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Halogen
Terms modified by Halogen Selected AbstractsTrace Water-Promoted Oxidation of Benzylic Alcohols with Molecular Oxygen Catalyzed by Vanadyl Sulfate and Sodium Nitrite under Mild ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Zhongtian Du Abstract An inexpensive catalytic system consisting of vanadyl sulfate and sodium nitrite was developed for the oxidation of benzylic alcohols with molecular oxygen under mild conditions. Benzyl alcohols with various substitutions were efficiently converted to their corresponding aldehydes with high conversion and selectivity under 80,°C (e.g., 4-nitrobenzyl alcohol was smoothly oxidized to 4-nitrobenzyl aldehyde with 94% yield under 0.5,MPa of molecular oxygen). Halogen, noble metals, extra base or complicated ligands were avoided. Addition of a trace of water to this system before the reaction was crucial for the high efficiency. [source] Halogen, hydrogen and electrostatic interactions in 2-amino-5-chloro-1,3-benzoxazol-3-ium nitrate and 2-amino-5-chloro-1,3-benzoxazol-3-ium perchlorateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Rafal Kruszynski In the title compounds, C7H6ClN2O+·NO3, and C7H6ClN2O+·ClO4,, the ions are connected by N,H...O hydrogen bonds and halogen interactions. Additionally, in the first compound, co-operative ,,, stacking and halogen..., interactions are observed. The energies of the observed interactions range from a value typical for very weak interactions (1.80,kJ,mol,1) to one typical for mildly strong interactions (53.01,kJ,mol,1). The iminium cations exist in an equilibrium form intermediate between exo- and endocyclic. This study provides structural insights relevant to the biochemical activity of 2-amino-5-chloro-1,3-benzoxazole compounds. [source] ChemInform Abstract: Weak Interactions Between Trivalent Pnictogen Centers: Computational Analysis of Bonding in Dimers X3E···EX3 (E: Pnictogen, X: Halogen).CHEMINFORM, Issue 37 2009Jani Moilanen 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] Substitution of Acetylenic Groups for Halogen in the Quinonoid Ring.CHEMINFORM, Issue 31 2006V. S. Romanov 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] Chamigrenelactone, a Polyoxygenated Sesquiterpene with a Novel Structural Type and Devoid of Halogen from Laurencia obtusa.CHEMINFORM, Issue 1 2005Enrique Dorta No abstract is available for this article. [source] Synthesis of Some Halogen- and Nitro-Substituted Nicotinic Acids and Their Fragmentation under Electron Impact.CHEMINFORM, Issue 51 2004L. V. Dyadyuchenko Abstract For Abstract see ChemInform Abstract in Full Text. [source] Halogen- and N-Haloimide-Promoted Homo- and Heterocoupling of ,-(N-Carbamoyl)alkylcuprates and ,-(Alkoxy)alkylcuprates.CHEMINFORM, Issue 33 2004R. Karl Dieter Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Selective Halogen,Magnesium Exchange Reaction via Organomagnesium Ate Complex.CHEMINFORM, Issue 41 2001Atsushi Inoue 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: Metalation and Halogen,Metal Exchange in the Imidazo[1,2-a]quinoxaline Series.CHEMINFORM, Issue 26 2001Stephanie Parra 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] Simultaneous Determination of Fluorine, Chlorine, Bromine and Iodine in Six Geochemical Reference Materials Using Pyrohydrolysis, Ion Chromatography and Inductively Coupled Plasma-Mass SpectrometryGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 4 2009Hélène Balcone-Boissard halogènes; pyrohydrolyse; chromatographie ionique; spectrométrie de masse couplée à une source de plasma induit; matériaux géologiques de référence Concentrations of halogens (fluorine, chlorine, bromine and iodine) were determined in six geochemical reference materials (BHVO-2, GS-N, JG-1, JR-1, JB-1b, JB-2). Halogens were first extracted from powdered samples using a pyrohydrolysis technique, then hydrolysis solutions were analysed by ion chromatography for F and Cl and inductively coupled plasma-mass spectrometry for Br and I. The detection limits in solutions were 100 ,g l,1 for both F and Cl and 10 ng l,1 for Br and I. Considering the extraction procedure, performed on a maximum of 500 mg of sample and producing 100 ml of pyrohydrolysis solution, detection limits in rock samples were 20 mg kg,1 for F and Cl and 2 ,g kg,1 for Br and I. The mean analytical errors on the studied composition ranges were estimated at 10 mg kg,1 for F and Cl, 100 ,g kg,1 for Br and 25 ,g kg,1 for I. The concentration values, based on repeated (generally > 10) sample analysis, were in good agreement generally with published values and narrowed the mean dispersion around mean values. Large dispersions are discussed in terms of samples heterogeneity and contaminations during sample preparation. Basaltic RMs were found to be more suitable for studies of halogen compositions than differentiated rock material, especially granites , the powders of which were heterogeneous in halogens at the 500 mg level. Les concentrations en halogènes (fluor, chlore, brome et iode) on été déterminées dans 6 matériaux géologiques de référence (BHVO-2, GS-N, JG-1, JR-1, JB-1b, JB-2), distribués par le GSJ, l'USGS et le CRPG. Les halogènes étaient d'abord extraits des échantillons, disponibles sous forme de poudre, par pyrohydrolyse. F et Cl sont ensuite analysés par chromatographie ionique, Br et I par spectrométrie de masse couplée à une source de plasma induit. Les limites de détection sont de 100 ,g l,1 pour F et Cl, et de 10 ng l,1 pour Br et I, respectivement. L'extraction des halogènes était réalisée sur 500 mg de poudre de roche, produisant 100 ml de solution d'extraction. Ainsi, pour les échantillons de roche, les limites de détection étaient de 20 mg kg,1 pour F et Cl, et 2 ,g kg,1 pour Br et I. L'erreur analytique moyenne sur la gamme de concentration étudiée est estimée à 10 mg kg,1 pour F et Cl, 100 ,g kg,1 pour Br et 25 ,g kg,1 pour I. Les valeurs de concentrations données, obtenues par l'analyse répétée (> 10) du même échantillon étaient en accord avec les valeurs reportées dans la littérature. Elles présentent en général une plus faible dispersion autour de la valeur moyenne. Dans le cas d'une importante dispersion des résultats, celle-ci est discutée en terme d'hétérogénéité de l'échantillon analysé et de contamination durant la préparation du matériel de référence. Les échantillons de référence de composition basaltique se révèlent être plus appropriés pour étudier les compositions en halogènes que les matériaux correspondant à des roches différenciées, en particulier des granites dont la distribution en halogènes apparaît hétérogène dans les poudres à l'échelle d'un aliquot de 500 mg. [source] Mechanistic Insights into Direct Amide Bond Formation Catalyzed by Boronic Acids: Halogens as Lewis Bases,ANGEWANDTE CHEMIE, Issue 38 2010Dr. Tommaso Marcelli Wasser raus! DFT-Rechnungen sagen voraus, dass eine Wassereliminierung aus einem tetraedrischen Intermediat der geschwindigkeitsbestimmende Schritt der Titelreaktion ist. Diese Umwandlung ist den Rechnungen zufolge hoch stereoselektiv und liefert cis -Amide als die kinetischen Produkte (siehe Schema). Die überlegene Aktivität von ortho -Halogenphenylboronsäuren resultiert aus dem Lewis-basischen Charakter von Halogenatomen. [source] Oxidative Addition of Halogens on Open Metal Sites in a Microporous Spin-Crossover Coordination Polymer,ANGEWANDTE CHEMIE, Issue 47 2009Gloria Agustí Dr. Innige Verbindung: Die Einwirkung von X2 (Cl2, Br2, I2) auf das poröse Spin-Crossover-Material {Fe(pz)[PtII(CN)4]} (pz=Pyrazin) führt durch oxidative Addition zum Halogenid-Einbau in die koordinativ ungesättigten [PtII(CN)4]2, -Einheiten. Eine Serie gemischtvalenter {Fe(pz)[PtII/IV(CN)4(X)]}-Gerüste mit charakteristischem kooperativem Spinübergang wurde erhalten. [source] ChemInform Abstract: Novel Formation of 2-Arylquinolines and 1,3-Benzoxazines from 2-(1-Alkenyl)acylanilides and Active Halogens.CHEMINFORM, Issue 4 2008Kentaro Okuma 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] 4-Aminophenyldiphenylphosphinite (APDPP), a New Heterogeneous and Acid Scavenger Phosphinite , Conversion of Alcohols, Trimethylsilyl, and Tetrahydropyranyl Ethers to Alkyl Halides with Halogens or N-Halosuccinimides.CHEMINFORM, Issue 9 2007Nasser Iranpoor 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] Reactions of Substituted 2,3,7-Triazabicyclo[3.3.0]oct-2-enes and 1,2,7-Triazaspiro[4.4]non-1-enes with Halogens.CHEMINFORM, Issue 36 2005A. P. Molchanov Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Nonenzymatic Kinetic Resolution of Secondary Alcohols: Enantioselective SN2 Displacement of Hydroxy Groups by Halogens in the Presence of Chiral BINAP.CHEMINFORM, Issue 30 2001Govindasamy Sekar 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] 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] The relationship between disinfection by-product formation and structural characteristics of humic substances in chloraminationENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2003Wells W. Wu Abstract The influence of structural characteristics of humic substances on disinfection by-product (DBP) formation was investigated for seven humic substances isolated from aquatic and terrestrial sources. The structural characterizations included 13C nuclear magnetic resonance (13C NMR) spectroscopy and ultraviolet (UV) spectroscopy. The aqueous humic substances were chloraminated at pH 7.0 and 8.5, with and without the presence of the bromide ion, and analyzed for total organic halogen (TOX), trihalomethanes (THMs), and haloacetic acids (HAAs). Aromatic contents determined by 13C NMR and differential UV absorbance at 254 nm statistically correlated with TOX formation for the humic substances investigated at p < 0.08. In contrast, a lack of correlation was observed for THM and HAA formation and these parameters. This paper also compiles relevant literature and discusses the contrasting reaction response of DBP precursor material to chlorination and chloramination. [source] Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardnessEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 6 2002Norbert Hofmann This study compares commercially available light-emitting diode (LED) lights with a quartz tungsten halogen (QTH) unit for photo-activating resin-based composites (RBC). Shrinkage strain kinetics and temperature within the RBC were measured simultaneously using the ,deflecting disc technique' and a thermocouple. Surface hardness (Knoop) at the bottom of 1.5-mm thick RBC specimens was measured 24 h after irradiation to indicate degree of cure. Irradiation was performed for 40 s using either the continuous or the ramp-curing mode of a QTH and a LED light (800 mW cm,2 and 320 mW cm,2, respectively) or the continuous mode of a lower intensity LED light (160,mW cm,2). For Herculite XRV and Filtek Z250 (both containing only camphoroquinone as a photo-initiator) the QTH and the stronger LED light produced similar hardness, while in the case of Definite (containing an additional photo-activator absorbing at lower wavelength) lower hardness was observed after LED irradiation. The temperature rise during polymerization and heating from radiation were lower with LED compared to QTH curing. The fastest increase of polymerization contraction was observed after QTH continuous irradiation, followed by the stronger and the weaker LED light in the continuous mode. Ramp curing decreased contraction speed even more. Shrinkage strain after 60 min was greater following QTH irradiation compared with both LED units (Herculite, Definite) or with the weaker LED light (Z250). [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] Brominated 4-(Trifluoromethyl)pyrimidines: A Convenient Access to Versatile IntermediatesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2004Levente Ondi An expedient route to all three monobrominated and all three dibrominated isomers of 4-(trifluoromethyl)pyrimidine, and to several other halogenated pyrimidines, is described. Key steps are the electrophilic introduction of the halogen in the 5-position of 2- or 4-pyrimidinones, the bromodeoxygenation of pyrimidinones or thiopyrimidinones using phosphorus tribromide, and the partial debromination of dibromo-4-(trifluoromethyl)pyrimidines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] The First Enantioselective Halo Aldol Reaction of Ethyl Propiolate and AldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004Dianjun Chen Abstract The first enantioselective halo aldol reaction of ethyl propiolate with aldehydes has been established by using Jacobsen's chiral cyclohexylsalen ligand. The reaction was conducted at ,20 °C in dichloromethane with Et2AlI as the source of halogen and Lewis acid promoter. Excellent geometric selectivity (only the Z isomer) has been achieved for all 14 examples examined. The reaction works well with aromatic aldehydes; it also works with aliphatic aldehydes and ,,,-unsaturated aldehydes, albeit with diminished yields and ee. This method provides the first enantioselective synthesis of ,-iodo Morita,Baylis,Hillman (MBH) esters. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Novel Amino Acids and Dehydroamino Acids Containing the Benzo[b]thiophene MoietyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2003Ana S. Abreu Abstract Several novel amino acids and dehydroamino acids containing the benzo[b]thiophene moiety were prepared by Michael addition or sequential Michael addition and palladium-catalyzed C,C or C,N cross couplings. The substrates for Michael addition were the methyl esters of N,N -bis(tert -butyloxycarbonyl)dehydroalanine [Boc2,,Ala,OMe] and N -(4-toluenesulfonyl)- N -(tert -butyloxycarbonyl)dehydroalanine [Tos,,Ala(N -Boc),OMe], and the nucleophiles were aromatic thiols and 3-iodobenzylamine. The addition of mercaptobenzo[b]thiophenes directly to Tos,,Ala(N -Boc),OMe gave stereoselectively, in good yields, the E -isomer of the corresponding dehydrocysteine. When thiophenols and 3-iodobenzylamine were used as nucleophiles the presence of an additional function (halogen or amine) allowed a subsequent palladium-catalyzed cross-coupling reaction with functionalized benzo[b]thiophenes (boronic acids, a halogen or an amine). Using this strategy, several racemic amino acid and dehydroamino acid derivatives, which are linked to the benzo[b]thiophene moiety by an aromatic spacer, were obtained in good yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Highly Chemo- and Regioselective Reduction of Aromatic Nitro Compounds Catalyzed by Recyclable Copper(II) as well as Cobalt(II) PhthalocyaninesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Upendra Sharma Abstract Copper/cobalt phthalocyanines were established for the first time as catalysts for the very efficient chemo- and regioselective reduction of aromatic nitro compounds to generate the corresponding amines. The selective reduction of nitro compounds was observed in the presence of a large range of functional groups such as aldehyde, keto, acid, amide, ester, halogen, lactone, nitrile and heterocyclic functional groups. Furthermore, the present method was found to be highly regioselective towards the reduction of aromatic dinitro compounds in a short time with high yields. In most of the cases the conversion and selectivity were >99% as monitored by GC-MS. The reduction mechanism was elucidated by UV-vis and electrospray ionization quadrupole time-of-flight tandem mass spectrometry. [source] Relative energies of conformations and sulfinyl oxygen-induced pentacoordination at silicon in 4-bromo- and 4,4-dibromo-4-silathiacyclohexane 1-oxide: A computational studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005Fillmore Freeman Abstract The equilibrium geometries and relative energies of the chair, twist, and boat conformations of cis - and trans -4-bromo-4-silathiacyclohexane 1-oxide and 4,4-dibromo-4-silathiacyclohexane 1-oxide have been calculated at the B3LYP/6-311G(d,p) and MP2/6-311+G(d,p) theoretical levels. The axial (SO) chair conformers of the sulfoxides are of lower energy than the chair conformers of the corresponding equatorial (SO) sulfoxides. The chair conformer of the axial (SO) trans -4-bromo-4-silathiacyclohexane 1-oxide is only 0.10 kcal/mol more stable than the corresponding 1,4-boat conformer which is stabilized by a transannular coordination of the sulfinyl oxygen with silicon that results in trigonal bipyramidal geometry at silicon. The 1,4-boat structure of equatorial (SO) trans -4-bromo-4-silathiacyclohexane 1-oxide is a transition state and is 5.77 kcal/mol higher in energy than the respective chair conformer. The 1,4-boat conformer of axial (SO) 4,4-dibromo-4-silathiacyclohexane 1-oxide is also stabilized by transannular coordination of the sulfinyl oxygen and silicon, but it is 4.31 kcal/mol higher in energy than the corresponding chair conformer. The relatively lower stability of the 1,4-boat conformer of 4,4-dibromo-4-silathiacyclohexane 1-oxide may be due to repulsive interactions of the axial halogen and sulfinyl oxygen atom. The relative energies of the conformers and transition states are discussed in terms of hyperconjugative interactions, orbital interactions, nonbonded interactions, and transannular sulfinyl oxygen-silicon coordination. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Accuracy of LED and Halogen Radiometers Using Different Light SourcesJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 4 2006Howard W. Roberts dmd ABSTRACT Purpose:, To determine the accuracy of commercially available, handheld light-emitting diode (LED) and halogen-based radiometers using LED and quartz-tungsten-halogen (QTH) curing lights with light guides of various diameters. Methods:, The irradiance of an LED curing light (L.E.Demetron 1, SDS/Kerr, Orange, CA, USA) and a QTH curing light (Optilux 501, SDS/Kerr) were measured using multiple units of an LED (Demetron L.E.D. Radiometer, SDS/Kerr) and a halogen radiometer (Demetron 100, SDS/Kerr) and compared with each other and to a laboratory-grade power meter (control). Measurements were made using five light guides with distal light guide diameters of 4, 7, 8, 10, and 12.5 mm. For each light guide, five readings were made with each of three radiometers of each radiometer type. Data were analyzed with two-way analysis of variance/Tukey; ,=0.05. Results:, In general, both handheld radiometer types exhibited significantly different irradiance readings compared with the control meter. Additionally, readings between radiometer types were found to differ slightly, but were correlated. In general, the LED radiometer provided slightly lower irradiance readings than the halogen radiometer, irrespective of light source. With both types of handheld radiometers, the use of the larger-diameter light guides tended to overestimate the irradiance values as seen in the control, while smaller-diameter light guides tended to underestimate. CLINICAL SIGNIFICANCE The evaluated LED or halogen handheld radiometers may be used interchangeably to determine the irradiance of both LED and QTH visible-light-curing units. Measured differences between the two radiometer types were small and probably not clinically significant. However, the diameter of light guides may affect the accuracy of the radiometers, with larger-diameter light guides overestimating and smaller-diameter guides underestimating the irradiance value measured by the control instrument. [source] QUARTZ-TUNGSTEN-HALOGEN AND LIGHT-EMITTING DIODE CURING LIGHTSJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 3 2006Kraig S. Vandewalle DDS Curing lights are an integral part of the daily practice of restorative dentistry. Quartz-tungsten-halogen (QTH), plasma-arc (PAC), argon laser, and light-emitting diode (LED) curing lights are currently commercially available. The QTH curing light has a long, established history as a workhorse for composite resin polymerization in dental practices and remains the most common type of light in use today. Its relatively broad emission spectrum allows the QTH curing light to predictably initiate polymerization of all known photo-activated resin-based dental materials. However, the principal output from these lamps is infrared energy, with the generation of high heat. Filters are used to reduce the emitted heat energy and provide further restriction of visible light to correlate better with the narrower absorbance spectrum of photo-initiators. The relatively inefficient emission typically requires corded handpieces with noisy fans. PAC lights generate a high voltage pulse that creates hot plasma between two electrodes in a xenon-filled bulb. The irradiance of PAC lights is much higher than the typical QTH curing light, but PAC lights are more expensive and generate very high heat with an inefficient emission spectrum similar to that of QTH bulbs. Light emitted from an argon laser is very different from that emitted from the halogen or PAC lights. The photons produced are coherent and do not diverge; therefore, lasers concentrate more photons of specific frequency into a tiny area. With very little infrared output, unwanted heat is minimized. However, argon lasers are very expensive and inefficient due to a small curing tip. LED curing lights have been introduced to the market with the promise of more efficient polymerization, consistent output over time without degradation, and less heat emission in a quiet, compact, portable device. This review evaluates some of the published research on LED and QTH curing lights. [source] Preparation of halogenated derivatives of thiazolo[5,4- d]thiazole via direct electrophilic aromatic substitutionJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2008Vladimir Benin Chlorination and bromination reactions of thiazolo[5,4- d]thiazole led to the generation of its mono- and dihalogenated derivatives. These are the first instances of successful direct electrophilic aromatic substitution in the thiazolo[5,4- d]thiazole ring system. X-ray analysis demonstrates that both 2-bromothiazolo[5,4- d]-thiazole and 2,5-dibromothiazolo[5,4- d]thiazole are planar structures, with strongly manifested ,-stacking in the solid state. Theoretical analysis of the pyridine-catalyzed halogenation (MP2/6-31+G(d) and B3LYP/6-31+G(d) calculations) reveals that introduction of one halogen actually leads to a slightly enhanced reactivity towards further halogenation. Several halogenation mechanisms have been investigated: 1) The direct C-halogenation with N-halopyridine as electrophile; 2) C-halogenation via intermediate N-halogenation, and 3) C-halogenation following an addition - elimination pathway, with intermediate formation of a cyclic halonium ion. The theoretical studies suggest that the direct C-halogenation is the favored mechanism. [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] Spin,spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethersMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007Wallace S. Brey Abstract The 19F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin,spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||||||||||||||