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Halogen Atom (halogen + atom)
Selected AbstractsSuccessive Substitution of Halogen Atoms in 4,6-Dihaloquinolines in Palladium-Catalyzed Reactions with Amines and Arylboronic Acids.CHEMINFORM, Issue 2 2006I. P. Beletskaya Abstract For Abstract see ChemInform Abstract in Full Text. [source] Non-Covalent Interactions of Organic Halogen Compounds with Aromatic Systems , Analyses of Crystal Structure DataEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Dariusz 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] Palladium-Catalyzed Amination of 3,5-Dihalopyridines , a Convenient Route to New PolyazamacrocyclesHELVETICA CHIMICA ACTA, Issue 7 2005Alexei Pd-Catalyzed amination of 3,5-dibromo- and 3,5-dichloropyridine (1a and 1b, resp.) with linear polyamines 2 leads to the formation of a new family of pyridine-containing macrocycles 3 with an ,exo'-oriented pyridine N-atom (Schemes,1 and 2). The dependence of the macrocycle yield on the nature of the halogen atom, the length of the polyamine chain and C/N atom ratio, and the composition of the catalytic system is studied. The synthesis of mono- and bis(5-halopyridin-3-yl)-substituted polyamines 4, 5, 8, 9, and of 3,5-bis(polyamino)-substituted pyridines 6 is described (Schemes,3 and 4), and the use of these compounds as intermediates on the way to the macrocycles 7, 16, and 18 with larger cavity (,cyclodimers' and ,cyclotrimers') is demonstrated (Schemes,5,10). [source] Ring-opening reactions of 5-(aryl)thianthrenium bromides with aryl thiolatesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2002Ding-Quan Qian Abstract A series of 5-(aryl)thianthrenium bromides (6a,e) with aryl (Ar) groups phenyl (a), p -tolyl (b), p -anisyl (c), p -chlorophenyl (d) and p -bromophenyl (e) was prepared by reaction of thianthrene 5-oxide with the appropriate Grignard reagent ArMgBr. Reactions of 6a,e with aryl thiolates (Ar,SNa, Ar,,=,phenyl, p -tolyl and p -chlorophenyl, 7a,c) were carried out in MeCN at room temperature. Products from 6a,c were a small amount of arene [benzene (8a) and toluene (8b)], and substantial amounts of ArSAr, (9), thianthrene (Th) and a trisulfide, namely a 2-(ArS)-2,-(Ar,S)-diphenyl sulfide (10). Products from reactions of 6d,e were smaller amounts of 9 and 10 but substantial amounts of 1,4-di(Ar,S)benzene (11) and a tetrasulfide (12a,c). The reactions that lead to products 9,12 are attributed to ligand coupling (LC) pathways in sulfuranes formed by attack of Ar,S, at the sulfonium S atom of 6. In the formation of 11 and 12 the halogen atom (Cl, Br) is first displaced from 6d,e by Ar,S,, giving a new thianthrenium ion (14) from which sulfurane formation (15) follows. Products 10 and 12 result from opening of the thianthrenium ring of sulfuranes 13 and 15 through LC. Products were assayed with a combination of GC and isolation with TLC, and were identified with a combination of GC (authentic compounds), x-ray crystallography (10a), elemental analyses and high-resolution mass spectrometry. The reactions of 6 are compared with earlier reactions of 5-(alkoxy)-and 5-(alkyl)thianthrenium salts (1 and 2). Copyright © 2002 John Wiley & Sons, Ltd. [source] Engineering functional materials by halogen bondingJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2007Pierangelo Metrangolo Abstract Engineering functional materials endowed with unprecedented properties require the exploitation of new intermolecular interactions, which can determine the characteristics of the bulk materials. The great potential of Halogen Bonding (XB), namely any noncovalent interaction involving halogens as electron acceptors, in the design of new and high-value functional materials is now emerging clearly. This Highlight will give a detailed overview on the energetic and geometric features of XB, showing how some of them are quite constant in most of the formed supramolecular complexes (e.g., the angle formed by the covalent and the noncovalent bonds around the halogen atom), while some others depend strictly on the nature of the interacting partners. Then, several specific examples of halogen-bonded supramolecular architectures, whose structural aspects as well as applications in fields as diverse as enantiomers' separation, crystal engineering, liquid crystals, natural, and synthetic receptors, will be fully described. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: PolymChem 45: 1,15, 2007 [source] Predictive 3D-Quantitative Structure-Activity Relationship for A1 and A2A Adenosine Receptor LigandsMOLECULAR INFORMATICS, Issue 11-12 2009Olga Yuzlenko Abstract The use of QSAR applications to develop adenosine receptor (AR) antagonists is not so common. A library of all xanthine derivatives, obtained at the Department of Technology and Biotechnology of Drugs, was created. Sixty-three active adenosine A1 receptor ligands and one hundred thirty nine active adenosine A2A receptor ligands were used for 3D-QSAR investigation. The 3D-QSAR equations with a high predictive power in estimating the binding affinity values of potential A1 and A2A ARs ligands were derived. For the first time, hybrid shape-property descriptors were used in 3D-QSAR for xanthine ARs ligands. The obtained models were characterized by a high regression and cross-validation coefficients. Two types of the model validation were tested , dividing the library into the training set for model development and external set for model validation and increasing the number of library components and checking the model by cross-validated regression coefficient. The analysis of the results depicts that for the A1 AR binding activity it is important for ligands to possess R1 -propyl substituents along with the phenyl or benzyl substituents bearing halogen atom and phenethyl moiety. For A2A AR affinity it could be favorable to introduce phenethyl or phenyl substituent connected with the tricyclic ring by the alkoxy chain. The nature of R1 group may not significantly affect the A2A AR affinity. High predictive power of the equations suggests their use for further development of adenosine receptor antagonists within xanthine derivatives. [source] Bacterial hydrolytic dehalogenases and related enzymes: Occurrences, reaction mechanisms, and applicationsTHE CHEMICAL RECORD, Issue 2 2008Tatsuo Kurihara Abstract Dehalogenases catalyze the cleavage of the carbon,halogen bond of organohalogen compounds. They have been attracting a great deal of attention partly because of their potential applications in the chemical industry and bioremediation. In this personal account, we describe occurrences, reaction mechanisms, and applications of bacterial hydrolytic dehalogenases and related enzymes, particularly L -2-haloacid dehalogenase, DL -2-haloacid dehalogenase, fluoroacetate dehalogenase, and 2-haloacrylate reductase. L -2-Haloacid dehalogenase is a representative enzyme of the haloacid dehalogenase (HAD) superfamily, which includes the P-type ATPases and other hydrolases. Structural and mechanistic analyses of this enzyme have yielded important insights into the mode of action of the HAD superfamily proteins. Fluoroacetate dehalogenase is unique in that it catalyzes the cleavage of the highly stable CF bond of a fluorinated aliphatic compound. In the reactions of L -2-haloacid dehalogenase and fluoroacetate dehalogenase, the carboxylate group of Asp performs a nucleophilic attack on the ,-carbon atom of the substrate, displacing the halogen atom. This mechanism is common to haloalkane dehalogenase and 4-chlorobenzoyl-CoA dehalogenase. DL -2-Haloacid dehalogenase is unique in that a water molecule directly attacks the substrate, displacing the halogen atom. The occurrence of 2-haloacrylate reductase was recently reported, revealing a new pathway for the degradation of unsaturated aliphatic organohalogen compounds. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 67,74; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20141 [source] Destabilizing effect of a fluorouracil extra base in a hybrid RNA duplex compared with bromo and chloro analoguesACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2001William Cruse In the presence of cobalt, rhodium or iridium hexammine salts, the RNA/DNA hybrid r-GCUUCGGC-dXU (with X = F, Cl or Br) crystallizes as a double-stranded helix with four consecutive G,U and C,U mismatches. The deoxy chloro- and bromouracil derivatives are isomorphous, space group C2, unit-cell parameters a = 53.80, b = 19.40, c = 50.31,Å, , = 109.9°, with the same infinite helix arrangement in the packing along the c axis with one extra DNA halogenouracil base included in the stacking. However, the fluorouracil derivative, with unit-cell parameters a = 53.75, b = 19.40, c = 45.84,Å, , = 105.7°, is not isomorphous. The corresponding extra DNA base dFU of the second strand is ejected out of the helical stack, leading to a shortening of the c axis. The specific destabilization of the fluorouracil for the duplex building is analyzed in terms of the polarization effect of the halogen atom attached to the 3,-terminal base that modulates its interactions. [source] Mercury binding on activated carbonENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2006Bihter Padak Abstract Density functional theory has been employed for the modeling of activated carbon (AC) using a fused-benzene ring cluster approach. Oxygen functional groups have been investigated for their promotion of effective elemental mercury binding on AC surface sites. Lactone and carbonyl functional groups yield the highest mercury binding energies. Further, the addition of halogen atoms has been considered to the modeled surface, and has been found to increase the AC's mercury adsorption capacity. The mercury binding energies increase with the addition of the following halogen atoms, F > Cl > Br > I, with the fluorine addition being the most promising halogen for increasing mercury adsorption. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] An Efficient Synthesis of Substituted meta -Halophenols and Their Methyl Ethers: Insight into the Reaction MechanismEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2010Faiz Ahmed Khan Abstract An expeditious synthetic methodology leading to substituted meta -halophenols and their corresponding methyl ether derivatives through acid-mediated fragmentation of suitably substituted dihalonorbornyl ketones has been devised. The reaction sequence consists of TBTH-mediated (TBTH is tri- n -butyltin hydride) selective bridgehead halogen reduction of easily accessible Diels,Alder adducts derived from 1,2,3,4-tetrahalo-5,5-dimethoxycyclopentadiene and ,-substituted vinyl acetates, with subsequent conversion into the requisite bicyclic ketones by a two-step hydrolysis/oxidation approach. An extensive mechanistic investigation based on isotope labeling and cross experiments has been carried out and plausible mechanistic pathways based on these results have been proposed. The absence of halogen atoms at the bridgehead positions steers the reaction through a novel pathway involving the incorporation of proton (or deuterium) followed by elimination of HX (or DX), so the described methodology also provides a reliable route to ortho-para dideuteratedphenolic derivatives. [source] Non-Covalent Interactions of Organic Halogen Compounds with Aromatic Systems , Analyses of Crystal Structure DataEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Dariusz 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] Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2003Pedro Braña Abstract The potential energy surface for the Cl + propene reaction was analyzed at the MP2 level using Pople's 6-31G(d,p) and 6-311+G(d,p), and Dunning's cc-pVDZ and aug-cc-pVDZ basis sets. Two different channels for the addition reaction leading to chloroalkyl radicals and five alternative channels for the abstraction reaction leading to C3H + HCl were explored. The corresponding energy profiles were computed at the QCISD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory. Theoretical results suggest that the previously established mechanism consisting of (1) direct abstraction and (2) addition,elimination steps is instead made up of (1) addition through an intermediate and (2) two-step abstraction processes. No direct abstraction mechanism exists on the potential energy surface. The kinetic equations derived for the new mechanism are consistent with the pressure dependence experimentally observed for this reaction. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 2044,2062, 2003 [source] Broadband Near-IR Emission in Tm/Er-Codoped GeS2,In2S3 -Based Chalcohalide GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Yinsheng Xu The near IR emission spectra of Tm/Er-codoped GeS2,In2S3 -based chalcohalide glasses are studied with an 808 nm laser as excitation source. A broad emission with a full-width at half-maximum of ,170 nm is recorded in a 0.5Tm2S3,0.1Er2S3 -codoped 70GeS2,20In2S3,10CsBr (in mol%) glass. The luminescence mechanisms are discussed with different CsI concentration, different halogen atoms, and different In content. These results suggest that both halogen (X) atoms and [InSxX4,x] structural units can enhance the emission intensity located at 1460 nm. [source] Copper(II) chloride and bromide complexes with 2-methyl-2H -tetrazol-5-amine: an X-ray powder diffraction studyACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Ludmila S. Ivashkevich The complex catena -poly[[dibromidocopper(II)]-bis(,-2-methyl-2H -tetrazol-5-amine)-,2N4:N5;,2N5:N4], [CuBr2(C2H5N5)2]n, (I), and the isotypic chloride complex catena -poly[[dichloridocopper(II)]-bis(,-2-methyl-2H -tetrazol-5-amine)-,2N4:N5;,2N5:N4], [CuCl2(C2H5N5)2]n, (II), were investigated by X-ray powder diffraction at room temperature. The crystal structure of (I) was solved by direct methods, while the Rietveld refinement of (II) started from the atomic coordinates of (I). In both structures, the Cu atoms lie on inversion centres, adopting a distorted octahedral coordination of two halogen atoms, two tetrazole N atoms and two 5-amine group N atoms. Rather long Cu,Namine bonds allow consideration of the amine group as semi-coordinated. The compounds are one-dimensional coordination polymers, formed as a result of 2-methyl-2H -tetrazol-5-amine ligands bridging via a tetrazole N atom and the amine N atom. In the polymeric chains, adjacent Cu atoms are connected by two such bridges. [source] Dihalodimethyltin(IV) complexes of 2-(pyrazol-1-ylmethyl)pyridineAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2003Pedro Álvarez-Boo Abstract Reaction of dichloro- and dibromodimethyltin(IV) with 2-(pyrazol-1-ylmethyl)pyridine (PMP) afforded [SnMe2Cl2(PMP)] and [SnMe2Br2(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (1H, 13C) spectroscopies. Structural studies by X-ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (SnC = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (SnCl = 2.4908(16), 2.5447(17) Å; SnBr = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (SnN = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the SnN(pyridine) bond length is markedly longer than the SnN(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||