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Aromatic System (aromatic + system)

Distribution by Scientific Domains
Chemistry85%
Distribution within Chemistry
General & Introductory Chemistry32%
Organic Chemistry24%

Selected Abstracts

Non-Covalent Interactions of Organic Halogen Compounds with Aromatic Systems , Analyses of Crystal Structure Data

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005
Dariusz Swierczynski
Abstract The Cambridge Structural Database showed in mid 2002 about 20.000 structures containing halogen atoms and aryl rests with distances d between the aryl center and the halogen atom, which would allow both hydrogen bonds with the aromatic hydrogens and/or van der Waalsinteractions with the ,-cloud. The latter are characterized by short distances d and by small angles , between the vector along the aryl centroid,halogen line and the perpendicular vector originating in the aryl center (the plane normal). The cases with d < 3.0 Å for F; and d < 3.5 Å for Cl, Br or I (outliers neglected), and , , 10 ± 5°, indicating predominating van der Waals forces, amount to several hundreds. The majority of fragments exhibit larger d and , values, in line with avoidance of electrostatic repulsion between the negative partial charges of the halogens and the ,-cloud center, and with an increasing electrostatic attraction with the aromatic hydrogen atoms. The corresponding hydrogen bonds are characterized by longer distances d and by angle values of , > 60° (about 40 % of the fragments), with only very few cases close to linear hydrogen bonds (then with , = 90°). Compounds containing metal,halogen bonds were omitted in view of possible strong orientational interferences. The structures were screened with four different halogen binding modes, all of them containing the halogen attached to a carbon atom, but with different hybrizations at the connecting carbon centers. The results show only small differences in the distance distributions, with a slight preference for smaller , values for sp2 frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

ChemInform Abstract: A Facile Debromination Reaction: Can Bromide Now Be Used as a Protective Group in Aromatic Systems?

CHEMINFORM, Issue 4 2002
Han Young Choi
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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]

ChemInform Abstract: Selective Oxidation at Carbon Adjacent to Aromatic Systems with IBX.

CHEMINFORM, Issue 27 2001
K. C. Nicolaou
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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]

Hoop-Shaped Condensed Aromatic Systems: Synthesis and Structure of Iron, and Ruthenium,Hepta(organo)[60]fullerene Complexes

CHEMISTRY - AN ASIAN JOURNAL, Issue 8 2007
Yutaka Matsuo Dr.
Abstract Potassium reduction of iron, and ruthenium,penta(organo)[60]fullerene complexes, [M(,5 -C60R5)(,5 -Cp)] (1,a: M=Fe, R=Ph; 1,b: M=Fe, R=Me; 1,c: M=Ru, R=Ph; 1,d: M=Ru, R=Me; Cp=C5H5) gave mono- and dianions of these complexes. Treatment of the dianion 1,a with ,-bromodiphenylmethane gave three different iron,hepta(organo)[60]fullerenes, [Fe{,5 -C60Ph5(CHPh2)2}(,5 -Cp)], as a mixture of regioisomers. All three compounds were fully characterized by physical methods, including X-ray crystallography and electrochemical measurements. One of the three compounds contains a new hoop-shaped condensed aromatic system. [source]

Xenoestrogenic gene exression: Structural features of active polycyclic aromatic hydrocarbons

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2002
T. Wayne Schultz
Abstract Estrogenicity was assessed using the Saccharomyces cerevisiae -based Lac-Z reporter assay and was reported as the logarithm of the inverse of the 50% molar ,-galactosidase activity (log[EC50,1]). In an effort to quantify the relationship between molecular structure of polycyclic aromatic hydrocarbons (PAHs) and estrogenic gene expression, a series of PAHs were evaluated. With noted exceptions, the results of these studies indicate that the initial two-dimensional structural warning for estrogenicity, the superpositioning of a hydroxylated aromatic system on the phenolic A-ring of 17-,-estradiol, can be extended to the PAHs. This two-dimensional-alignment criterion correctly identified estrogenicity of 22 of the 29 PAHs evaluated. Moreover, the estrogenic potency of these compounds was directly related to the size of the hydrophobic backbone. The seven compounds classified incorrectly by this structural feature were either dihydroxylated naphthalenes or aromatic nitrogen-heterocyclic compounds; all such compounds were false positives. Results with dihydroxylated naphthalenes reveal derivatives that were nonestrogenic when superimposed on the phenolic A-ring of 17-,-estradiol had the second hydroxyl group in the position of the C-ring or were catechol-like in structure. Structural alerts for nitrogen-heterocyclic compounds must take into account the position of the hydroxyl group and the in-ring nitrogen atom; compounds with the hydroxyl group and nitrogen atom involved with the same ring were observed to be nonactive. [source]

Structure, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes.

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2006

Abstract The geometry of the heteropentalenes formed by two phosphole units has been determined at the DFT level. The magnetic susceptibility and the nuclear magnetic shielding at the nuclei of these systems have also been calculated using gauge-including atomic orbitals and a large Gaussian basis set to achieve near Hartree,Fock estimates. A comparative study of the various isomers, of their flattened analogs, and of the parent phosphole molecule, shows that the [3,4-c] isomer is the most aromatic system in the set considered, assuming diatropicity and degree of planarity as indicators, even if it is the less stable in terms of total molecular energy. Plots of magnetic field-induced current densities confirm diatropicity of P-containing bis-heteropentalenenes, showing, however, significant differences from the analogous systems with distinct heteroatoms. The maps give evidence of spiral flow nearby CC bonds, compatible with prevalent distortive behavior of , electrons exalted by pyramidalization at P, and competing against the , electron compression, which would favor planar structure. © 2005 Wiley Periodicals, Inc. J Comput Chem 27: 344,351, 2006 [source]

Hydrogen-bonding versus,,, stacking interactions in dipyrido[f,h]quinoxaline-6,7-dicarbonitrile and 6,7-dicyanodipyrido[f,h]quinoxalin-1-ium chloride dihydrate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2008
Leonid Kozlov
The solvent-free title compound, C16H6N6, is an aromatic derivative of phenanthroline with an extended , system. It exhibits a remarkable ,,, columnar stacking in the crystal structure, with interplanar distances of 3.229,(3) and 3.380,(3),Å, the shorter spacing being between the two molecules within the asymmetric unit. Adjacent units along the stacked arrays are rotated in-plane with respect to one another by approximately 120°. The hydrochloride derivative, C16H7N6+·Cl,·2H2O, in which one of the phenanthroline N atoms has been protonated, crystallized as a dihydrate. The supramolecular organization in this compound is characterized by continuous hydrogen bonding between the component species, yielding two-dimensional hydrogen-bonded networks. This study demonstrates the high significance of the ,,, stacking interactions in the solvent-free aromatic system and how they can be undermined by introducing hydrogen-bonding capacity into the ligand. [source]

Synthesis and In-Vitro Cytotoxicity Evaluation of Novel Naphtindolizinedione Derivatives, Part II: Improved Activity for Aza-Analogues

ARCHIV DER PHARMAZIE, Issue 2 2009
Andrea Defant
Abstract Our previous investigation on potential antitumor agents now got enriched by the evaluation of in-vitro activity against a full panel of NCI cancer cell lines for five new compounds. The concurrent presence in the molecular structure of a nitrogen atom in the aromatic system and a N,N -dimethylaminoethyl amide chain play a decisive role to enhance cytotoxicity. The N,N -anti compound 14 shows a higher activity than its N,N -syn isomer, exhibiting the best selective inhibition against the melanoma MALME-3M cell line, with a GI50 -value (= 30 nM) corresponding to a 330-fold increase in activity compared to the corresponding deaza-analogue. Compound 14 is efficiently synthesized by aminolysis of the ester obtained as a single regio-isomer by an one-pot three-component procedure involving metal-assisted cyclization under microwave irradiation conditions. [source]

[1a(1a,,5,,9a,)]-1,1a,4,5,7,8,9,9a-Octahydro-3-hydroxy-1,1,2,5-tetramethyl-7-methylene-6H -cyclopropa[3,4]cyclo­hept[1,2- e]inden-6-one

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000
N. T. Do Valle
Interest in the title structure, C20H24O2, lies in the novel cis ring junction between the three- and seven-membered rings. This stereochemical arrangement causes the methylene moiety and the cycloheptane ring to be twisted out of the plane of the aromatic ring. The cyclopropane ring is also twisted out of the plane of the aromatic system. The molecules are linked by an O,H,O hydrogen bond [O,O 2.741,(3),Å]. [source]

CH-Directed Anion,, Interactions in the Crystals of Pentafluorobenzyl-Substituted Ammonium and Pyridinium Salts

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2010
Markus Albrecht Prof.
Abstract Simple pentafluorobenzyl-substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4, water co-crystallisation seems to suppress effective anion,, interactions of bromide with the electron-deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen-bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (,1 interaction). In 6 the CH,anion hydrogen bonding is more symmetric and fixes the anion on top of the ring (,6). A similar structure-controlling effect is observed in case of the 1,4-diazabicyclo[2.2.2]octane derivatives 7. Here the position of the anion (Cl, Br, I) is shifted according to the length of the weak CH,halide interaction. The hexafluorophosphate 7,d reveals that this "non-coordinating" anion can be located on top of an aromatic , system. In the methyl-substituted pyridinium salts 9 and 10 different locations of the bromide anions with respect to the , system are observed. This is due to different conformations of the mono- versus disubstituted pyridine, which leads to different directions of the weak, but structurally important, HMeBr bonds. [source]

Hoop-Shaped Condensed Aromatic Systems: Synthesis and Structure of Iron, and Ruthenium,Hepta(organo)[60]fullerene Complexes

CHEMISTRY - AN ASIAN JOURNAL, Issue 8 2007
Yutaka Matsuo Dr.
Abstract Potassium reduction of iron, and ruthenium,penta(organo)[60]fullerene complexes, [M(,5 -C60R5)(,5 -Cp)] (1,a: M=Fe, R=Ph; 1,b: M=Fe, R=Me; 1,c: M=Ru, R=Ph; 1,d: M=Ru, R=Me; Cp=C5H5) gave mono- and dianions of these complexes. Treatment of the dianion 1,a with ,-bromodiphenylmethane gave three different iron,hepta(organo)[60]fullerenes, [Fe{,5 -C60Ph5(CHPh2)2}(,5 -Cp)], as a mixture of regioisomers. All three compounds were fully characterized by physical methods, including X-ray crystallography and electrochemical measurements. One of the three compounds contains a new hoop-shaped condensed aromatic system. [source]

Conformational and tautomeric eccentricities of 2-acetyl-1,8-dihydroxynaphthalenes

MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2007
Poul Erik Hansen
Abstract Tautomerism in aromatic systems with oxygen substitutents is rare. This is investigated in 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (1) and in 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene (2). The tautomeric nature of 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene is supported by long-range hydrogen,hydrogen coupling between the OH-1 and the OH-8 and by the isotope effects on 13C caused by deuteration at the CH3CO methyl group. Compound 2 participates in a degenerate equilibrium between two equivalent nonsymmetrical rotamers (2A and 2B), each having two intramolecular O···HO hydrogen bonds: one involving an acetyl oxygen and the neighboring hydroxyl group, and the other between the oxygen centers at positions 1 and 8. In addition, each rotamer is involved in a tautomeric equilibrium, with a structure having an OH-substituted exocyclic double bond (2AT or 2BT). DFT calculations for a large set of compounds highlight the factors controlling the unusual rotational and tautomeric behaviors. A very important factor seems to be the repulsive interaction between the O -1 and O -8 centers, which is modulated by formation of an OH-1···O-8 or OH-8···O1 hydrogen bond. Steric interactions, mesomeric release of electrons from the oxygen at position 8, and a strong OH···O···C hydrogen bond are other factors. Solid-state 13C NMR spectra of 2,7-diacetyl-1,8-dihydroxy-3,6-dimethylnaphthalene at different temperatures demonstrated no averaging in the solid, whereas partially deuterated 2-acetyl-1,8-dihydroxy-3,6-dimethylnaphthalene showed an isotope effect at C-1 of 1.5 ppm, indicating tautomerism in the solid state. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Synthesis and magnetic properties of poly(p-phthaloyl-disacetylaceton-ethylenediimine) metal complexes,

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2002
Yun-Pu Wang
Abstract Macrocyclic Schiff-base ligand, bisacetylaceton-ethylenediimine (BAE) and its transition metal complexes M(BAE) (M,=,Cu2+, Ni2+) were synthesized. The complexes having characteristics of aromatic systems and well-defined one-dimensional structures, reacted with p-phthaloyl chloride, to obtain polymer complexes. The complexes were characterized by elemental analysis, inductively coupled plasma (ICP), FT-IR, and thermal analysis and show good thermal stability. ESR spectra analysis discovered that there are free radicals in the chain of polymers, indicating that a weak magnetic spin-exchange interaction operates between the metal ions and free radicals. It is found that, as the bridging p -phthaloyl group is able to propagate the magnetic exchange interaction, the polymer complexes show paramagnetic properties by measurement of temperature dependence of the magnetic property, and obey Curie,Weiss law. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Tuning the Polarization Along Linear Polyaromatic Strands for Rationally Inducing Mesomorphism in Lanthanide Nitrate Complexes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2007
Emmanuel Terazzi Dr.
Abstract The opposite orientation of the ester spacers in the rodlike ligands L,4C12 (benzimidazole-OOC-phenyl) and L,5C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional tricoordination to trivalent lanthanides, LnIII, and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L,4C12)(NO3)3] (Ln=La,Lu) vanishes in [Ln(L,5C12)(NO3)3], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L,4C12, L,5C12, [Ln(L,4C12)(NO3)3], but not for [Ln(L,5C12)(NO3)3]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L,5C12)(NO3)3] to [Ln(L,6C12)(NO3)3] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model. [source]