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Benzene Ring (benzene + ring)
Kinds of Benzene Ring Selected AbstractsOne-Step Conversion of Aromatic Hydrocarbon Bay Regions into Unsubstituted Benzene Rings: A Reagent for the Low-Temperature, Metal-Free Growth of Single-Chirality Carbon Nanotubes,ANGEWANDTE CHEMIE, Issue 37 2010Nitroethylen ist ein leistungsfähiges ,maskiertes Acetylen", das in einem Schritt durch Diels-Alder-Cycloaddition und Rearomatisierung Kohlenwasserstoff-Bay-Regionen in unsubstituierte Benzolringe umwandeln kann und so die gezielte Synthese gleichförmiger, einwandiger Kohlenstoffnanoröhren aus kurzen Kohlenwasserstofftemplaten, wie aromatischen Gürteln und geodätischen Nanoröhren-Endstücken, ermöglicht (siehe Schema). [source] Dynamics of Benzene Rings in MIL-53(Cr) and MIL-47(V) Frameworks Studied by 2H,NMR Spectroscopy,ANGEWANDTE CHEMIE, Issue 28 2010Daniil Die Rotationsdynamiken von Benzolringen im flexiblen MIL-53- und im starren MIL-47-Gerüst wurden durch 2H-NMR-Spektroskopie untersucht. In beiden Fällen werden 180°-Flips beobachtet, wobei der Flip-Prozess in MIL-53 schneller ist. Zur Simulation der experimentellen Spektren (links) reicht die Berücksichtigung der quadrupolaren Wechselwirkung nicht aus (Mitte): Auch der paramagnetische Effekt muss einbezogen werden (rechts). [source] ChemInform Abstract: ipso-Acylation of 5,13-Di-tert-butyl-8,16-dimethyl[2.2]metacyclophane with Acid Anhydrides: Through-Space Electronic Interaction Among the Two Benzene Rings.CHEMINFORM, Issue 44 2009Tomoe Shimizu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] A Dendrimer Chiroptical Switch Based on the Reversible Intramolecular Photoreaction of Anthracene and Benzene RingsCHEMISTRY - AN ASIAN JOURNAL, Issue 8 2010Wenjie Liu Dr. Abstract A series of Fréchet-type dendrimers with 9-benzyloxymethylanthracene cores were synthesized and characterized. The chiral source for the dendrimers was an (S)-2-methyl-1-butoxy group in the 3-position of the benzene ring. Irradiation at 366,nm of a dilute benzene solution led to the formation of two diastereomers (1:1) through a quantitative intramolecular [4,+4,] cycloaddition between the central anthracene ring and the neighboring benzene ring. The process can be reversed with 254,nm UV light or heat. The benzene rings in the dendrons work as a light-harvesting system. The optical rotation values measured for the reversible process showed fatigue resistance. Thus, a promising new type of chiroptical switch has been created that has optical rotation values as output signals. [source] Structure,activity relationships for gene activation oestrogenicity: Evaluation of a diverse set of aromatic chemicalsENVIRONMENTAL TOXICOLOGY, Issue 1 2002T. Wayne Schultz Abstract Structure,activity relationships for oestrogenicity were developed based on 120 aromatic chemicals evaluated in the Saccharomyces cerevisiae -based Lac -Z reporter assay. Relative gene activation was compared to 17,-estradiol and varied over eight orders of magnitude. Analysis of the data compared to 17,-estradiol identified three structural criteria that were related to xenoestrogen activity and potency: (1) the hydrogen-bonding ability of the phenolic ring mimicking the A-ring, (2) a hydrophobic centre similar in size and shape to the B- and C-rings, and (3) a hydrogen-bond donor mimicking the 17,-hydroxyl moiety of the D-ring, especially with an oxygen-to-oxygen distance similar to that between the 3- and 17,-hydroxyl groups of 17,-estradiol. Binding data were segregated into activity clusters including strong, moderate, weak, and detectable gene expression, and those compounds that were inactive. The hydrogen-bonding ability of hydroxy group in the 3-position on 17,-estradiol was observed to be essential for gene activation. Compounds with a 4-hydroxyl substituted benzene ring and a hydrophobic moiety of size and shape equivalent to the B-ring of 17,-estradiol were generally observed to be weakly active compounds. Moderately active compounds have a 4-hydroxyl substituted benzene ring with a hydrophobic moiety equivalent in size and shape to the B- and C-ring of 17,-estradiol, or have a high hydrogen-bond donor capacity owing to the presence of halogens on a nonphenolic ring. Strongly active compounds, similar to 4,4,-diethylethylene bisphenol (DES), possess the same hydrophobic ring structure as described for moderately active compounds and an additional hydroxyl group with an oxygen-to-oxygen distance close to that exhibited by the 3- and 17-hydroxyl groups of 17,-estradiol. © 2002 by Wiley Periodicals, Inc. Environ Toxicol 17: 14,23, 2002 [source] Chemoselective Reagents for Covalent Capture and Display of Glycans in Microarrays,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2010Emiliano Cló Abstract Glycobiology has made very significant progress in the past decades. However, further progress will significantly depend on the establishment of novel methods for miniaturized, high-throughput analysis of glycan,protein interactions. Robust solid-phase chemical tools and new, chemoselective reagents for biologically meaningful display of surface-immobilized glycans are likely to play a key role. Here we present four new bifunctional linkers that allow highly chemoselective capture of unprotected glycans in solution to form glycan-linker conjugates for direct construction of glycan microarrays (glycochips). The bifunctional linkers carry O -linked aminooxy moieties, some with N -substituents at one end and an amino group at the other. In addition, they contain a substituted benzene ring for UV traceability and improved purification of glycan-linker conjugates. NMR spectroscopic studies in solution proved that N -substituted aminooxy linkers provided model glycan-linker conjugates with the ,-glucopyranoside configuration, i.e. the ring-closed form required for biological recognition. Then an ensemble of glycan-linker conjugates were assembled from mannobiose, lactose, and N -acetyl-lactosamine and used for covalent printing of glycan microarrays. The stability of oximes were studied both in solution and on-chip. In solution, two of the linkers provided glycan-linker conjugates with a remarkable stability at pH 4 or higher, on-chip this relative stability was upheld. Two of the linkers, with different properties, are recommended for the glycobiology toolbox for the construction of glycan microarrays from unprotected glycans. [source] One-Pot Synthesis of Fluorinated 1-Benzoyl-3,4-dihydroisoquinolines from [2-(o -Alkynylphenyl)ethyl]amines by a Hydroamination/Oxidation SequenceEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2010René Severin Abstract Fluorinated 1-benzoyl-3,4-dihydroisoquinolines can easily be synthesized by a new one-pot procedure from corresponding fluorinated [2-(o -alkynylphenyl)ethyl]amines in high yields. The one-pot process consists of an initial [Ind2TiMe2]-catalyzed intramolecular alkyne hydroamination and a subsequent Pd-catalyzed oxidation of the benzyl side chain of the resulting hydroamination product. The process tolerates electron-donating and -withdrawing substituents on the benzene ring that is converted into the benzoyl side chain of the products as well as ortho -substitution. [source] N -Acetylation as a Means to Activate Polyfluoroarylamines for Selective ortho -Hydrodefluorination by Zinc in Aqueous Ammonia: A Concise Route to Polyfluorobenzo Azaheterocycles,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2007Sergey S. Laev Abstract N -Acetylation of polyfluoroarylamines is proposed as a meansto remove the amino group blocking effect of their hydrodefluorination by zinc in aqueous ammonia. With pentafluoroacetanilide, the Zn ion specific effect has been demonstrated to be responsible for ortho hydrodefluorination. This regiochemistry is accompanied by the removal of a fluorine atom from the para position, which occurs predominantly in the initial phase of the process in the absence of deliberately added zinc salt. The CuCl2 additive has been found to accelerate the reaction and to propel it to double defluorination. Quantum chemical calculations suggest a diminished electron affinity of pentafluoroaniline, which is responsible for its inertness in relation to the hydrodefluorination reaction. The pentafluoroaniline radical anion, which essentially has a nonplanar structure, is prone to easy fragmentation to give an aminotetrafluorophenyl radical. For pentafluoroacetanilide, CVA experiments and quantum chemical calculations predict that the pentafluorophenyl moiety serves as the electron receptor and that the acetamido group is twisted out of coplanarity with the benzene ring; thus, together with the electron-withdrawing effect of the acetyl group, the amino group blocking effect is suppressed. On this ground, the selective ortho hydrodefluorination of polyfluoroacetanilides is developed as an important protocol for the expeditious and general synthesis of polyfluorobenzo azaheterocycles via readily accessible polyfluoroarylamines from base polyfluoroarenes. Its applicability has been illustrated by preparing quinolines that possess a polyfluorinated benzene moiety by the Skraup synthesis utilizing crude polyfluoroacetanilide hydrodefluorination products as starting materials. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Novel Promising Benzoazacrown Ethers as a Result of Ring Transformation of Benzocrown Ethers: Synthesis, Structure, and Complexation with Ca2+EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2003Sergey P. Gromov Abstract A series of promising benzoazacrown ethers with the nitrogen atom conjugated with the benzene ring were synthesized using a novel synthetic procedure based on stepwise transformation of the macroheterocycle. The structures and spectral properties of the resulting benzoazacrown ethers and their complexes with Ca2+ were studied by X-ray diffraction and 1H, 13C, and 15N NMR spectroscopy including the 2D NOESY technique. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Inhibitory effects of gallic acid ester derivatives on Saccharomyces cerevisiae multidrug resistance protein Pdr5pFEMS YEAST RESEARCH, Issue 3 2010Luciana Pereira Rangel Abstract Overexpression of the Saccharomyces cerevisiae ABC transporter Pdr5p confers resistance to a range of structurally unrelated xenobiotics. This property allows Pdr5p to be used as a target for novel multidrug resistance reversal reagents or chemosensitizers. Herein, we report the effects of gallic acid derivatives with substitutions either on the ester moiety or in the benzene ring on the activity of Pdr5p. Compounds with a longer side chain (8,16 carbons) resulted in greater inhibition of Pdr5p ATPase. Derivatives with side chains of 8,12 carbons that retained hydroxyl groups on the benzene ring extensively inhibited Pdr5p ATPase activity. These compounds almost completely inhibited the efflux of the Pdr5p fluorescent substrate Rhodamine 6G and at 25 ,M chemosensitized the Pdr5p-overexpressing strain AD124567 to fluconazole (0.4 mg mL,1). Gallic acid derivatives may be a new class of Pdr5p inhibitors. [source] 5-Benzyl-3-methylimidazolidin-4-one-Derived Reactive Intermediates of Organocatalysis , A Comforting Resemblance of X-Ray, NMR, and DFT Solid-Phase, Liquid-Phase, and Gas-Phase StructuresHELVETICA CHIMICA ACTA, Issue 1 2009Abstract The X-ray crystal structures of three (E)-1-cinnamoylidene iminium PF6 salts of 5-benzyl-3-methylimidazolidin-4-ones (2,2-dimethyl-, cis -2-(tert -butyl)-, and cis -2-styryl-substituted; 2,4, resp.) are reported (Figs.,3,5). In the 2,2-dimethyl and in the cis -2-styryl derivative, 2 and 4, respectively, a CH bond of the cis -substituent in 2-position points to the center of the benzene ring of the benzyl group above the five-membered ring (Fig.,6,,a and b). NMR Measurements (Fig.,8) provide evidence that the same structure is present in solution, and that a fourth derivative of this type, 5 (Scheme), has (Z)- instead of (E)-configuration around the CN bond. In the cis -2-(tert -butyl) derivative 3, the benzyl group is located over the iminium , -system (Figs.,4 and 6,,c). Overlays with DFT-calculated crotonylidene analogs, A and B, show that the theoretical and experimental structures are almost superimposable (Fig.,9 and Table). The structures are discussed in view of their role as reactive intermediates in organocatalysis and in view of the help synthetic organic chemists may experience from theory. [source] Isolation and X-Ray Structures of Reactive Intermediates of Organocatalysis with Diphenylprolinol Ethers and with ImidazolidinonesHELVETICA CHIMICA ACTA, Issue 11 20085-Repulsion, A Survey, Comparison with Computed Structures, the Geminal-Diaryl Effect at Work, with 1-Acyl-imidazolidinones: The Abstract Reaction of 2-phenylacetaldehyde with the Me3Si ether of diphenyl-prolinol, with removal of H2O, gives a crystalline enamine (1). The HBF4 salts of the MePh2Si ether of diphenyl-prolinol and of 2-(tert -butyl)-3-methyl- and 5-benzyl-2,2,3-trimethyl-1,3-imidazolidin-4-one react with cinnamaldehyde to give crystalline iminium salts 2, 3, and 4. Single crystals of the enamine and of two iminium salts, 2 and 3, were subjected to X-ray structure analysis (Figs.,1, 2, and 6), and a 2D-NMR spectrum of the third iminium salt was recorded (Fig.,7). The crystal and NMR structures confirm the commonly accepted, general structures of the two types of reactive intermediates in organocatalysis with the five-membered heterocycles, i.e., D, E (Scheme,2). Fine details of the crystal structures are discussed in view of the observed stereoselectivities of the corresponding reactions with electrophiles and nucleophiles. The structures 1 and 2 are compared with those of other diphenyl-prolinol derivatives (from the Cambridge File CSD; Table,1) and discussed in connection with other reagents and ligands, containing geminal diaryl groups and being used in enantioselective synthesis (Fig.,4). The iminium ions 3 and 4 are compared with N -acylated imidazolidinones F and G (Figs.,9, 12, and 13, and Table,3), and common structural aspects such as minimalization of 1,5-repulsion (the ,A1,3 -effect'), are discussed. The crystal structures of the simple diphenyl-prolinol,HBF4 salt (Fig.,3) and of Boc- and benzoyl-(tert -butyl)methyl-imidazolidinone (Boc-BMI and Bz-BMI, resp.; Figs.,10 and 11) are also reported. Finally, the crystal structures are compared with previously published theoretical structures, which were obtained from high-level-of-theory DFT calculations (Figs.,5 and 8, and Table,2). Delicate details including pyramidalization of trigonal N-atoms, distortions around iminium CN bonds, shielding of diastereotopic faces, and the , -interaction between a benzene ring and a Me group match so well with, and were actually predicting the experimental results that the question may seem appropriate, whether one will soon start considering to carry out such calculations before going to the laboratory for experimental optimizations. [source] Stability of Hoogsteen -Type Triplexes , Electrostatic Attraction between Duplex Backbone and Triplex-Forming Oligonucleotide (TFO) Using an Intercalating ConjugateHELVETICA CHIMICA ACTA, Issue 5 2008Daniel Globisch Abstract Syntheses are described for two novel twisted intercalating nucleic acid (TINA) monomers where the intercalator comprises a benzene ring linked to a naphthalimide moiety via an ethynediyl bridge. The intercalators Y and Z have a 2-(dimethylamino)ethyl and a methyl residue on the naphthalimide moiety, respectively. When used as triplex-forming oligonucleotides (TFOs), the novel naphthalimide TINAs show extraordinary high thermal stability in Hoogsteen -type triplexes and duplexes with high discrimination of mismatch strands. DNA Strands containing the intercalator Y show higher thermal triplex stability than DNA strands containing the intercalator Z. This observation can be explained by the ionic interaction of the protonated dimethylamino group under physiological conditions, targeting the negatively charged phosphate backbone of the duplex. This interaction leads to an extra binding mode between the TFO and the duplex, in agreement with molecular-modeling studies. We believe that this is the first example of an intercalator linking the TFO to the phosphate backbone of the duplex by an ionic interaction, which is a promising tool to achieve a higher triplex stability. [source] X-ray crystallographic analysis and differential scanning calorimetry of two polymorphic forms of 2,6-diphenyl-1,4-dithiinHETEROATOM CHEMISTRY, Issue 6 2004Xuehua Piao 2,6-Diphenyl-1,4-dithiin 2 exists in the two polymorphic forms. The dithiin 2L, mp 62,63°C, was assigned as the metastable form, while the dithiin 2H, mp 79,80°C, was assigned as the stable form, mainly on the basis of differential scanning calorimetry (DSC) analysis. X-Ray crystallographic analysis showed that the largest difference in the molecular structure between 2L and 2H is found in the coplanarity between the benzene ring and the double bond part of the dithiin ring; the benzene ring and the double bond are nearly coplanar for 2L, whereas these are far from being coplanar for 2H. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:424,427, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20035 [source] The chain-breaking antioxidant activity of phenolic compounds with different numbers of O-H groups as determined during the oxidation of styreneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2009Ivan Tikhonov The technique based on monitoring oxygen consumption was applied to test 18 polyphenols (PP) and model phenolics as a chain-breaking antioxidant during the oxidation of styrene initiated by 2,2,-azobis(2,4-dimethylvaleronitril) at 37°C. The chain-breaking capability of PP was characterized by two parameters: the rate constant k1 for the reaction of antioxidants with the peroxy radical produced from styrene and the stoichiometric coefficient of inhibition, f, which shows how many kinetic chains are terminated by one molecule of PP. Rate constants k1 × 105 (in M,1 s,1) were found to be 10 (catechol), 27 (pyrogallol), 34 (3,6-di-tert-Bu-catechol), 4.3 (protocatechic acid), 12 (gallic acid), 15 (caffeic acid), <0.01 (chrysin), 1.3 (kaempferol), 19 (quercetin), 5.3 (baicalein), 16 (epicatechin), 32 (epigallocatechin), 9.0 (dihydroquercetin), 3.3 (resveratrol), and 16 (nordihydroguaiaretic acid). The value of k1 increases when going from one to two and three adjacent O-H groups in a benzene ring (catechol and pyrogallol derivatives, respectively). At the same time, two O-H groups in metaposition in a A-ring of flavonoids actually do not participate in the inhibition. For the majority of PP, f is near to 2 independent of the number of OH groups. The correlation of k1 with the structure of PP and the OH bond dissociation enthalpy has been discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 92,100, 2009 [source] Fluid flow and heat transfer investigations in shell and dimple heat exchangersINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2005A. Witry Abstract Heat transfer and pressure drop characteristics are investigated here using experimental and analytical techniques for a dimple plate heat exchanger. The analysis uses the log mean temperature difference method (LMTD) in all its calculations. Whilest the shell side flow highly resembles the flow over a rough or wavy plate, the tube side passage in these represents the flow over short hexagonal tube banks with the flowing across the sectional areas between the hexagons having the shape of a benzene ring. Local and global experimental measurements are carried out around the heat exchanger. Furthermore, analytical models for both sides of the heat exchanger were obtained from the literature. Reasonable cross match between experimental and analytical results could be obtained. Copyright © 2005 John Wiley & Sons, Ltd. [source] Palladium-Catalyzed Cyclopropanation of Unsaturated Endoperoxides.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009A New Peroxide-Preserving Reaction Abstract Unsaturated bicyclic endoperoxides are efficiently cyclopropanated with excess diazomethane in the presence of catalytic palladium(II) acetate [Pd(OAc)2] in a stereoselective manner. This method represents a new peroxide-preserving transformation. Whereas the unsaturated endoperoxides in the [2.2.1],series are attacked by the carbene from the exo face, the analogs with larger bridges are preferentially attacked from the face syn to the peroxo bridge. Only in the case of the benzannelated [2.2.2],system does the attack occur exclusively from the face proximal to the benzene ring. Certain strained cyclopropanated endoperoxides are reduced by diazomethane to give cis -diols. 2-Methylfuran endoperoxide gives rise to cis -1-formyl-2-acetylcyclopropane in excellent yield. [source] Synthesis and structure of some imines containing furoxan ring derived from isosafroleJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2004Nguyen Huu Dinh A series of 14 imines containing furoxan and benzene rings has been prepared starting from isosafrole. The structure of reported compounds have been confirmed by elemental analysis, EI MS, UV, IR, and NMR spectroscopy. It is shown that, on treatment with Na2S2O4, the nitro group on the benzene ring was reduced to amino group, but the N,O group of the furoxan ring was not. The 1H- and 13C NMR signals are assigned based on their spin-spin splitting patterns, in some cases, NOESY and HMBC spectra are used. The NOESY spectra indicate that for reported imines, the benzene and the furoxan rings could not be co-planar; the imine group has E -configuration. [source] Ring transformations of heterocyclic compounds.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 20022,4,6-Triarylpyrylium perchlorates 1 react with methyleneindolines 3in situ generated from the corresponding methylindolium salts 2, which are spiro-fused with a cycloalkane, benzanellated cycloalkene or a heterocyclic system. These diastereoselective 2,5-[C4+C2] pyrylium ring transformations are carried out in the presence of triethylamine/acetic acid in boiling ethanol to give the dispiroindolines 4 with a trans configuration of the more bulky substituents at the cyclohexadiene ring. By the same type of transformation the dispiro compounds 7/10 with an additional fused benzene ring are obtained from the pyrylium salt 1a and 6/9, the benzo-fused analogues of 3. Spectroscopic data of the transformation products as well as their mode of formation are discussed. [source] Synthesis of 14C-labelled EM-800 (SCH 57050) and EM-652·HCl (SCH 57068·HCl, acolbifene), pure selective estrogen receptor modulatorsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 11 2004Jean-Yves Sancéau Abstract EM-800 (SCH 57050) and EM-652·HCl (SCH 57068·HCl, acolbifene) are orally active pure selective estrogen receptor modulators. The corresponding 14C2 -radiolabelled compounds 1 and 2 were synthesized for metabolic studies with uniform labelling of two carbons within the benzene ring of the 2H-1-benzopyran moiety by optical resolution of racemic (±)-[14C2]EM-343 4. This pivotal intermediate amine was prepared in 6 steps with 38% yield from commercially available [U- 14C2]resorcinol (3). Resolution by selective crystallization of the diastereomeric mixture of (S)-(+)-camphorsulfonates salts gave the desired (+)-[14C2]EM-652·(+)-CSA 13. Moreover, the racemic amine 4 was recovered from mother liquors by basic treatment, and resolved again. We obtained salt 13, at a 52% yield with 97% diastereomeric excess by repeating the resolution,racemization process. Finally, the corresponding dipivaloate (+)-[14C2]EM-800 1 and hydrochloride salt (+)-[14C2]EM-652·HCl 2 were prepared at respective specific activities of 19.7 and 24.5 µCi/mg with 96.3% radiochemical purity. Copyright © 2004 John Wiley & Sons, Ltd. [source] Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acidJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2006Vilve Nummert Abstract Infrared spectra of 25 substituted phenyl esters of benzoic acid C6H5CO2C6H4 -X (XH, 3-Cl, 3-F, 3-CN, 3-NO2, 3-CH3, 3-OH, 3-NH2, 4-Cl, 4-F, 4-NO2, 4-CN, 4-OCH3, 4-CH3, 4-NH2, 2-Cl, 2-F, 2-I, 2-NO2, 2-CF3, 2-CN, 2-CH3, 2-OCH3, 2-N(CH3)2, 2-C(CH3)3), 8 alkyl benzoates C6H5CO2R (XCH3, CH2CH3, CH2Cl, CH2CN, CH2CCH, CH2CH2Cl, CH2CH2OCH3, CH2C6H5), and 22 phenyl esters of substituted benzoic acids X-C6H4CO2C6H5 (X3-Cl, 3-NO2, 3-CH3, 3-N(CH3)2, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-C(CH3)3, 4-OCH3, 4-NH2, 2-Cl, 2-F, 2-Br, 2-I, 2-NO2, 2-CN, 2-CF3, 2-CH3, 2-OCH3, 2-NH2) were recorded in tetrachloromethane in the region of 400,4000,cm,1. Carbonyl stretching frequencies ,CO for meta - and para -substituted phenyl esters of benzoic acid and phenyl esters of meta -substituted benzoic acids were shown to correlate with the substituent constants ,o. The influence of the through resonance effect on ,CO was found to be important in the case of +Rpara substituents in the benzoyl part of phenyl benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate with the inductive substituent constant ,I only. In the benzoyl part of the esters the carbonyl stretching frequencies of cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter equations: (,CO)cis,=,(,CO)o,+,c1,I,+,c3,and (,CO)trans,=,(,CO)o,+,c1,p+,+,c3, (R,=,0.99). The trans isomers of phenyl esters of ortho -substituted benzoic acids showed direct resonance similar to that for para derivatives. The positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition of resonance between the phenyl ring and the carboxy-group caused by bulky ortho substituents. The existence of cis/trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at B3LYP/6-311+G** level for the ortho -substituted benzoates. In the case of alkyl benzoates good correlations of ,CO values were obtained when both the Taft ,* and the steric constants were used. For meta - and para -substituted phenyl benzoates s - trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular relative to the carbonyl bond plane was supported. Copyright © 2006 John Wiley & Sons, Ltd. [source] Kinetics of oxidation of acidic amino acids and their monoamides by N -chloroarylsulphonamides in aqueous acidic mediumJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2004B. Thimme Gowda Abstract Twelve sodium salts of N -chloroarylsulphonamides were employed as oxidants for studying the kinetics of oxidation of two acidic amino acids (aspartic and glutamic acid) and their monoamides (aspargine and glutamine) in aqueous acidic medium under various conditions, to see how the oxidative strength of these reagents vary with substitution. The sodium salts of N -chloroarylsulphonamides employed are of the general formulae i -X-C6H4SO2NaNCl·xH2O (where i -X,=,4-C2H5, 4-F, 4-Cl or 4-Br) and i -X- j -Y-C6H3SO2NaNCl·xH2O [where i -X- j -Y,=,2,3-(CH3)2, 2,4-(CH3)2, 2,5-(CH3)2, 2-CH3 -4-Cl, 2,4-Cl2 and 3,4-Cl2]. The reactions show second-order kinetics in [oxidant], fractional order in [amino acid] and an inverse dependence on [H+]. Addition of the reduced product of the oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. Mechanisms in conformity with the observed kinetics are discussed. The effective oxidizing species of the oxidants is Cl+ in different forms. The oxidizing strengths of N -chloroarylsulphonamides depend on the ease with which Cl+ is released from them. The study reveals that the introduction of electron-withdrawing groups such as halides to the benzene ring eases the release of Cl+ from the reagent and hence increases the oxidizing strengths of the N -chloroarylsulphonamides. The effect of substituents on Ea of the reactions was analysed by optimising Ea with reference to log,A, and log,A with reference to Ea of the parent oxidant. Copyright © 2004 John Wiley & Sons, Ltd. [source] Substituent chemical shifts of N -arylsuccinanilic acids, N -arylsuccinimides, N -arylmaleanilic acids, and N -arylmaleimidesMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2009Hye Sun Lee Abstract NMR spectra of a series of N -arylsuccinanilic acids, N -arylsuccinimides, N -arylmaleanilic acids, and N -arylmaleimides were examined to estimate the electronic effect of the amide and imide groups on the chemical shifts of the hydrogen and carbon nuclei of the benzene ring. Copyright © 2009 John Wiley & Sons, Ltd. [source] Styrene,substituted-styrene copolymerization using diphenylzinc,metallocene,methylaluminoxane systemsPOLYMER INTERNATIONAL, Issue 8 2006Franco M Rabagliati Abstract Homopolymerization of disubstituted styrenes (2,4- and 2,5-dimethylstyrene) and trisubstituted styrene (2,4,6-trimethylstyrene) and their copolymerization with styrene were carried out using diphenylzinc,metallocene,methylaluminoxane initiator systems for metallocene (n -BuCp)2TiCl2 and for half-metallocene CpTiCl3. The studied comonomers were found to be less reactive than p -tertbutylstyrene, p -methylstyrene and styrene. The results indicate that, even though the methyl group has I+ inductive effect, di- and tri-methylstyrenes are reluctant to undergo either homopolymerization or copolymerization. This behavior suggests that the reactivity is regulated not only by the inductive effect of the alkyl group but also by the steric impediment caused by the crowding of the substituents on the benzene ring. Copyright © 2006 Society of Chemical Industry [source] Structural elucidation of metabolites of ginkgolic acid in rat liver microsomes by ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry and hydrogen/deuterium exchangeRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2009Z. H. Liu Ginkgolic acids have been shown to possess allergenic as well as genotoxic and cytotoxic properties. The question arises whether the metabolism of ginkgolic acids in the liver could decrease or increase their toxicity. In this study, the invitro metabolism of ginkgolic acid (15:1, GA), one component of ginkgo acids, was investigated as a model compound in Sprague-Dawley rat liver microsomes. The metabolites were analyzed by ultra-performance liquid chromatography coupled with photodiode array detector/negative-ion electrospray ionization tandem mass spectrometry (UPLC-PDA/ESI-MS/MS) and hydrogen/deuterium (H/D) exchange. The result showed that the benzene ring remained unchanged and the oxidations occurred at the side alkyl chain in rat liver microsomes. At least eight metabolites were found. Among them, six phase I metabolites were tentatively identified. This study might be useful for the investigation of toxicological mechanism of ginkgolic acids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preferred conformations in the solid state of some ,-(p -phenylsulfinyl)- p -substituted acetophenonesACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2000Paulo R. Olivato Information on the geometrical structures of ,-(p -phenylsulfinyl)- p -substituted acetophenones X,PhC(O)CH2S(O)Ph,Y [X = OMe, Y = H (1); X = NO2, Y = OMe (2); X = OMe, Y = NO2 (3); IUPAC names: (1) 4-methoxyphenyl phenylsulfinylmethyl ketone; (2) 4-nitrophenyl 4-methoxyphenylsulfinylmethyl ketone; (3) 4-methoxyphenyl 4-nitrophenylsulfinylmethyl ketone] have been obtained from X-ray diffraction analyses. A comparison of these results with those previously obtained from X-ray diffraction and ab initio computations of ,-methylsulfinylacetophenone, PhC(O)CH2S(O)Me, indicated that (1) and (2) adopt in the crystal a cis1 conformation and (3) assumes a quasi-gauche geometry. The stabilization of these conformations in the crystal is discussed in terms of the dipole moment coupling, Coulombic and intramolecular charge transfer interactions between the oppositely charged atoms of the C=O and S=O dipoles. The p -substituted benzene ring is quasi -coplanar with the sulfinyl group for (1) and (3), but is quasi -perpendicular for (2). Conjugation and repulsion between the sulfinyl sulfur lone pair and the ,-benzene ring seem to be responsible for the observed geometries. [source] The twinned crystal structure of tripotassium benzene-1,3,5-tris(trifluoroborate)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Daniel Franz The title compound, 3K+·C6H3B3F93,, crystallizes as discrete anions and cations which are connected by K...F and K..., interactions. Two of the ,BF3 residues attached to the aromatic ring adopt a conformation with all F atoms out of the plane of the aromatic ring, whereas the third residue has an almost synperiplanar conformation for one of the F,B,C,C torsion angles. It is remarkable that only one of the K+ cations interacts with the arene ring and that only one side of the aromatic ring coordinates to a K+ cation. As a result, a sandwich structure does not occur. All K+ ions show a coordination mode that cannot be conveniently described with a polyhedron. The anions are located in the (102) planes with the K+ cations located between these planes. The investigated crystal was a nonmerohedral twin with the fractional contribution of the minor twin component being 0.405,(4). The title compound is the first example of a structure containing a benzene ring substituted with three ,BF3 groups. Only eight other structures have been reported in which a benzene ring carries at least one ,BF3 group. Just five of these contain a K+ ion, but in none of these is the K+ ion coordinated to the aromatic ring. [source] Structural comparisons between methylated and unmethylated nitrophenyl lophinesACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Diana Yanover The lophine derivative 2-(2-nitrophenyl)-4,5-diphenyl-1H -imidazole, C21H15N3O2, (I), crystallized from ethanol as a solvent-free crystal and from acetonitrile as the monosolvate, C21H15N3O2·C2H3N, (II). Crystallization of 2-(4-nitrophenyl)-4,5-diphenyl-1H -imidazole from methanol yielded the methanol monosolvate, C21H15N3O2·CH4O, (III). Three lophine derivatives of methylated imidazole, namely, 1-methyl-2-(2-nitrophenyl)-4,5-diphenyl-1H -imidazole methanol solvate, C22H17N3O2·CH4O, (IV), 1-methyl-2-(3-nitrophenyl)-4,5-diphenyl-1H -imidazole, C22H17N3O2, (V), and 1-methyl-2-(4-nitrophenyl)-4,5-diphenyl-1H -imidazole, C22H17N3O2, (VI), were recrystallized from methanol, acetonitrile and ethanol, respectively, but only (IV) produced a solvate. Compounds (III) and (IV) each crystallize with two independent molecules in the asymmetric unit. Five imidazole molecules in the six crystals differ in their molecular conformations by rotation of the aromatic rings with respect to the central imidazole ring. In the absence of a methyl group on the imidazole [compounds (I),(III)], the rotation angles are not strongly affected by the position of the nitro group [44.8,(2) and 45.5,(1)° in (I) and (II), respectively, and 15.7,(2) and 31.5,(1)° in the two molecules of (III)]. However, the rotation angle is strongly affected by the presence of a methyl group on the imidazole [compounds (IV),(VI)], and the position of the nitro group (ortho, meta or para) on a neighbouring benzene ring; values of the rotation angle range from 26.0,(1) [in (VI)] to 85.2,(1)° [in (IV)]. This group repulsion also affects the outer N,C,N bond angle. The packing of the molecules in (I), (II) and (III) is determined by hydrogen bonding. In (I) and (II), molecules form extended chains through N,H...N hydrogen bonds [with an N...N distance of 2.944,(5),Å in (I) and 2.920,(3),Å in (II)], while in (III) the chain is formed with a methanol solvent molecule as the mediator between two imidazole rings, with O...N distances of 2.788,(4),2.819,(4),Å. In the absence of the imidazole N,H H-atom donor, the packing of molecules (IV),(VI) is determined by weaker intermolecular interactions. The methanol solvent molecule in (IV) is hydrogen bonded to imidazole [O...N = 2.823,(4),Å] but has no effect on the packing of molecules in the unit cell. [source] Dimorphic forms of 3,6-dinitrodurene in a single space groupACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009José Alberto Galicia Aguilar 3,6-Dinitrodurene (1,2,4,5-tetramethyl-3,6-dinitrobenzene), C10H12N2O4, has been crystallized in two polymorphic forms which may be distinguished by their colours in the solid state. Polymorph I gives clear colourless prismatic crystals, while polymorph II crystallizes in the dark and under an inert atmosphere as irregular purple blocks. Both forms belong to the space group C2/c, with both asymmetric units containing two half-molecules. One molecule is located on an inversion centre and the other lies on a twofold axis. The polymorphism arises from different orientations of the twofold axis: in form I, this axis passes through the mid-points of two C,C bonds of the benzene ring and, as a consequence, all atoms in the asymmetric unit are in general positions. In form II, the N atoms of the nitro groups and the Cipso atoms are located on the binary axis. Comparing phases I and II, slightly different conformations are observed for the nitro substituents, while the stacking structures are very similar. [source] A three-dimensional hydrogen-bonded network in bis(4-hydroxyanilinium) selenate(VI) dihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Jan Janczak The title compound, 2C6H8NO+·SeO42,·2H2O, contains 4-hydroxyanilinium cations, selenate(VI) anions and water molecules. One of the two independent cations is nearly planar (excluding the ammonium H atoms), while the other is markedly nonplanar, with the hydroxy and ammonium groups displaced from the plane of the benzene ring. This results from the antiparallel orientation of the cations, which interact through oppositely polarized ammonium and hydroxy groups. Ionic and hydrogen-bonding interactions join the oppositely charged units into a three-dimensional network. This work demonstrates the usefulness of 4-aminophenol in the crystal engineering of organic,inorganic hybrid compounds. [source] | |||||||||||||||||||||||||||||||||||||||||||