Position Of Methyl Substituent Research Articles

Experimental Study for the Influence of Methyl Substituent's Position on Quinoline for Inhibition of Aluminium Corrosion in Hydrochloric Acid

Experimental Study for the Influence of Methyl Substituent's Position on Quinoline for Inhibition of Aluminium Corrosion in Hydrochloric Acid

Four Slip-Stacked Arrangements, Three Types of Photophysics: Crystal Structure and Solid-State Fluorescence of 3,6-Diaryl Substituted Furo[3,4-c]furanone Polymorphs and Regioisomers.

Six symmetrical 3,6-diaryl (aryl=phenyl, 2-, 3- and 4-tolyl, 2,4- and 3,5-xylyl) substituted furo[3,4-c]furanones (DFF) were synthesized. The computational analysis, based on density functional theory, found eight possible centrosymmetrical slipped π-stack arrangements, formed according to electron repulsion minimization principle, as for previously reported for π-isoelectronic diketopyrrolopyrroles (DPP). One of these slipped stack arrangements was found to form infinite columns in the crystals of a new polymorph of parent phenyl derivative (with centre-to-centre distance CC=6.975 Å), other three types of stacks were found for 3-tolyl (CC=6.153 Å), 4-tolyl (CC=3.849 Å) and 2,4-xylyl (CC=4.856 Å) derivatives by single crystal X-ray diffractometry. All six derivatives show intense solution fluorescence in blue/green region, with a maximum driven entirely by a number and position of methyl substituents on phenyl rings. On the other hand, the solid-state fluorescence from yellow over orange to red is observed only for four derivatives and its presence/absence, spectral position and vibronic structure is driven exclusively by the slips in π-stacks (with interplanar distance always less than 3.5 Å) of almost planar DFF molecules, resulting in J-type emission, H-type excimer-like emission and H-type quenching.

Effect of methyl substituents on the biodegradation of two-ring polycyclic aromatic hydrocarbons in crude oil identified by aerobic biodegradation simulations

Existing studies determining the effects of substituted methyl groups on polycyclic aromatic hydrocarbon biodegradation were mostly limited to an individual compound or a class of compounds. The simultaneous transformation of the multiple series of methyl-substituted two-ring polycyclic aromatic hydrocarbons (61 compounds) in crude oil through laboratory simulations has been examined, including naphthalenes, fluorenes, biphenyls, and dibenzofurans. The biodegradation sequences were in the order of dimethylnaphthalenes > trimethylnaphthalenes > biphenyls > dibenzofurans, tetramethylnaphthalenes > pentamethylnaphthalenes > fluorenes. Polycyclic aromatic hydrocarbon biodegradation was depending on both the number and the position of methyl substituents. For naphthalenes, fluorenes, biphenyls, and dibenzofurans, the more methyl groups in the parent compound, the more resistant it was to biodegradation. Among the polycyclic aromatic hydrocarbons with the same number of methyl groups, the more ortho-methyl substitutes, the more challenging it was to be decomposed. In the case of dimethylnaphthalenes or trimethylnaphthalenes with the same number of methyl and ortho-methyl substituents, their biodegradability reduced as the number of α substituents increased. The number of ortho-methyl substituents had a greater impact than that of α/β substituents. The relative significance of these two factors has not been confirmed in previous studies.

Dihydroquinolylazotetrazole dyes in aqueous solutions: Effect of substituents and pH on spectral properties, acid-base equilibria and thermal Z‒E isomerization

Spectral, luminescent and photochemical properties of a series of hetarylazo dyes with dihydroquinoline and tetrazole moieties, which differ by the position of methyl substituent at the tetrazole fragment, were investigated in aqueous solutions at various pH by stationary spectrophotometry, fluorimetry and time-resolved methods. The results were supported by quantum chemical calculations. From the pH-dependence of the absorption spectra, it has been shown that azonium cations and dications additionally protonated at the tetrazole fragment are formed upon protonation of the E isomers. Opposite to the azonium cations studied earlier, the long-wavelength absorption band of the azonium cations is hypsochromically shifted relative to that of the neutral form. Weak fluorescence in aqueous solutions growing in acidic media is the specific feature of the dyes. Time-resolved experiments have shown that proton transfer reactions play important role in the transformations of the dyes after excitation in aqueous solutions.

Naturally Occurring Oxazole Structural Units as Ligands of Vanadium Catalysts for Ethylene-Norbornene (Co)polymerization

1,3-Oxazole and 4,5-dihydro-1,3-oxazole are common structural motifs in naturally occurring peptides. A series of vanadium complexes were synthesized using VCl3(THF)3 and methyl substituted (4,5-dihydro-1,3-oxazol-2-yl)-1,3-oxazoles as ligands and analyzed using NMR and MS methods. The complexes were found to be active catalysts both in ethylene polymerization and ethylene-norbornene copolymerization. The position of methyl substituent in the ligand has considerable impact on the performance of (co)polymerization reaction, as well as on the microstructure, and thus physical properties of the obtained copolymers.

New insights into the dissociation dynamics of methylated anilines.

Aniline, an important model system for biological chromophores, undergoes ultrafast H-atom loss upon absorption of an ultraviolet photon. By varying the number and position of methyl substituents on both the aromatic ring and amine functional group, we explore the ultrafast production of photofragments as a function of molecular structure. Both N-methyl aniline and 3,5-dimethyl aniline show altered H-atom loss behaviour compared to aniline, while no evidence for CH3 loss was found from either N-methyl aniline or N,N-dimethyl aniline. With the addition of time-resolved photoelectron spectroscopy, the photofragment appearance times are matched to excited state relaxation pathways. Evidence for a sequential excited state relaxation mechanism, potentially involving a valence-to-Rydberg decay mechanism, will be presented. Such a global, bottom-up approach to molecular photochemistry is crucial to understanding the dissociative pathways and excited state decay mechanisms of biomolecule photoprotection in nature.

Optically transparent aromatic poly(ester imide)s with low coefficients of thermal expansion. 2: Effect of the introduction of alkyl‐substituted p‐biphenylene units

AbstractA series of ester‐linked tetracarboxylic dianhydrides (TA‐X) were synthesized from trimellitic anhydride chloride and 4,4′‐biphenol analogs containing different numbers and positions of methyl substituents. Aromatic poly(ester imide)s (PEsIs) were polymerized from TA‐Xs and 2,2′‐bis(trifluoromethyl)benzidine to investigate the film properties systematically. A significant substituent effect on the target properties (Tg, optical transparency, the linear coefficient of thermal expansion (CTE) and ductility) was observed. A PEsI containing 2,2′,3,3′,5,5′‐hexamethyl‐substituted p‐biphenylene units was chemically imidized in a homogeneous state. It was highly soluble at room temperature, even in less hygroscopic non‐amide solvents such as cyclopentanone (CPN), and provided a stable CPN solution with a high solid content. The CPN‐cast PEsI film was almost colorless as suggested from the rather low yellowness index (3.2), high light transmittance at 400 nm (71.5%) and very low haze (1.15%). This PEsI film also had a high Tg (294 °C, determined by thermomechanical analysis) in addition to a low CTE (21.7 ppm K−1), moderate film ductility and very low water uptake. A structural modification of the PEsI by copolymerization with a tetracarboxylic dianhydride with a rigid/linear structure was effective in further reducing the CTE while maintaining the other excellent target properties. Thus, some of the PEsIs developed in this work are promising candidates as novel plastic substrates for use in image display devices. © 2017 Society of Chemical Industry

Effect of methyl substituents on the electronic transitions in simple meso-aniline-BODIPY based dyes: RI-CC2 and TD-CAM-B3LYP computational investigation

The S0→Si, i=1–5 electronic transitions of four 8-(4-aniline)-BODIPY and four 8-(N,N-dimethyl)-BODIPY dyes, differ by number and position of methyl substituents in the BODIPY frame, were investigated theoretically using ab initio the coupled cluster doubles (CC2) and TD-CAM-B3LYP methods. Methyl substituents in the BODIPY frame and the aniline fragment at the meso position disturb energy of local excitations S0→S1, S0→S3, and S0→S4 weakly in comparison with the fully unsubstituted BODIPY molecule. These transitions in experimental spectra form the most long-wave absorption bands at ca. 500nm as well as absorption bands in the region of 300–400nm. At the same time, the presence of aniline fragments leads to the appearance of new S0→S2 transitions of the charge transfer character in electronic spectra of BODIPYs. We also found a linear relationship between vertical energy of these charge transfer transitions and the electron donating power of an aniline fragment and electron accepting power of the BODIPY core depending on the number and position of methyl groups. The CC2 method provides the best overall description of the excitation energies in line with the experimental observations. On average, the quality of TD-CAM-B3LYP is almost equal to that of CC2, however the TD method with the CAM-B3LYP functional slightly underestimates the CT excitation energy.

Mutagenicity of heteroaromatic amines: Computational study on the influence of methyl substituents

Quantum mechanical calculations were performed to elucidate the factors determining the variations in mutagenic activity within groups of isomeric heteroaromatic amines that differ in the position of methyl substituents. Formation energies for noncovalent complexes and covalent DNA adducts were evaluated by means of high level quantum chemical methods. According to the computational results in this work, covalent adduct stability is proposed to influence the relative mutagenicities of structurally related heterocyclic amines. The stability of covalent C8-dG DNA adducts was found to be mainly determined by π-stacking interactions between the fused ring system of the heteroaromatic amines and the flanking nucleobases. Relative mutagenicity of amines of very related structure is proposed to be regulated by both nitrenium ion and covalent adduct stabilities.

Investigation of the phenylation of methyl-quinolines using tritium-labeled nucleogenic phenyl cations

The phenylation of methylquinolines by nucleogenic phenyl cations was studied. This reaction led to a product mixture through electrophilic addition and electrophilic substitution, with composition depending on the methyl substituent position. In the case of 4-methylquinoline, the electron-donating methyl group in the para position markedly increased the yield of N-phenylquinolinium derivative, while the low yield of the quinolinium salt in the case of 8-methylquinoline was due to the two factors - low basicity of the nitrogen atom in comparison to 4-methylquinoline and steric hindrance by the methyl group, which led to predominant electrophilic substitution.

INVESTIGATION OF THE PHENYLATION OF METHYLQUINOLINES USING TRITIUM-LABELED NUCLEOGENIC PHENYL CATIONS

The phenylation of methylquinolines by nucleogenic phenyl cations was studied. This reaction led to a product mixture through electrophilic addition and electrophilic substitution, with composition depending on the methyl substituent position. In the case of 4-methylquinoline, the electron-donating methyl group in the para position markedly increased the yield of N‑phenylquinolinium derivative, while the low yield of the quinolinium salt in the case of 8‑methylquinoline was due to the two factors – low basicity of the nitrogen atom in comparison to 4-methylquinoline and steric hindrance by the methyl group, which led to predominant electrophilic substitution. Authors: N. E. Shchepina, V. V. Avrorin, G. A. Alexandrova, G. A. Badun, I. I. Boiko, and S. N. Shurov English Translation in Chemistry of Heterocyclic Compounds, 2013, 49 (3), pp 428-434 http://link.springer.com/article/10.1007/s10593-013-1264-7

Iminoether Complexes of the Type, fac‐[Re(CO)3L{HNC(CH3)OCH3}]BF4 (L = Bipyridine or a Substituted Bipyridine): Synthesis and Properties

AbstractThe methyl acetimidate (an iminoether) complexes, fac‐[Re(CO)3L{HNC(CH3)OCH3}]BF4 [where L = 2,2′‐bipyridine (bipy), 4,4′‐Me2bipy, 5,5′‐Me2bipy, or 6,6′‐Me2bipy], were formed when fac‐[Re(CO)3(CH3CN)3]BF4 in acetonitrile/methanol was treated with 2,2′‐bipyridine (bipy) or the dimethyl‐2,2′‐bipyridines (4,4′‐Me2bipy, 5,5′‐Me2bipy, or 6,6′‐Me2bipy). Structural analysis of the four fac‐[Re(CO)3L{HNC(CH3)OCH3}]BF4 complexes revealed that all of the complexes crystallize with the iminoether ligand in the Z configuration and that distortions in L that involved the two pyridyl rings are minor except for 6,6′‐Me2bipy, which is highly distorted. This distortion of the 6,6′‐Me2bipy ligand is reflected in the NMR‐spectroscopic data. Upon complex formation, the methyl group signal in the 13C NMR spectrum shifted downfield significantly for 6,6′‐Me2bipy, but this did not occur in the 13C NMR spectrum of the 5,5′‐Me2bipy complex. The reaction times for forming the respective fac‐[Re(CO)3L{HNC(CH3)OCH3}]BF4 complexes for these two ligands were comparable, which indicated that the differences in the distortion of L and the methyl substituent position have little influence on the ease of iminoether formation. However, a higher steric bulk of the alcohol (methanol, ethanol, and2‐propanol) decreases the ease of fac‐[Re(CO)3(5,5′‐Me2bipy){HNC(CH3)OR}]BF4 formation. Isopropanol did not form the iminoether complex after two days of heating the reaction mixture at reflux. The low reactivity of the alcohols tested versus the amines that were tested previously suggests that selective bioconjugation to the fac‐{99mTc(CO)3}+ core through an amidine linkage is feasible for biomolecules that have both amine and hydroxy groups. Finally, a comparison of the C≡N bond lengths that were obtained for the fac‐[Re(CO)3(CH3CN)3]BF4/PF6 complexes with those values obtained for other rhenium acetonitrile complexes revealed that there is no significant difference between the C≡N bond lengths and that there is no correlation to the acetonitrile reactivity. It is possible that the fac‐{Re(CO)3}+ core stabilizes the transition state for amine or alcohol addition.

Influence of Methyl Substituent Position on Redox Properties of Nitroaromatics Related to 2,4,6‐Trinitrotoluene

AbstractThe environmental remediation of military installation sites is very important due to frequently large presence of carcinogenic derivatives of explosives in the ground and in ground waters. These nitroaromatic explosives and their derivatives are assessed by sensing devices. It is highly important to have insight on the reasons affecting the reduction potentials of these compounds. The redox properties of mono‐, di‐ and tri‐nitroaromatic compounds are studied with cyclic voltammetry at a glassy carbon electrode for comparison. We show that the presence of a methyl group in the aromatic system leads into more negative reduction potentials. The ease of nitro group reduction vary from meta>para>ortho positions relative to a methyl group. The redox properties were also studied at various pH ranging from 2 to 10. Acidic environments facilitated the reduction processes at lower potentials. These findings will have a profound influence upon understanding the processes during reductive decontaminations of the polluted sites as well as for construction of highly sensitive sensors for their determination.

Two new lead(II) coordination polymer and discrete complex containing bipyridine ligands with different positioned methyl substituents: synthesis, characterization, crystal structure determination, and luminescent properties

Lead(II) coordination polymer [Pb(5,5′-dmbpy)(μ-NO3)2] n (1) and mononuclear complex [Pb(6,6′-dmbpy)(NO3)2] (2) (where 5,5′-dmbpy is 5,5′-dimethyl-2,2′-bipyridine and 6,6′-dmbpy is 6,6′-dimethyl-2,2′-bipyridine) were synthesized from reaction of lead(II) nitrate with 5,5′-dmbpy and 6,6′-dmbpy, respectively. Both complexes were thoroughly characterized by elemental analysis, infrared, 1H and 13C NMR, UV–Vis, emission spectroscopy, as well as single-crystal X-ray diffraction. Polymer 1 possesses one-dimensional (1D) chain structure, whilst complex 2 exhibits a discrete complex which provide an extended chain parallel to the [001] direction, via weak intermolecular C–H···O hydrogen bonding. Coordination number of Pb2+ in 1 and 2 are 8 and 6, respectively, with the stereochemically active lone pair, resulting in the hemidirected geometry for both complexes. The nitrate anions exhibit a tridentate chelating/bridging mode in 1, and a bi-chelating mode in 2. The supramolecular features in these complexes are guided/influenced by weak directional intermolecular C–H···O hydrogen bonding (1 and 2) together with π–π and C–H···π (1) interactions. The luminescence studies of 1 and 2 confirmed that the position of methyl substituent on 2,2′-bipyridine rings has a profound effect on the fluorescence emissions.

Effect of Oxygen Incorporation into Cyclohexanone Ring on Antifeedant Activity

Effect of Oxygen Incorporation into Cyclohexanone Ring on Antifeedant ActivityThe behaviour of the peach potato aphidMyzus persicae(Sulz.) was studied during settling on plants. The experiment involved observing peach potato aphid activity after the application of some natural and synthetic cyclohexanones and the, respective ε-lactones and epoxy-ε-lactones which were obtained from the cyclohexanones. Stereochemistry, and the number and position of methyl substituents were important for the biological activity of the starting compounds: only trimethyl-substituted cyclohexanones were active,i.e.3.3.5-trimethylcyclohexanone (deterrent) and 2.2.6-trimethylcyclohexanone (attractant). The effect of oxygen incorporation into the cyclohexanone ring on deterrent activity varied depending on the starting compound. The ε-lactones that derived from saturated cyclohexanones were either weak attractants or were inactive, except the deterrent ε-lactone with three methyl groups at positions 3.7.7. None of the products of unsaturated ketone isophorone (weak deterrent) oxidation,i.e.epoxy isophorone, epoxy lactone, or unsaturated lactone, affected aphid settling. Of the two epoxy ketones obtained from (+)-dihydrocarvone that was inactive, only (2S, 5S)-2-methyl-5-((S)-1-methyloxiranyl)-cyclohexanone was a strong deterrent. Both epoxy-ε-lactones that derived from (+)-dihydrocarvone were strong deterrents.

The effect of the position of methyl substituents on photophysical and photochemical properties of [Ru(x,x′-dmb)(CN)4]2− complexes: experimental confirmation of the theoretical predictions

The molecular geometry, electronic structure and electronic spectra and the energy levels of the molecular orbitals responsible for the photophysical characteristics of a series of solvent tunable [Ru(x,x'-dmb)(CN)(4)](2-) complexes (where x,x'-dmb = x,x'-dimethyl-2,2'-bipyridine) were calculated by density-functional theory-based quantum chemical methods, with the purpose of proposing for experimental study the best candidate for sensitizing electron- and energy transfer processes or for light induced structural changes in the molecule. The methods applied include geometry optimization using the B3LYP functional combination and various basis sets, time-dependent density functional theory with the B3LYP and PBE0 functionals, with and without explicit inclusion of coordinated solvent H(2)O molecules and the conductor-like polarizable continuum model for solvation. The accuracy of the theoretical predictions was tested by experiments: the model compounds have been synthesized and characterized by various spectroscopic methods, such as (1)H-NMR, UV-Vis absorption and emission spectroscopy and by cyclic voltammetry. Excellent correlation was found between the theoretically calculated and the experimentally determined photophysical and photochemical characteristics. The electronic transition energies measured in water are superbly reproduced by TD-PBE0 and well by TD-B3LYP, but the performance of both functionals is worse if the solvent is acetonitrile.

On the reactivity of methylbenzenes

Alkylated aromatic hydrocarbons, including the methylbenzenes, are a major and growing component of liquid transportation fuels. Reactivity (or lack thereof) for the methylbenzenes in combustion systems, measured by octane rating, ignition delay, and laminar flame speed, varies widely with the number and position of methyl substituents. At present this behaviour is not fully understood. This study demonstrates how the low temperature and ignition reactivity of methylbenzenes is controlled by the presence of isolated methyl groups and adjacent methyl pairs (the ortho effect); this allows for the development of octane number correlations. Introduction of an isolated methyl group, adjacent only to CH ring sites, consistently increases the research octane number (RON) by around 26. This phenomenon is explained by the formation of relatively unreactive benzyl free radicals. When an adjacent pair of methyl substituents is present the RON consistently decreases by between 8 and 26, compared to the case when these methyl groups are isolated from each other (this effect generally diminishes with increasing degree of substitution). Research octane numbers for all aromatics with zero to three methyl substituents are accurately described by the empirical relationship RON = 98 + 24.2 n m − 25.8 n p , where n m is the total number of methyl groups and n p is the number of contiguous adjacent methyl pairs. The ortho effect is attributed to the unique oxidation chemistry of o-methylbenzyl, o-methylbenzoxyl, and o-methylphenyl type radicals here we provide a preliminary exploration of this chemistry and highlight areas requiring further research. It is shown that the o-methylbenzyl radical can react with two oxygen molecules to form 1,2-diformylbenzene + 2OH + H, a highly chain-branching process. This chemistry is expected to largely explain the two-stage ignition and negative temperature coefficient (NTC) behavior witnessed for polymethylbenzenes with adjacent methyl pairs. Similar chain branching mechanisms exist in the oxidation of o-methylbenzoxyl radicals that also form during o-xylene ignition.

Separation of Tocopheryl Acetate Isomers on Porous Graphitic Carbon

Vitamin E is a collective term for tocopherols and tocotrienols that includes isomers differing in the number and position of methyl substituents. An LC impurity method was required to determine the purity of RRR-α-tocopheryl acetate, especially with regard to the amounts of the β- and γ-isomers which have one fewer methyl substituents. Using the Hypercarb porous graphitic carbon column, a normal phase LC method was developed that separates α-, β-, γ-, and δ-tocopheryl acetates using a mobile phase of 25:85 (v/v) THF:hexane. The area response with detection at 205 nm is linear for column loadings of 0.006–10 μg of α-tocopheryl acetate. It was also noted that SRR-α-tocopheryl acetate is partially resolved from RRR-α-tocopheryl acetate under these conditions.

Synthesis and characterization of fluorescent polyphenol species derived from methyl substituted aminopyridine based Schiff bases: The effect of substituent position on optical, electrical, electrochemical, and fluorescence properties

A series of pyridine based Schiff bases (3-MAPDHB, 4-MAPDHB, and 6-MAPDHB) which differ from each other by the position of methyl group were synthesized. Obtained Schiff bases were converted to their polyphenol species (P-3-MAPDHB, P-4-MAPDHB, and P-6-MAPDHB) by oxidative polymerization reaction (OP) using NaOCl as the oxidant. The structures of the synthesized compounds were characterized by solubility tests, FT-IR, UV–vis, NMR, TG-DTA, DSC and SEC techniques. The HOMO–LUMO energy levels and electrochemical ( E ′ g ) and optical ( E g ) band gaps were calculated from cyclic voltammetry (CV) and UV–vis measurements, respectively. Electrical conductivities of both doped and undoped states of the synthesized polyphenols were measured by four-point probe technique using a Keithley 2400 electrometer. P-3-MAPDHB showed the highest conductivity increase when doped with iodine. The effects of the position of methyl substituent bound with pyridine ring on electrochemical and electrical properties were also discussed. Their abilities of processing in gas sensors were also discussed depending on the increasing conductivities during exposure to iodine vapour. Photoluminescence (PL) properties of the synthesized materials were determined in solution forms using different solvents. Fluorescence measurements were carried out in various concentrated solutions to determine the optimum concentrations to obtain the maximal PL intensities. As a result, the presented pyridine based polyphenols are good candidates for electronic, opto-electronic, and photovoltaic applications due to polyconjugated structures and low band gaps. Additionally, the new polyphenols have high thermal stabilities and could be used in aerospace applications.

Thermodynamic and Kinetic Characterization of Porous Graphitic Carbon in Reversed‐Phase Liquid Chromatography

The thermodynamics and kinetics of solute transfer on porous graphitic carbon (PGC) are studied for two series of aromatic hydrocarbons, alkylbenzenes and methylbenzenes. The retention behavior is characterized as a function of temperature, pressure, length of alkyl chain, and number and position of methyl substituents. In the thermodynamic studies, the retention factor (k) increases with an increase in the length of alkyl chain or number of methyl substituents. The data indicate that increases in the number of methylene and methyl substituents result in more negative changes in molar enthalpy (ΔHsm). Hence, the transition from mobile to stationary phase is a more energetically favorable, exothermic process with each methylene or methyl group added. The data also show that the change in molar volume (ΔVsm) is close to zero, which is consistent with an adsorption mechanism on PGC. Enthalpy‐entropy compensation is observed for both homologous series, and the compensation temperature suggests that the retention mechanism is distinctly different for the methylene and methyl groups. In the kinetic studies, the rate of solute transfer increases with an increasing number of methylene and methyl groups. The activation enthalpy from the stationary phase to transition state (ΔH‡s) is found to increase with an increasing number of methylene and methyl groups. But the activation enthalpy from the mobile phase to transition state (ΔH‡m) is much smaller than ΔH‡s and, at the same time, is very similar for all the solutes. The activation volumes (ΔV‡s and ΔV‡m) are very close to zero, again owing to the adsorption mechanism on PGC. These results demonstrate that the retention mechanism for PGC, which is based on adsorption, is different from that for octadecylsilica, the most widely used stationary phase in liquid chromatography.