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Aromatic C (aromatic + c)

Distribution by Scientific Domains

Chemistry	70%
Earth and Environmental Science	23%

Distribution within Chemistry

Organic Chemistry	50%
Crystallography	24%

Selected Abstracts

ChemInform Abstract: Palladium-Catalyzed Oxidative Ethoxycarbonylation of Aromatic C,H Bond with Diethyl Azodicarboxylate.

CHEMINFORM, Issue 31 2008
Wing-Yiu Yu
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]

Platinum-Catalyzed Aromatic C,H Silylation of Arenes with 1,1,1,3,5,5,5-Heptamethyltrisiloxane.

CHEMINFORM, Issue 50 2007
Miki Murata
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, please click on HTML or PDF. [source]

Suzuki,Miyaura Coupling Reaction by Pd(II)-Catalyzed Aromatic C,H Bond Activation Directed by an N-Alkyl Acetamino Group.

CHEMINFORM, Issue 46 2007
Zhangjie Shi
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, please click on HTML or PDF. [source]

Direct Synthesis of Aryl Halosilanes Through Iridium(I)-Catalyzed Aromatic C,H Silylation by Disilanes.

CHEMINFORM, Issue 10 2004
Tatsuo Ishiyama
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

The Ruthenium-Catalyzed Silylation of Aromatic C,H Bonds with Triethylsilane.

CHEMINFORM, Issue 9 2004
Fumitoshi Kakiuchi
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Effect of long-term combined nitrogen and phosphorus fertilizer application on 13C CPMAS NMR spectra of humin in a Typic Hapludoll of northeast China

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2009
J. J. Zhang
Summary Because of its insolubility, heterogeneity and structural complexity, humin is the least understood among the three fractions of soil humic substances. This research aimed to evaluate the long-term effect of combined nitrogen and phosphorus (NP) fertilizer addition on the chemical structure of humin under maize (Zea mays L.) monoculture in a Typic Hapludoll of northeast China. Soil samples were collected 12 and 25 years after the initiation of the fertilizer treatment. Soil humin was isolated using NaOH-Na4P2O7 extraction to remove humic and fulvic acids, which was followed by HF-HCl treatment to remove most of the inorganic minerals. Solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy was used to characterize the chemical structure of the humin isolates. Results showed that the organic carbon (C) content of humin increased after NP fertilizer addition, compared with a no-fertilizer (CK) treatment. 13C CPMAS NMR indicated that O-alkyl C and aromatic C of humin decreased, while alkyl C and the ratios of alkyl C/O-alkyl C, aliphatic C/aromatic C and hydrophobic C/hydrophilic C all increased in the NP fertilizer treatment. The long-term application of NP fertilizer changed the molecular structure of soil humin to be more alkyl and hydrophobic, and was thus beneficial to the sequestration and stability of organic C in soil. [source]

Structural, Spectroscopic, and Proton-Coupled Electron-transfer Behavior of Pyrazolyl-3,5-bis(benzimidazole)-Bridged Homo- and Heterochiral RuIIRuII, OsIIOsII, and OsIIRuII 2,2,-Bipyridine Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2010
Sujoy Baitalik
Abstract The homo- and heterobimetallic complexes [(bpy)2MII(H2pzbzim)M,II(bpy)2](ClO4)3·nH2O (1, 3, 5) and their corresponding deprotonated complexes [(bpy)2MII(pzbzim)M,II(bpy)2](ClO4)·nH2O (2, 4, 6) [where MII, M,II = Ru (1, 2) = Os (3, 4); MII = Os and M,II = Ru (3, 5); bpy = 2,2,-bipyridine; H3pzbzim = pyrazole-3,5-bis(benzimidazole)] were synthesized, separated to their heterochiral (a, ,,/,,) and homochiral (b, ,,/,,) diastereoisomers, and characterized by elemental analyses, ESI-MS, and 1H NMR spectroscopy. The X-ray structures of 1a, 3a, and 5a show the involvement of two pyridine rings of two bpy ligands in strong intramolecular nonbonded ,,, interaction. The occurrence of a C,H···, interaction between an aromatic C,H and the ,-cloud of a pyridine ring leads to strong electronic shielding of this proton (1H NMR). In all cases, the two diastereoisomers show practically no differences in their absorption spectra, redox potentials, and pK values. The large shifts in the E1/2 values to less positive potentials and substantial redshifts in the MLCT bands that occur on deprotonation of 1, 3, and 5 are energetically correlated. From the profiles of E1/2(1), (2) vs. pH over the pH range 1,12, the equilibrium constants and standard redox potentials for all the complex species in the metal oxidation states II·II, II·III, and III·III and the bridged ligand in the protonation states H2pzbzim,, Hpzbzim2,, and pzbzim3, have been evaluated. Using these values the bond dissociation free energies for the benzimidazole N,H bonds have been estimated. Spectroelectrochemical studies have been carried out for 1a, 3a, and 5a in the range 400,1100 nm. With stepwise oxidation of the metal centers replacement of MLCT bands by LMCT bands occur gradually with the observation of sharp isosbestic points. In the case of 1a, a band observed at ,max = 910 nm for the RuIIRuIII species has been ascribed to intervalence charge transfer (IVCT) transition. [source]

Magnetic, 57Fe Mössbauer, and IR Monitoring of the Thermal Spin Transition in a New Family of Iron(II) Spin-Transition Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003
Arno F. Stassen
Abstract A new family of iron(II) tetrafluoroborate and perchlorate spin-crossover compounds has been synthesised and is discussed. The iron(II) ion is surrounded by six 1-ethyltetrazole ligands, which are halogen-substituted on the C2 atom of the ethyl group. The spin-crossover temperatures T1/2 are high compared to the unsubstituted (1-alkyltetrazole)iron(II) complexes. The shape of the spin-transition curve (i.e. ,HS vs. T) varies largely over the different complexes and appears to be influenced neither by the crystal packing, nor by the electronic effects. The temperature-dependent spin-transition behaviour has been studied by magnetic susceptibility and by 57Fe-Mössbauer spectroscopy. These data have been supported by temperature-dependent mid-range infrared spectroscopy: the thermally induced spin transition has been observed by direct monitoring of the aromatic C,H stretching frequency. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Alkyne Hydroarylations with Chelating Dicarbene Palladium(II) Complex Catalysts: Improved and Unexpected Reactivity Patterns Disclosed Upon Additive Screening,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009
Andrea Biffis
Abstract Palladium(II) complexes with a ligand set made from a chelating N-heterocyclic dicarbene ligand and two weakly coordinating anions (generally introduced in situ upon addition of 2 equiv. of a suitable silver salt) were found to be very active and selective catalysts for the room-temperature hydroarylation of alkynes at low catalyst loading (0.1 mol-%). Moreover, the screening of various strong acids as reaction promoters revealed that both the strength of the acid and the coordinating ability of its conjugated base influence the catalytic performance. Most remarkably, the use of HBF4 together with a dicarbene Pd complex catalyst provides a dramatic change in the selectivity of the reaction, with the prevalent formation of a product stemming from the insertion of two molecules of alkyne into the aromatic C,H bond. The results presented herein highlight the fact that the dicarbene ligand, apart from stabilising the catalyst, is also able to enhance catalytic activity and, most notably, to steer the reaction selectivity towards novel products. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Effect of long-term combined nitrogen and phosphorus fertilizer application on 13C CPMAS NMR spectra of humin in a Typic Hapludoll of northeast China

Thickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007
H.-L. Cheng
Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source]

Use of mid-infrared spectroscopy in the diffuse-reflectance mode for the prediction of the composition of organic matter in soil and litter

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2008
Bernard Ludwig
Abstract Mid-infrared spectroscopy (MIRS) is assumed to be superior to near-infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid-infrared region including part of the near-infrared region (7000,400,cm,1) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by 13C CPMAS-NMR spectroscopy. A partial least-square method and cross-validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid-infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF , 0.70, 0.8 , a , 1.2, r , 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O-alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl,to,aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse-reflectance mode were generally not superior to those of NIRS. [source]

Near-infrared spectroscopy can predict the composition of organic matter in soil and litter

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006
Thomas Terhoeven-Urselmans
Abstract The usefulness and limitations of near-infrared reflectance spectroscopy (NIRS) for the assessment of several soil characteristics are still not sufficiently explored. The objective of this study was to evaluate the ability of visible and near-infrared reflectance (VIS-NIR) spectroscopy to predict the composition of organic matter in soils and litter. Reflectance spectra of the VIS-NIR region (400,2500 nm) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by 13C-CPMAS-NMR spectroscopy. A modified partial least-square method and cross-validation were used to develop equations for the different constituents over the whole spectrum (1st to 3rd derivation). Near-infrared spectroscopy predicted well the C : N ratios, the percentages of O-alkyl C and alkyl C, the ratio of alkyl C to O-alkyl C, and the sum of phenolic oxidation products: the ratios of standard deviation of the laboratory results to standard error of cross-validation (RSC) were greater than 2, the regression coefficients (a) of a linear regression (measured against predicted values) ranged from 0.9 to 1.1, and the correlation coefficients (r) were greater than 0.9. Satisfactorily (0.8 , a , 1.2, r , 0.8, and 1.4 , RSC , 2.0) assessed were the contents of C, N, and production of DOC, the percentages of carbonyl C and aromatic C and the ratio of alkyl C to aromatic C. However, the N-mineralization rate and the microbial biomass were predicted unsatisfactorily (RSC < 1.4). The good and satisfactory predictions reported above indicate a marked usefulness of NIRS in the assessment of biological and chemical characteristics of soils and litter. [source]

Density functional study on the structural conformations and intramolecular charge transfer from the vibrational spectra of the anticancer drug combretastatin-A2

JOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2009
L. Padmaja
Abstract Combretastatin-A2 (CA2), a potential anticancer drug in advanced preclinical development, is extracted from the medicinal plant Combretum caffrum. The NIR-FT Raman and FT-IR spectral studies of the molecule were carried out and ab initio calculations performed at the B3LYP/6-31G(d) level to derive the equilibrium geometry as well as the vibrational wavenumbers and intensities of the spectral bands. The vibrational analysis showed that the molecule has a similar geometry as that of cis-stilbene, and has undergone steric repulsion resulting in twisting of the phenyl ring with respect to the ethylenic plane. Vibrational analysis was used to investigate the lowering of the stretching modes, and enhancement of infrared band intensities of the C,H stretching modes of Me2 may be attributed to the electronic effects caused by back-donation and induction from the oxygen atom. Analysis of phenyl ring modes shows that the CA2 stretching mode 8 and the aromatic C,H in-plane bending mode are equally active as strong bands in both IR and Raman spectra, which can be interpreted as the evidence of intramolecular charge transfer (ICT) between the OH and OCH3groups via conjugated ring path and is responsible for bioactivity of the molecule. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On the origin of topological differences between experimental and theoretical crystal charge densities

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2000
Anatoliy Volkov
Topological analysis of experimental and theoretical (molecular and crystal) electron densities of p -nitroaniline and p -amino- p,-nitrobiphenyl reveals considerable discrepancies between experiment and theory for the bond critical points properties. Particularly large differences occur for the positive curvature along the bond path (,3). The differences become somewhat smaller when more extended basis sets and correlation effects are introduced in the theoretical calculations. The effect of the crystal matrix on the properties of bond critical points is evaluated for the p -nitroaniline molecule using the 6-21G** and 6-31G** basis sets. The differences between the isolated molecule and the molecule in the crystal are too small to explain the quantitative disagreement between the theoretical and experimental topologies reported in the literature and found in the current study. For most bonds, the observed changes in the properties of the electron density agree well for both basis sets but some discrepancies are found for changes in ,3 for N,H and aromatic C,C bonds. When the theoretical densities are projected into the multipole density functions through refinement of the theoretical structure factors, the topological properties change and differences between theory and experiment are reduced. The main origin of the observed discrepancies is attributed to the nature of the radial functions in the experimental multipole model. [source]

Proton transfer versus nontransfer in compounds of the diazo-dye precursor 4-(phenyldiazenyl)aniline (aniline yellow) with strong organic acids: the 5-sulfosalicylate and the dichroic benzenesulfonate salts, and the 1:2 adduct with 3,5-dinitrobenzoic acid

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009
Graham Smith
The structures of two 1:1 proton-transfer red,black dye compounds formed by reaction of aniline yellow [4-(phenyldiazenyl)aniline] with 5-sulfosalicylic acid and benzenesulfonic acid, and a 1:2 nontransfer adduct compound with 3,5-dinitrobenzoic acid have been determined at either 130 or 200,K. The compounds are 2-(4-aminophenyl)-1-phenylhydrazin-1-ium 3-carboxy-4-hydroxybenzenesulfonate methanol solvate, C12H12N3+·C7H5O6S,·CH3OH, (I), 2-(4-aminophenyl)-1-phenylhydrazin-1-ium 4-(phenyldiazenyl)anilinium bis(benzenesulfonate), 2C12H12N3+·2C6H5O3S,, (II), and 4-(phenyldiazenyl)aniline,3,5-dinitrobenzoic acid (1/2), C12H11N3·2C7H4N2O6, (III). In compound (I), the diazenyl rather than the aniline group of aniline yellow is protonated, and this group subsequently takes part in a primary hydrogen-bonding interaction with a sulfonate O-atom acceptor, producing overall a three-dimensional framework structure. A feature of the hydrogen bonding in (I) is a peripheral edge-on cation,anion association also involving aromatic C,H...O hydrogen bonds, giving a conjoint R12(6)R12(7)R21(4) motif. In the dichroic crystals of (II), one of the two aniline yellow species in the asymmetric unit is diazenyl-group protonated, while in the other the aniline group is protonated. Both of these groups form hydrogen bonds with sulfonate O-atom acceptors and these, together with other associations, give a one-dimensional chain structure. In compound (III), rather than proton transfer, there is preferential formation of a classic R22(8) cyclic head-to-head hydrogen-bonded carboxylic acid homodimer between the two 3,5-dinitrobenzoic acid molecules, which, in association with the aniline yellow molecule that is disordered across a crystallographic inversion centre, results in an overall two-dimensional ribbon structure. This work has shown the correlation between structure and observed colour in crystalline aniline yellow compounds, illustrated graphically in the dichroic benzenesulfonate compound. [source]

A structural systematic study of three isomers of difluoro- N -(4-pyridyl)benzamide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2008
Joyce McMahon
The isomers 2,3-, (I), 2,4-, (II), and 2,5-difluoro- N -(4-pyridyl)benzamide, (III), all with formula C12H8F2N2O, all exhibit intramolecular C,H...O=C and N,H...F contacts [both with S(6) motifs]. In (I), intermolecular N,H...O=C interactions form one-dimensional chains along [010] [N...O = 3.0181,(16),Å], with weaker C,H...N interactions linking the chains into sheets parallel to the [001] plane, further linked into pairs via C,H...F contacts about inversion centres; a three-dimensional herring-bone network forms via C,H...,(py) (py is pyridyl) interactions. In (II), weak aromatic C,H...N(py) interactions form one-dimensional zigzag chains along [001]; no other interactions with H...N/O/F < 2.50,Å are present, apart from long N/C,H...O=C and C,H...F contacts. In (III), N,H...N(py) interactions form one-dimensional zigzag chains [as C(6) chains] along [010] augmented by a myriad of weak C,H...,(arene) and O=C...O=C interactions and C,H...O/N/F contacts. Compound (III) is isomorphous with the parent N -(4-pyridyl)benzamide [Noveron, Lah, Del Sesto, Arif, Miller & Stang (2002). J. Am. Chem. Soc.124, 6613,6625] and the three 2/3/4-fluoro- N -(4-pyridyl)benzamides [Donnelly, Gallagher & Lough (2008). Acta Cryst. C64, o335,o340]. The study expands our series of fluoro(pyridyl)benzamides and augments our understanding of the competition between strong hydrogen-bond formation and weaker influences on crystal packing. [source]