylcyclopropene

The energy of combustion of liquid 1,3,3-trimethylcyclopropene was obtained in isoperibolic calorimeter at T = 298.15 K. The saturated vapour pressures were determined by the comparative ebulliometry in the temperature range 295–310 K. The normal boiling temperature and the enthalpy of vaporization were estimated based on p-T-data. The enthalpy of vaporization was measurement by calorimetric method at T = 298.15 K. The density was determined by pycnometric method at T = 293.15 K. The formation enthalpies of the compound in liquid and gas states were determined using the obtained experimental data. The enthalpies of formation in the gaseous state for cyclopropene and its methyl-substituted derivatives were estimated by G4 method.

New cyclic and acyclic imidazole-based sensitizers for achieving highly efficient photoanodes for dye-sensitized solar cells by a potential-assisted method

A series of systematically tailored aryl acyclic (biphenyl, dye 1 and 2), cyclic (phenanthrene, dye 3 and 4) and methyl-substituted (dye 5) imidazole derivatives were synthesized and characterized for application in dye-sensitized solar cells (DSSCs).

Pyrolysis of Furan and Its Methylated Derivatives: A Shock-Tube/TOF-MS and Modeling Study.

In this study, the pyrolysis of furan (F) and its two methyl-substituted derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) was investigated behind reflected shock waves at pressures near 1 bar in Ne as the bath gas. Concentration-time profiles of different stable species (reactants, intermediates, and products) were recorded simultaneously with high-repetition time-of-flight mass spectrometry and compared to results from simulations with a recently published, combined F/2-MF/2,5-DMF oxidation mechanism that was slightly modified already in another publication to describe the formation of H atoms in these pyrolysis systems. The temperature ranges covered in our experiments were chosen in line with the different thermal stabilities of the three reactants (F: T = 1050-1920 K; 2-MF: T = 1060-1900 K; 2,5-DMF: T = 1000-1800 K). In general, we obtained satisfactory agreement of the experimental and modeling results. To clarify the most important reaction routes for the formation of the detected species, we performed extensive sensitivity and rate-of-production analyses. The influence of increasing methylation of the furan ring on the formation and consumption of the different species is discussed in detail. Experimental concentration-time profiles are given in tabular form in the Supporting Information to enable tests of future mechanism developments.

Stereoselective synthesis of a new methyl-substituted inositol derivative

The stereoselective synthesis of methyl-substituted inositol derivative is described. Diene diacetate which is a key compound was first prepared via three steps starting from 2-methyl-p-benzoquinone. Osmium-catalyzed regio- and stereoselective dihydroxylation of diene diacetate afforded cis-diol diasetate, which then produced tetra acetate via acetylation with Ac2O-pyridine. Oxidation and acetylation of the other alkene moiety in the compound gave a hexaacetate compound stereoselectively. Finally, the acetate groups were removed by NH3 leading to formation of the desired new methyl-substituted inositol derivative having a muco-inositol-type stereochemical pattern in the six-membered ring. Spectroscopic methods were used for characterization of all synthesized compounds.