Synthesis of E- and Z-o-Methoxy-Substituted 2,3-Diphenyl Propenoic Acids and Its Methyl Esters

A series of stereoisomeric o-methoxy-substituted 2,3-diphenyl propenoic acids and their methyl esters have been synthesized. The E isomers were prepared by a modified Perkin condensation (substituted benzaldehyde, phenylacetic acid, Et₃N/acetic anhydride). The difficult to access Z isomers were obtained conveniently in good yields when the appropriate coumarin derivatives were allowed to react with KOH and CH₃I in DMSO.     

Recognition of Multiple Methyl Groups on Aromatic Rings by a Polyaromatic Cavity

The methyl group is a small substituent, usually showing relatively weak or no interactions with other functional groups and metal ions. Herein, we present the recognition of the number of methyl groups on synthetic and natural aromatic compounds (i.e., benzene and xanthine derivatives, respectively) by the 1 nm‐sized polyaromatic cavity of a coordination capsule in water. Detailed competitive encapsulation experiments as well as X‐ray crystallographic analysis revealed that multiple guest–host CH₃–polyaromatic interactions in the confined nanospace are key driving forces for the high selectivity.     

水杨酸甲酯清除羟基自由基活性的研究

利用脉冲辐解技术研究了水杨酸甲酯清除羟基自由基反应的瞬态吸收谱,测定了水杨酸甲酯与羟基自由基反应的表观速率常数。辅以常规检测方法,测定了水杨酸甲酯对羟基自由基的清除率。结果表明,水杨酸甲酯能快速有效清除羟基自由基。探讨了水杨酸甲酯清除羟基自由基的反应机制。     

Synthesis and Electronic Properties of 1,2‐Hemisquarimines and Their Encapsulation in a Cucurbit[7]uril Host

The synthesis of a new class of robust squaraine dyes, colloquially named 1,2‐hemisquarimines (1,2‐HSQiMs), through the microwave‐assisted condensation of aniline derivatives with the 1,2‐squaraine core is reported. In CH₃CN, 1,2‐HSQiMs show a broad absorption band with a high extinction coefficient and a maximum at around λ=530 nm, as well as an emission band centered at about λ=574 nm, that are pH dependent. Protonation of the imine nitrogen causes a redshift of both absorption and emission maxima, with a concomitant increase in the lifetime of the emitting excited state. Encapsulation of the chromophore into a cucurbit[7]uril host revealed fluorescence enhancement and increased photostability in water. The redox characteristics of 1,2‐HSQiMs indicate that charge injection into TiO₂ is possible; this opens up promising perspectives for their use as photosensitizers for solar energy conversion.     

High pressure photochemistry of alkenes. 6. the caee of 1-methylcyclopentene at 184.9 and 147.0 nm

The degradaiion of the 184.9 nm photoexcited 1-methyl-1-cyclopentene molecule shows the involvement of various excited isomers. The most important fragmentation products are 1- and 2-methyl-1,3-cyclopentadiene. These products are probably the result of a one-step elimination process of a hydrogen molecule. This process has also been observed in the case of the 184.9 nm photochemistry of cyclopenten. On the other hand, the involvement of isomers, although possible, is not so obvious at 147.0 nm. Moreover, in this case, the 1- and 2-methyl-1,3-cyclopentadiene formation is the result of hydrogen atom elimination in a two-step process. Cyclopentadiene, ethylene, and various C₃ and C₄ compounds are formed as well as methyl radicals and hydrogen atoms. These products are probably formed in successive elimination reactions as this is also observed in acyclic alkenes.     

Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2-Oxamidato and μ2-Dithioxamidato Ligands

Six new diiridium complexes containing 2-methyl-6-phenylpyridyl as the cyclometalating ligand with a μ₂-oxamidato or a μ₂-dithioxamidato ligand as the bridge have been synthesized in 60–73 % yields. These complexes were revealed by multinuclear NMR spectroscopy to contain inseparable mixtures of diastereomers (rac, ΔΔ/ΛΛ and meso, ΔΛ) with bridges in anti and syn configurations. The remarkable variety of isomers present was confirmed by X-ray crystallography on single crystals grown from mixtures of each complex. In one complex with a N,N’-bis(4-trifluoromethylphenyl)-μ₂-oxamidato bridge, two single crystals of anti and syn isomers were structurally determined. Two single crystals of the μ₂-dithioxamidato bridge complex were found to contain rac and meso forms of the syn isomer. Hybrid DFT computations on the four isomers of each diiridium complex revealed negligible energetic preferences for one isomer despite the methyl groups in the 2-methyl-6-phenylpyridyl cyclometalating ligands being close to the neighboring methyl groups and the bridge, thus supporting the experimental findings of isomer mixtures. Two distinct broad emissions with maxima at 522–529 nm and at 689–701 nm observed in these complexes in dichloromethane are attributed to mixed metal-ligand to ligand charge transfer (MLLCT) excited states involving the pyridyl and bridge moieties respectively with the aid of electronic structure computations.     

1, 8-Dihydroxyanthraquinone-Ca(II) Reaction. Spectrofluorimetric Determination of Traces of Ca(II)

Abstract

1, 8-Dihydroxyanthraquinone (1, 8-DHAn) shows a fluorescent reaction with Ca(II) ion in ethanol-water mixtures and ammoniacal medium.

In the present work the 1, 8-DHAn-Ca(II) complex has been studied spectrofluorimetrically. The complex shows two excitation maxima at 485 nm and 495 nm and its emission maximum is centered at 615 nm. A 2:1 (R:C) stoichiometry and a log K_est of 7.38±0.22 for the overall equilibrium have been found for the complex.

A new method for the spectrofluorimetric determination of Ca(II) between 50 and 550 ngml^?1 has been proposed. The interference level of foreign ions has been established.     

Mass spectra of halogenated esters: 8. Methyl esters of 2,3-dichloro-, bromochloro- and dibromopropenoic acids

The mass spectral fragmentation of methyl esters of E and Z isomers of 2,3-dichloro-, 2-bromo-3-chloro-, 3-bromo-2-chIoro- and 2,3-dibromopropenoic acids have been investigated. The M^+˙ peak is shown with all isomers, the [M ? OCH₃]⁺, [M ? X]⁺, [M ? OCH₃ ? CO]⁺, [M ? OCH₃ ? CO ? X]^+˙ and [M ? OCH₃ ? CO ? X ? X]⁺ ions constituting abundant peaks in all spectra. The results, particularly from the bromochloro isomers, show that a halogen atom is eliminated from the 3- rather than the 2- position and from the Z rather than the E isomer. Bromine as a bulky atom is preferentially lost.     

3-羟基哒嗪及其CH3，NO2和Cl取代衍生物质子转移过程的理论研究

用密度泛函理论(DFT)B3LYP方法,在6-311 G*基组下,对3-羟基哒嗪及其CH3,NO2和Cl取代衍生物分子醇式和酮式结构互变异构化反应进行了研究,优化化合物的几何构型,寻找反应的过渡态,通过振动分析和内禀反应坐标(IRC)分析加以证实,计算了反应的活化能.结果表明,3(2H)-哒嗪酮及其带取代基的衍生物不论是单体,还是相对应的二聚体,比其相对应的异构体能量低,表明在通常情况下是以3(2H)-哒嗪酮及其衍生物形式稳定存在的,这与前人通过实验数据对3-羟基哒嗪互变异构体的比率进行预测的结果是一致的.根据计算结果讨论了异构化反应的机理.     

Methyl group transfer upon gas phase decomposition of protonated methyl benzoate and similar compounds

Gas phase decompositions of protonated methyl benzoate and its conjugates have been studied by using electrospray ionization‐collision induced dissociation‐tandem mass spectrometry. Loss of CO₂ molecule, thus transfer of methyl group, has been observed. In order to better understand this process, the theoretical calculations have been performed. For methyl benzoate conjugates, it has been found that position of substituent affects the loss of CO₂ molecule, not the electron donor/withdrawing properties of the substituent. Therefore, electrospray ionization‐mass spectrometry in positive ion mode may be useful for differentiation of isomers of methyl benzoate conjugates.     

3-羟基哒嗪及其CH3,NO2和CI取代衍生物质子转移过程的理论研究

用密度泛函理论(DFT)B3LYP方法,在6-311+G*基组下,对3-羟基哒嗪及其CH3,NO2和Cl取代衍生物分子醇式和酮式结构互变异构化反应进行了研究,优化化合物的几何构型,寻找反应的过渡态,通过振动分析和内禀反应坐标(IRC)分析加以证实,计算了反应的活化能.结果表明,3(2H)-哒嗪酮及其带取代基的衍生物不论是单体,还是相对应的二聚体,比其相对应的异构体能量低,表明在通常情况下是以3(2H)-哒嗪酮及其衍生物形式稳定存在的,这与前人通过实验数据对3-羟基哒嗪互变异构体的比率进行预测的结果是一致的.根据计算结果讨论了异构化反应的机理.     

Methyl torsional potentials of rotational isomers of m-methylanisole studied by spectral hole-burning spectroscopy

Laser-induced fluorescence (LIF) excitation spectra of m-methylanisole in a supersonic jet were measured. Two series of progressions were observed in the spectrum, originating at 36048 and 36115 cm⁻¹, which were successfully assigned to the transitions to the methyl internal rotational vibronic levels of the two isomers, i.e. cis and trans isomers, with the aid of hole-burning spectrum measurements and quantum-chemical calculations. The progression for the trans isomer was observed up to the 6a₁ band, while only the 3a₁ band in addition to the 0a₁ and 1e bands was observed for the cis isomer. This finding can be explained by the conformational change upon the electronic excitation; the 60° rotation of the methyl torsional angle takes place for the trans isomer but not for the cis isomer.     

UV absorption spectra of 3-aminorhodanine derivatives

3-Aminorhodanine condenses readily with isothiocyanates to form unsymmetrical thioureas of the rhodanine series. The UV spectra of arylidene derivatives of 3-aminorhodanine consist of four bands: a short-wave band with a maximum up to 242 nm, a “thioamide” band with a maximum at 264–290 nm, a “dithiocarbonate” band with maxima at 290–370 nm, and a long-wavelength K band with maxima at 310–520 nm. The K absorption band is the most characteristic band for the arylidene derivatives of 3-aminorhodanine, and the maxima for 3′,5-diarylidene derivatives are generally shifted to the short-wave region, while the maxima for the 5-monoarylidene derivatives are usually shifted to the long-wave region.     

High-Performance Liquid Chromatographic Determination of Trace Quantities of Azinphos Methyl and Azinphos Methyl Oxon in Various Water Sources by Direct Injection and Trace Enrichment

Abstract

A high-performance liquid chromatographic (HPLC) method is described for the determination of trace amounts of the organophosphate insecticide, azinphos methyl and its degradation product, azinphos methyl oxon, by direct injection and by trace enrichment. The compounds were analyzed on a uBondapak C₁₈ column with UY detection at 224 nm. The mobile phase for the analysis was acetonitrile-water (50:50) at a flow rate of 1.3 ml/min. Ten minutes were required for the chromatographic analysis. Water from three sources, public water supply, stream, and ocean was analyzed for azinphos methyl and azinphos methyl oxon at concentrations as low as 11.9 and 11.3 ppb, respectively, without a clean-up, concentration or derivatization step. Azinphos methyl was quantitated at 0.29 ppb and azinphos methly oxon at 0.29 ppb by employing a concentration step involving a C₁₈ Sep-Pak cartridge. The coefficients of variation for all determinations ranged from 0.77 to 9.06%. Peak heights were used for quanti-tation. Several other pesticides have been shown not to interfere with the analysis of either compound.     

Determination of the Microstructure of Some Methyl Methacrylate-Butadiene Copolymers by 220 MHz Proton Magnetic Resonance Spectroscopy

Abstract

Proton magnetic resonance (PMR) spectroscopy at 220 MHz has been used to gain information about the relative proportions of various methyl methacrylate centered triads and pentads in some methyl methacrylate (MMA)-butadiene (BU) copolymers prepared with a free-radical catalyst. The PMR peaks used are the MMA α-methyl peaks recorded using CDCL₃ as solvent, and the MMA α methyl peaks recorded using C₅D₅N as solvent. Measured triad and pentad fractions are in good agreement with those calculated from the reactivity ratios r₁ = 0.17 and r₂ = 0.60, where MMA = Monomer 1. Surprisingly, the α-methyl peaks provide information also about the ratio of cis-1,4- to trans-1, 4-butadiene units in the copolymer. Proportions of 1,2-butadiene units are obtained from the relative areas of peaks due to vinyl and vinylene protons.     

Distyryl-boradiazaindacenes: facile synthesis of novel near IR emitting fluorophores

Boradiazaindacenes with methyl substituents at 3 and 5 positions were for the first time shown to undergo efficient double condensation reactions with an aromatic aldehyde yielding a series of extended conjugation dyes. These new fluorophores have absorption maxima in the range of 650-660 nm. The dyes reported here have large quantum yields with 20 nm Stokes' shifted emission peaks. The straightforward synthesis of such red shifted BODIPY derivatives is important in relation to the synthesis of novel and useful fluorescent chemosensors. In addition, this facile transformation may make these new fluorophores' building blocks in the construction of large functional supramolecular systems.     

Liquid Chromatographic Analysis of Bile Acid Methyl Esters

Abstract

Methods have been developed for the qualitative and quantitative analysis of hydroxy and keto derivatives of methyl cholanates utilizing a ¼″ by 1′ μPorasil column, various mixtures of hexane and ethyl acetate and a refractive index detector. The system has been calibrated for some of the methyl dihydroxycholanates using 3α;,7α-dihydroxy-12-oxocholanate as an internal standard and applied to the analysis of the mixtures of diols resulting from the reduction of methyl 3,12-dioxocholanate with NaBH₄ and with Raney nickel.     

Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates

The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH₃]⁺, in methyl 2,2- and 2,4-dichlorobutanoate; [M? Cl]⁺, in methyl 3-chlorobutanoate; [M? Cl? HCl]⁺, in methyl 3,4-dichlorobutanoate; [M? Cl? CH₂CO]⁺, in methyl 3,3-dichlorobutanoate and [M? Cl? COOCH₃]^+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the stereoisomers are nearly identical, the loss of a chlorine atom and the McLafferty rearrangement giving the higher peaks in the spectrum of the threo form.     

Fullerene C<Subscript>60</Subscript> in copolymerization of allyl chloride with methyl methacrylate

The effect of fullerence C₆₀ on the copolymerization of allyl chloride and methyl methacrylate has been studied. With the use of UV spectroscopy, it has been shown that, with an increase in the conversion, the redistribution of optical densities of two π-π* absorption maxima due to fullerene at λ_max = 407 and 330 nm is observed. A difference in the kinetics of copolymer’s formation in the absence and presence of fullerene has been found.     

Synthesis and Photophysical Properties of Some PEG Substitued Titanyl Phthalocyanine Derivatives

Summary: Polyethylene glycol substituted titanyl phthalocyanine was prepared in two steps starting from phthalonitrile and characterized by FT-IR, UV-vis spectrophotometry, and fluorescence spectrophotometry. The titanyl phthocyanine derivatives (TiOPcs) showed high solubility in common organic solvents, such as, CH₃Cl and DMF. These compounds decreased in absorbance intensity with increase of molecular weight of polyethylene glycol at maxima wavelength of visible range. The fluorescence spectra showed a fluorescence emission near 690 nm with a quantum yield of 0.05–0.32 (λ_ex = 625 nm).