Low field chemical shifts in 13carbon NMR spectra of 1,3-dehydroadamantane compounds possessing “inverted carbon atoms”

1,3-Dehydroadamantanes, which possess “inverted carbon atoms” in a cyclopropyl moiety, display low field ¹³C-NMR chemical shifts for carbon atoms situated across from the cyclopropyl group. This long range effect also shows in 2,4-dehydroadamantane and is therefore not due to the presence of especially strained inverted carbons.     

Modeling adsorption rate of organic micropollutants present in landfill leachates onto granular activated carbon

The overall adsorption rate of single micropollutants present in landfill leachates such as phthalic acid (PA), bisphenol A (BPA), diphenolic acid (DPA), 2,4-dichlorophenoxy-acetic acid (2,4-D), and 4-chloro-2-methylphenoxyacetic acid (MCPA) on two commercial activated carbons was studied. The experimental data obtained were interpreted by using a diffusional model (PVSDM) that considers external mass transport, intraparticle diffusion, and adsorption on an active site. Furthermore, the concentration decay data were interpreted by using kinetics models. Results revealed that PVSDM model satisfactorily fitted the experimental data of adsorption rate on activated carbon. The tortuosity factor of the activated carbons used ranged from 2 to 4. The contribution of pore volume diffusion represented more than 92% of intraparticle diffusion confirming that pore volume diffusion is the controlling mechanism of the overall rate of adsorption and surface diffusion can be neglected. The experimental data were satisfactorily fitted the kinetic models. The second-order kinetic model was better fitted the experimental adsorption data than the first-order model.     

Assignment of configurations of conjugated dienic pheromones by fuzzy classification of carbon-13 chemical shifts

The configurations of conjugated dienes, and some sex pheromones and analogous compounds, can be characterized by a fuzzy classification method applied to the ¹³C chemical shifts of the dienic carbons. A fuzzy relation matrix of 12 model dienes is set up, and a fuzzy parameter (λ) is established. If λ ≥ 0.95 in the similarity test of two dienes, then both dienes have the same configuration. Some empirical rules dealing with the influence of terminal groups and assignment of the order of dienic carbons are presented. Configurations of 14 compounds prepared by different methods were established reliably. After correct assignments of dienic carbons, the method was used to quantify the isomeric composition of (10,12)-pentadecadienyl acetate, (9,11)-tridecadienyl acetate and (9,11)-tetradecadienyl acetate by the inverted gated decoupling technique; the results agreed well with those obtained by gas chromatography.     

Pore structure and adsorption performance of the KOH-activated carbons prepared from corncob

Carbonaceous adsorbents with controllable surface area were chemically activated with KOH at 780 degrees C from chars that were carbonized from corncobs at 450 degrees C. The pore properties, including BET surface area, pore volume, pore size distribution, and mean pore diameter of these activated carbons, were characterized by the t-plot method based on N(2) adsorption isotherms. Two groups are classified according to the types of adsorption/desorption isotherms. Group I corncob-derived activated carbons, with KOH/char ratios from 0.5 to 2, exhibited BET surface area ranging from 841 to 1221 m(2)/g. Group II corncob-derived activated carbons, with KOH/char rations from 3 to 6, showed high BET surface areas, from 1976 to 2595 m(2)/g. From scanning electron microscopic (SEM) results, the surface morphology of honeycombed holes on corncob-derived activated carbons was significantly influenced by the KOH/char ratios. The adsorption kinetics of methylene blue, basic brown 1, acid blue 74, 2,4-dichlorophenol, 4-chlorophenol, and phenol from water at 30 degrees C were studied on the two groups of activated carbons, which were suitably described by two simplified kinetic models, pseudo-first-order and pseudo-second-order equations. The effective particle diffusivities of phenols and dyes at the corncob-derived activated carbons of group II are higher than those of ordinary activated carbons. The high-surface-area activated carbons were demonstrated to be promising adsorbents for pollution control and for other applications.     

Synthetic approaches to 5,7- and 5,8-dimethoxyquinoline. Sonochemical dehalogenation of substituted 2,4-dichloroquinolines. Use of the 2D COLOC spectrum for the NMR assignment of 5,8-dimethoxyquinoline

Summary Sonochemical dehalogenation of 2,4-dichloroquinoline is very facile. However, with 5,7-dimethoxy-2,4-dichloroquinoline the reaction proceeds stepwise to provide the title dimethoxyquinolines which cannot be prepared via theSkraup reaction. The¹³C NMR chemical shift assignments for 5,8-dimethoxyquinoline are presented. These were made by utilising the coupling connectivities from the bridgehead carbons in the 2D COLOC spectrum.

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Synthese von 5,7- und 5,8-Dimethoxychinolin. Sonochemische Dehalogenierung von substituierten 2,4-Dichlorochinolinen. NMR-Spektroskopische Zuordnung von 5,8-Dimethoxychinolin mittels eines COLOC-Experiments

Zusammenfassung 2,4-Dichlorchinoline können sonochemisch leicht dehalogeniert werden. Mit 5,7-Dimethoxy-2,4-dichlorchinolin verläuft die Reaktion in mehreren Schritten zu den Titelverbindungen, die mittelsSkraup-Reaktion nicht hergestellt werden können. Das¹³C-NMR-Spektrum von 5,8-Dimethoxychinolin wurde, ausgehend von den Brückenkopfkohlenstoffatomen, mit Hilfe eines COLOC-Experiments zugeordnet.

     

Cast Polyurethanes: Effect of Chain Extenders on Thermal Mechanical and Dynamic Mechanical Properties

Effects of various diol chain extenders on thermal, mechanical, and viscoelastic properties of polyurethanes are discussed. Elastomers were prepared by using polyester (polyethylene-co-propylene adipate), toluene-2,4-diisocyanate, and α,ω-aliphatic diols. The properties imparted by the extenders are explained on the basis of the number of methylene carbons in the extenders. Butanediol-extended polymer showed superior properties, which are ascribed to regularity in the backbone chain of the polymer and ease of formation of hydrogen bonds.     

Fabrication of bimetallic nanoparticles modified hollow nanoporous carbons derived from covalent organic framework for efficient degradation of 2,4-dichlorophenol

Bimetallic nanoparticles modified hollow-structured nanoporous carbons (NPCs) have been fabricated via a convenient one-step carbonizing strategy derived from covalent organic framework. The Pd/Fe/NPCs, Pt/Fe/NPCs and Rh/Fe/NPCs were obtained and can be used as Fenton-like catalysts with good stability and reusability. The catalytic activity was evaluated by the degradation of 2,4-dichlorophenl (2,4-DCP). These fabricated bimetallic catalysts exhibited much higher catalytic activity than Fe/NPCs at room temperature. The enhancement of catalytic ability was benefited from synergetic catalytic effect of bimetallic nanoparticles and accelerated mass transfer of hollow structure. Additionally, the enhanced catalytic mechanism of bimetallic catalysts was studied in detail and the reasonable reaction pathway was proposed. Besides, the bimetallic catalysts were successfully used for degradation of 2,4-DCP in actual industrial wastewater and the removal efficiency could reach 74.3% within 120 min, which demonstrated the promising potential application of bimetallic catalysts in the removal of pollutants in environment.     

Porogen effect on characteristics of banana pith carbon and the sorption of dichlorophenols

Banana pith was used as precursor material to prepare carbon with and without porogens. Characterization of the carbons showed higher BET surface area (1285 m2/g) for ZnCl2-treated carbon, comparatively. Adsorption experiments were conducted to study the removal of 2,4-dichlorophenol (DCP) from aqueous solutions using the carbons under varying experimental conditions. Decrease in pH increased the percentage removal. All the carbons studied showed greater percentage of DCP removal with decrease in the initial concentration of DCP. Kinetic studies showed that the adsorption of DCP on the carbons was a rapid process. Nonlinear forms of pseudo-first-order and pseudo-second-order models were used to fit the experimental data. Among these the pseudo-first-order model described the data with high correlation coefficients and low percentage error values. Four nonlinear isotherm models including the Langmuir, Freundlich, Toth, and Sips were used to analyze the experimental DCP isotherms under different pH (2-4) conditions. Adsorption capacities (Qmax) from the Langmuir model were found to be 129.4, 67.7, and 49.9 mg/g for ZnCl2-treated, KOH-treated, and porogen-free carbon, respectively, at pH 2. From desorption studies it seemed that chemisorption played a major role in the adsorption process. The results indicated that ZnCl2-treated carbon could effectively remove phenols from wastewater.     

13C shieldings of several diacetylenic alcohols

The ¹³C spectra of several conjugated diynols and symmetrical diynediols, represented by the parent compounds 2,4-pentadiyn-1-ol and 2,4-hexadiyne 1,6-diol, respectively, have been determined and individual resonances assigned. The data show close similarities to those observed with related 2-yn-1-ols. Mutual shielding interactions between the conjugated triple bonds result in upfield shifts of both the α- and β-sp-hybridized carbon nuclei by c. 4.5 ppm, relative to the ethynyl prototype. The deshielding γ effect induced by the hydroxyl group at the interior sp-hybridized carbons is discussed.     

Tetrathienyl Corannulene Compounds with Highly Sensitive Photochromism

We have designed and synthesized photochromic tetrathienyl corannulene compounds, 1,2,7,8-tetrakis(2-methyl-5-phenylthiophen-3-yl)corannulene ( 1 ) and 1,2,7,8-tetrakis(2,4-dimethyl-5-phenylthiophen-3-yl)corannulene ( 2 ), by fusing two units of photochromic terarylene with a curved aromatic corannulene with a promising antenna effect. Compound 1 exhibited highly sensitive photoreactivity, with a large molar absorption coefficient of 8.2×10⁴ M⁻¹ cm⁻¹ and practically photon-quantitative photocyclization. On the other hand, a terarylene derivative with a planar aromatic phenanthrene, 9,10-bis(2,4-dimethyl-5-phenylthiophen-3-yl)phenanthrene ( 4 ) showed no photoreactivity. The reason for such a difference was attributed to the predominance of the photoreactive atropisomers amplified by energy migration, and the shortened distance between reactive carbons induced by the curved structure.     

Synthesis and NMR spectroscopy (1H 13C) of 1-(2′-benzothiazolyl)-3(5),4-polymethylenepyrazoles and related compounds

A series of 3(5),4-trimethylene and 3(5),4-tetramethylenepyrazoles (tetrahydroindazoles) have been prepared from 2-acylcyclanones using two methods: direct reaction with a substituted hydrazine and through an NH-pyrazole followed by nucleophilic substitution. The results mainly concern the 2-benzothiazolyl substituent, but 2,4-dinitrophenyl derivatives were also studied for comparison. The orientation of the reactions (isomer ratio), the deshielding in ¹H nmr of the 5-methyl and 5-methylene signals when a benzothiazolyl residue is at position 1, and the ring strain effect on heterocyclic carbons chemical shifts, are discussed.     

Diastereoselective assembling of 21-C-alkylated nickel(II) complexes of inverted porphyrin on a platinum(II) template

Reaction of 21-C-methyl and 21-C-benzyl nickel(II) complexes of inverted meso-tetratolylporphyrin with platinum(II) dichloride or its bis(benzonitrile) complex yields a chloroplatinum(II) species containing two nickel(II) carbaporphyrinoids in a cis arrangement. One of the carbaporphyrinoids coordinates to the platinum ion with the external nitrogen while the other is bound with the external nitrogen and one ortho-carbon of the adjacent meso-aryl ring. The reaction is highly chemoselective. (1)H and (13)C NMR experiments in solution show the diastereoselectivity of the reaction. Single-crystal X-ray data confirm the presence of the diastereomer with opposite configurations of the Ni(II)-coordinated carbons in the subunits of the dimer. Cyclovoltammetric measurements reveal an anodic shift of the nickel(II) oxidation potentials of dimers with respect to those of the parent monomers and two different reduction couples. Reaction of unsubstituted inverted porphyrin with Pt(PhCN)(2)Cl(2) in chlorobenzene yields a monomeric platinum(II) complex of inverted porphyrin. This complex displays a markedly upfield (195)Pt NMR shift compared to tetraphenylporphyrinatoplatinum(II). Under strongly basic conditions deprotonation of the external nitrogen of inverted porphyrin and both electrochemical and chemical oxidation of platinum(II) center are observed.     

A convenient route to prepare isodicyclopentadiene—precursor of 1,5-dihydro-pentalene

A new route to prepare tricyclo[5.2.1.0^2,6]deca-2,4-diene (isodicyclopentadiene) was developed. This new route passes through a brominated (5-bromotricyclo[5.2.1.0^2,6]dec-3-ene) derivative obtained from tricycle[5.2.1.0^2,6]dec-3-ene (8,9-dihydrodicyclopentadiene) and NBS with a good yield. The complete assignment of protons and carbons on nuclear magnetic resonance spectra was done for dicyclopentadiene and the chemically transformed compounds by 2D NMR techniques.     

Synthesis of 1,2,4-triazole and thiazole analogs of ketoconazole

The synthesis of 1,2,4-triazole and thiazole analogs of ketoconazole is described in which one of the α azole ring carbons is linked to C-2 of the ketal by means of a three methylene tether. Lithiation of 1-methyl-1,2,4-triazole and thiazole and subsequent alkylation with 2-(2,4-dichlorophenyl)-2-(3-iodopropyl)-1,3-dioxolane produced, after an aqueous acidic workup, 2,4-dichlorophenyl 3-[5-(1-methyl-1,2,4-triazolyl) and 2-thiazolyl]propyl ketones, respectively. Ketalization with glycerol furnished the corresponding diastereomeric pairs of cis and trans 1,3- dioxolanes. The reaction of 2,4-dichlorophenyl 3-[5-(1-methyl-1,2,4-triazolyl)]propyl ketone with 3-mercapto-1,2-propanediol produced the corresponding diastereomeric cis and trans hydroxymethyl 1,3-oxathiolanes. The diastereomeric racemates were separated by column chromatography and their stereochemistry established by nOe nmr experiments. Some of these racemic cis ketal alcohols were converted by benzyl bromide to the corresponding benzyl ethers. Several of these racemic cis-ketals were reacted, first with methanesulfonyl chloride, then with 1-acetyl-4-(4-hydroxyphenyl)piperazine, to furnish the title compounds.     

Conformational and configurational studies on 3-azabicyclo[3.3.1]nonane (3-abn) derivatives and related systems employing carbon-13 NMR spectroscopy

The ¹³C nmr spectra of 4 cis-2,4-diphenyl-3-azabicyclo[3.3.1]nonanes, 11 cis-2,4-diaryl-3-azabicyclo[3.3.1]-nonan-9-ones, 26 cis-2,4-diaryl-3-azabicyclo[3.3.1]-nonan-9-ols or acetates thereof, 5 cis-2,4-diaryl-3-azabi-cyclo[4.3.1]decan-10-ones or -10-ols and 5 cis-2,4-diphenyl-3-aza-7-thiabicyclo[3.3.1]nonan-9-ones, -9-ols or 9-yl acetates have been recorded. Except for the 7-thia compounds, which appear to exist mainly in the configuration and conformation with the nitrogen-containing ring in the boat form, these compounds seem to exist overwhelmingly in chair-chair conformations. The configuration of the 9-ols and their acetates (syn or anti to the nitrogen-containing ring) has been deduced from the spectra. In a number of cases, the structures assigned differ from those earlier postulated. Broadening of one set of aryl signals (probably those due to the ortho carbons) in the case of N-methyl (but not N-H) compounds without ortho substituents is ascribed to restricted phenyl rotation.     

Calorimetric evaluation of activated carbons modified for phenol and 2,4-dinitrophenol adsorption

Two commercial activated carbons with differences in their superficial chemistry, one granular and the other pelletised, were modified for use in phenol and 2,4-dinitrophenol adsorption. In this paper, changes to the activated carbon surface will be evaluated from their immersion calorimetry in water and benzene, and they will then be compared with Area BET, chemical parameters, micropore size distributions and hydrophobicity factors of the modified activated carbons. The activated carbons were modified using 60 % solutions of phosphoric acid (H₃PO₄), nitric acid (HNO₃), zinc chloride (ZnCl₂) and potassium hydroxide (KOH); the activated carbon/solution ratio was 1:3 and impregnation was conducted 291 K for a period of 72 h before samples were washed until a constant pH was obtained. Water immersion calorimetry showed that the best results were obtained from activated carbons modified with nitric acid, which increased from ?10.6 to ?29.8 J g^?1 for modified granular activated carbon, and ?30.9 to ?129.3 J g^?1 for pelletised activated carbon. Additionally, they showed the best results in phenol and 2.4-dititrophenol adsorption. Those results indicate that impregnation with nitric acid under the employed conditions could generate a greater presence of oxygenated groups on their surface, which favours hydrogen bond formation and the increased adsorption of polar compounds. It should also be noted that immersion enthalpy in benzene for modified activated carbon with nitric acid is the method with the lowest value, which is consistent with the increased presence of polar groups on its surface. Regarding hydrophobicity factors, it was observed that granular carbons modified with nitric acid and potassium hydroxide have the lowest ratios, indicating greater interaction with water.     

Synthesis and structural study of novel 5-aryl substituted 2-amino-4,7-dioxopyrido[2,3-d]pyrimidines

The tide compounds 4a-c have been prepared in a one-step procedure from 2,4-diamino-6-hydroxy-pyrimidine (1) and the corresponding arylidene substituted Meldrum's acids 2a-e in very good yields. Semiempirical theoretical calculations (AMI) reveal two favoured conformations ( A and B ) for compounds 4a-e. The ¹H-nmr determinations, by using Karplus and Altona equations, clearly indicate that conformation A, with the aryl group on C5 in a pseudoaxial position, is that predominant in solution. The calculated charge density values for the olefinic carbons are in agreement with the experimental push-pull effect observed in the ¹³C-nmr spectra.     

2,3-二芳基马来酸酐环合反应机理的计算研究

在B₃LYP/6-311+G(d,p)//HF/3-21G水平上研究了2,3-二芳基马来酸酐环合反应机理.2,3-二芳基马来酸酐环合反应有两条反应途径:(1)反应过程中涉及的各种构型始终保持反式,即中心成环碳原子上的取代基团甲基或氢原子位于分子平面的异侧,这些构型具有C₂对称性;(2)反应过程中涉及的各种构型始终保持顺式,即中心成环碳原子上的取代基团甲基或氢原子位于分子平面的同一侧面,这些构型可具有Cs对称性.二芳基乙烯类化合物环合反应的位垒计算结果与Woodward-Hoffman原理一致,计算结果支持在环合碳原子上引入甲基能改善反应的热不可逆反应性能的实验结果.电荷分析表明,在环合碳原子上引入甲基,能增加二芳基乙烯类化合物体系对氧的稳定性,与实验结果一致.2,3-二芳基马来酸酐化合物的闭环结构的LUMO和HOMO能隙小于开环结构的能隙,说明闭环结构的最大吸收波长大于开环结构的最大吸收波长,与实验结果一致.     

Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.     

Some new information on the formation of substituted 4‐amino‐1‐substituted phenyl‐1H‐pyrazoles from β‐enaminones and diazonium tetrafluoroborates

Upon reaction of 2‐methyl‐, 3‐ethoxycarbonyl, and 4‐ethoxycarbonylbenzenediazonium tetrafluoroborate with 1‐cyclopropyl‐3‐phenylaminohex‐2‐en‐1‐one 3‐cyclopropylcarbonyl‐1‐(substituted phenyl)‐5‐ethyl‐4‐phenylamino‐1H‐pyrazoles are formed. On the other hand, the reaction of 1‐cyclopropyl‐3‐phenylaminohex‐2‐en‐1‐one and 5‐methylaminohept‐4‐en‐3‐one with sterically more demanding 2‐ethoxycarbonylbenzenediazonium tetrafluoroborate does not give the corresponding pyrazoles but the probable intermediates on the route to the pyrazoles: 1‐cyclopropyl‐3‐phenyliminohexane‐1,2,4‐trione 2,4‐bis(2‐ethoxycarbonylphenylhydrazone) and 3‐methyliminoheptane‐2,4,5‐trione 2,4‐bis(2‐ethoxycarbonylphenylhydrazone), respectively. All the compounds were identified on the basis of ¹H‐ and ¹³C‐NMR spectra. The structure of 1‐cyclopropyl‐3‐phenyliminohexane‐1,2,4‐trione 2,4‐bis(2‐ethoxycarbonylphenylhydrazone) was confirmed by means of ¹⁵N‐NMR spectra and X‐ray. The bis(2‐ethoxycarbonylphenylhydrazones) were found to show atropoisomerism due to a hindered rotation around the bond between the carbons of imino group and the hydrazono group next to carbonyl. In the case of the crystalline cyclopropyl derivative, the unit cell was found out to contain two molecules of opposite chirality. J. Heterocyclic Chem., (2011).