bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Cutting Temperature in Near Dry Machining
Authors: Li Kuan-Ming , Liang Steven Y.
Published: May 2006

Near dry machining refers to the condition of applying cutting fluid at relatively low flow rates, on the order of 2-100ml∕h, as opposed to the conventional way of using either a large quantity, typically of about 10l∕min, as in wet machining; or no fluid at all, as in dry machining. One important expectation of applying fluids is to control the cutting temperature, which is an important parameter for tool life and part dimensional accuracy in machining processes. In this context, the understanding of cutting temperature variation corresponding to the near dry cooling and lubrication is of interest. This paper models the temperature distributions in the cutting zone under through-the-tool near dry cooling condition. The heat source method is implemented to estimate the cutting temperatures on the tool-chip interface and the tool-workpiece interface. For the temperature rise in the chip, the effects of the primary heat source and the secondary heat source were modeled as moving heat sources. For the temperature rise in the tool, the effects of the secondary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear, were modeled as stationary heat sources. For the temperature rise in the workpiece, the primary heat source, the heat loss due to cooling, and the rubbing heat source due to the tool flank wear were modeled as moving heat sources. The model describes the dual effects of air-oil mixture in near dry machining in terms of the reduction of cutting temperature through the cooling effect, as well as the reduction of heat generation through the lubricating effect. To pursue model calibration and validation, embedded thermocouple temperature measurement in cutting medium carbon steels with uncoated carbide insets were carried out. The model predictions and experimental measurements show reasonable agreement and results suggest that the combination of the cooling and the lubricating effects in near dry machining reduces the cutting temperatures on the tool-chip interface by about 8% with respect to dry machining. Moreover, the cutting speed remains a dominant factor in cutting temperature compared with the feed and the depth of cut in near dry machining processes.
Self-heating and the temperature dependence of the dc characteristics of GaN heterostructure field effect transistors
Authors: McAlister S. P. , Bardwell J. A. , Haffouz S. , Tang H.
Published: May 2006

Self-heating is an important issue for GaN heterostructure field effect transistors (HFETs), especially in high power applications. Here we report the temperature dependence of the dc characteristics of some GaN HFETs including the variation of the transconductance. We present the characteristics as a function of added power, instead of voltage bias, and use the temperature data to transform the power dependence into a dependence on the average device temperature. For similar devices on sapphire and SiC, at 20 V VDS and 0 V VG, the temperature increase for the same added power is ∼2.7 times greater in the sapphire-based device.
Terahertz emission properties of arsenic and oxygen ion-implanted GaAs based photoconductive pulsed sources
Authors: Salem B. , Morris D. , Salissou Y. , Aimez V. , Charlebois S. , Chicoine M. , Schiettekatte F.
Published: May 2006

In this work we compare the characteristics of asymmetrically excited small-aperture antenna-type pulsed terahertz emitters fabricated using an ion implantation process. Our photoconductive materials consist of high resistivity GaAs substrates. Multienergy implantations of arsenic (1.2 and 2MeV) and oxygen (180, 450, and 700keV) have been used to obtain an almost uniform density of vacancies over the optical absorption depth in bulk GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort laser pulses. Ion implantation followed by a thermal annealing process introduces nonradiative centers in our substrates which reduce the carrier lifetime and modify the shape of our terahertz pulses. Results obtained as functions of the laser excitation power and bias voltage are discussed and a comparison of the performance of these devices with conventional small-aperture antennas is given.
Low leakage a-Si:H thin film transistors deposited on glass substrates using hot-wire chemical vapor deposition
Authors: Taghibakhsh F. , Karim K. S. , Madan A.
Published: May 2006

Stable, low leakage current hot-wire chemical vapor deposition (HWCVD) thin film transistors (TFTs) were fabricated using graphite filament on Corning 1737 glass substrates. TFTs were deposited using a bottom gate, inverted staggered, self-aligned, low temperature process with a molybdenum metal gate, a trilayer consisting of a HWCVD a-Si:Hi layer sandwiched between two plasma enhanced chemical vapor deposition (PECVD) a-SiNx:H layers, followed by a PECVD n+ a-Si:H Ohmic contact layer, and a final aluminum metal for source and drain contacts. Ion∕Ioff ratio exceeds 108 and the leakage current is less than 10−13A, while the field effect mobility is in the range of 0.13cm2∕Vs and the subthreshold slope is 0.6V∕decade. Time stress bias measurements show β of 0.156 for HW a-Si TFTs, showing superior stability compared to their fully PECVD counterparts.
Deposition of hafnium oxide from Hf t-butoxide and nitric oxide
Authors: Zhang Z. , Xia B. , Gladfelter W. L. , Campbell S. A.
Published: May 2006

The high-κ stack consisting of an optional nitride interfacial layer and a HfO2 layer was studied. The result shows that nitride or oxynitride interfacial layers can be controllably formed down to a few angstroms. The growth of both interfacial layers is self-limited. The introduction of nitric oxide with hafnium t-butoxide during the high-κ deposition leads to smaller effective oxide thickness (EOT) and gate leakage current. EOTs below 1.0nm have been achieved with this combination of sources. The beneficial effect of nitric oxide can be explained in terms of reduced interfacial EOT, reduction of carbon contamination, and possibly a small trace amount of nitrogen incorporation.
Study of temperature influence on electron beam induced deposition
Authors: Li Wei , Joy David C.
Published: May 2006

A study of the temperature dependence of the electron beam induced deposition (EBID) of tungsten was carried out in a temperature range of −30–75°C under two conditions of beam energy and beam current using WF6 as the precursor gas. An Arrhenius relationship was found for the temperature dependence of the deposition rate which is consistent with an electron stimulated desorption mechanism for this process. In addition, the mechanism for EBID under different conditions was discussed.
Investigation of the optical properties of InGaAs(N):(Sb) quantum wells grown by metal organic vapor phase epitaxy
Authors: Chen W. C. , Su Y. K. , Chuang R. W. , Hsu S. H.
Published: May 2006

Dilute-nitride materials have attracted much attention due to their capability of operating in the wavelength range of optical communication. However, their optical properties degrade with the nitrogen incorporation into the host material such as InGaAs or GaAs, which can be recovered slightly by performing thermal treatment. More recently, the surfactant effect of Sb was verified by molecular beam epitaxy grown samples. Adding Sb into dilute-nitride materials can help to maintain the luminescence efficiency while increasing the emission wavelength toward 1.55μm. But its effect on the metal organic vapor phase epitaxy grown samples is not very clear. In this article, we performed a series of experiments on the InGaAsN(Sb) quantum wells to clarify the role of Sb. The photoluminescence (PL) intensities of InGaAsN:Sb were higher than those of the undoped samples and the extent of blueshift after annealing was slighter than that of the InGaAsN quantum wells. However, the PL intensities were still low and thus we tried another material (InGaAs:Sb) to achieve the 1.3μm emission. The temperature dependent PL measurements were also carried out to investigate the optical properties of InGaAs:Sb quantum wells.
Characteristics and diagnostics of an ultrahigh vacuum compatible laser ablation source for crossed molecular beam experiments
Authors: Gu Xibin , Guo Ying , Kawamura Ed , Kaiser Ralf I.
Published: May 2006

We present the design and the characteristics of an ultrahigh vacuum compatible laser ablation source which can be operated in a crossed molecular beam machine at pressures as low as 10−9Torr. This unit provides intense supersonic beams of up to 3×1013cm−3 reactant species (carbon atoms, dicarbon, and tricarbon) in the interaction region of a crossed molecular beam machine. Practical delay time windows between the pulsed valve releasing the seeding gas and the laser have been determined to be between 16 630 and 16645μs, i.e., firing the laser 150–165μs after the 80μs pulsed valve trigger. The concentration of the dicarbon and tricarbon clusters can be maximized/minimized by adjusting the laser focus (a tighter laser focus leads to an enhanced atomic carbon component) and the laser power (multiphoton dissociation). We achieved stable peak velocities between 800 and 3800ms−1 and speed ratios S of up to 6.
Hexaruthenium and octaruthenium carbonyl cluster complexes derived from 2-amino-6-methylpyridine  Novel coordination modes for 2-imidopyridines
Authors: Cabeza Javier A , Río Ignacio del , García-Álvarez Pablo , Miguel Daniel
Published: May 2006

The hexanuclear ruthenium cluster [Ru6(µ3-H)2(µ-H)2(µ4-κ2-ampy)2(CO)14] (1) and the octanuclear one [Ru8(µ-H)(µ4-κ2-ampy)3(µ3-κ2-Hampy)(µ-CO)2(CO)15] (2) have been prepared by treating [Ru6(µ3-H)2(µ5-κ2-ampy)(µ-CO)2(CO)14] with 2-amino-6-methylpyridine (H2ampy) in decane at reflux temperature. Their metal atoms are supported by ligands that derive from the activation of one (complex 2) or both NH bonds (complexes 1 and 2) of the H2ampy amino fragment. Both contain at least one ampy ligand featuring an unprecedented coordination type: the imido N atom caps a triangle of metal atoms while the pyridine nitrogen is attached to an additional metal atom. One of the ampy ligands of cluster 2 also displays another unprecedented coordination type: it caps a distorted square of metal atoms through the imido N atom while the pyridine nitrogen is attached to one of the atoms included in that square.Key words: ruthenium, cluster compounds, amido ligands, imido ligands.
Organogold(I) macrocycles and [2]catenanes containing pyridyl and bipyridyl substituents  Organometallic catenanes as ligands
Authors: Habermehl Nicolle C , Mohr Fabian , Eisler Dana J , Jennings Michael C , Puddephatt Richard J
Published: May 2006

The synthesis of achiral gold(I) macrocycles [RCH(4-C6H4OCH2C≡CAu)2(µ-Ph2PZPPh2)] and the corresponding chiral gold(I) [2]catenanes, bearing substituents R = 2-pyridyl, 4-pyridyl, and 4-(2,2′-bipyridyl), is reported. The gold(I) compounds form by self-assembly on reaction of oligomeric digold(I) diacetylides [{RCH(4-C6H4OCH2C≡CAu)2}n] or the isocyanide complexes [RCH(4-C6H4OCH2C≡CAuC≡N-t-Bu)2] with diphosphine ligands Ph2PZPPh2, Z = CC or (CH2)nwith n = 25, or on reaction of [Au2(O2CCF3)2(µ-Ph2PZPPh2)] with diacetylenes RCH(4-C6H4OCH2C≡CH)2in the presence of a base. The equilibrium between macrocycles and chiral [2]catenanes in solution was established by NMR spectroscopy, while the structures of several [2]catenanes in the solid state were established crystallographically. The coordination of the gold(I) compounds with R = 4-(2,2′-bipyridyl) to platinum(IV), by formation of the corresponding [PtIMe3(bipy)] units, is established, showing that organometallic [2]catenanes can act as ligands.Key words: gold, macrocycle, catenane, platinum.
Syntheses, characterization, and crystal structures of the tetramethylammonium salts of the novel weakly coordinating anions [MeCO2{B(C6F5)3}] and [MeCO2{B(C6F5)3}2]
Authors: Mitu Simona , Baird Michael C
Published: May 2006

The novel compounds [Me4N][MeCO2{B(C6F5)3}] and [Me4N][MeCO2{B(C6F5)3}2] are prepared and characterized spectroscopically and crystallographically. The compounds are salts of the unisolable acids MeCO2H·B(C6F5)3 and MeCO2H·2B(C6F5)3, respectively, which are sufficiently strong that they can protonate isobutene and initiate its carbocationic polymerization. The 1:1 adduct contains a conventional, monodentate acetate ion coordinated to the B(C6F5)3, while the 2:1 adduct contains a bridging acetate ligand.Key words: weakly coordinating anions, carbocationic polymerization, isobutene, polyisobutene.
Ethylene and 1-hexene polymerization using zirconium iminophosphonamide complexes
Authors: Tomaszewski Robert , Vollmerhaus Rainer , Al-Humydi Abdulaziz , Wang Qinyan , Taylor Nicholas J , Collins Scott
Published: May 2006

Ethylene polymerization was studied using a variety of iminophosphonamide (PN2) complexes of zirconium. Bis(PN2) dichloride complexes [Ph2P(NR′)2]2ZrX2 (X = Cl; 1a: R′ = p-tolyl; 1b: R′ = Bn; 1c: R′ = C6F5) or dimethyl complexes (X = Me; 2a: R′ = p-tolyl; 2b: R′ = Bn) and cyclopentadienyl(PN2)zirconium dichloride complexes [η5-C5R′′5][R2P(NR′)2]ZrCl2 (3a: R′ = p-tolyl, R = Ph, R′′ = H; 3b: R′ = SiMe3, R = Et, R′′ = H; 3c: R′ = C6F5, R = Ph, R′′ = H; 3e: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = H; 3f: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = Me) or dimethyl analogs [η5-C5H5][R2P(NR′)2]ZrMe2 (4a: R′ = p-tolyl, R = Ph; 4b: R′ = SiMe3, R = Et) were evaluated under a range of conditions using methylaluminoxane (PMAO) activator. Complexes 1 and 2 behave as precursors to single-site polymerization catalysts under the conditions studied, while complexes 3 or dialkyls 4 show more complex behavior and formation of poly(ethylene) with a bimodal molecular weight distribution. In contrast, activation of dialkyl complexes 4 with [Ph3C][B(C6F5)4] and polymerization in the presence of small amounts of PMAO or TIBAL as scavenger, led to single-site behavior. PMAO reacts with the neutral dialkyls via ligand abstraction to produce a number of P-containing species that may explain the multi-site behavior observed when using this activator. Dialkyls 4 react cleanly with [Ph3C][B(C6F5)4] in haloarene or even dichloromethane solution to furnish the corresponding cationic alkyls 5, which were characterized by multinuclear NMR spectroscopy. Fluxional dinuclear species are formed in the presence of excess dialkyl and these are susceptible to CH activation to form µ-Me,µ-CH2 complexes one of which could be isolated in pure form. The cationic alkyls initiate the polymerization of 1-hexene at room temperature in chlorobenzene solution, but extensive chain transfer occurs and the systems are not living.Key words: single site, early metal olefin polymerization catalysis.
1-Bromoindene  A new synthon for the preparation of (indenyl)Ni(II)(PPh3)Br
Authors: Boucher Sylvain , Zargarian Davit
Published: May 2006

The oxidative addition of the carbonbromine bond in 1-bromoindene to Ni(PPh3)4 gives the complex (indenyl)Ni(PPh3)Br (1) in 95% yield. In contrast, other nickel(0) species such as Ni(PMe3)4 and Ni(COD)2 promote the oxidative coupling of 1-bromoindene to 1,1′-biindene. Complex 1 has been characterized by NMR spectroscopy (1H, 13C, 31P) and single-crystal X-ray structural analysis.Key words: indenyl complexes, oxidative addition, oxidative coupling.
Chiral lithium amides on polymer support  Synthesis and use in deprotonation of ketones
Authors: Majewski Marek , Ulaczyk-Lesanko Agnieszka , Wang Fan
Published: May 2006

A number of chiral secondary amines attached to Merrifield resin or to noncrosslinked (soluble) polystyrene support were synthesized. The corresponding lithium amides, generated from these amines by treatment with BuLi, react with tropinone, a model symmetrical ketone, to give the corresponding enolates enantioselectively (ee up to 75%). The enolates were trapped either as the corresponding aldol adducts by a reaction with benzaldehyde or as ring-opening products in a reaction with a chloroformate.Key words: chiral lithium amides, polymer-supported reagents, deprotonation, enolates, tropinone.
A binuclear bis{bis(dimethylphosphino)methane}disilver(I) complex with weakly bonded hexafluoroacetylacetonato ligands
Authors: Yuan Zheng , Dryden Neil H. , Vittal Jagadese J. , Puddephatt Richard J.
Published: May 2006

The new complex [Ag2(hfac)2(μ-dmpm)2] (hfac = hexafluoroacetylacetonato, dmpm = Me2PCH2PMe2) has been prepared and characterized both spectroscopically and by an X-ray structure determination (orthorhombic, Pbca (No. 61), a = 9.960(2), b = 14.694(3), c = 22.548(3) Å, Z = 4, R = 0.0495, Rw = 0.0532). The data indicate that the hfac− ligands have mostly ionic character and it is suggested that this may be responsible for the low volatility of complexes [Ag(hfac)Ln] compared to [Cu(hfac)Ln]; these complexes are of interest as precursors for chemical vapour deposition of silver.
The interaction of D-penicillamine with aldehydes and ketones: 2-phenyl-5,5-dimethylthiazolidine-4-carboxylic acid
Authors: Bell R.A. , Britten J.F. , Howard-Lock H.E. , Lock C.J.L. , Schmidt M.
Published: May 2006

The reaction of D-penicillamine and benzaldehyde yielded 2-phenyl-5,5-dimethylthiazolidine-4-carboxylic acid. The structure was determined by single crystal X-ray diffraction. Crystals were monoclinic, P21, a = 9.785(2), b = 6.941(1), c = 10.399(2) Å, β = 114.06(3)°, Z = 2. Intensities were measured on a Rigaku AFC6R diffractometer with Cu Kα radiation and 1881 reflections were used to determine the structure. R = 0.076, wR = 0.048. The compound exists as an amino acid in the 2S,4S configuration. The conformation of the thiazolidine ring is determined by intermolecular hydrogen bonding. Bond lengths and angles are normal. 1H and 13C NMR spectra showed that epimerization takes place in d4-CH3OH solution, and the ratio of 2S,4S diastereomer to 2R,4S diastereomer at room temperature is 65:35.
Vinyl ether hydrolysis. XXIX. 1-Methoxy-1,3-butadiene: reaction mechanism and implication for hydrolysis of the mutagen fecapentaene-12
Authors: Chiang Yvonne , Eliason Robert , Guo Gary H.-X. , Kresge A. Jerry
Published: May 2006

The hydrolysis of cis- and trans-1-methoxy-1,3-butadiene in aqueous solution occurs by hydron transfer to the δ-carbon atom with little or no β-hydronation to give crotonaldehyde as essentially the sole aldehyde product. The reaction gives appreciable hydronium-ion isotope effects in the normal direction [Formula: see text] and shows general acid catalysis; five carboxylic acid catalytic coefficients for hydrolysis of the trans isomer give a good Brønsted relation with the exponent α = 0.59. This is taken as evidence that these reactions occur by the conventional mechanism for vinyl ether hydrolysis involving rate-determining hydron transfer to substrate carbon followed by rapid formation and decomposition of a hemiacetal intermediate. Comparison of the reactivity of the present dienyl ethers with that of their monoenyl analog, methyl vinyl ether, shows that introduction of the second double bond decreases reactivity considerably: the hydronium-ion catalytic coefficient is reduced by a factor of 8.3 for the trans isomer and by a factor of 160 for the cis isomer. This reduction supports a hypothesis advanced to explain the occurrence of reaction by a different mechanism recently discovered in the hydrolysis of the strongly mutagenic polyenyl ether, fecapentaene-12.
Oxidation of DL-penicillamine by chromium(VI). Kinetics of formation of the thioester intermediate
Authors: Perez-Benito Joaquin F. , Lamrhari Driss , Arias Conchita
Published: May 2006

The kinetics of formation of the thioester involved as an intermediate in the reaction between chromium(VI) and DL-penicillamine in aqueous media (pH = 1–8) containing different buffers (acetate, citrate, and phosphate) has been studied by monitoring the disappearance of chromium(VI) at 370 nm and application of the initial-rates method. The initial rate is directly proportional to the initial concentrations of both oxidant and reductant, and the rate vs. pH plots show bell-shaped profiles. The reaction is catalyzed by the buffer present in the medium, the catalytic power of each buffer increasing in the order acetate < citrate < phosphate. This is explained in terms of a mechanism involving the formation of a complex between the acidic form of the buffer and HCrO4− previous to the formation of the thioester. Potassium chloride and sodium sulfate do not seem to have important specific effects on the reaction rate, their effect being that of an acceleration of the reaction as the ionic strength increases. On the contrary, the sulfates of magnesium, manganese(II), and zinc (the latter only in the presence of acetate buffer) have specific effects, indicating the probable formation of several complexes. The spectrophotometric detection of the thioester at 430 nm has allowed to confirm some of the conclusions extracted from the measurement of initial rates, and suggests that this intermediate might approach a steady-state behavior in the three buffers at pH > 6.25, and also that a bimolecular reaction with DL-penicillamine might be involved in its destruction.
Indenone synthesis. Improved synthetic protocol and effect of substitution on the intramolecular Friedel–Crafts acylation
Authors: Galatsis Paul , Manwell Jeffrey J. , Blackwell James M.
Published: May 2006

An improved protocol for the construction of substituted indenones is presented. Also the effect of substitution on the intramolecular Friedel–Crafts acylation was noted. Specifically, if there is no substitution at the 2-position of the indenone poor yields of cyclized material were obtained, if at all, while the substitution of a methyl or ethyl group greatly improved the yield of cyclized material. Placement of a large group (e.g., benzyl) resulted in a diminuation of the improved yield. The new synthetic procedure could, in principle, allow for the construction of 2,3-disubstituted indenones. One example of this reaction mode was presented.
A precise analysis of the 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts
Authors: Schaefer Ted , Kunkel Jeremy P. , Schurko Robert W. , Bernard Guy M.
Published: May 2006

The 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane, as a dilute solution in a CS2–C6D12–TMS solvent mixture at 300 K, is analyzed to yield 8 chemical shifts and 22 distinct coupling constants, nJ(H,H), n = 2–6. The coupling constant between H-2 and the para proton indicates, first, that the bisected conformer (phenyl plane perpendicular to the pseudo plane of the dithiane ring) is most stable and, second, that the apparent twofold barrier to rotation about the Csp2—Csp3 bond is 9.6 kJ/mol. The AM1, STO-3G, and STO-3G* computations confirm the twofoldedness of the barrier; the AM1 barrier is 9.4 kJ/mol. The empirical equation, [Formula: see text] reproduces the vicinal coupling constants of the CH2CH2CH2 fragments and implies puckering angles [Formula: see text] of 54°, 61°, and 64°, respectively. It is implied that 3J at [Formula: see text] is larger than at [Formula: see text] This results is discussed in terms of the latest theoretical approach to 3J in the HCCH fragment. The 4J(H,H) signs and magnitudes for the CH2CH2CH2 fragment agree reasonably well with theory. For the CH2SCH fragment, 4J(H,H) values are positive, in contrast to corresponding numbers in the propanic fragment, perhaps the first experimental values for certain rigid orientations about a heteroatom. INDO MO FPT computations on propane, dimethyl ether, and dimethyl sulfide confirm the experimental trend in 4J(H,H). 2J(H,H) and 5J(H,H) values are compared to those in related molecules. The striking differential shifts of the axial and equatorial protons are attributed to differential van der Waals interactions with the 3p lone-pair orbital on sulfur. A comparison of the ring proton chemical shifts with those in phenylcyclohexane and isopropylbenzene implies that C—S bonds are weaker net electron donors by hyperconjugation than are C—C bonds. It is also proposed that the ortho protons are deshielded by intramolecular van der Waals interactions with the 3p orbitals on the sulfur atoms.
Synthesis and characterization of O, O-alkylene dithiophosphate derivatives of dimethyl-and trimethylgermane. Crystal structure of
Authors: Drake John E. , Mislankar Anil G. , Ratnani Raju
Published: May 2006

The O, O-alkylene dithiophosphate derivatives of dimethyl- and trimethylgermane [Formula: see text], [Formula: see text], [Formula: see text],[Formula: see text], [Formula: see text], and Me3Ge[S2POCH2CEt2CH2O] have been prepared in 70–85% yields by reaction of the salts of the appropriate O,O-alkylene dithiophosphoric acid with dichlorodimethyl-and chlorotrimethylgermane. The compounds were characterized by infrared, Raman, and 1H, 13C, and 31P NMR spectroscopy. The crystal structure of [Formula: see text], was determined and it crystallizes as monoclinic in the space group P21/a (No. 14) with the cell parameters a = 12.368(6) Å, b = 6.897(2) Å, c = 17.923(3) Å, β = 99.00(3)°, V = 2450(2) Å3, Z = 4, R = 0.0455, and Rw = 0.0394. The environment about germanium is essentially that of a distorted tetrahedron resulting in a S—Ge—S angle of 89.9(1)° and a C—Ge—C angle of 121.6(5)°. In contrast with analogous non-cyclic diorganodithiophosphatogermanes, the terminal sulfur atoms are oriented towards germanium rather than away from it to give an average [Formula: see text] intramolecular distance of 3.49(3) Å. The spectra are interpreted as indicating that the dithiophosphate groups are linked in identical fashion in all compounds 1–6. The 1H and 13C NMR spectra are of particular interest in that, unlike the spectra reported previously for related species, the substituents on the atoms in both the five- and six-membered rings maintain their non-equivalence in solution.
Stereospecific addition of aryltellurium(IV) trichlorides to 3-methylcyclohexene: the X-ray crystal structure of p-anisyl(trans-2-chloro-trans-3-mnethyl-1-cyclohexyl)tellurium(IV) dichloride
Authors: Borecka Bozena , Cameron T. Stanley , Malik M. Azad , Smith Barry C.
Published: May 2006

Aryltellurium(IV) trichlorides react with 3-methyl-1-cyclohexene to give aryl(trans-2-chloro-trans-3-methyl-1-cyclohexyl)tellurium(IV) dichlorides. The X-ray crystal structure of p-anisyl(trans-2-chloro-trans-3-methyl-1-cyclohexyl)tellurium(IV) dichloride is reported. Single crystals of p-MeOC6H4(trans-2-Cl-trans-3-MeC6H9)TeCl2 are triclinic, space group [Formula: see text] (No. 2) with a = 10.419(2) Å, b = 10.906(3) Å, c = 8.285(3) Å, α = 92.40(3)°, β = 95.85(2)°, γ = 61.71(3)°, V = 824.6 Å3, D(calcd) = 1.761 g cm−1 for Z = 2. The structure was refined to R = 0.0444 (Rw = 0.0458).
Syntheses of 3-(substituted)-2,4,6-triphenylverdazyls
Authors: Katritzky Alan R. , Belyakov Sergei A. , Durst H. Dupont , Xu Ruixin , Dalal Naresh S.
Published: May 2006

Two series of 2,4,6-triphenylverdazyls substituted at the C(3) position of the heterocyclic ring are obtained using new convenient synthetic methodology. Thus, crown ether assisted solid–liquid phase-transfer catalysis promotes the formation of 3-n-alkyl-substituted 2,4,6-triphenylverdazyls in the reactions of 1,3,5-triphenylformazan with n-alkyl bromides. Under PTC conditions, methylation of 3-(4-nitrophenyl)-1,5-diphenylformazan with methyl iodide exclusively gives the corresponding verdazyl radical. 3-Substituted 2,4,6-triphenylverdazyls containing various di(cyclo)alkylamino moieties at the C(3) position of the verdazyl ring are prepared by the reaction of 1,3,5-triphenylformazan with the corresponding 1-[N,N-di(cyclo)alkylaminomethyl]benzotriazoles under the efficient catalysis of barium hydroxide monohydrate. Sonication of this reaction allows the yields of the verdazyls to be substantially increased. A bis-verdazyl N,N-bonded in the C(3) positions was synthesized. All the radicals obtained were characterized by microanalysis, and by UV–visible and ESR spectroscopy.
Photolysis of 3-chloro-3-aryldiazirines in the presence of amines and allyl alcohol
Authors: Liu Michael T. H. , Romashin Yuri N. , Venkatachalam T. K.
Published: May 2006

When photolysis of arylchlorodiazirines is performed in the presence of either alkyl- or allyl-substituted amines, either N-alkyl- or N-allyl-substituted amines result as the sole high-yield (64-93%) products. Photolysis in the presence of phenylallylamine produces a rearranged product in poor yield (11–15%) whereas the reaction of allyl alcohol with arylchlorocarbene gives exclusively diallyl acetals in high yield (70%). The rate constants for these reactions were obtained by laser flash photolysis. Allyl phenyl ether forms a cyclopropanated product when treated with arylchlorocarbene. The different behaviour of these compounds may be attributed to the nucleophilicity at the nitrogen and oxygen centres of these compounds, when the latter are subjected to the substitutions described above. The formation of a cyclopropanated product when allyl phenyl ether is used differs from the reaction of bis (methoxycarbonyl) carbene with allyl ethers, as reported in the literature. The formation of this cyclopropanated product demonstrates the absence of an oxonium ylide intermediate during the reaction.
The photochemistry of 2,3-benzobicyclo[4.2.0]octa-2,4,7-triene
Authors: Asplund Charlotte Lee , Bender Christopher Owen , Dolman Douglas
Published: May 2006

2,3-Benzobicyclo[4.2.0]octa-2,4,7-triene (11) was prepared by Shapiro reaction from 2,3-benzobicyclo[4.2.0]octa-2,7-dien-4-one (10). Triene 11 was found to be thermally and photochemically reactive. Benzocyclooctatetraene (i.e., COT 12) was the unique product formed when solutions of 11 were heated at 150 °C for 5.5 h. The direct irradiation of triene 11 gave benzosemibullvalene (i.e., SB 14, 23%, Φ = 0.069), COT 12 (39%, Φ = 0.11), and naphthalene (8%, Φ = 0.025). Sensitized irradiations of 11 gave SB 14, (54%, Φ = 0.082), COT 12 (2%, Φ = 0.003), and naphthalene (4%, Φ = 0.009). Studies with deuterium-labelled triene (11a) indicated that the formation of SB 14 from the direct irradiation of triene 11 derives from the operation of two reaction pathways, the major one (83%) of which appears to be a Zimmerman di-π-methane rearrangement; the minor pathway involves a 1,2-shift of the C1—C6 bond to C1—C5. By contrast, SB 14 formed from sensitized irradiation appears to be provided uniquely by a Zimmerman di-π-methane rearrangement.
On N-acetylcysteine. Part II. Oxidation of N-acetylcysteine by hydrogen peroxide: kinetic study of the overall process
Authors: Abedinzadeh Zohreh , Arroub Jlil , Gardès-Albert Monique
Published: May 2006

The oxidation kinetics of N-acetylcysteine (RSH) by hydrogen peroxide has been studied at neutral pH at different concentration ratios from 0.2 to 20 (4 × 10−4 mol L−1 ≤ [RSH]0 ≤ 2 × 10−2 mol L−1, 10−4 mol L−1 ≤ [H2O2]0 ≤ 10−2 mol L−1). In all the cases studied, N-acetylcystine (RSSR) is the only oxidized product formed. Our kinetic data have focused on the importance of the concentration ratio to reach the stoichiometric oxidation of N-acetylcysteine by hydrogen peroxide. Indeed non-stoichiometric oxidation of RSH occurs at relatively low concentration ratios (R < 2.5) whereas stoichiometric oxidation is observed when R > 2.5. Moreover, it has been shown that in the first minutes of the reaction there is the formation of a complex between RSH and H2O2, the stoichiometry of the complex being RSH concentration-dependent for a given R (R > 2.5). Reaction mechanisms have been quantitatively established and the k values of each step determined.
Practical synthesis of 4-aryl- and 4-heteroarylazetidin-2-ones: applications in the synthesis of the Taxol® side chain
Authors: Rey Allan W. , Droghini Robert , Douglas James L. , Vemishetti Purushotham , Boettger Susan D. , Racha Saibaba , Dillon John L.
Published: May 2006

A convenient, high-yielding procedure has been developed for the kilogram-scale synthesis of (±)-cis-3-acetoxy-4-phenylazetidin-2-one (3), a β-lactam that has been used in the semi-synthesis of Taxol®. The Staudinger reaction between hydrobenzamide (5) and acetoxyacetyl chloride in the presence of a base provided the α-benzylideneiminotoluene protected β-lactam 8. Without isolation of the intermediate β-lactam, the protecting group was removed under various reductive or hydrolytic conditions. The overall yields were about 80%. The synthesis of other (±)-cis-4-aryl- and 4-heteroarylazetidin-2-ones by this methodology has also been accomplished. These compounds are of value for the synthesis of 3′-Taxol® side-chain analogs and their preparation demonstrates the generality of this approach.
Conformationally induced and conjugatively amplified doubly degenerate uneven sulfuranes
Authors: Innes Elizabeth A. , Csizmadia Imre G. , Rivail Jean-Louis , Loos Michel , Kucsman Árpád
Published: May 2006

Sulfuranes, containing hypervalent or 10 valence electron central sulfur atoms of the type CH3(H)SCl2 (I), H2N(H)SCl2 (II), HO(H)SCl2 (III), (H2N)2SCl2 (IV), and (HO)2SCl2 (V) have been studied by ab initio MO computations. All sulfuranes exhibited pseudo trigonal bipyramide structure as appropriate 5 valence electron pairs. The two chlorine atoms were in apical positions and the other two ligands were in equatorial position. The fifth electron pair was a lone pair, also located in an equatorial position. The lone pair "pushed away" the S—Cl bonds from the ideal axis of the trigonal bipyramide and therefore the ClSCl bond angle was always less than 180°. With the changing conformations of the equatorial groups the axial bond lengths are varied. Even though the compounds had constitutionally identical S—Cl bonds at certain torsional angles of the equatory ligands the two S—Cl bond lengths became unequal. The difference between the two bond lengths was used as a measure of the extent of unevenness of the sulfurane structures. This led to the creation and annihilation of certain critical points on the conformational Potential Energy Surfaces.
Lewis acid catalyzed Diels–Alder reactions of two useful dienyl phosphate esters
Authors: Liu Hsing-Jang , Feng Waiseng Martin , Kim Jeung Bea , Browne Eric N.C.
Published: May 2006

The Lewis acid catalyzed Diels–Alder reactions of dienyl phosphate esters 1 and 2 were examined. 2-Diethylphosphoryloxy-1,3-butadiene (1) was found to react with a variety of α,β-unsaturated carbonyl compounds under Lewis acid catalysis with excellent regioselectivity to give synthetically useful cyclohexene derivatives. The adducts were produced in accordance with the normal rules governing the Diels–Alder addition. In the presence of stannic chloride acyclic α,β-unsaturated ketones such as ethyl vinyl ketone and methyl vinyl ketone reacted rapidly with diene phosphate 1 to give exclusively the para-addition products 8 and 9 in excellent yields. When diene 1 was treated with the complex cyclic enone ester 14 in the presence of ferric chloride the single para-rule adduct 15 was obtained in good yield. The stannic chloride catalyzed Diels–Alder reactions of trans-2-diethylphosphoryloxy-1,3-pentadiene (2) were also studied. Diene phosphate 2 reacted efficiently with a number of acyclic α,β-unsaturated ketones such as methyl vinyl ketone, ethyl vinyl ketone, and trans-3-penten-2-one with complete regio- and stereoselectivity to give single cyclohexene derivatives 38, 39, and 40.
Photophysics of some substituted 3H-indole probe molecules and their charged species
Authors: Belletête Michel , Sarpal Ranjit S. , Durocher Gilles
Published: May 2006

The spectroscopic and photophysical parameters of neutral and cationic species of the following molecules have been discussed: 2-phenyl-3,3-dimethyl-3H-indole (1), 2-[(p-amino)phenyl]-3,3-dimethyl-3H-indole (2), 2-[(p-dimethylamino)phenyl]-3,3-dimethyl-3H-indole (3), 2-[(p-amino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (4), 2-[(p-methylamino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (5), 2-[(p-dimethylamino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole (6). Solvatochromic shifts have been interpreted in terms of the nature of the substituent groups and the state of solute–solvent interactions and complexation. The theoretical radiative decay rate constant [Formula: see text] along with the bandwidth of the absorption profile of the different species involved have been used to discuss the geometrical changes from one species to the other in the ground state. The mirror-image relationship between absorption and fluorescence spectra has proven to be a good tool to discuss any geometrical changes occurring in the excited state. A radiationless torsional mechanism takes place in the excited state relaxation of the various species. The protonation of the ring nitrogen atom generates a highly planar cationic species which retains its conformation in the relaxed excited state. The very effective quenching of the monocation fluorescence is interpreted by the formation of a non-emissive TICT state.
Mixed alkali effect in 0.2[xKNO3 + (1 − x)NaNO3] + 0.8glycerol systems
Authors: Mahiuddin Sekh
Published: May 2006

Density, electrical conductivity, and fluidity of 0.2[xKNO3 + (1 − x)NaNO3] + 0.8glycerol systems were measured as functions of temperature (363.15 to428.15 K) and composition (0.0to 1.0 mole fraction). Densities were linear functions of temperature. The temperature dependence of conductivity and fluidity has been analysed by using the Vogel–Tammann–Fulcher (VTF) equation. Deviation from additivity has been observed in the electrical conductivity, fluidity isotherms to a lesser extent, and in electrical conductivity under isofluidity condition. The onset of the mixed alkali effect (MAE) in the present system has been explained by the anion polarization model.
AM1 calculational and experimental evidence that a β-nitroxyl group significantly enhances the thermodynamic and kinetic acidities of ketones
Authors: Werstiuk Nick Henry , Roy Chandra Deo
Published: May 2006

The kinetics of NaOD-catalysed H/D exchange of 3,3,5,5-tetramethylcyclohexanone (1), 1-hydroxy-4-oxo-2,2,6,6-tetrame-thylpiperidine (2), 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (3), 9-hydroxynorpseudopelletierine (4), and norpseudopelle-tierine-9-oxyl (5) have been studied in 60:40 dioxane–D2O(v/v) at 25.0 °C. The second-order rate constants are 9.20 × 10−3, 6.39 × 10−2, 1.59, 2.20 × 10−2, and 5.67 × 10−1 L mol−1 s−1 for 1, 2, 3, 4, and 5, respectively. Gas-phase enthalpies of ionization (the values are 363.0, 359.4, 352.0, 360.7, and 354.1 kcal mol−1 for 1, 2, 3, 4, and 5, respectively) calculated with AM1 correlate with the relative rates of enolization. Thus replacement of the β-hydroxylamino groups of 2 and 4 with a nitroxyl group produces sizable increases in the kinetic and thermodynamic acidities of the hydrogens α to the carbonyl group.
An intermolecular Diels–Alder approach to (±)-isoacanthodoral
Authors: Liu Hsing-Jang , Ulibarri Gerardo , Nelson Lloyd A. K.
Published: May 2006

The total synthesis of marine sesquiterpenoid isoacanthodoral (3), in racemic form, has been accomplished, using the boron trifluoride catalyzed Diels–Alder reaction of dienone ester 4 and isoprene as the key step.
Micellar catalysis in mixed anionic/cationic surfactant systems
Authors: Favaro Yvette L. , Reinsborough Vincent C.
Published: May 2006

Dye solubility and stopped-flow kinetic studies were conducted in sodium dodecylsulfate/dodecyltrimethylammonium bromide and sodium dodecylsulfate/decyltrimethylammonium bromide micellar solutions with excess anionic surfactant. The enhanced rate in the presence of anionic micelles of the Ni2+(aq)/pyridine-2-azo-p-dimethylaniline (PADA) complexation reaction was used as a probe of the mixed micellar situation. PADA solubilities and the kinetic parameters derived through the Robinson model for micellar catalysis were consistent with a complete incorporation of the cationic surfactant into the sodium dodecylsulfate micelles.
Palladium(0)-catalyzed addition of Me3SnSnMe3 to alkyl 2-alkynoates and N,N-dimethyl-2-alkynamides. Facile preparation of alkyl (Z)- and (E)-2,3-bis(trimethylstannyl)-2-alkenoates and (E)-N,N-dimethyl-2,3-bis(trimethylstannyl)-2-alkenamides
Authors: Piers Edward , Skerlj Renato T.
Published: May 2006

Treatment (tetrahydrofuran (THF), room temperature or reflux) of the alkyl 2-alkynoates 9–26 with (Me3Sn)2 in the presence of a Pd(0) catalyst ((Ph3P)4Pd) provides good to excellent yields of the corresponding alkyl (Z)-2,3-bis(trimethylstannyl)-2-alkenoates 47–64. The latter substances are thermally labile and, as demonstrated by a number of examples, are transformed upon heating (75–95 °C) into the thermodynamically more stable E isomers. The Pd(0)-catalyzed addition of (Me3Sn)2 to N,N-dimethyl-2-alkynamides 44–46 is quite slow and the initially formed products ((Z)-N,N-dimethyl-2,3-bis(trimethylstannyl)-2-alkenamides) rearrange to the corresponding E isomers at room temperature.
Completeness profiles of one-electron basis sets
Authors: Chong Delano P.
Published: May 2006

The completeness profile is used to provide a visual assessment of the quality of one-electron basis sets. The approach is illustrated by examples of a number of basis sets for the carbon atom. New insight is gained regarding the superiority of spin density calculations using Chipman's basis sets. Keywords: One-electron basis sets.
Evidence of a solvent-mediated barrier to radiationless decay in the state of thiophosgene in solution
Authors: Li Jieming , Steer Ronald P.
Published: May 2006

Thiophosgene, Cl2CS, has been excited in the near-uv and the resulting quantum yields of [Formula: see text] fluorescence and of Cl2CS consumption have been measured as a function of solvent composition (perfluoro-n-hexane, n-hexane, CCl4), temperature, and excitation wavelength. In agreement with previous work it is shown that (i) nonradiative processes dominate the decay of the [Formula: see text] state in solution, and (ii) perfluoroalkane solvents act as inert "heat baths". The process by which the [Formula: see text] state is apparently "quenched" by CCl4 and n-hexane has been discovered. The nonradiative process leading to [Formula: see text] decay involves activation and crossing a barrier, the height of which is a function of the nature and composition of the solvent. CCl4 and n-hexane do not quench the excited state, but instead accelerate its rate of relaxation by lowering the barrier between the bound, radiative portion of the surface and a dark, unbound region. There is evidence that CCl4 or n-hexane form clusters around a Cl2CS solute molecule in mixed perfluoroalkane–CCl4 or n-hexane solutions. Barrier crossing leads to photodecomposition via at least two parallel paths, one free radical (Cl + ClCS) and the other likely molecular (Cl2 + CS), the relative contributions of which are a function of excitation wavelength. Keywords: thiophosgene, photochemistry, solvent-mediated barrier crossing.
Crystal chemistry of tetraradial species. Part 7. Lithium tetrakis(1-imidazolyl)-borate solvate, Liiv[Liiv(H2O)(MeOH)]-[B(C3H3N2)4]2•MeOH, a 3-dimensional polymer; with observations on the geometry of imidazole rings
Authors: Knop Osvald , Bakshi Pradip K.
Published: May 2006

The title compound is a 3-dimensional polymer with a completely ordered triclinic structure [Formula: see text] a = 12.380(2) Å, b = 14.434(2) Å, c = 9.683(3) Å, α = 90.36(2)°, β = 105.44(2)°, γ = 90.75(2)°, Z = 2). Every B atom is tetrahedrally coordinated by N(1) atoms of the imidazole rings, every Li(1) atom is tetrahedrally coordinated by N(3) atoms, and every Li(2) atom is coordinated by two N(3) and two oxygen atoms, one from the H2O molecule and one from a MeOH molecule. The imidazole rings connected by the B—N(1) and Li—N(3) bonds thus generate a 3-dimensional covalent polymeric network. The MeOH molecules of coordination are hydrogen-bonded to unengaged N(3) atoms, thereby supplementing the covalent bonding system. The H2O molecules are hydrogen-bonded to the MeOH molecules of solvation to form centrosymmetric [Ow … OMeOH]2 rings, which in turn are connected to the covalent network by OMeOH—H … N(3) bonds to the remaining unengaged N(3) atoms. Every atom in the structure except the H(C) hydrogens is thus involved in the 3-dimensional bond system. The excellent consistency of the bond lengths and endocyclic bond angles [Formula: see text] in the eight imidazole rings of the title compound has provided an opportunity for investigating the effect of substitution on the geometry of the imidazole ring in a sample of 17 substituted imidazoles. While the bond lengths have been found at most weakly correlated, the multilinear correlations of the [Formula: see text] in this sample are highly significant. Among the substituents the NO2, group is the most ipso- [Formula: see text] -expanding and the anionic B (in the title compound) the most ipso- [Formula: see text] -contracting. Protonation or deprotonation at the N atoms affect the ipso C—N—C angles considerably. Limited comparisons are drawn with the results of the classical investigations by Domenicano et al. on the effect of substitution on the geometry of the benzene ring. Keywords: hydrogen bond, imidazole, lithium compounds, polymers, tetrahedral boron ions.
Formation of methyl 2-arylhydrazono-3-oxobutanoates and 2-arylhydrazono-3-oxobutanenitriles during the coupling reaction of arenediazonium ions with methyl 3-aminocrotonate and 3-aminocrotononitrile
Authors: Brown D. Sean , Jollimore Jason V. , Merrin Marcus P. , Vaughan Keith , Hooper Donald L.
Published: May 2006

Reaction of aryldiazonium salts with methyl 3-aminocrotonate (1) affords high yields of the methyl 2-arylhydrazono-3-oxobutanoates (4); analogous diazonium coupling with 3-aminocrotononitrile (2) gives the 2-arylhydrazono-3-oxobutanenitriles (5). The hydrazones are the product of diazonium coupling at the C2-vinylic carbon, concomitant with hydrolysis of the 3-amino substituent to the 3-oxo derivative; there is no evidence for the formation of a triazene (6), which would be the product of N-coupling. All hydrazones (4a–e and 5a–d) have been fully characterized by IR and 1H and 13C NMR spectroscopy; the NMR spectra of the methyl 2-arylhydrazono-3-oxobutanoates (4) suggest the presence of two isomeric intramolecularly H-bonded forms in solution. Selected compounds were further characterized by elemental analysis and mass spectrometry. A mechanism is proposed for the conversion of 1 or 2 into 4 or 5, and these observations are compared with previously reported observations of diazonium coupling reactions with unsaturated systems. Keywords: hydrazone, diazonium, aminocrotonate, aminocrotononitrile, hydrogen bonding.
Antiferromagnetism and metamagnetism in 1,4-diazine and pyridine complexes of nickel(II)
Authors: Otieno Tom , Thompson Robert C.
Published: May 2006

Several nickel(II) complexes containing pyridine (py), pyrazine (pyz) or methylpyrazine (mepyz) have been synthesized and characterized by vibrational and electronic spectroscopy, differential scanning calorimetry, and magnetic susceptibility studies to cryogenic temperatures. A comparison of the magnetic properties of the polymeric diazine-bridged complexes, Ni(pyz)2X2 (X = Cl or NO3), Ni(pyz)(p-CH3C6H4SO3)2, Ni(mepyz)(NO3)2, and Ni(pyz)3(CH3SO3)2•CH3OH with those of the related monometallic systems, Ni(py)4X2 (X = Cl, p-CH3C6H4SO3 or CH3SO3) and Ni(mepyz)4(NO3)2•H2O provides evidence for weak antiferromagnetic coupling between metal centers mediated by bridging diazine ligands in the former group of compounds. The magnetic properties were analyzed employing a model for S = 1 which takes into account zero-field splitting and employs a molecular field term to account for weak magnetic exchange. The compounds Ni(pyz)Cl2 and Ni(py)Cl2 show metamagnetic behaviour with critical fields of 13 and 2 kOe, respectively, at 2 K. In these compounds nickel ions, linked in chains by bridging chlorides, exhibit intrachain ferromagnetic and interchain antiferromagnetic exchange. In Ni(pyz)Cl2 bridging pyrazine ligands are considered to provide the pathway for the antiferromagnetic coupling resulting in a high critical field. Keywords: nickel(II), pyrazine, pyridine, complexes, metamagnetism, antiferromagnetism.