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Heteroatoms
Terms modified by Heteroatoms Selected AbstractsKatalytische C-C-, C-N- und C-O-Ullmann-KupplungenANGEWANDTE CHEMIE, Issue 38 2009Florian Monnier Dr. Abstract Kupferkatalysierte Ullmann-Kondensationen sind Schlüsselreaktionen in der organischen Synthese zur Bildung von Kohlenstoff- Heteroatom- und Kohlenstoff-Kohlenstoff-Bindungen. Die mit diesen Methoden erhältlichen Strukturmotive sind in biologisch aktiven Molekülen und vielen Materialvorstufen weit verbreitet. Dementsprechend waren intermolekulare Ullmann-Reaktionen zur Kupplung von Aryl- und Vinylhalogeniden mit N-, O- und C-Nucleophilen Gegenstand zahlreicher Studien, und dieser Kurzaufsatz beleuchtet die aktuellsten und wichtigsten Entwicklungen auf diesem Gebiet seit 2004. [source] ChemInform Abstract: [Sn9HgSn9]6- : An Intermetalloid Zintl Ion with Two Sn9 Connected by Heteroatom.CHEMINFORM, Issue 37 2010Li Yong Abstract The new compound (III) crystallizes in the space group P with Z = 2 (single crystal XRD). [source] ChemInform Abstract: New Heteropolyanions of the M2X2W20 Structure Type with Antimony(III) as a Heteroatom.CHEMINFORM, Issue 34 2002M. Piepenbrink 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] Self-Assembly of [B -SbW9O33]9, Subunit with Transition Metal Ions (Mn2+, Cu2+, Co2+) in Aqueous Solution: Syntheses, Structures and Magnetic Properties of Sandwich Type Polyoxometalates with Subvalent SbIII HeteroatomCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2008Jing-Ping Wang Prof. Abstract Rational self-assembly of Sb2O3 and Na2WO4, or (NH4)18[NaSb9W21O86] with transition-metal ions (Mn2+, Cu2+, Co2+), in aqueous solution under controlled conditions yield a series of sandwich type complexes, namely, Na2H2[Mn2.5W1.5(H2O)8(B -,-SbW9O33)2],32,H2O (1), Na4H7[Na3(H2O)6Mn3(,-OAc)2(B -,-SbW9O33)2],20,H2O (OAc=acetate anion) (2), NaH8[Na2Cu4Cl(B -,-SbW9O33)2],21,H2O (3), Na8K[Na2K(H2O)2{Co(H2O)}3(B -,-SbW9O33)2], 10,H2O (4), and Na5H[{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2],11.5,H2O (5). These structures are determined by using the X-ray diffraction technique and further characterized by obtaining IR spectra and performing elemental analysis. Structure analysis reveals that polyoxoanions in 1 and 5 comprise of two [B -,-SbW9O33]9, building units, whereas 2, 3, and 4 consist of two isomerous [B -,-SbW9O33]9, building blocks, which are all linked by different transition-metal ions (Mn2+, Cu2+, or Co2+) with different quantitative nuclearity. It should be noted that compound 2 represents the first one-dimensional sinusoidal chain based on sandwich like tungstoantimonate building blocks through the carboxylate-bridging ligands. Additionally, 3 is constructed from sandwiched anions [Na2Cu4Cl(B -,-SbW9O33)2]9, linked to each other to form an infinitely extended 2D network, whereas 5 shows an interesting 3D framework built up from offset sandwich type polyoxoanion [{Co(H2O)2}3W(H2O)2(B -,-SbW9O33)2]6, linked by Co2+ and Na+ ions. EPR studies performed at 110,K and room temperature reveal that the metal cations (Mn2+, Cu2+, Co2+) reside in a square-pyramidal geometry in 2, 3, and 4. The magnetic behavior of 1,4 suggests the presence of weak antiferromagnetic coupling interactions between magnetic metal centers with the exchange integral J=,0.552,cm,1 in 2. [source] Direct Substitution of the Hydroxy Group at the Allylic/propargylic Position with Carbon- and Heteroatom- centered Nucleophiles Catalyzed by Yb(OTf)3CHINESE JOURNAL OF CHEMISTRY, Issue 4 2008Wen HUANG Abstract An efficient and highly selective Yb(OTf)3 -catalyzed direct substitution of the hydroxy group at the allylic and propargylic positions with a variety of heteroatom- and carbon-centered nucleophiles, such as alcohols, thiols, amines, amides and active methylene compounds has been developed. The advantages of the present catalytic system are wide availability of the starting materials, especially for tolerance to thiols, no need for dried solvents and additives, mild conditions, short time of reaction, simple manipulation and environmentally friendly catalyst that can be recovered and reused at least ten times without significant reduction of activity. [source] How Do the Different Defect Structures and Element Substitutions Affect the Nonlinear Optical Properties of Lacunary Keggin Polyoxometalates?EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2006A DFT Study Abstract Systematic DFT calculations have been carried out on the lacunary ,-Keggin polyoxometalate derivatives [PW11O39]7,, [XW9O34]n, (X = AlIII, SiIV, GeIV, PV, AsV, and SbV), [XW9M2O39]n,, and [XW9M3O40]n, (X = PV and SiIV, M = MoVI, VV, NbV, and TaV) to investigate the geometric structure and element substitution effects on the molecular nonlinear optical response. Analysis of the computed static second-order polarizability (,0) predicts that the molecular nonlinear optical activity of lacunary Keggin polyoxometalate derivatives can be modified by replacing the central heteroatom and the addenda metal atom. Substitution of the central Al atom or the addenda V atom causes significant enhancement in the molecular nonlinearity. Moreover, the ,0 values are substantially dependent on the defect structures. This class of inorganic complexes possesses remarkably large molecular optical nonlinearity, especially for the partial substitution complex [SiW9Nb2O39]10, (IIIc), which has a computed ,0 value of 2071.0 a.u. Thus, lacunary Keggin polyoxometalates could become excellent candidates in the field of second-order NLO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis, Solution-State and Solid-State Structural Characterization of Monocationic Nitrido Heterocomplexes [M(N)(DTC)(PNP)]+ (M = 99Tc, Re; DTC = Dithiocarbamate; PNP = Heterodiphosphane)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2004Cristina Bolzati Abstract Mono-cationic nitrido heterocomplexes of general formula [M(N)(DTC)(PNP)]+ (where M is 99Tc or Re, DTC is the mono-anionic form of a dithiocarbamate ligand, and PNP is a diphosphane ligand with a tertiary amine-containing five-membered spacer) were prepared by ligand-exchange reactions with the labile precursors [M(N)Cl2(PPh3)2] in dichloromethane/alcohol mixtures. The molecular structure of the representative rhenium complex [Re(N)(dedc)(pnp2)][PF6] (1) displays a distorted, square-pyramidal geometry with the dithiocarbamate sulfur and the diphosphane phosphorus atoms spanning the four coordination positions on the equatorial plane. If the additional interactions between the nitrido nitrogen and the weakly bonded transN -diphosphane heteroatom, the molecular geometry can be viewed as pseudo-octahedral. The structure in solution, as established by multinuclear NMR spectroscopy and ESI spectrometry, is monomeric, and identical to that shown in the solid state. Replacement of the phenyl groups on the phosphorous atoms in complexes 1, 2, 5, and 6 with alkyl groups modified neither the course of the reaction nor the composition of the resulting complexes. These results, together with the observation that no symmetrical complexes containing two identical bidentate ligands were produced in these reactions, strongly supports the conclusion that a mixed coordination sphere, composed by a combination of ,-donor and ,-acceptor atoms around the [M,N]2+ group, constitutes a highly stable system. Compounds containing dangling alkyl-substituted groups in the outer sphere (3, 4, 7, and 8) were fully characterized by multinuclear NMR spectroscopy and ESI mass spectrometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Thermodynamic Study of ,H Complexes in Nucleophilic Aromatic Substitution Reactions: Relative Stabilities of Electrochemically Generated RadicalsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008Iluminada Gallardo Abstract The mechanism for the electrochemical oxidation of ,H complexes, such as 1-hydro-1-alkoxy/sulfoxy or -fluoro-2,4-dinitro/2,4,6-trinitrocyclohexadienyl anions, has been widely studied by means of cyclic voltammetry and controlled-potential electrolysis. Previous studies have shown that the electrochemical oxidation of ,H complexes, formed by the addition of carbon or nitrogen nucleophiles followed by a two electron mechanism, corresponding to the formal elimination of the hydride anion (nucleophilic aromatic substitution of hydrogen mechanism, the NASH mechanism). For these ,H complexes (Nu, = OH,, ,OR, ,SR, ,F), the electrochemical reaction takes place by a one-electron mechanism and is followed by the radical elimination of the leaving group with the consequent recovery of the starting material. This mechanism is similar to that proposed for the electrochemical oxidation of ,X complexes (nucleophilic aromatic substitution of a heteroatom, the NASX mechanism). The operating mechanism in each case, the NASH or NASX, can be rationalized in terms of thermodynamics. The standard potentials of the , complex and/or the leaving group as well as the bond dissociation energies (BDEs) are determinant factors. This study has not led to a significant improvement in the electrochemical preparation of aromatic-substituted compounds, but does help to understand and predict the usefulness or uselessness of using the nucleophilic aromatic substitution route to obtain a desired product. Finally, the current approach extends the electrochemical methodology to different chemical fields, for example, to general nondestructive methods for the detection, identification, and quantification of either organic pollutants or explosives in different solvents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Enzymology and molecular biology of prokaryotic sulfite oxidation,FEMS MICROBIOLOGY LETTERS, Issue 1 2001Ulrike Kappler Abstract Despite its toxicity, sulfite plays a key role in oxidative sulfur metabolism and there are even some microorganisms which can use it as sole electron source. Sulfite is the main intermediate in the oxidation of sulfur compounds to sulfate, the major product of most dissimilatory sulfur-oxidizing prokaryotes. Two pathways of sulfite oxidation are known: (1) direct oxidation to sulfate catalyzed by a sulfite:acceptor oxidoreductase, which is thought to be a molybdenum-containing enzyme; (2) indirect oxidation under the involvement of the enzymes adenylylsulfate (APS) reductase and ATP sulfurylase and/or adenylylsulfate:phosphate adenylyltransferase with APS as an intermediate. The latter pathway allows substrate phosphorylation and occurs in the bacterial cytoplasm. Direct oxidation appears to have a wider distribution; however, a redundancy of pathways has been described for diverse photo- or chemotrophic, sulfite-oxidizing prokaryotes. In many pro- and also eukaryotes sulfite is formed as a degradative product from molecules containing sulfur as a heteroatom. In these organisms detoxification of sulfite is generally achieved by direct oxidation to sulfate. [source] X-Ray Structure Analyses of syn/anti -Conformers of N -Furfuroyl-, N -Benzoyl-, and N -Picolinoyl-Substituted (2R)-Bornane-10,2-sultam DerivativesHELVETICA CHIMICA ACTA, Issue 8 2008Karolina Koszewska Abstract The synthesis and the X-ray structure of the three new N -(arylcarbonyl)-substituted derivatives 2a,2c of (2R)-bornane-10,2-sultam are presented and discussed. Direct comparison of the solid-state analyses shows that the dipole-directed SO2/CO anti- /syn- conformations may be very sensitive to weak electronic/electrostatic repulsions of the heteroatom lone pairs. The optimum interactions are reached when the lone pair of the , -positioned heteroatom is oriented in the O(3)C(11)N(1) plane. Such rare syn -conformations may be observed with at least up to 1.8,kcal/mol higher energy as compared to their ground states. Additionally, these anti/syn- conformations are also very sensitive to external influences such as, for example, the crystal-packing forces. [source] Synthesis, Structure, and Optical Properties of Terminally Sulfur-Functionalized Core-Substituted Naphthalene-Bisimide DyesHELVETICA CHIMICA ACTA, Issue 9 2006Alfred B, aszczyk Abstract The synthesis, characterization, and optical properties of a series of new 2,6-disubstituted naphthalene-bisimide dyes as molecular rods comprising terminal AcS groups is reported. The first series of dyes (1,3), comprising phenylhetero (Ph-X) core substituents, cover a broad range of the VIS spectrum, ranging from yellow (2) over red (3) to blue (1). The second series of dyes contains benzylhetero (Bn-X) core substituents (4,7). For the same heteroatom connecting the substituent to the naphthalene core, both series were found to display comparable colors. For the second series, the colors were blue (4), red (5), and violet (6, 7). The Ph-X-substituted dyes 1,3 are nonfluorescent, in contrast to the Bn-X-substituted compounds 4,7. This rich variety of optical features that can be adjusted by rather small alterations of the core substituents makes these structurally very comparable molecular rods ideal candidates for optically triggered molecular-transport investigations. Also, thanks to the terminal AcS groups, these compounds can be placed between nobel-metal electrodes for optically triggered transport experiments. [source] Catalytic, Asymmetric Vinylogous Mukaiyama Aldol Reactions of Pyrrole- and Furan-Based Dienoxy Silanes: How the Diene Heteroatom Impacts StereocontrolADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Claudio Curti Abstract Denmark's chiral bisphosphoramide/silicon tetrachloride system performs as an excellent Lewis base-Lewis acid catalyst for the vinylogous Mukaiyama aldol reaction of pyrrole- and furan-based dienoxy silanes with aromatic and heteroaromatic aldehydes. This asymmetric methodology provides a powerful synthetic entry to a variety of ,-hydroxylated ,-butenolide-type frameworks with high efficiency and valuable margins of regio-, diastereo-, and enantioselectivity. Notably, the nature of the heteroatom within the vinylogous dienoxy silane donor heavily impacts the diastereocontrol, with syn -configured aldol adducts emerging from pyrroles bearing electron-withdrawing N -protecting groups (Boc, Ts, and Cbz) and anti -configured adducts prevailing when furan- or N -alkyl/alkenylpyrrole donors are involved. [source] Poly(urethanes) containing silarylene and/or germarylene unitsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008C. A. Terraza Abstract A series of 10 poly(urethanes) were synthesized by solution polymerization from bis(chloroformates) and aromatic diamines, containing both silicon or germanium as central atom. So, the polymers prepared contain two silicon atoms or two germanium atoms exclusively or combinations of both. Me, Et, and Ph groups were bonded to the central atoms according to the nature of the monomers employed. Poly(urethanes) were characterized by FTIR, 1H, 13C, and 29Si NMR spectroscopy and the results agreed with the proposed structures. Additionally, intrinsic viscosity values were established in DMSO solutions and thermal analyses were developed. In all cases, thermostable oligomers were obtained, which showed a degradation process beginning at ,240,260°C. Polymers showed a thermal dependence with the nature of the heteroatom employed. Thus, in general, when germanium was used as central atom, the thermal stability was higher than the polymers containing silicon which agrees with the lower polarity and higher energy of the CGe bond in comparison with the CSi one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source] Structural, electronic, and optical properties of 9-heterofluorenes: A quantum chemical studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2007Run-Feng Chen Abstract Density-functional theory studies were applied to investigate the structural, electronic, and optical properties of 9-heterofluorenes achieved by substituting the carbon at 9 position of fluorene with silicon, germanium, nitrogen, phosphor, oxygen, sulfur, selenium, or boron. These heterofluorenes and their oligomers up to pentamers are highly aromatic and electrooptically active. The alkyl and aryl substituents of the heteroatom have limited influence, but the oxidation of the atom has significant influence on their molecular structures and properties. The highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) interaction theory was successfully applied to analyze the energy levels and the frontier wave functions of these heterofluorenes. Most heterofluorenes belong to type B of interaction with low-lying LUMO and have the second kind of wave function. Carbazole and selenafluorene have type C of interaction with high-lying HOMO and the third kind of wave function. Types C and D of heterofluorenes, such as carbazole, oxygafluorene, sulfurafluorene, and selenafluorene also have high triplet state energies. The extrapolated HOMO and LUMO for polyheterofluorenes indicate that polyselenonafluorene has the lowest LUMO; polycarbazole has the highest HOMO; polyselenafluorene has the highest bandgap (Eg); and polyborafluorene has the lowest Eg. Heterofluorenes and their oligomers and polymers are of great experimental interests, especially those having extraordinary properties revealed in this study. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Balance of xanthophylls molecular and protonated molecular ions in electrospray ionizationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2005Thais Guaratini Abstract This paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen-containing carotenoid) with a conjugated ,-system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi-empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI-MS to form M+, and [M + H]+, respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M+, or [M + H]+ for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin. Copyright © 2005 John Wiley & Sons, Ltd. [source] A theoretical density functional study of association of Zn2+ with oxazolidine and its thio derivatives in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2010Zaki S. Safi Abstract We have performed density functional theory (DFT) calculations in order to study the gas-phase interaction of oxo- and thio-oxazolidine derivatives with Zn2+. The calculations were performed at B3LYP/6-311+(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn2+ with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn2+ bridging between the heteroatom at position 2 or 4 of the 4- or 2-enol (or the 4- or 2-enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn2+ association has a clear catalytic effect on the tautomerization processes which connect the oxo,thione forms with the enol,enethiol tautomers. Hence, although the enol,enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn2+ complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn2+ binding energies. Copyright © 2010 John Wiley & Sons, Ltd. [source] Substituent effect on local aromaticity in mono and di-substituted heterocyclic analogs of naphthaleneJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010Afshan Mohajeri Abstract A quantitative study on local aromaticity has been performed on a series of mono- and di-substituted biheterocycles (quinoline, isoquinoline, quinoxaline, quinazoline). Three electronically based indices (PDI, ATI, and FLU) have been employed to investigate the substituent effect on the , -electron delocalization in both heterocycle and benzenoid rings. Three typical substituents (Cl, OCH3, and CN) with different inductive and resonance power have been selected. Generally, substituent causes a reduction in aromaticity irrespective of whether it is electron attracting or electron donating. It is shown that the maximum aromaticity exhibits a similar trend of Cl,>,CN,>,OCH3 for all the studied rings. Moreover, it is found that the substituent situation with respect to the heteroatom has a significant influence on the aromaticity. It results from our study that in di-substituted derivatives, irrespective of whether the two substituents form a meta or para isomer, they preferably choose the position which leads to the maximum aromaticity character. Copyright © 2009 John Wiley & Sons, Ltd. [source] Silyl-Terminated Ethylene- co -Norbornene Copolymers by Organotitanium-Based CatalystsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2009Roberto Marconi Abstract Ethylene (E) and norbornene (N) were copolymerized in the presence of PhSiH3 as chain-transfer agent with [Ti(,5:,1 -C5Me4SiMe2NBut)(,1 -Me)2] precatalyst combined with [Ph3C][B(C6F5)4]. The silane was introduced at chain-ends of E- co -N copolymers with concomitant reinitiation of the growing polymer chain. The concentrations of the silane and polymer molecular weight are inversely correlated. The characteristic signals of SiH2Ph chain-ends were observed by 1H NMR. The Si heteroatom is predominantly adjacent to ethylene units in E- co -N copolymers with high N content. [source] Spatial substituent effects of various fluorinated groups on the 13C chemical shifts in cyclohexanesMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007Yvan Carcenac Abstract The effect of introduction of fluorinated groups (CH2F, CHF2, CF3, C2F5, OCF3, SCF3) on the 13C NMR chemical shifts in cyclohexanes is examined. The two main effects are caused by location at the , and , carbon positions. Comparison of the various data allowed the calculation of increments corresponding to the introduction of fluorinated groups at axial or equatorial positions on the cyclohexane ring. The introduction of fluorine atoms in methoxy and thiomethoxy groups has only a slight effect through the heteroatom on the 13C chemical shifts. Copyright © 2007 John Wiley & Sons, Ltd. [source] Electron ionization mass spectra of phosphorus-containing heterocycles.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2006The electron ionization mass spectra of 27 cis - and trans -annelated 1,4,4a,5,6,7,8,8a-octahydro-2H -3,1,2-benzoxazaphosphinine 2-oxides were recorded to clarify the effects of the ring heteroatom (O or N), ring annelation, the P configuration and the substituents attached to the ring or to the N and P atoms. For compounds 1,12 different alkyl radical and alkene losses and the cleavage of the P,heteroatom bonds, instead of the P,C bonds, were representative and dependent mainly on the substitution on the N and P atoms. The replacement of Ph and OPh by N(CH2CH2Cl)2 on the P atom had a dramatic influence on the fragmentation process: new fragment ions were obtained and very little M+. (1,3%) was formed. Only slight differences were found between some of the corresponding isomers, but interestingly the compounds formed clear groups on the basis of the differences in their fragmentation, depending on the ring-N and ring-P substituents. Copyright © 2006 John Wiley & Sons, Ltd. [source] Direct Substitution of the Hydroxy Group at the Allylic/propargylic Position with Carbon- and Heteroatom- centered Nucleophiles Catalyzed by Yb(OTf)3CHINESE JOURNAL OF CHEMISTRY, Issue 4 2008Wen HUANG Abstract An efficient and highly selective Yb(OTf)3 -catalyzed direct substitution of the hydroxy group at the allylic and propargylic positions with a variety of heteroatom- and carbon-centered nucleophiles, such as alcohols, thiols, amines, amides and active methylene compounds has been developed. The advantages of the present catalytic system are wide availability of the starting materials, especially for tolerance to thiols, no need for dried solvents and additives, mild conditions, short time of reaction, simple manipulation and environmentally friendly catalyst that can be recovered and reused at least ten times without significant reduction of activity. [source] Vapor pressures and thermodynamics of oxygen-containing polycyclic aromatic hydrocarbons measured using knudsen effusion,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2008Jillian L. Goldfarb Abstract Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs) are ubiquitous environmental pollutants resulting from the incomplete combustion of coal and fossil fuels. Their vapor pressures are key thermodynamic data essential for modeling fate and transport within the environment. The present study involved nine PAHs containing oxygen heteroatoms, including aldehyde, carboxyl, and nitro groups, specifically 2-nitrofluorene, 9-fluorenecarboxylic acid, 2-fluorenecarboxaldehyde, 2-anthracenecarboxylic acid, 9-anthracenecarboxylic acid, 9-anthraldehyde, 1-nitropyrene, 1-pyrenecarboxaldehyde, and 1-bromo-2-naphthoic acid. The vapor pressures of these compounds, with molecular weights ranging from 194 to 251 g/mol, were measured using the isothermal Knudsen effusion technique in the temperature range of 329 to 421 K. The corresponding enthalpies of sublimation, calculated via the Clausius-Clapeyron equation, are compared to parent, nonoxygenated PAH compound data to determine the effect of the addition of these oxygen-containing heteroatoms. As expected, the addition of ,CHO, ,COOH, and ,NO2 groups onto these PAHs increases the enthalpy of sublimation and decreases the vapor pressure as compared to the parent PAH; the position of substitution also plays a significant role in determining the vapor pressure of these OPAHs. [source] Synthesis and Physical Chemistry of s -Tetrazines: Which Ones are Fluorescent and Why?EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 35 2009Yong-Hua Gong Abstract New fluorescent tetrazines have been prepared and their electrochemistry and fluorescence efficiency evaluated. The occurrence of fluorescence as well as the wavelength were found to be strongly dependent on the substituents, which have to be electronegative heteroatoms. This has been rationalized through a computational study that showed that the crucial factor is the nature of the HOMO, which determines the existence or not of fluorescence. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Tripodands with Phenyl and Thiophenyl Rings and Nitrogen Bridgehead Atoms,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Martin Baier Abstract The flexible tripodands 7,9 and 15 with phenyl and thiophenyl rings as "legs" and nitrogen as bridgehead atoms have been synthesized by three-component condensation reactions of the corresponding amine with the aryl halide. The more rigid species 10,14 and 17 were built up from the podands 7,9 as well as from their iodine substitution products 33,35 by a sequence of ethynylation and C,C coupling reactions. Podand 16 was prepared from tris-iodide 36 by Sonogashira coupling with phenylacetylene. In the cases of 7, 12, 15,17, 22, 24, 35, 36, and 41 the structural parameters were determined by X-ray studies. With the exception of 7, 12, and 17, all structures show either close intermolecular contacts between heteroatoms (15, 22, 24, 35, and 36), C,H···N hydrogen bonding (41), or are closely packed as a result of ,···, stacking (16). We were able to isolate silver triflate complexes of 9, 10, and 16, and in the case of 9 we obtained crystals suitable for X-ray diffraction studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Fused Tetracyclic Heterocycles by Thermally Initiated Intramolecular Criss-Cross Cycloaddition of 3-Substituted HomoallenylaldazinesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2005Hana Zachová Abstract The thermally initiated intramolecular criss-cross cycloaddition of 3-substituted homoallenylaldazines 5 has been explored. Their cyclization led to interesting new fused heterocyclic systems 6 consisting of four five-membered rings with two nitrogen heteroatoms. The azines were prepared by the reaction of homoallenyl aldehydes 4 with hydrazine. The homoallenyl aldehydes 4 were synthesized by the Claisen rearrangement of new N,N -disubstituted 4-[(2-methylprop-1-en-1-yl)oxy]but-2-yn-1-amines 3a,f prepared by Mannich reaction of 2-methylprop-1-en-1-yl prop-2-yn-1-yl ether (2). The success of the reaction was based on the improved solvent-free synthesis of 1-chloro-2-methylpropyl prop-2-yn-1-yl ether (1) and its conversion to isolable 2-methylprop-1-en-1-yl prop-2-yn-1-yl ether (2) in high yield. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The Large Electrochemical Capacitance of Microporous Doped Carbon Obtained by Using a Zeolite Template,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2007O. Ania Abstract A novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na,Y zeolite as a scaffold. Liquid-phase impregnation and in,situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas-phase impregnation with propylene, enables pore-size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore-size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (SBET,=,1680,m2,g,1), the templated carbon material displays a large gravimetric capacitance (340,F,g,1) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2,V in an aqueous medium with good cycleability,-beyond 10,000,cycles,and is extremely promising for use in the development of high-energy-density supercapacitors. [source] Synthesis, CD Spectra, and Enzymatic Stability of ,2 -Oligoazapeptides Prepared from (S)-2-Hydrazino Carboxylic Acids Carrying the Side Chains of Val, Ala, and LeuHELVETICA CHIMICA ACTA, Issue 12 2003Gérald Lelais , -Peptides offer the unique possibility to incorporate additional heteroatoms into the peptidic backbone (Figs.,1 and 2). We report here the synthesis and spectroscopic investigations of ,2 -peptide analogs consisting of (S)-3-aza- , -amino acids carrying the side chains of Val, Ala, and Leu. The hydrazino carboxylic acids were prepared by a known method: Boc amidation of the corresponding N -benzyl- L - , -amino acids with an oxaziridine (Scheme,1). Couplings and fragment coupling of the 3-benzylaza- ,2 -amino acids and a corresponding tripeptide (N -Boc/C -OMe strategy) with common peptide-coupling reagents in solution led to ,2 -di, ,2 -tri-, and ,2 -hexaazapeptide derivatives, which could be N -debenzylated (4,9; Schemes,2,4). The new compounds were identified by optical rotation, and IR, 1H- and 13C-NMR, and CD spectroscopy (Figs.,4 and 5) and high-resolution mass spectrometry, and, in one case, by X-ray crystallography (Fig.,3). In spite of extensive measurements under various conditions (temperatures, solvents), it was not possible to determine the secondary structure of the ,2 -azapeptides by NMR spectroscopy (overlapping and broad signals, fast exchange between the two types of NH protons!). The CD spectra of the N -Boc and C -OMe terminally protected hexapeptide analog 9 in MeOH and in H2O (at different pH) might arise from a (P)- 314 -helical structure. The N -Boc- ,2 -tri and N -Boc- ,2 -hexaazapeptide esters, 7 and 9, were shown to be stable for 48,h against the following peptidases: pronase, proteinase,K, chymotrypsin, trypsin, carboxypeptidase,A, and 20S proteasome. [source] Functionalization of Porous Carbon Materials with Designed Pore Architecture,ADVANCED MATERIALS, Issue 3 2009Andreas Stein Abstract Recent progress in syntheses of porous carbons with designed pore architecture has rejuvenated the field of carbon chemistry and promises to provide new advanced materials. In order to reap the full benefit of designer carbons, it is necessary to develop chemistries for functionalizing the porous carbon surfaces. This Review examines methods of functionalizing porous carbon through direct incorporation of heteroatoms in the carbon synthesis, surface oxidation and activation, halogenation, sulfonation, grafting, attachment of nanoparticles and surface coating with polymers. Methods of characterizing the functionalized carbon materials and applications that benefit from functionalized nanoporous carbons with designed architecture are also highlighted. [source] Efficient generation of Heisenberg Hamiltonian matrices for VB calculations of potential energy surfacesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2009A. M. Tokmachev Abstract The spin-Hamiltonian valence bond theory relies upon covalent configurations formed by singly occupied orbitals differing by their spin counterparts. This theory has been proven to be successful in studying potential energy surfaces of the ground and lowest excited states in organic molecules when used as a part of the hybrid molecular mechanics,valence bond method. The method allows one to consider systems with large active spaces formed by n electrons in n orbitals and relies upon a specially proposed graphical unitary group approach. At the same time, the restriction of the equality of the numbers of electrons and orbitals in the active space is too severe: it excludes from the consideration a lot of interesting applications. We can mention here carbocations and systems with heteroatoms. Moreover, the structure of the method makes it difficult to study charge-transfer excited states because they are formed by ionic configurations. In the present work we tackle these problems by significant extension of the spin-Hamiltonian approach. We consider (i) more general active space formed by n ± m electrons in n orbitals and (ii) states with the charge transfer. The main problem addressed is the generation of Hamiltonian matrices for these general cases. We propose a scheme combining operators of electron exchange and hopping, generating all nonzero matrix elements step-by-step. This scheme provides a very efficient way to generate the Hamiltonians, thus extending the applicability of spin-Hamiltonian valence bond theory. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Polyesters based on two silarylene or germarylene moieties: Synthesis under phase-transfer conditionsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009L. H. Tagle Abstract Polyesters (PEs) containing two heteroatoms (Si and/or Ge) in the main chain, derived from the acid dichlorides bis(4-chloroformylphenyl) ethylmethylsilane, bis(4-chloroformylphenyl) diethylsilane, bis(4-chloroformylphenyl) diethylgermane, and bis(4-chloroformylphenyl) di- nbutylgermane and from the diphenols bis(4-hydroxyphenyl) ethylmethylsilane, bis(4-hydroxyphenyl) diethylsilane, bis(4-hydroxyphenyl) diethylgermane, and bis(4-hydroxyphenyl) di- nbutylgermane, were synthesized under phase-transfer conditions with three quaternary ammonium salts as phase-transfer catalysts and three NaOH concentrations in the aqueous phase. PEs were characterized with IR and NMR spectroscopy, including 29Si-NMR. In general, the yields and intrinsic viscosities were low, and in some cases, an increase in these parameters was shown as a result of the catalyst effect. An increase in the NaOH concentration caused a decrease in the yields because of a hydrolytic process. PEs with Si were thermally more stable than those with Ge. The glass-transition temperatures decreased when the side chains bonded to the heteroatoms were longer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] | ||||||||||||||||||||||||||||||||||