Adjacent Methyl Research Articles

The pronounced NTC behavior of 1,2,4-trimethylbenzene at high-pressure oxidation

This study presents experimental and modeling results of the 1,2,4-trimethylbenzene (T124MBZ) oxidation in a jet-stirred reactor at equivalence ratios of 0.4 and 2.0, temperature range of 450–1000 K, and pressure of 12.0 atm. Compared with the oxidation at atmospheric pressure, a pronounced negative temperature coefficient (NTC) behavior of T124MBZ was observed between 622 K and 773 K under fuel-lean condition. A detailed chemical kinetic model involving 865 species and 5092 reactions was developed. In addition, the model was validated against experimental results of laminar burning velocities and ignition delay times. The present model reasonably reproduces these experimental data. The dominant consumption channels for T124MBZ are H-abstraction reactions on methyl groups by OH radicals. The H-abstraction reactions on the 1- and 2- methyl sites by OH radicals are the most promoting in pre- and mid- NTC phases, and H2O2(+M) = 2OH(+M) is the most promoting in the post-NTC phase, while the reaction on the 4-methyl site is the most inhibiting across pre-, mid-, and post-NTC phases. This difference arises from the fact that the dominant consumption pathway for 2,4-dimethylbenzyl and 2,5-dimethylbenzyl involves H-transfer, while the 4-methyl site cannot undergo an H-transfer reaction due to the absence of adjacent methyl groups. The competition between the two consumption channels of ·QOOH radicals (decomposition and second O2 addition), resulting in the reduction of OH radicals as temperature increases, leads to diminished OH production. This causes the emergence of pronounced NTC behavior at high pressure.

Unraveling the C–C coupling mechanism on Ni–O–Fe asymmetric sites for photocatalytic nonoxidative coupling of methane

Photocatalytic non-oxidative coupling of methane is an attractive strategy for CH4 to C2 conversion, how to facilitate the photogenerated charge separation and accelerate the C–C coupling to promote the reaction kinetics remains a great challenge. Herein, a symbiotic r-Fe2O3/NiO heterostructure with robust interfaces is constructed in situ. The coherent interface not only provides unique Ni–O–Fe asymmetric sites, but also achieves the separation and transport of photogenerated charge. The unbalanced charge density distribution of two adjacent methyl or methylene at the Ni–O–Fe asymmetric site alleviates the dipole repulsion of the C–C coupling, and promotes C–C coupling to form C2 hydrocarbons. Under visible light irradiation, the optimal r-Fe2O3/NiO performs a brilliant C2 activity up to 71.00 μmol g−1h−1, and the C2H4 yield can reach a high value of 40.46 μmol g−1h−1 and the selectivity of 56.98 %. This work provides new insights into the coupling of C–C to generate C2 hydrocarbons.

Butyl (2,2-Dibutoxybutanoyl)-ʟ-Tryptophanate

The multicomponent reaction between ʟ-tryptophan 1, 2-oxobutanoic acid 2, and 1-butanol in the presence of SiMe3Cl was studied using microwave irradiation conditions. The main product was identified as an unreported acetal-containing compound, namely, butyl (2,2-dibutoxybutanoyl)-ʟ-tryptophanate (3), yielding 89%. NMR experiments demonstrated that the adjacent methylene protons of the acetal group appeared as two signals exhibiting their behavior as diastereotopic protons. DFT/B3LYP calculations revealed an asymmetric molecular structure with specific angles, leading to an explanation of the NMR results. The calculated chemical shifts showed slight differences with the experimental values and suggested magnetic anisotropy and inductive deprotection around the methylene hydrogen atoms in the acetal location. The reaction mechanism was proposed in which SiMe3Cl plays a crucial role by promoting water removal through key steps.

Tricoordinate Beryllium Radicals and Their Reactivity.

The one-electron reduction of [(CAAC)Be(Dur)Br] (CAAC = cyclic alkyl(amino)carbene, Dur = 2,3,5,6-tetramethylphenyl = duryl) with lithium sand in diethyl ether yields the first neutral, tricoordinate, and moderately stable beryllium radical, [(CAAC)(Et2O)BeDur]• (2-Et2O), which undergoes a facile second one-electron reduction concomitant with the insertion of the beryllium center into the endocyclic C-NCAAC bond and a cyclopropane-forming C-H bond activation of an adjacent methyl group. In situ generation of 2-Et2O and addition of PMe3 yield the stable analogue, [(CAAC)(Me3P)BeDur]• (2-PMe3), which serves as a platform for PMe3-ligand exchange with stronger donors, generating the radicals [(CAAC)LBeDur]• (2-L, L = isocyanides, pyridines, and N-heterocyclic carbenes). X-ray structural analyses show trigonal-planar beryllium centers and strong π backbonding from the metal to the CAAC ligand. The EPR signals of all six isolated [(CAAC)LBeDur]• radicals display significant, albeit small, hyperfine coupling to the 9Be nucleus. DFT calculations show that the spin density is mostly delocalized over the CAAC π framework and, where present, the isocyanide CN moiety, with only a small proportion (3-6%) on the beryllium center. 2-PMe3 proved thermally unstable at 80 °C, first undergoing radical hydrogen abstraction with the solvent, followed by insertion of beryllium into the endocyclic C-NCAAC bond and PMe3 transfer to the former carbene carbon atom. The reactions with diphenyl disulfide and phenyl azide occur at the beryllium center and yield the corresponding Be(II) phenyl sulfide and amino complexes, respectively, the latter concomitant with radical transfer and hydrogen abstraction by the beryllium-bound nitrogen center.

Synthesis and properties of biodegradable poly(ethylene succinate) containing two adjacent side methyl groups

To adjust the structure and properties of biodegradable poly(ethylene succinate) (PES), a series of novel poly(ethylene succinate-co-2,3-butylene succinate) (2,3-PEBS) copolyesters with low contents of 2,3-butylene succinate unit (2,3-BS) were successfully synthesized in this research via a two-stage melt polycondensation. 2,3-PEBS showed the same main chain structure as PES, except that a few of two adjacent side methyl groups were randomly linked with the main chain; therefore, 2,3-PEBS may be regarded as novel PES containing two adjacent side methyl groups. The thermal parameters, crystallization behavior, and mechanical property of 2,3-PEBS copolyesters and PES were systematically studied and compared with each other. The compositions of ethylene succinate (ES) to 2,3-BS deviated significantly from the feed ratio of ethylene glycol to 2,3-butanediol (2,3-BDO) due to the low reactivity of 2,3-BDO. The results revealed that the introduction of a small amount of two adjacent side methyl groups brought an obvious variation in the thermal and mechanical properties of PES. However, 2,3-PEBS displayed the same crystallization mechanism and crystal structure as PES. Through the introduction of a few of two adjacent side methyl groups, novel PES with significantly improved mechanical properties was synthesized, which should be interesting and important for a better understanding of the structure and properties to prepare novel biodegradable polymers from a sustainable viewpoint.

Regio-controllable [2+2] benzannulation with two adjacent C(sp3)-H bonds.

Regiocontrol in traditional cycloaddition reactions between unsaturated carbon compounds is often challenging. The increasing focus in modern medicinal chemistry on benzocyclobutene (BCB) scaffolds indicates the need for alternative, more selective routes to diverse rigid carbocycles rich in C(sp3) character. Here, we report a palladium-catalyzed double C-H activation of two adjacent methylene units in carboxylic acids, enabled by bidentate amide-pyridone ligands, to achieve a regio-controllable synthesis of BCBs through a formal [2+2] cycloaddition involving σ bonds only (two C-H bonds and two aryl-halogen bonds). A wide range of cyclic and acyclic aliphatic acids, as well as dihaloheteroarenes, are compatible, generating diversely functionalized BCBs and hetero-BCBs present in drug molecules and bioactive natural products.

Dominant changes in centre Fe atom of decamethyl-ferrocene from ferrocene in methylation

Staggered decamethyl-ferrocene (*Fc) becomes the lower energy conformer at low temperature, whereas the eclipsed conformer of ferrocene (Fc) is more stable. The powerful infrared (IR) spectroscopy which has remarkably provided signatures of ferrocene (Fc) in eclipsed and staggered conformers recently is employed to investigate methylation of Fc. The most significant consequences of the full methylation of Fc in the IR spectra are the blue shift of the band at ~ 800 cm−1 in Fc to ~ 1500 cm−1 in *Fc, and the enhancement of the C–H stretch band at ~ 3200 cm−1 region in *Fc. Further analysis reveals large impact of Fc methylation on core electron energies of the centre Fe atom (1s22s22p63s23p6). The Fe core electron energy changes can be as large as ~ 10 kcal mol−1 and are directional—the Fe 2pz and 3pz orbitals along the *Cp–Fe–*Cp axis (Cp centroids, vertical) change more strongly than other Fe core electrons in px and py orbitals. The directional inner shell energy changes are evidenced by larger inner shell reorganization energy. Energy decomposition analysis (EDA) indicates that methyl groups in *Fc apparently change the physical energy components with respect to Fc. The large steric energy of *Fc evidences that the closest hydrogens on adjacent methyl groups of the same *Cp ring in crystal structure are 0.2–0.4 Å closer than the hydrogens on nearest-neighbour methyl groups on opposing rings in *Fc. A significant increase in Pauli repulsive energy contributes to the large repulsive steric energy in *Fc.

Stereoselective Knoevenagel reaction between pyrimidine carbaldehyde bearing an adjacent aryl group and active cyano-containing methylene compounds

The Knoevenagel reaction between cyanoacetic acid and 4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-methanesulfonylamino)-5-pyrimidinecarboxaldehyde (1), which contains an aryl group adjacent to the formyl group in the pyrimidine-5-carbaldehyde moiety, was found to proceed stereoselectively to give an alkene product bearing cyano and phenyl groups in a cis relationship. Similar selective reactions also occurred between 1 and several active methylene compounds bearing a cyano group. An X-ray structure analysis of the alkene products and molecular orbital calculations suggested that the attractive CN/π interaction between the cyano and 4-fluorophenyl groups of 1 plays an important role in the selectivity by stabilizing the carbocation intermediates.

Biodegradable surfactants from side streams of the vegetable oils production in technical systems

This work reports the structure of surfactants synthesized from by-products of the vegetable oil production. These are raw materials that do not compete with food products; they are low-cost phosphatidic sludge that can be used directly for chemical transformation. Fatty acid monoetanolamides derived from side streams of the vegetable oils production do not have residues of the original phosphatides or acylglycerols as determined by spectral methods. There are clearly reflected cross-peaks between the amide group and the adjacent methylene group. This indicates a high conversion of substrate and further confirms the amidation reaction. The main acyl residue of the synthesized surfactants are hydrocarbon chain of linoleic acid however, while the detection of methylene groups near double bonds indicates the presence of other fatty acids (oleic, linolenic and gadolein), this corresponds to the fatty acid composition of the original phosphatidic sludge. Synthesized surfactants are effective emulsifiers-stabilizers for dispersed systems. The use of environmentally friendly components in the composition of surfactants improves their biodegradability to 83–86%.

Changes in the Distribution of Membrane Lipids during Growth of Thermotoga maritima at Different Temperatures: Indications for the Potential Mechanism of Biosynthesis of Ether-Bound Diabolic Acid (Membrane-Spanning) Lipids.

ABSTRACTMembrane-spanning lipids are present in a wide variety of archaea, but they are rarely in bacteria. Nevertheless, the (hyper)thermophilic members of the order Thermotogales harbor tetraester, tetraether, and mixed ether/ester membrane-spanning lipids mostly composed of core lipids derived from diabolic acids, C30, C32, and C34 dicarboxylic acids with two adjacent mid-chain methyl substituents. Lipid analysis of Thermotoga maritima across growth phases revealed a decrease of the relative abundance of fatty acids together with an increase of diabolic acids with independence of growth temperature. We also identified isomers of C30 and C32 diabolic acids, i.e., dicarboxylic acids with only one methyl group at C-15. Their distribution suggests they are products of the condensation reaction but are preferably produced when the length of the acyl chains is not optimal. Compared with growth at the optimal temperature of 80°C, an increase of glycerol ether-derived lipids was observed at 55°C. Our analysis only detected diabolic acid-containing intact polar lipids with phosphoglycerol (PG) head groups. Considering these findings, we hypothesize a biosynthetic pathway for the synthesis of membrane-spanning lipids based on PG polar lipid formation, suggesting that the protein catalyzing this process is a membrane protein. We also identified, by genomic and protein domain analyses, a gene coding for a putative plasmalogen synthase homologue in T. maritima that is also present in other bacteria producing sn-1-alkyl ether lipids but not plasmalogens, suggesting it is involved in the conversion of the ester-to-ether bond in the diabolic acids bound in membrane-spanning lipids.IMPORTANCE Membrane-spanning lipids are unique compounds found in most archaeal membranes, but they are also present in specific bacterial groups like the Thermotogales. The synthesis and physiological role of membrane-spanning lipids in bacteria represent an evolutionary and biochemical open question that points to the differentiation of the membrane lipid composition. Understanding the formation of membrane-spanning lipids is crucial to solving this question and identifying the enzymatic and biochemical mechanism performing this procedure. In the present work, we found changes at the core lipid level, and we propose that the growth phase drives the biosynthesis of these lipids rather than temperature. Our results identified physiological conditions influencing the membrane-spanning lipid biosynthetic process, which can further clarify the pathway leading to the biosynthesis of these compounds.

Discovery of HN37 as a Potent and Chemically Stable Antiepileptic Drug Candidate.

We previously reported that P-retigabine (P-RTG), a retigabine (RTG) analogue bearing a propargyl group at the nitrogen atom in the linker of RTG, displayed moderate anticonvulsant efficacy. Recently, our further efforts led to the discovery of HN37 (pynegabine), which demonstrated satisfactory chemical stability upon deleting the ortho liable -NH2 group and installing two adjacent methyl groups to the carbamate motif. HN37 exhibited enhanced activation potency toward neuronal Kv7 channels and high in vivo efficacy in a range of pre-clinical seizure models, including the maximal electroshock test and a 6 Hz model of pharmacoresistant limbic seizures. With its improved chemical stability, strong efficacy, and better safety margin, HN37 has progressed to clinical trial in China for epilepsy treatment.

Marinoterpins A-C: Rare Linear Merosesterterpenoids from Marine-Derived Actinomycete Bacteria of the Family Streptomycetaceae.

The chemical examination of two undescribed marine actinobacteria has yielded three rare merosesterterpenoids, marinoterpins A–C (1–3, respectively). These compounds were isolated from the culture broth extracts of two marine-derived actinomycetes associated with the family Streptomycetaceae, (our strains were CNQ-253 and AJS-327). The structures of the new compounds were determined by extensive interpretation of 1D and 2D NMR, MS, and combined spectroscopic data. These compounds represent new chemical motifs, combining quinoline-N-oxides with a linear sesterterpenoid side chain. Additionally, consistent in all three metabolites is the rare occurrence of two five-ring ethers, which were derived from an apparent cyclization of methyl group carbons to adjacent hydroxy-bearing methylene groups in the sesterterpenoid side chain. Genome scanning of AJS-327 allowed for the identification of the marinoterpin (mrt) biosynthetic cluster, which consists of 16 open-reading frames that code for a sesterterpene pyrophosphate synthase, prenyltransferase, type II polyketide synthase, anthranilate:CoA-ligase, and several tailoring enzymes apparently responsible for installing the N-oxide and bis-tetrahydrofuran ring motifs.

Combined Effects of Methylated Cytosine and Molecular Crowding on the Thermodynamic Stability of DNA Duplexes

Methylated cytosine within CpG dinucleotides is a key factor for epigenetic gene regulation. It has been revealed that methylated cytosine decreases DNA backbone flexibility and increases the thermal stability of DNA. Although the molecular environment is an important factor for the structure, thermodynamics, and function of biomolecules, there are few reports on the effects of methylated cytosine under a cell-mimicking molecular environment. Here, we systematically investigated the effects of methylated cytosine on the thermodynamics of DNA duplexes under molecular crowding conditions, which is a critical difference between the molecular environment in cells and test tubes. Thermodynamic parameters quantitatively demonstrated that the methylation effect and molecular crowding effect on DNA duplexes are independent and additive, in which the degree of the stabilization is the sum of the methylation effect and molecular crowding effect. Furthermore, the effects of methylation and molecular crowding correlate with the hydration states of DNA duplexes. The stabilization effect of methylation was due to the favorable enthalpic contribution, suggesting that direct interactions of the methyl group with adjacent bases and adjacent methyl groups play a role in determining the flexibility and thermodynamics of DNA duplexes. These results are useful to predict the properties of DNA duplexes with methylation in cell-mimicking conditions.

Biocatalytic reductive desymmetrization of prochiral 1,3-diketone and its application to microbial hormone synthesis

Microorganisms screened from yeast and bacteria were used as biocatalysts to synthesize optically active hydroxyketones with an asymmetric quaternary carbon containing adjacent ethyl and methyl groups based on the microbial reductive desymmetrization of prochiral cyclic 1,3-diketones. Candida cacaoi NBRC 10231 and Pichia farinosa NBRC 10896, two types of yeast species, were found to preferentially reduce only one carbonyl group to give the (2R,3S)-form. In contrast, three types of bacterial species, Morganella morganii NBRC 3168, Providencia rettgeri NBRC 13501, and Escherichia fergusonii NBRC 102419, preferentially produced the (2S,3S)-form with excellent stereoselectivity. Starting from (2R,3S)-hydroxyketone prepared using Candida cacaoi NBRC 10231, which exhibits both high reactivity and stereoselectivity, the characteristic chain structure of avenolide, a type of microbial hormone, was successfully synthesized.

Steric Hindrance of Methyl Group on the Reaction Pathway of Hydrodesulfurization in the Presence of Quinoline

Steric hindrance of methyl on reaction pathway of hydrodesulfurization in presence of quinoline was investigated over a NiMo/Al2O3 catalyst at 4.0 MPa and 320 °C. The results show that steric hindrance of methyl changed the main pathway of HDS while presence of quinoline further exacerbated this transformation. Changes in inhibitory factor curve show that quinoline poisoning on DBT HDS is a relatively mild. When adjacent methyl is present, even at low concentration, the inhibitory factor of quinoline on 4,6-DMDBT HDS is still greater than 85%. At high levels, the inhibitory factor of quinoline on DDS pathway even exceeds 99%. Quinoline poisons HYD pathway of DBT HDS to a stable level in a short time (30 to 60 min). However, after 6 h of reaction, HYD pathway yield of 4,6-DMDBT HDS is still increasing. Quinoline simultaneously poisons HYD and DDS pathways of 4,6-DMDBT HDS to a stable level within 120 min, and then DDS pathway will continue to be poisoned, thereby increasing HYD pathway yield. Regardless of presence of adjacent methyl in sulfur-containing molecules, an increase in quinoline concentration will lead to an increase in HYD/DDS pathway yield ratio. Addition of quinoline inhibits conversion of hydrogenated intermediates to DDS products by poisoning C–S bond dissociation center (such as CUS active site) and leads to formation of deep hydrogenated products.

Reutilization of cathode material from spent batteries as a heterogeneous catalyst to remove antibiotics in wastewater via peroxymonosulfate activation

Recycling of valuable secondary source of materials from spent batteries brings great opportunity for recyclers at end-of-life but a challenging issue. Peroxymonosulfate (PMS)-based advanced oxidation has been considered an efficient approach to eliminate refractory antibiotic in wastewater. In this study, a cathode material (CM) recovered from spent lithium-ion batteries (LIBs) was explored to serve as a direct catalyst to activate peroxymonosulfate for the first time. The CM catalyst included 94% LiCoO2 and 6% other substances (e.g. Co3O4) via a facile calcination process. The reactions between PMS and CM for levofloxacin hydrochloride (LFX) decomposition were investigated. Removal efficiency of LFX displayed close correlations with system parameters including CM catalyst dosage, PMS dosage, LFX concentration, pH value and inorganic ions. An optimal removal of 94% was obtained at CM-850 = 0.4 g/L and PMS = 0.5 mM within 60 min, and the first order reaction kinetic rate constant was 0.07597 min−1. Moreover, 32% total organic carbon had been removed after the reaction. In CM catalyst, the varied valence of Co2+/Co3+ underpinned PMS activation, and the SO4− and non-radical 1O2 were of critical significance in LFX degradation. Adjacent methyl in tertiary amine of LFX molecule was the initial cleavage site. Furthermore, the CM catalysts in PMS activation exhibited prominent stability, the degradation efficiency was 80% after four catalytic cycles. Such strategy advances the development of direct recycling of spent batteries for advanced oxidation based on peroxymonosulfate.

Effects of branch structure of alkylbenzenes on spray auto-ignition of n-decane and alkylbenzenes blends

Spray auto-ignition characteristics of the blends of n-decane and several alkylbenzenes were carried out on a heated constant-volume spray combustion chamber. The derived cetane numbers of the fuel blends were determined, and the temperature-dependent ignition delay times and combustion durations were measured across a range of temperatures from 808 to 911 K. The results reveal that blending alkylbenzene to n-decane inhibits fuel spray auto-ignition propensity. For mono-alkylbenzenes, the fuel blend containing toluene has a higher derived cetane number than those with ethylbenzene and n-propylbenzene, but has a lower derived cetane number than the fuel blend containing n-butylbenzene. For those binary fuels containing ethylbenzene, n-propylbenzene and n-butylbenzene, their derived cetane numbers increase with the side alkyl chain length. The derived cetane numbers of the fuel blends with C8H10 isomers follow the trend of n-decane/ o-xylene > n-decane/ethylbenzene > n-decane/ m-xylene ∼ n-decane/ p-xylene, given the alkylbenzene blending fraction. For the blends with C9H12 isomers, those containing 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene have the highest and lowest derived cetane numbers, respectively, while the fuel blends containing 1,2,4-trimethylbenzene, n-propylbenzene and i-propylbenzene have comparatively intermediate derived cetane numbers. The blending effects of alkylbenzenes on ignition delay time are consistent with the observation on fuel derived cetane numbers. Both the number and proximity of substituted methyl groups significantly affect fuel auto-ignition propensity, and the adjacent methyl groups could increase the auto-ignition propensity. The combustion duration for the test fuels, except for n-decane and the n-decane/ n-butylbenzene blend, monotonically decreases with increased temperature. The non-monotonic dependence of combustion duration on temperature, for neat n-decane and the n-decane/ n-butylbenzene blend, may result from the increased diffusive burnt fraction. Finally, the comparison between gas-phase and spray auto-ignition reactivity of the test fuels highlights the contribution of both fuel physics and chemistry in spray auto-ignition.

Synergistic effect of carboxylmethyl group and adjacent methylene substitution in pyrazolium ionic liquid promote the conversion of CO2 under benign condition

The carboxyl functionalized ionic liquids normally show better catalytic activity than the corresponding ionic liquids without functional group for the coupling reaction of carbon dioxide and epoxides. However, a long alkyl chain, at least propyl, is required as bridge between carboxyl group and N atom of aromatic heterocycle to ensure the catalytic activity. Inclusion of long alkyl chain indicates the low synthetic yield and harsh synthetic conditions. It is rarely reported that the carboxyl functionalized ionic liquid with methyl would present the high catalytic activity. With the help of ethyl substituted on the other N atom of pyrazolium ring, the carboxylmethyl pyrazolium ionic liquid (CMEPzBr) would present the excellent catalytic activity (yield >99%). Moreover, the product yield still keeps larger than 90% even under 70 °C and 1.0 MPa CO2 initial pressure. The role of methylene appeared on the near N atom is elucidated by density functional theory. The catalytic activity of carboxylmethyl imidazolium ionic liquid is not refined greatly when methylene is substituted on the other N atom of imidazolium ring. The optimal reaction conditions are investigated along with the recyclability and reusability.

The effect of molecular structures of alkylbenzenes on ignition characteristics of binary n-heptane blends

Alkylbenzenes are major aromatic constituents of real transportation fuels and important surrogate components. In this study, the structural impact of nine alkylbenzenes on their ignition characteristics is experimentally and computationally investigated with particular emphasis on the blending effect with significantly more reactive normal alkanes. Experimental comparisons of mono-alkylbenzenes (toluene, ethylbenzene, n-propylbenzene, iso-propylbenzene) from a modified CFR engine showed that the difference in pure alkylbenzene reactivity significantly diminished when blended with n-heptane, as the strength of the radical scavenging effect of all three alkylbenzenes is similar. Among C8H10 isomers, the reactivity of pure ethylbenzene and o-xylene and their blends with n-heptane showed a complex competing effect between the difference in CH bond energy and the existence of intermediate/low-temperature chemistry caused by adjacent methyl pairs. A similar structural impact was also observed for C9H12 isomers and their blends with n-heptane, while the influence of CH bond energy was more noticeable than C8H10 molecules. Kinetic simulations of the alkylbenzene/n-heptane blends highlighted the effect caused by adjacent methyl pairs that is referred to as the “ortho effect”. Analysis of ethylbenzene and o-xylene showed that o-xylene's intermediate/low-temperature pathways initiated by benzylperoxy radical – benzylhydroperoxide isomerization (RO2 – QOOH) produce additional active radicals such as OH and CH2O, which accelerates the oxidation chemistry of more reactive n-heptane. This study provides knowledge on the blending effect of alkylbenzene compounds with n-heptane on their ignition characteristics that is useful to develop surrogates that can better mimic the reactivity of real fuels.

Structure and SO2 Absorption Properties of Guanidinium-Based Dicarboxylic Acid Ionic Liquids

A new series of functionalized ionic liquids (ILs) with 1,1,3,3-tetramethylguanidine ([TMG]+) cations as well as dicarboxylic acid anions {[−OOC–(CH2–CH2)n–COO–], where n = 1, 3, and 5} was synthesized, and their SO2 absorption properties were investigated. A high SO2 absorption capacity of the prepared ILs was achieved. The molar ratios of SO2 to [TMG][succinic acid] {([TMG][SUC]) (n = 1)}, [TMG][suberic acid] {([TMG][SUB]) (n = 3)}, and [TMG][dodecanedioic acid] {([TMG][DOD]) (n = 5)} were 4.76, 5.96, and 5.96, respectively. The evidence of spectroscopic measurements and quantum chemical calculations confirmed that SO2 could interact with the carboxyl and adjacent methylene groups on the anion as well as the amino group on the cation. The SO2 absorption capacity of these ILs was strongly influenced by their asymmetry and space resistance. The high symmetry and large steric hindrance could reduce the SO2 absorption capacity of ILs.