Position Of Aromatic Ring Research Articles

Insights into the role of potent thiadiazole based Schiff base derivatives in targeting type-II diabetes: A combine in-vitro and in-silico approaches

A novel series of varied substituted thiadiazole based Schiff base analogues (1–21) were designed and characterized using NMR (13C, 1H) and HREI-mass spectrometry, and secerned against the enzymes responsible for hyperglycemia i-e α-amylase and α-glucosidase. Newly designed analogues demonstrated distinct inhibitory activities having IC50= 1.10 ± 0.50 to 21.40 ± 0.20 µM (for alpha-amylase) and 2.50 ± 0.05 to 21.40 ± 0.10 µM (for alpha-glucosidase) in contrast to acarbose a well-known marketed drug (IC50 = 3.16 ± 0.22 & 4.8 ± 0.21 µM for α-amylase and α-glucosidase, respectively). Compound (20) with tri-fluoromethyl at para position of aromatic ring revealed as lead candidate among the members of synthesized series, having effective inhibitory activity against enzymes α-amylase and α-glucosidase. The excellent activity of compound (20) might be due to involvement of fluoro atom interacting via H-bonding with the active sites of enzymes α-amylase and α-glucosidase being targeted. Furthermore, for exploration of binding interactions of potent drugs, molecular docking was performed. For investigation of drug likeness and toxicity, ADME analysis was also conducted.

Characterization of thermodynamic properties on Al3+/dopamine system

The interactions of dopamine (Dop−) with aluminum were studied in NaCl(aq) at different ionic strengths (0.15 ≤ I/mol dm−3 ≤ 1.0) and temperatures (288.15 ≤ T/K ≤ 310.15). The investigations were carried out by using ISE-[H+] potentiometry, UV–Vis spectrophotometry and 1H NMR. The results obtained from the different techniques were in good agreement, both in terms of speciation model and stability constants of the complexes. The speciation model is featured by mononuclear complexes, namely: AlDop; AlDopOH; AlDop(OH)2 and AlDop(OH)3 (charges omitted). From 1H NMR investigations, it resulted that both the amino and the phenolic groups in meta position of aromatic ring are involved in the protonation equilibria, while the Al3+ complexation occurs from the catechol side of the ligand. The dependence on the ionic strength and temperature of the complex formation constants was modelled by a modified extended Debye-Hückel equation, containing a term for the dependence on T/K. The SIT approach allowed the calculation of the specific ion interaction coefficients of the aluminum:dopamine complexes. From the enthalpy change values obtained, it resulted that the formation of the species is exothermic in nature and that the entropy is the driving force of the processes. The sequestering ability of dopamine towards Al3+ was evaluated by the calculation of pL0.5 parameter at different ionic strengths, pHs and temperatures; the dependence of the pL0.5 on these variables was modelled by using an empirical predictive equation that allows the calculation of the effective sequestering ability of dopamine at desired conditions. The precipitates collected at the end of the potentiometric titrations were studied by means of thermogravimetric (TGA) analysis.

Bringing Selectivity in H/D Exchange Reactions Catalyzed by Metal Nanoparticles through Modulation of the Metal and the Ligand Shell

Ru and Rh nanoparticles catalyze the selective H/D exchange in phosphines using D2 as the deuterium source. The position of the deuterium incorporation is determined by the structure of the P-based substrates, while activity depends on the nature of the metal, the properties of the stabilizing agents, and the type of the substituent on phosphorus. The appropriate catalyst can thus be selected either for the exclusive H/D exchange in aromatic rings or also for alkyl substituents. The selectivity observed in each case provides relevant information on the coordination mode of the ligand. Density functional theory calculations provide insights into the H/D exchange mechanism and reveal a strong influence of the phosphine structure on the selectivity. The isotope exchange proceeds via C-H bond activation at nanoparticle edges. Phosphines with strong coordination through the phosphorus atom such as PPh3 or PPh2Me show preferred deuteration at ortho positions of aromatic rings and at the methyl substituents. This selectivity is observed because the corresponding C-H moieties can interact with the nanoparticle surface while the phosphine is P-coordinated, and the C-H activation results in stable metallacyclic intermediates. For weakly coordinating phosphines such as P(o-tolyl)3, the interaction with the nanoparticle can occur directly through phosphine substituents, and then, other deuteration patterns are observed.

Concerted effects of substituents in the reaction of [rad]OH with 2-, 3-, and 4-hydroxybiphenyls

Studies on the distribution of products in radiolytic hydroxylation of hydroxybiphenyls (HBPs) to obtain information on the concerted effect of substituent groups at the OH addition site have been conducted. Liquid chromatography was used to analyze the radiolytic products. Results show that OH is selectively added to the free positions of aromatic rings and the directing effect of the substituents was –OH > phenol > phenyl. The yields of each product are provided; these reflect the charge distribution in the HBP, such that the phenyl ring modified the ortho-para directing effect of the –OH substituent. The ratio of addition of the OH to the HBPs obtained provide a quantitative basis for considering the effect of substituents in determining the site of OH attack on these compounds and provides additional valuable data on the attack of the OH for studies on the degradation of aromatic compounds present in polluted waters.

Computationally designed ligands enable tunable borylation of remote C–H bonds in arenes

<h2>Summary</h2> An ideal way to synthesize multi-substituted arenes is the selective installation of any group on any position of aromatic rings with any substituent. However, reactant-controlled selective functionalization of both <i>meta</i>- and <i>para</i>-C–H bonds is essentially impossible because of their intrinsically contradictory electronic and steric demands. Here, we report the first examples of catalysts that can direct the tunable borylation of a variety of arenes with precise control at either <i>meta</i> or <i>para</i> site through the computational design of ligands. A wide range of hydrogen bond acceptors can serve as directing groups, including Weinreb amides, phosphonates, and boronates, which can be easily transformed into many different types of functional groups. This work also showcases the critical role of transition-state calculations in catalyst design for remote C–H activation.

Novel insight into the mechanism of coal hydropyrolysis using deuterium tracer method

In this work, the mechanism of coal hydropyrolysis was investigated by using deuterium tracer method. To figure out how hydrogen reacts with coal at the temperature below 400 °C, chars from coal pyrolysis in D2 and N2 atmospheres when the pyrolysis temperature is at 150 to 400 °C were measured by isotope ratio mass spectrometry (IRMS) and electron paramagnetic resonance spectroscopy. The results show that H2 can react with stable radicals in coal during coal pyrolysis without catalyst at temperature as low as 200 °C. To obtain deep insight on which hydrogen transfer pathways affect pyrolysis product distributions of coal, IRMS combined with elemental analyzer and 2H NMR were used to obtain quantitative and qualitative date of deuterium in products. The results suggest that hydrogen atoms are introduced into tar mainly through radicals induce effect during coal pyrolysis without catalyst. And some of non-volatile radicals can abstract hydrogen atoms from H2. Hydrogen atom of H2 can incorporate all structural groups in the tar during coal pyrolysis, and it incorporates preferentially into 1-and 2-ring aromatic carbon and aliphatic carbon in the β or further positions of aromatic ring.

Investigation on the structure-performance of phthalic acid carboxyl position and carbon nitride towards efficient photocatalytic degradation of organic pollutants

Polymeric carbon nitride as photocatalysts to address environmental issues attract broad interest. Anchoring aromatic ring on CN surface can improve its charge pair separation, but the effect of functional group position of aromatic ring on its performance is ignored. Herein, we used three isomers of phthalic acid (phthalic acid, isophthalic acid and terephthalic acid) and urea to synthesize modified carbon nitride as a photocatalyst to remove sulfamethazine (SMZ). The phthalic acid may act as group modification and enhanced the absorption of longer wavelengths of carbon nitride, while part of isophthalic acid and terephthalic acid may enter the framework of carbon nitride as benzene ring and the others may act as the amorphous carbon in carbon nitride. Consequently, the phthalic acid modified carbon nitride (PA-CN) exhibited the optimal degradation performance for SMZ removal (0.0737 min−1). It was further revealed that the O2− and h+ played the significant role in the photocatalytic process. This study reveals the effect of the position of organic acid functional groups on the performance of carbon nitride, and points out that PA-CN can be applied to the purification of wastewater containing refractory pollutants.

Synthesis and Evaluation of Anticonvulsant Activity of Some Quinazoline Analogues

Aim: A new series of Quinazoline 4(3H)-one derivative were prepared by reacting quinazoline 4(3H)-one hydrazide with substituted aromatic aldehydes. Quinazoline is used as a potent pharmacological agent with various biological activities such as antimicrobial, antiviral, antitumor, convulsion, anxiety, anti-inflammatory, and analgesic. In this background, we have synthesized a series of Quinazoline 4(3H)-one derivatives (4a-4f) and screened for their anticonvulsant activity. &#x0D; Methods: In this work, Schiff bases were prepared by treating quinazoline 4(3H)-one hydrazide with aromatic aldehydes. Six compounds (4a-4f) were screened for anticonvulsant activity by Isoniazid (INH) and Pentylenetetrazole (PTZ) induced convulsions in mice.&#x0D; Results: All the compounds were given satisfactory reaction yields that representing the efficiency of the employed synthetic route. In INH induced convulsion model, delayed the onset of convulsion significantly 4a, 4b, 4d, 4e, 4f when compared to an induction control group. Whereas delayed onset of convulsion was non-significant for 4c. In PTZ induced convulsion model, delayed the onset of convulsion significantly 4a, 4d, 4e, 4f when compared to induction control group. Whereas delayed onset of convulsion was non-significant for 4b and 4c.&#x0D; Conclusion: This indicates the anticonvulsant activity to these derivatives which might be due to potentiating GABA activity in the CNS. This anticonvulsant activity was due to presence of electron-donating group like OH, NH2, OCH3 and electron-withdrawing group like CF3 at 2nd and 4th position of aromatic ring attached to hydrazide.

Sustainable production and co-immobilization of cold-active enzymes from Pseudomonas sp. for BTEX biodegradation

Toluene/o-Xylene Monooxygenase (ToMO) is equipped with a broad spectrum of aromatic substrate specificity (such as BTEX; benzene, toluene, ethylbenzene, and isomers of xylenes). TOMO has can hydroxylate more than a single position of aromatic rings in two consecutive monooxygenation reactions. Catechol 1,2-dioxygenase (C1,2D) is an iron-containing enzyme able to cleave the ring of catechol (the converted product from ToMO) for complete detoxification of BTEX. In this study, cold-active ToMO and C1,2D were produced using newly isolated psychrophilic Pseudomonas S2TR-14 in the minimal salt medium supplemented with crustacean waste and different concentrations of used motor oil (0.2–2% (v/v)). Crude ToMO and C1,2D were immobilized into micro/nano biochar-chitosan matrices and used for BTEX biodegradation. The results showed that the highest enzyme production (12 U/mg for ToMO and 22 U/mg for C1,2D) was achieved at the presence of 0.5% v/v used motor oil compared to the control group without motor oil (0.07 and 0.06 U/mg). High immobilization yield was achieved due to covalent bonding of ToMO (92.26% for micro matrix and 77.20% for nano matrix) and C1,2D (87.57% for micro matrix and 74.79% for nano matrix) with matrices. FTIR spectra confirmed the immobilization of enzymes on the surface of microbiochar and nanobiochar-chitosan matrices as proper support. The immobilization increased the storage stability of the enzymes with more than 50% residual activity after 30 days at 4 ± 1 °C, while the free form of enzymes had less than 10% of its activity. Immobilized enzymes degraded more than 80% of BTEX (~200 mg/L in groundwater and ~10,000 mg/kg in soil) at 10 ± 1 °C in groundwater and soil. Therefore, integrated use of microbiochar and nanobiochar with chitosan for co-immobilization of ToMO and C1,2D can be a potential way to remove petroleum hydrocarbons with higher efficiency from contaminated groundwater and soil.

Molecular stiffness and aromatic ring position – Crucial structural factors in the self-assembly processes of phenyl alcohols

The combination of dielectric, infrared, and diffraction studies was used to study the impact of the phenyl ring and molecular stiffness on the self-assembly phenomena in four model aromatic alcohols: 1-phenyl-1-propanol, 3-phenyl-1-propanol, 1-phenyl-2-propyn-1-ol and 3-phenyl-2-propyn-1-ol. Firstly, it is shown that even highly sterically hindered molecules can associate and organize themselves into nanosized clusters. However, their size, concentration, and degree of order decrease with growing steric hindrance and intramolecular stiffness. Secondly, a twofold intermolecular assembly via O-H…π and O-H…O schemes is proved to exist in the aromatic alcohols. Consequently, the mechanism of hindering effect of the phenyl ring on the self-assembly is ascribed to its double role: (i) as a steric hindrance and (ii) as a source of O-H…π interactions, competitive with the hydrogen bonds of O-H…O scheme. Finally, it is shown that the growing tendency to self-association does not implicate the increase in the intermolecular ordering on a scale greater than one nanometer.

Molecular Docking Q-SAR Studies of Benzimidazole as Antifungal Nucleus

Benzimidazole and its derivatives are used in organic synthesis and vermicides or fungicides as they inhibit the action of certain microorganisms. The molecules to be analysed were aligned on an appropriate template, which is considered to be common substructure. The protein structure of PDB name along with their inhibitor was retrieved from RCSB Protein Data Bank (PDB entry code: 6T1O). The protein structure were subjected to energy minimization and charge calculation (AMBER7FF99), docking score of compounds on 6T1O PDB describe the ligand interaction. Virtual library of benzimidazoles derivatives to find lead structures to test against C. albicans. Twenty compounds were designed in which heterocyclic ring is substituted at NH group of Substituted ortho-phenylenediamine moiety while some compound also bearing chloro and nitro group on para position of aromatic ring.

Effect of the heteroatom presence in different positions of the model asphaltene structure on the self-aggregation: MD and DFT study

In this study, a series of heteroatoms including nitrogen, oxygen, and sulfur were added to different positions of the model asphaltene structure to study the effect of the heteroatom presence in the self-aggregation of the model asphaltenes. Molecular Dynamics was used to calculate Solubility Parameters, Radial Distribution Function, and Relative Solubility Parameters. Additionally, Reactivity Parameters, Electrostatic Potential, Reduced Density Gradient, and Independent Gradient Model were calculated using the Density Functional Theory to further investigate the Molecular Dynamics results. This study indicated that heteroatoms' diversity and their positions in the model asphaltene structure had an essential role in forming the model asphaltene aggregates. Four different sites in the model asphaltene structure were selected to study the impact of the heteroatom position in the self-aggregation. The presence of heteroatoms in the aliphatic side-chain proved to be more effective in increasing the self-aggregation process in comparison to the aromatic ring position. The heteroatoms' presence in the terminal position of the aliphatic side-chain increased the self-aggregation strength more than other sites in the aliphatic side-chain based on the terminal heteroatoms' ability to perform hydrogen bond formation. Additionally, heteroatoms in the middle of the aliphatic side-chain increased the CH…C dispersion interaction by the carbons' polarization. The heteroatoms in the aliphatic side-chain sites, especially in the terminal position, decreased the asphaltenes' solubility in the heptane and toluene more than the aromatic ring position.

Development of Novel Diclofenac Analogs Designed to Avoid Metabolic Activation and Hepatocyte Toxicity.

Diclofenac (DCF) is widely used as a nonsteroidal anti-inflammatory drug; however, it is associated with severe liver injury. This adverse reaction is thought to be related to the reactive quinone imine (QI) and acyl glucuronide (AG) metabolites of DCF, but it remains controversial which reactive metabolites mainly contribute to DCF-induced toxicity. In this study, we synthesized five types of DCF analogs that were designed to mitigate the formation of reactive QI and/or AG metabolites and evaluated their metabolic stability, cyclooxygenase (COX) inhibitory activity, and toxicity to cryopreserved human hepatocytes. Compounds with fluorine at the 5- and 4′-positions of aromatic rings exhibited modest and high metabolic stability to oxidation by cytochrome P450, respectively, but induced cytotoxicity comparable to DCF. Replacing the carboxylic group of DCF with its bioisosteres was effective in terms of stability to oxidative metabolism and glucuronidation; however, sulfonic acid and sulfonamide groups were not preferable for COX inhibition, and tetrazole-containing analogs induced strong cytotoxicity. On the other hand, compounds that have fluorine at the benzylic position were resistant to glucuronidation and showed little toxicity to hepatocytes. In addition, among these compounds, those with hydrogen at the 4′-position (2a and 2c) selectively inhibited the COX-2 enzyme. Throughout these data, it was suggested that compounds 2a and 2c might be novel safer and more efficacious drug candidates instead of DCF.

Synthesis and Biological Evaluation of Halogenated E-Stilbenols as Promising Antiaging Agents.

The increased risk of illness and disability is related to the age inevitable biological changes. Oxidative stress is a proposed mechanism for many age-related diseases. The crucial importance of polyphenol pharmacophore for aging process is largely described thanks to its effects on concentrations of reactive oxygen species. Resveratrol (3,5,4′-trihydroxy-trans-stilbene, RSV) plays a critical role in slowing the aging process but has a poor bioavailabity after oral intake. In this present work, a series of RSV derivatives was designed, synthesized, and evaluated as potential antioxidant agents. These derivatives contain substituents with different electronic and steric properties in different positions of aromatic rings. This kind of substituents affects the activity and the bioavailability of these compounds compared with RSV used as reference compound. Studies of Log P values demonstrated that the introduction of halogens gives the optimum lipophilicity to be considered promising active agents. Among them, compound 6 showed the higher antioxidant activity than RSV. The presence of trifluoromethyl group together with a chlorine atom increased the antioxidant activity compared to RSV.

α-Functionalisation of Ketones Through Metal-Free Electrophilic Activation.

Triflic anhydride mediated activation of acetophenones leads to highly electrophilic intermediates that can undergo a variety of transformations when treated with nucleophiles. This electrophilic ketone activation gives access to α‐arylated and α‐oxyaminated acetophenones under metal‐free conditions in moderate to excellent yields and enables extension to the synthesis of arylated morpholines via generation of vinylsulfonium salts. Computational investigations confirmed the transient existence of intermediates derived from vinyl triflates and the role of the oxygen atoms at the para position of aromatic ring in facilitating their stabilisation.

Preventive potential and mechanism of dietary polyphenols on the formation of heterocyclic aromatic amines

AbstractThermal processing is the most important and popular domestic cooking method. More than 30 heterocyclic aromatic amines have been identified in cooked meat using various methods. This review highlights preventive potential and mechanism of dietary polyphenols on the formation of heterocyclic amines. Tea, coffee, fruits, vegetable, and spice extracts rich in polyphenols exerted significant inhibition against the formation of heterocyclic aromatic amines. Some polyphenols, such as naringenin and epigallocatechin 3‐O‐gallate, can actively participate into food chemistry reaction to trap Strecker aldehyde and lower the formation of heterocyclic aromatic amines. In addition, some polyphenols can lower the mutagenicity of heterocyclic aromatic amines. More specifically, polyphenols possessing two hydroxyl groups at the meta position of aromatic ring are the most efficient one, but the presence of carboxylic or alkyl groups as substituents in the aromatic ring slightly reduced the inhibitory effect.

Systematic study of catalytic degradation of nitrobenzene derivatives using core@shell composite micro particles as catalyst

Polystyrene-poly(N-isopropylmethacrylamide-acrylic acid) [Pst@pnIPM-Ac] core@shell micro particles were synthesized by two step method and used as template for the fabrication of silver nanoparticles (silver-NPs). Silver-NPs were loaded in shell of core@shell micro particles from in-situ reduction of AgNO3 salt using NaBH4 as reductant. Pure Pst@pnIPM-Ac core@shell micro particles and silver-NPs endowed silver-Pst@pnIPM-Ac core@shell composite micro particles were characterized by Fourier transform infrared spectroscopy (FT-Ir), UV visible spectroscopy (UV vis), transmission electron microscopy (TEM) and dynamic light scattering (DLS). Morphological analysis revealed that micro particles showed core@shell morphology while the diameter of Pst core and pnIPM-Ac shell was found in range of 0.12 to 0.14 μm and 0.081 to 0.083 μm, respectively. Pst@pnIPM-Ac micro particles showed response to change in pH of the medium due to presence of acrylic acid (Ac) unit in polymer network. Catalytic properties of silver-Pst@pnIPM-Ac core@shell hybrid micro particles were checked by reducing the nitrobenzene derivatives (NbD) possessing different substitute at para position of aromatic ring [p-nitro toluene (p-NT) and p-chloro nitrobenzene (p-CNB)] using NaBH4 as reductant. Values of apparent rate constant (kapp) were found to be 0.1532 and 0.103 min−1 for the reduction of p-NT and p-CNB, respectively. Effect of concentration of NaBH4 and catalyst dose on the value of kapp for reduction of p-NT was also investigated. Kinetic analysis illustrated that NbD reduction followed Langmuir-Hinshelwood mechanism. Prepared silver-Pst@pnIPM-Ac composite micro particles catalyst was found to be efficient for reduction of NbD. Recyclability and reusability of reported catalyst was also checked for the reduction of p-NT. It was observed that silver-Pst@pnIPM-Ac core@shell composite micro particles maintained the percentage activity in the range of 97–100 % for three successive cycles for the reduction of p-NT. The protocol adopted for the catalytic reduction of p-NT was proved to be effective.

Design, Synthesis and Molecular Docking Studies of Novel Thiadiazole Analogues with Potential Antimicrobial and Antiinflammatory Activities.

Chemical modification of thiadiazole may lead to a potent therapeutic agent. In this study, biological properties of thiadiazole derivatives were evaluated by assessing their antimicrobial and anti-inflammatory activities. A series of novel derivatives of N-(5-(1-methyl-indol-3-yl)-1,3,4-thiadiazol-2- yl)-2-(5-substitutedphenyl)-3-(phenylamino)-4,5-dihydropyrazol-1-yl) acetamide have been synthesized and evaluated for their antimicrobial activity. Anti-inflammatory activity was done using carrageenan-induced inflammation in rat paw edema model. In-silico molecular docking studies of the synthesized compounds were performed on crystal structures of Aspergillus niger, Bacillus subtilis, Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Cyclooxygenase-2 (obtained from www.rcsb.org) using GRIP batch docking method of V-life MDS 3.0 software. The structures of the newly synthesized compounds were confirmed by FT-IR, 1H-NMR, 13C-NMR and Mass spectroscopy. Antimicrobial and Anti-inflammatory activity study of the novel synthesized compounds were screened. Synthesized compounds having methoxy substitution on the 3rd and 4th positions of aromatic ring are utmost active amongst all the derivatives. Compounds 6d, 6i, 6j and 6l were found to possess good anti-inflammatory activity having percentage of inhibition to the extent of 46.8%, 48.1%, 49.4%, and 48.5% as compared with Diclofenac. The experimental results were further supported by molecular docking analysis describing the better interaction patterns.

Catechol thioethers with physiologically active fragments: Electrochemistry, antioxidant and cryoprotective activities

A number of asymmetrical thioethers based on 3,5-di-tert-butylcatechol containing sulfur atom bonding with physiologically active groups in the sixth position of aromatic ring have been synthesized and the electrochemical properties, antioxidant, cryoprotective activities of new thioethers have been evaluated. Cyclic voltammetry was used to estimate the oxidation potentials of thioethers in acetonitrile. The electrooxidation of compounds at the first stage leads to the formation of o-benzoquinones. The antioxidant activities of the compounds were determined using 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH) assay, experiments on the oxidative damage of the DNA, the reaction of 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH) induced glutathione depletion (GSH), the process of lipid peroxidation of rat liver (Wistar) homogenates in vitro, and iron(II) chelation test. Compounds 1–9 have greater antioxidant effectiveness than 3,5-di-tert-butylcatechol (CatH2) in all assays. The variation of physiologically active groups at sulfur atom allows to regulate lipophilic properties and antioxidant activity of compounds. Thioethers 3, 4 and 7 demonstrate the combination of radical scavenging, antioxidant activity and iron(II) binding properties. The researched compounds 1–9 were studied as possible cryoprotectants of the media for cryopreservation of the Russian sturgeon sperm. Novel cryoprotective additives in cryomedium reduce significantly the content of membrane-permeating agent (DMSO). A cryoprotective effect of an addition of the catechol thioethers depends on the structure of groups at sulfur atom. The cryoprotective properties of compounds 3, 4 and 7 are caused by combination of catechol fragment, bonded by a thioether linker with a long hydrocarbon chain and a terminal ionizable group or with a biologically relevant acetylcysteine residue.

Mechanistic study of methylbenzene dealkylation in methanol-to-olefins catalysis on HSAPO-34

Methylbenzenes entrained within the cavities of silicoaluminophosphate zeotype HSAPO-34 react with methanol in H+-mediated dealkylation to give ethylene and propylene in methanol-to-olefins catalysis. Methylbenzenes dealkylation on solid acids is proposed to occur either via the side-chain mechanism, where an exocyclic CC undergoes successive methylation prior to CC cleavage for olefin elimination, or the paring mechanism, where ring contraction to a bicyclohexenyl cation precedes CC cleavage for olefin elimination. Distinct dealkylation mechanisms prescribe distinct combinations of C atoms—from aromatic methyl, aromatic ring, and methanol/dimethyl ether—to comprise the olefin product. Site-specific isotope tracing that distinguishes between isotope labels in aromatic methyl and aromatic ring positions for each methylbenzene shows that tetramethylbenzene gives ethylene via the side-chain mechanism and penta- and hexamethylbenzene give propylene via the paring mechanism. The ratio of propylene selectivity to ethylene selectivity increases in methanol reactions on HSAPO-34 entrained with a distribution of methylbenzenes deliberately manipulated towards increasing fractions of penta- and hexamethylbenzene, corroborating the conclusion that aromatic precursors and dealkylation mechanisms for ethylene diverge from those for propylene.