Synthesis of a phloroacetophenon[4]arene consisting of four isomers via the one-pot,acid-catalysed condensation of phloroacetophenone with benzaldehyde

A phloroacetophenon[4]arene (3) consisting of four isomers was synthesised for the first time via the condensation of phloroacetophenone and benzaldehyde in a one-pot reaction with refluxing toluene in the presence of catalytic amounts of TsOH·H₂O for a maximum yield of 64%. The conformational elucidation of four isomers (3a–d) by ¹H NMR spectroscopy and X-ray crystal structure analysis showed them to be cone, partial cone, 1,3-alternate and 1,2-alternate types of conformations, respectively.     

Structural determination of nerve agent markers using gas chromatography mass spectrometry after derivatization with 3‐pyridyldiazomethane

Nerve agents are a class of organophosphorous chemicals that are prohibited under the Chemical Weapons Convention. Their degradation products, phosphonic acids, are analyzed as markers of nerve agent contamination and use. Because the phosphonic acids are non‐volatile and very polar, their identification by GC‐MS requires a derivatization step prior to analysis. Standard derivatization methods for gas‐chromatography electron‐impact mass‐spectrometry analysis give very similar spectra for many alkyl phosphonic acid isomers, which complicates the identification process. We present a new reagent, 3‐pyridyldiazomethane, for preparing picolinyl ester derivatives of alkyl methylphosphonic acids facilitating the determination of their structure by enhancing predictable fragmentation of the O‐alkyl chain. This fragmentation is directed by the nitrogen nucleus of the pyridyl moiety that abstracts hydrogen from the O‐alkyl chain, inducing radical cleavage of the carbon–carbon bonds and thereby causing extensive fragmentation that can be used for detailed structure elucidation of the O‐alkyl moiety. The separability of related isomers was tested by comparing the spectra of the picolinyl esters formed from twelve hexyl methylphosphonic acid isomers. Spectral library matches and principal component analysis showed that the picolinyl esters were more effectively separated than the corresponding trimethylsilyl derivatives used in the standard operating procedures. The suggested method will improve the unambiguous structural determination process for phosphonic acids. Copyright © 2013 John Wiley & Sons, Ltd.     

Ab initio Molecular Orbital Study of Dithiopyrrolopyrrole and Its Structural Isomers

Abstract

Ab initio molecular orbital calculations at HF/6-31G*, HF/6-311+G**, and B3LYP/6-311+G** levels of theory for geometry optimization are reported for 1,4-dithiopyrrolo[3,4-c]pyrrole (DtPP, 1) and its twelve structural isomers (2–13). Compounds 1–3 include 2 C─CH and 2 NH─CS structural units. Structural isomers 4–7 include 2 C–CH units, together with 2 NH and 2 C–S groups. Isomers 8–13 possess 2 CH, 2 C, 2 NH, and 2 C─S fragments. According to these calculations, isomers 2, 4, and 8, are more stable than 1.     

A Facile Synthesis of Stable Phosphorus Ylides Containing Chlorine and Sulfur Derived from 6-Chloro-2-benzoxazolethiol and 2-Chloro-phenothiazine

Stable crystalline phosphorus ylides containing chlorine and sulfur were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylene-dicarboxylates in the presence of 6-chloro-2-benzoxazolethiol and 2-chloro-phenothiazine. These stable ylides exist in solution as a mixture of two geometrical isomers. This is caused by the conjugation of the ylide moiety with the adjacent carbonyl group, which results in a restricted rotation around the respective carbon-carbon bond.     

A Facile,One-Pot Synthesis of Azoic Compounds and Anthraquinone Derivatives Containing Dialkyl Phosphoryl Moieties in Multicomponent Reactions

Protonation of the reactive 1:1 intermediates produced in the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates by 1-amino-anthraquinone or 1,5-diphenylcarbazone as a core dye leads to vinyl phosphonium salts, which undergo Michael addition with conjugate base of NH compounds to produce stable phosphorus ylides as novel dyes in fairly good yields. These ylides can exist in two geometrical isomers (Z) and (E) for 3, because the negative charge of the ylide moiety of these compounds are strongly conjugated with the adjacent carbonyl group. Rotation around the carbon–carbon double bond is slow in the (Z) and (E) geometrical isomers on the NMR time scale at ambient temperature. These compounds are assigned by their IR, ¹H, ¹³C NMR spectral data as well as their mass spectroscopic data.     

Preparation and chromatographic evaluation of new branch-type diamide-embedded octadecyl stationary phase with enhanced shape selectivity

A novel branch-type diamide-embedded octadecyl stationary phase was prepared by facile amidation. The preparation of this new phase involves the synthesis of new bifunctional silane ligand and surface modification of spherical silica via anchoring of silane coupling agent. The obtained diamide-embedded octadecyl stationary phase demonstrated excellent hydrophobic selectivity, as well as enhanced shape and planarity selectivity in comparison to commercial polymeric and monomeric C₁₈ phases, respectively, as revealed by the systematic investigation into its liquid chromatographic retention of isomeric polycyclic aromatic hydrocarbons. The applicability of this new stationary phase was further testified by the effective separation of isomeric compounds belong to different chemical classes, including chain isomers of alkylbenzenes, and positional isomers of substituted aromatics. An in-depth analysis of the separation mechanisms other than molecular shape recognition involved in the new stationary phase was performed using a linear solvation energy relationships model and compared with its monoamide and pure C₁₈ counterparts correspondingly. The performance of the new stationary phase in quantitative analysis of phenols from real-world samples was also evaluated.     

萘酚异构体在乙炔黑修饰电极上的电化学行为及测定

制备了乙炔黑修饰电极(AB/GCE),运用交流阻抗法研究了电极表面的特性。研究了1-萘酚(α-N)和2-萘酚(β-N)在该修饰电极上的循环伏安行为,探讨了修饰剂用量、底液种类及pH、浓度和扫速对伏安行为的影响。在pH6.0的B-R缓冲液中,α-N和β-N均出现一明显的不可逆氧化峰。在60~240mV·s-1扫速范围内,二者氧化峰电流与扫速均呈线性关系,表明该电极过程是受吸附控制的不可逆过程。计算了电极过程的部分动力学参数。运用线性扫描伏安法结合半微分技术对α-N和β-N进行了同时定量测定,发现α-N和β-N的半微分氧化峰电流值与其浓度在5.00×10-5~6.50×10-4mol·L-1范围内呈良好的线性关系(rα-N=0.996;rβ-N=0.997)。α-N和β-N的检出限(S/N=3)分别为5.04×10-7mol·L-1,6.69×10-7mol·L-1。加标回收率分别为97.20%~100.20%和95.40%~102.50%。     

Selective,Nanomolar Electrochemical Determination of Environmental Contaminants Dihydroxybenzene Isomers Found in Water Bodies Using Nanocrystalline Zeolite Modified Carbon Paste Electrodes

Nanocrystalline zeolites of different framework structures were prepared by the addition of suitable structure directing agents in the synthesis composition of conventional zeolites. Zeolite modified carbon paste electrodes were constructed for the simultaneous determination of dihydroxybenzene isomers. Nanocrystalline zeolite Beta modified carbon paste electrode exhibited the highest electrocatalytic activity. Under optimum conditions, wide linear range was obtained from 150 nM to 400 µM with lower detection limit of 100, 130, and 100 nM for hydroquinone, catechol, and resorcinol, respectively. The analytical performance of the proposed sensor was demonstrated in the simultaneous determination of dihydroxybenzene isomers in different environmental water samples.     

Vibrational analysis of buta-1,3-diene and its deutero and 13C derivatives and some of their rotational isomers

The wave numbers of trans-2,3-¹³C₂-buta-1,3-diene were calculated using a scaled quantum-chemical force field found at the MP2/6-31G*//MP2/6-31G* level of theory. The obtained results and the theoretical sets of wave numbers for twelve deutero and ¹³C derivatives of the trans form and five deutero and ¹³C derivatives of the gauche form of buta-1,3-diene found previously at the MP2/6-31G*//MP2/6-31G* level are compared with the corresponding experimental vibrational spectra corrected for the Fermi resonance. Combined analysis of the vibrational spectra of the above mentioned isotopomers was performed.     

Isolation, structural elucidation, and chemical transformation of interconvertible 8,12-hemiketal germacranolide sesquiterpenoids from Salvia castanea Diels f. tomentosa Stib.

From the aerial parts of Salvia castanea Diels f. tomentosa Stib., four new hemiketal germacranolide sesquiterpenoids, castanins C-F (1-4), were obtained as two pairs of interconvertible forms along with their acetates, 5 and 6. Their structures were elucidated by spectroscopic methods and X-ray analysis of the uninterconvertible isomeric acetates, 5 and 6. The computational study explained that the ratios of 1 and 2, 3 and 4, and their acetates (5 and 6) in the mixtures were 1:1, 1:2, and 1:3, respectively. In addition, the semisynthesis of castanins C (1) and D (2) was conducted by the photooxidation of castanin B (8), the major constituent of this plant. Compounds 5, 6, and 8 were also tested for their inhibitory activity toward MCF-7, HeLa, and HepG2 cell lines.