bluuebunny/crossref_metadata_2025 huggingface dataset:
The structures of dioxolan-2-ylium cations; carbon–oxygen bond distances in acetoxonium ions
Authors: Childs Ronald F. , Orgias Richard M. , Lock Colin J.L. , Mahendran Malivaganam
Published: May 2006

The X-ray structures of four dioxolan-2-ylium cations, 2-phenyl-1,3-dioxolan-2-ylium trifluoromethanesulfonate, 6, and 2-(4-methoxyphenyl)-1,3-dioxolan-2-ylium, 7, 2-(2,4-pentadienyl)-1,3-dioxolan-2-ylium, 8, and 2-(4-methoxyphenyl)-4,4-dimethyl-1,3-dioxolan-2-ylium, 9, hexafluoroantimonates, have been determined. Crystals of 6 are monoclinic, C2/c, a = 28.934(5), b = 6.022(2), c = 14.831(3) Å, β = 113.37(1)°, Z = 8; 1944 reflections were used to determine the structure; R = 0.0488, wR = 0.0477. Crystals of 7 are monoclinic, P21/c, a = 11.948(4), b = 10.686(3), c = 10.853(2) Å, β = 106.31(2)°, Z = 4; 2260 reflections were used to determine the structure; R = 0.0551, wR = 0.0807. Crystals of 8 are monoclinic, P21/c, a = 10.549(2), b = 10.457(3), c = 11.702(2) Å, β = 105.69(1)°, Z = 4; 2190 reflections were used to determine the structure; R = 0.0337, wR = 0.0299. Crystals of 9 are orthorhombic, Pmnb, a = 8.297(4), b = 15.269(3), c = 12.638(2) Å, Z = 4; 1736 reflections were used to determine the structure; R = 0.0796, wR = 0.0726. Intensities were measured on Syntex P21, or Nicolet P3 diffractometers at −65 °C with use of Mo Kα radiation. These structures are discussed in terms of the conjugation and charge distribution in these cations. In each case the cations are almost planar with very small twist angles between the plane of the C(2) substituent and that of the dioxolanylium ring. Cation 8 is the first reported example of the structure determination of an acyclic, substituted dienyl carbenium ion. The unsaturated five-carbon chain in 8 has an all-trans conformation about all the C—C bonds, but, apart from the C(2)—C(1′) distance, none of the other bond distances differ significantly from those found in corresponding neutral systems. The C(2)—C(1′) distance in 7 is significantly shorter than that of 6, suggesting enhanced conjugation of the aryl ring with the positive centre in the former cation. This suggestion is supported by the significant quinonoid-type distortion that is observed in the p-methoxyphenyl ring of 7. Systematic variations in the O(1)—C(5)/O(3)—C(4) bond distances are examined and it is shown that alkyl substitution at C(4)/C(5) leads to a large increase in their lengths, suggesting that the presence of a significant fraction of the positive charge is located on C(4) and (or) C(5). Support for this suggestion is found in a large variety of previously reported spectroscopic and calorimetric measurements.
What happens to formamide during C—N bond rotation? Atomic and molecular energetics and molecular reactivity as a function of internal rotation
Authors: Laidig Keith E. , Cameron Lynn M.
Published: May 2006

We investigate the energetics of rotation about the C—N bond in formamide at the molecular and atomic levels using the HF/6-31G**//HF/6-31G** level of theory. At the molecular level, the barrier to rotation results from a decrease in overall attractive energies upon rotation away from the planar conformation, primarily due to the lengthening of the C—N bond. At the atomic level, the barrier is due to the loss in interatomic attraction between the nitrogen and its bonded neighbors. We investigate the susceptibility of formamide to electrophilic attack at nitrogen and oxygen as well as nucleophilic attack at carbonyl carbon as a function of C—N bond rotation using the Laplacian model of reactivity. The model predicts the susceptibility to nucleophilic attack at carbonyl carbon to reach a maximum with a O—C—N—H torsional angle of 60°. As a mimic of solvent fields, we investigate the effect of solvation upon these predictions with the application of homogeneous electric fields. This geometry–reactivity relationship is related to proposed models of activation in the enzymatic catalysis of peptides.
Synthesis of diaminodideoxyalditol analogs of cisplatin as antitumor agents
Authors: Hanessian S. , Gauthier J.-Y. , Okamoto K. , Beauchamp A.L. , Theophanides T.
Published: May 2006

Acyclic vicinal polyol complexes related to cisplatin were synthesized from D-mannitol by stereocontrolled manipulation of the hydroxy groups. Controlled cleavage of a 3,4-diazido hexitol gave the corresponding D-threitol and D-xylitol analogs, which were converted to their diamino platinum complexes. The antitumor activity of these compounds is reported.
Structural studies of organoboron compounds LVIII. 4-(1′-azoniabicyclo[2.2.2]-octanyl)-2,2-diphenyl-2-borata-1,3-dioxa-1,2,3,4-tetrahydronaphthalene
Authors: Kliegel Wolfgang , Drückler Klaus , Rettig Steven J. , Trotter James
Published: May 2006

Two synthetic routes leading to 4-(1′-azoniabicyclo[2.2.2]octanyl)-2,2-diphenyl-2-borata-1,3-dioxa-1,2,3,4-tetrahydronaphthalene, 5, are described. Crystals of the product are orthorhombic, a = 18.099(2), b = 9.729(2), c = 12.113(2) Å, Z = 4, space group Pca21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.034 and Rw = 0.037 for 1421 reflections with I > 3σ(F2). Compound 5 represents the first structurally characterized crystalline adduct of a trialkylamine to a carbonyl compound in which the newly formed C—N bond is acyclic. The adduct is stabilized by the neighboring Lewis acid diphenylboryloxyaryl moiety. Bond distances involving the boron atom ((aryl)O—B = 1.515(4), (alkyl)O—B = 1.508(4), and C(phenyl)—B = 1.613(5) and 1.623(5) Å) represent relatively strong overall binding of the O,O-chelating ligand to the diphenylboron moiety.
The volumetric and thermochemical properties of L-ascorbic acid in water at 288.15, 298.15, and 308.15 K
Authors: Hakin Andrew W. , Mudrack Susan A. M. , Beswick Colin L.
Published: May 2006

Measurements have been made at 288.15, 298.15, and 308.15 K with a flow microcalorimeter and densimeter to obtain heat capacities and densities for L-ascorbic acid and sodium chloride in water. These data are reported in terms of apparent molar volumes [Formula: see text] and apparent molar heat capacities [Formula: see text] The volume of ionization (ΔV0) and heat capacity of ionization (ΔCP0) for the acid at 298.15 K have been calculated using a method that does not require volumetric and thermochemical data for the sodium salts of the acid. Details of our methodology are presented.
Pattern recognition for screening of crude oils using multivariate circular profiles
Authors: Lai Edward P.C. , Giroux Régi D. , Chen Nailin , Guo Runde
Published: May 2006

An appropriate pattern recognition method has been designed to visually discriminate between crude oils belonging to different geographic origins. Each oil is represented by a circular profile that consists of parameter axes that radiate from the centre like spokes on a wheel. One objective of this approach is to provide an optimum set of axes that will best differentiate one circular profile from another. Several parameters were considered for evaluating the oils: photo-acoustic spectroscopy (PAS), carbon-13 nuclear magnetic resonance (13C NMR, for %CA = aromatic carbon content), high-performance liquid chromatography (HPLC, for unsaturated, aromatic, and polar compounds), initial boiling point (IBP), American Petroleum Institute (API) gravity, and ultraviolet–visible spectrophotometry (for λmax = maximum absorption wavelength and εmax = maximum molar absorptivity). By computerized statistical evaluation, the selected parameters are PAS and HPLC for unsaturated, aromatic, and polar compounds.
Synthesis and characterization of 2,2-diphenyl-1-(5-acetonyl-2,4,6-trinitro-1,3-cyclohexadienyl)hydrazine, C21H19N5O7
Authors: Draper Donna L. , Barton Richard J. , Robertson Beverly E. , Nelson Barbara R. , Weil John A.
Published: May 2006

The reaction of 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazine with the enolate of acetone, followed by acidification, yields the title compound 2,2-diphenyl-1-(5-acetonyl-2,4,6-trinitro-1,3-cyclohexadienyl)hydrazine, C21H19N5O7. The identity of the latter was confirmed by a combination of mass spectrometry, FTIR, elemental analysis, and 1H NMR. Crystals were grown from dichloromethane –95% ethanol and the structure was determined by X-ray diffraction. Crystals are monoclinic, P21/c, a = 9.254(3), b = 13.531(3), c = 17.39(5) Å, β = 106.18(2)° at 225 K. R = 0.073, Rω = 0.038 for reflections with I > 2σ(I). The Zachariasen extinction factor, g, refined to 18(3) × 10−4. The cyclohexadiene ring is puckered with a primarily twist-boat conformation. Atoms C(1) to C(3), C(6), the nitro group on C(2), and the hydrazine moiety (N(8)—N(7)—H(7) attached to C(1)) all lie close to a common plane. The planes of the two phenyl rings, the acetonyl substituent, and the C(6) nitro group are each roughly perpendicular to this plane. The C(5) acetonyl and C(6) nitro groups are trans to each other.
A comprehensive thermodynamic investigation of water–ethanolamine mixtures at 10, 25, and 40 °C
Authors: Pagé Monique , Huot Jean-Yves , Jolicoeur Carmel
Published: May 2006

The density, isobaric specific heat capacity, and isentropic compressibility of water–ethanolamine (W–EA) mixtures have been measured at three temperatures (10, 25, and 40 °C) over the entire composition range. The results were used to calculate various thermodynamic excess functions of these mixtures, namely: the excess molar volume [Formula: see text] excess molar isentropic and isothermal compressibilities [Formula: see text] excess molar isobaric and isochoric heat capacities [Formula: see text] and excess molar isobaric expansion [Formula: see text] The corresponding partial molar quantities for ethanolamine in the mixtures were also computed. These excess and partial molar quantities were compared with those observed earlier in the water – ethylene glycol (W–EG) (1) and in the water–2-methoxyethanol (W–ME) (2) mixtures. The similarities and differences in the properties of these systems are interpreted on the basis of the specific molecular features of the cosolvents and the concepts of cooperative fluctuations and hydrogen-bonding connectivity in liquid water and dilute aqueous solutions.
13C magnetic resonance studies. 144. An examination of β-enolization in the bicyclo[3.3.1]- and [3.2.2]nonan-2-one system
Authors: Muir David J. , Stothers J.B.
Published: May 2006

While 3,3-dimethylbicyclo[3.3.1]nonan-2-one (5) is stable under strongly basic conditions (t-BuO−/t-BuOH/185 °C), its isomer, 3,3-dimethylbicyclo[3.2.2]nonan-2-one (6), is slowly transformed to 5. Similarly, 3,3-dimethylbicyclo-[3.2.2]non-6-en-2-one (8b) rearranges to a [3.3.1] isomer but the latter is not stable. Experiments with 3,3-dimethylbicyclo[3.3.1]non-6-en-2-one (7) revealed that it is converted to five compounds, none of which is 8b. The major product, 8,8-dimethylbicyclo[4.3.0]non-1(6),-en-7-one (11) arises from β-enolate rearrangement. Enone 11 undergoes slow reduction to cis- and trans-8,8-dimethylbicyclo[4.3.0]nonan-7-one, presumably by single electron transfer. Experiments with 11 alone showed that β-enolate rearrangement of 7 → 11 is unidirectional. Haller–Bauer cleavage to acidic products occurs as a minor process in the reactions of the unsaturated ketones. The structures of the products were established primarily from their 1H and 13C magnetic resonance spectra.
Stereocontrolled construction of 1,7-dimethyl A.B.C.[6.6.6] tricycles. Part I. Transannular Diels–Alder reactions of 14-membered macrocycles containing trans-dienophiles
Authors: Xu Yao-Chang , Roughton Andrew L. , Plante Raymond , Goldstein Solo , Deslongchamps Pierre
Published: May 2006

Transannular Diels–Alder reactions of 14-membered macrocyclic trienes possessing a methyl substituent on both the diene and dienophile moiety have been investigated. Macrocyclic structures 1a, 1b, and 1c having cis-trans-trans (CTT), trans-cis-trans (TCT), and trans-trans-trans (TTT) geometries could be stereoselectively constructed by coupling appropriately functionalized dienes 5 and dienophile 4 following an intramolecular displacement of an allylic halide by the anion of an appropriately located dimethyl malonate unit. The transannular Diels–Alder reaction performed on 1a led to a mixture of four major tricyclic products, including 34 possessing the unexpected trans-anti-cis (TAC) stereochemistry. When heated at 300 °C, macrocycle 1b underwent an unique conversion via an ene–retroene, Diels–Alder process, producing the unexpected tricycle 41 (racemic form) containing five contiguous chiral centers. A rationale for the above experimental facts is presented. In contrast to the previous results, the transannular Diels–Alder reaction of macrocycle 1c was straightforward, producing a 95% isolated yield of trans-anti-cis (TAC) tricycle 34. This investigation demonstrates a general methodology for the stereocontrolled synthesis of 1,2-dimethyl A.B.C[6.6.6] tricyclic compounds, which are potential precursors to polycyclic natural products such as steroids and terpenes.
Phthalocyanine-modified silica gels and their application in the purification of unsymmetrical phthalocyanines
Authors: Leznoff Clifford C. , McArthur Colin R. , Qin Yongnian
Published: May 2006

Five species of phthalocyanine-modified silica gels were prepared. The loadings of phthalocyanine on these silica gels were determined by acidic hydrolysis. The concept of using the aggregation phenomenon to advantage to aid chromatographic separation of unsymmetrical phthalocyanines was investigated by employing these modified silica gels as chromatographic media to purify unsymmetrical phthalocyanines. Four groups of phthalocyanine mixtures were prepared by mixed condensation. One of the desired unsymmetrical phthalocyanines was successfully purified by conventional column chromatography while others were separated by the new method described herein.
Predicting thermodynamic stability of diatomic dications: a case study of BeF2+
Authors: Kolbuszewski Marcin , Wright James S.
Published: May 2006

General criteria are discussed for the prediction of thermodynamically stable diatomic dications (i.e., cations of + 2 charge). For a diatomic AB2+, the most useful quantity for this purpose is Δ, the difference in energy between the attractive channel with asymptote A + B2+ and the repulsive channel with asymptote A+ and B+. Excluding noble gas compounds and using this measure, diatomic dications that may be thermodynamically stable include BeF2+, MgO2+, MgF2+, MgCl2+, and SiF2+, as well as several other less likely combinations. The dication BeF2+ was selected for further analysis. Ab initio calculations show that the X2Π state of this ion is thermodynamically stable by 1.08 eV and undergoes an avoided crossing that causes the effective dissociation energy to be 2.07 eV. The excited state A2∑+ is also very low-lying and predicted to be long-lived. The X2Π–A2∑+ band system is electric dipole allowed but very weak in intensity. Possible mechanisms of formation of BeF2+ are discussed.
Rotational analyses of bands of the system of cis-glyoxal
Authors: Dong R.Y. , Nanes R. , Ramsay D.A.
Published: May 2006

Rotational analyses have been carried out for the 510, 501, and 511 bands of the [Formula: see text] system of cis-glyoxal, where ν5 is the totally symmetric C—C=O bending frequency. The vibrational frequencies [Formula: see text] and [Formula: see text] are smaller than the corresponding frequencies for trans-glyoxal by nearly a factor of two. A vibronically induced band with a different type of rotational structure has been analysed and shown to be an a-type band. The coupling vibration is the out-of-plane C—H wagging vibration ν6(a2) and is similar in form and frequency to the vibronically active ν8(bg) vibration for trans-glyoxal.
Raman and infrared spectra, conformational stability, vibrational assignment, and ab initio calculations of cis-1,3-dichloropropene
Authors: Durig J.R. , Costner T.G. , Little T.S.
Published: May 2006

The Raman (3200−10 cm−1) and infrared (3200−20 cm−1) spectra of gaseous and solid cis-1,3-dichloropropene, cis-ClHC=CHCH2Cl, have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization data has also been obtained. These spectral data have been interpreted on the basis that the molecule exists predominantly in the gauche (allylic chlorine atom oriented gauche to the double bond) conformation in all physical phases. Some bands in the infrared spectrum of the gas could be due to a second higher energy conformer but the lack of corresponding Raman bands casts doubt on such an assignment. Ab initio Hartree–Fock gradient calculations employing the RHF/6-31G* basis set are consistent with two minima that correspond to the two equivalent gauche forms for the potential surface for the internal rotation about the C—C bond. These minima occur at dihedral angles, [Formula: see text] ClCCC, of 122° and 238° (0° corresponds to the syn conformation) and the gauche to gauche barrier at the 180° transition state, which corresponds to the anti structure, is 342 cm−1. The barrier from the gauche minima to the syn (0°) structure, which is also a transition state, is 2425 cm−1. Complete equilibrium geometries for the gauche structure have been determined with the RHF/3-21G*, RHF/6-31G*, and MP2/6-31G* basis sets. A normal coordinate analysis utilizing a harmonic force field calculation with the RHF/3-21G* basis set has been carried out for the gauche conformer. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.
Lignes monovariantes de l'isotherme 75 °C du système quaternaire réciproque: H3PO4–K2SO4–H2SO4–K3PO4–H2O
Authors: Bourguiba Néji , Jouini Tahar
Published: May 2006

The boundary curves and quaternary invariant points of the reciprocal system H3PO4–K2SO4–H2SO4–K3PO4–H2O were investigated at 75 °C and 1 atm by chemical analysis of solutions in equilibria, respectively, with two or three salts. Eleven compounds occur in this system. Only eight of them have crystallization areas inside Janecke's prism; these are K2SO4, K2SO4•KHSO4, K2SO4•7KHSO4•H2O, KHSO4, KH2PO4•KHSO4, KH5(PO4)2, KH2PO4, and a solid solution K8(H2PO4)1+x(HSO4)7−x, 0 ≤ x ≤ 1, of substitution type continuous between the two limiting compositions KH2PO4•7KHSO4 and KH2PO4•3KHSO4. The crystallization fields of 3K2HPO4•KH2PO4•2H2O, K2HPO4, and K3PO4•3H2O are very close to the solubility curves of the ternary system K3PO4–H3PO4–H2O. Results are explained and discussed.
Studies on the BAL2 mechanism for ester hydrolysis
Authors: Douglas Judy E. , Campbell Grant , Wigfield Donald C.
Published: May 2006

The preparation and alkaline hydrolysis of 18O-methyl 2,2-dimethylpropanoate and 18O-methyl triphenylacetate are reported. From mass spectral analysis of the carboxylic acid products, it is concluded that the former substrate is hydrolyzed exclusively by the BAC2 mechanism, whereas the latter substrate proceeds 95% by the BAC2 mechanism and 5% by the BAL2 mechanism. The balance between these two mechanisms is discussed.
Benzo-9-crown-3 ether: X-ray crystal structure, NMR studies in solution and the solid phase, and ab initio calculations of isotropic 13C chemical shifts using LORG with a D95V basis set
Authors: Buchanan G.W. , Driega A.B. , Moghimi A. , Bensimon C. , Kirby R.A. , Bouman T.D.
Published: May 2006

Using the X-ray crystal geometry as input, the 13C NMR chemical shifts of benzo-9-crown-3 ether have been calculated via ab initio methods using a localized orbital local origin (LORG) approach. Reasonable agreement is found between the calculated values for an isolated molecule in the gas phase and those obtained in the 13C CPMAS NMR spectrum. Solid phase 13C spectra of the C7,10-d4 derivative confirm the existence of a 7.9 ppm shift difference between these sites in the solid, whereas in solution they are conformationally averaged to one resonance. The effects of C—H bond length variation on calculated 13C shifts have been explored.
Global and internal molecular dynamics of poly(acrylamide-co-allyl 2-acetamido-2-deoxy-D-glucopyranoside) glycopolymers from 13C NMR relaxation studies
Authors: Roy René , Tropper François D. , Williams Antony J. , Brisson Jean-Robert
Published: May 2006

13C spin-lattice and spin–spin relaxation times and nuclear Overhauser enhancements have been used to examine the molecular dynamics of the α- (1) and β- (2) anomeric forms of poly(acrylamide-co-allyl 2-acetamido-2-deoxy-D-glucopyranoside) glycopolymers. The timescale of motions and the spatial restriction of these motions were determined by using various forms of the "model-free" approach. It is shown that the motions of the C—H vectors of the polymer backbone may be described by a scaled Lorentzian spectral density function, giving rise to an effective correlation time for overall tumbling. The temperature dependence of this correlation time suggests that the overall motion is dependent on viscosity. The overall motion of the polymer molecules is shown to be anisotropic in nature by including the spin–spin relaxation data in the analysis. The N-acetyl methyl and sugar hydroxymethyl (C6) groups exhibit internal motions. The activation energies associated with these internal motions are derived. The difference in relaxation rates between the α and β anomeric forms, though small, suggests that the motions of the sugar ring may be different for the two systems. This conclusion is supported by potential energy contour map calculations, which indicate that the β anomer (2) has almost twice the conformational flexibility of the α anomer (1).
Activity coefficients and standard Gibbs free energies of transfer of NaCl and KCl from water to aqueous solution of 2-butoxyethanol by EMF studies
Authors: MacPherson Yvonne , Palepu R.
Published: May 2006

From the emf measurements of the cell Na- or K-glass electrode|2-butoxyethanol, H2O, NaCl or KCl|Cl ion-selective electrode, the standard potentials were determined at 298 K for five different compositions of the solvent. From the emf data the mean activity coefficients of NaCl and KCl were calculated and fitted to an empirical equation. The standard Gibbs free energies of transfer of NaCl and KCl from water to mixtures of water and 2-butoxyethanol were calculated from the cell potential.
Substituent effects on azo coupling of indoles
Authors: Albar Hassan A. , Shawali Ahmad S. , Abdaliah Magda A.
Published: May 2006

The kinetics of the azo coupling of eight para-substituted benzenediazonium tetrafluoroborates 2a–h with indole and its 1-, 2-,and 3-methyl derivatives 1a–d, respectively, were studied in acetonitrile at 25 °C under pseudo-first-order conditions. The relation k1(obs) = k2[diazonium salt] was found applicable in all cases. The logarithms of the rate constants k2 for each reaction series were correlated by the Hammett equation. A plot of the values of the reaction constant, ρ, obtained against the acidity constants pKa of 1a–d gave a straight line: ρ = 2.97 – 0.15 pKa. These results indicate that the azo-coupling reactions of indoles 1a–d follow one general mechanism involving rate-limiting initial electrophilic attack at the 3-position for all four compounds, contrary to the previous conclusion of Jackson and Lynch that the final deprotonation step is rate limiting.
Synthesis, conformational analysis, and molecular structure of 5-ethyl-5,6-dihydro-11H-dibenzo[b,e]azepine-6-thione
Authors: Irurre J. , Marquillas F. , Alvarez-Larena A. , Piniella J.F.
Published: May 2006

5-Ethyl-5,6-dihydro-11H-dibenzo[b,e]azepine-6-thione has been synthesized and studied in the solid state and in solution by X-ray diffraction and 1H DNMR, respectively. The crystals are monoclinic, P21/n, a = 9.642(1), b = 13.757(2), c = 9.889((2) Å, β = 98.57(1)°, Z = 4. The structure has been solved by direct methods and refined to an R value of 0.040 for 1771 reflections with I > 2.5σ(I). The seven-membered ring has a slightly deformed boat conformation. The activation barrier associated with the inversion ring has been determined, being ΔG≠ = 21.6 kcal/mol.
Temperature dependence of the volumetric properties of binary mixtures containing oxaalkane + c-hexane
Authors: Peleteiro José , Tovar Clara A. , Carballo Enrique , Legido José L. , Romaní Luis
Published: May 2006

Excess molar volumes of mixtures of 2,5-dioxahexane + c-hexane, 2,5,8-trioxanonane + c-hexane, 2,5,8,11-tetraoxadodecane + c-hexane, and 2,5,8,11,14-pentaoxapentadecane + c-hexane were determined from density measurements at 283.15, 288.15, 298.15, and 308.15 K. These results allowed the following mixing quantities to be reported in the range of concentration: α, (δVE/δT)P, and (δHE/δP)T, at 298.15 K. The values obtained were then compared with the values calculated by using the Flory theory and the Nitta–Chao theory of liquid mixtures.
The vibrational dependence of the dipole moment of hydrogen fluoride
Authors: Barnes J.A. , Gough T.E. , Stoer M.
Published: May 2006

Molecular beam laser Stark spectroscopy has been used to measure the υ = 3 vibrational state dipole moment of hydrogen fluoride as 1.9614 ± 0.0021 debye. This measurement allows μυ to be expressed as a power series expansion in [Formula: see text] without the use of infrared intensity data. A detailed comparison is made with similar series based mainly on infrared intensity data and more recent ab initio calculations.
The role of molecular flexibility in accelerating intramolecular vibrational relaxation
Authors: Bethardy G.A. , Wang Xiaouang , Perry David S.
Published: May 2006

Evidence is presented to show that intramolecular vibrational relaxation (IVR) is faster in flexible molecules when the initially prepared vibration is close to the bond about which the large-amplitude motion occurs. In each of 1-pentyne, ethanol, and propargyl alcohol, IVR lifetimes are known for two different hydride stretches and in each molecule internal rotation connects gauche and trans conformers. In each case the vibration that is closer to the center of flexibility shows faster relaxation. This trend is supported by the available IVR lifetimes for other flexible molecules (hydrogen peroxide, 1-butene, n-butane, methyl formate, and propargyl amine) and for some "rigid" molecules (1-butyne, isobutane, propyne, trans-2-butene, and tert-butylacetylene). The lifetimes for the halogenated molecules, 2-fluoroethanol, 1,2-difluoroethane, trans-1-chloro-2-fluoroethane, and trifluoropropyne are all in the range expected for rigid molecules. An algorithm is presented for the consistent calculation of IVR lifetimes from discrete frequency-resolved spectra, which range from the sparse through intermediate coupling cases. Wherever possible, the reported lifetimes have been calculated (or recalculated) from the original line positions and intensities. The lifetimes may be compared directly to those deduced from homogeneously broadened spectral features with a Lorentzian contour.
Molecular beam kinetics: reactions of H and D atoms with alkali halides
Authors: Siska P.E. , Herschbach D.R.
Published: May 2006

Angular distributions of alkali atoms produced in crossed-beam reactions of H and D atoms (at ∼2800 K) with KF, CsF, KCl, CsCl, and KBr (at ∼ 1100–1200 K) have been measured. For these systems, the reaction exoergicity varies from ΔD0 ∼ 17 kcal/mol for H + KF to −4 kcal/mol for H + KBr; the thermal distribution of the reactant energy peaks near 12 kcal/mol with E ∼ 9 kcal/mol in relative translation and W ∼ 3 kcal/mol in vibration and rotation of the alkali halide. Kinematic analysis of the data is carried out by means of a least-squares procedure that includes averaging over the parent beam velocity distributions. The main results are (1) The reaction cross sections Qr vary from ∼1 to 30 Å2. The magnitude correlates with ΔD0 and with the identity of the halogen for a given alkali, decreasing as F → Cl → Br. For a given halogen, Qr is 2–3 times larger for the Cs reaction than for K and about 2 times larger for D than for H. (2) Temperature-dependence measurements for the CsCl case indicate the activation energy (in excess of endoergicity) is near zero. (3) The preferred direction of the reactively scattered alkali atoms with respect to the incident alkali halide varies with the halogen, from mainly forward for the KBr reaction to more sideways for the KF and CsF reactions. (4) The partitioning of energy between product translation E′ (M relative to HX) and internal excitation W′ (vibration and rotation of HX) can only be roughly estimated; our data are consistent with E′ ∼ W and W′ ∼ E + ΔD0 but a definitive analysis will require product velocity distributions or spectra. These results are discussed in terms of a dynamical model akin to Polanyi's DIPR model. This postulates that the motion of H or D is approximately separable from that of the heavier atoms and the preferred reaction geometry corresponds to a triangular H–X–M complex.
The meaning of "adiabatic"
Authors: Laidler Keith J.
Published: May 2006

In chemical kinetics the word "adiabatic" has come to refer to a process in which there is no change of quantum state, a meaning that has no connection with the thermodynamic meaning or with the etymology of the word. This usage is traced to early discussions of reversible adiabatic processes in classical and quantum mechanics, processes that came to be referred to simply as adiabatic.
Controlled variation of boundary-activated ion fragmentation processes in a quadrupole ion trap
Authors: March Raymond E. , Weir Mark R. , Londry Frank A. , Catinella Silvia , Traldi Pietro , Stone John A. , Jacobs W. Bradley
Published: May 2006

Fragmentation in a quadrupole ion trap of each of two isomeric molecular ions, obtained from 4-nitro-o-xylene and 4-nitro-m-xylene, has been investigated. It is demonstrated that the degree of fragmentation may be controlled by prolongation of both the duration for which the working point of the mass-selected species is held in the vicinity of a stability boundary and a prior collisional cooling period. The extent of fragmentation has been found to increase as the working point is held near the βz = 0 stability boundary while the relative abundances of fragment ions can be varied with the duration of the collisional cooling period. Under appropriate conditions for 4-nitro-o-xylene, >94% of the isolated ions can be fragmented; <5% of the ions are lost from the ion trap while 1% remain intact. As 99% of the charge of the fragmented ions is retained in the ion trap, the overall optimum efficiency of boundary-activated dissociation is >93%; the corresponding efficiency for 4-nitro-m-xylene is 74%. 50% of the selected ions can be fragmented in ≤3 ms. The results are compared with collision-activated dissociation studies carried out with a triple stage quadrupole–hexapole–quadrupole instrument. This technique of boundary-activated dissociation provides a general procedure which does not require careful tuning of the instrument as is required for the more commonly-used technique of resonance excitation.
1993 Syntex Award Lecture Photomedicine and photodynamic therapy
Authors: Dolphin David
Published: May 2006

Photodynamic therapy (PDT) involves the treatment of diseased tissue and cells using a photosensitizer and visible light. Such photomedical treatments have been known since the time of the ancient Egyptians but it was only just this year that this therapeutic modality was made available to modern medicine with the approval, in Canada, of Photofrin® for the treatment of bladder cancer. This paper reviews PDT with an emphasis on drug development, particulary for the second generation drugs, especially BPDMA (benzoporphyrin derivative-mono acid), which is now in human clinical trials.
Synthesis of the stereoisomers of a novel antibacterial agent and interpretation of their relative activities in terms of a theoretical model of the penicillin receptor
Authors: Wolfe Saul , Zhang Caijun , Johnston Blair D. , Kim Chan-Kyung
Published: May 2006

2,2-Dimethyl-3-(2′-hydroxypropyl)-5-carboxy-Δ3 -1,4-thiazine (1) is a designed antibacterial agent. Based on an analysis of how penicillin complexes to and reacts with a model of a penicillin-binding protein, 1 contains a functional group (C=N) that can react with a serine hydroxyl group of the receptor according to the putative reaction Enz-OH + C = N → Enz-O-C-NH. Compound 1 also contains additional substituents that are designed to position the O-H and C=N groups relative to one another in the enzyme–substrate complex in a geometry that attempts to reproduce the optimum geometry of approach of two such reactants. A most important assumption is that this optimum geometry can be computed ab initio. In a first preparation of 1, (±)-5-methyl-4-hexene-2-ol (2) was converted to the lithium salt of (±)-2-mercapto-2-methyl-5-tert-butyldimethylsiloxy-3- hexanone (7), which was condensed with the N-tert-butoxycarbonyl-D- and L-serine-β-lactones (3). The synthesis was completed by deprotection with formic acid and cyclization in water. The R and S enantiomers of 2 have now been obtained, and the absolute configuration of the alcohol established, by reaction of the R- and S-propylene oxides with an organometallic reagent prepared from β,β-dimethylvinyl bromide. The R alcohol has also been secured by lipase-catalyzed transesterification with trifluoroethyl butyrate, and chemical hydrolysis of the trifluoroethyl ester. The R and S enantiomers of 2 were converted to the R and S enantiomers of 7, and these were condensed with the R and S enantiomers of 3 to yield each of the stereoisomers of the chemically unstable 1 in ca. 95% optically pure form. Antibacterial activity resides in the 5S,8R and 5S,8S isomers. These findings are shown to be consistent with the theoretical model. It is hoped that the stability of the lead structure 1 can be improved, to allow binding experiments with penicillin recognizing enzymes to proceed.
Partial molar volumes of some drugs in water and ethanol at 35 °C
Authors: Iqbal M. , Jamal M. Asghar , Ahmed Maqsood , Ahmed Bashir
Published: May 2006

Partial molar volumes, V0, of six drugs, mostly anaesthetics, viz., cinchocaine HCl, lidocaine HCl, mepivacaine HCl, procaine HCl, propranolol HCl, tetracaine HCl, in water and ethanol, calculated from precision densities obtained at 35 °C from a vibrating tube densitometer, are reported in this work. The data represent the smaller volumes of drug molecules in ethanol than in water. Volume contribution of hydrochloride part were calculated and excluded from V0 to assess the volume of free base component of the solutes. Volumes of free bases were also found smaller in ethanol, although much closer to those in water. The differences in volumes are interpreted as due to hydrophobicity of solutes. Relative hydrophobicities were estimated from volumes of transfer from aqueous to organic media. Correlation of V0 with van der Waal volumes are also reported. The hydrophobicity of these compounds is proposed to play a key role in the resulting drug action. Possible mechanism of drug binding with the membrane structure is also discussed.
Rate constant and activation energy determination for reaction of e−(aq) and •OH with 2-butanone and propanal
Authors: Mezyk Stephen P.
Published: May 2006

The techniques of pulse radiolysis and absorption spectroscopy have been used to determine kinetic parameters for e−(aq) and •OH reaction with 2-butanone and propanal. The temperature dependent rate constants for hydrated electron reaction are given by ln k(T) = (28.96 ± 0.06) − (1970 ± 20)/T' (2-butanone, 275–343 K), and ln k(T) = (29.2 ± 0.2) − (2160 ± 50)/T (propanal, 275–310 K), where the given uncertainties are 1σ and only represent precision, and the rate constants are in units of M−1 s−1. For hydroxyl radical reaction over the same temperature ranges. ln k(T) = 25.32 ± 0.02) − (1460 ± 40)/T (2-butanone) and ln k(T) = (32.73 ± 0.03) − (3310 ± 100)/T (propanal).
Protonation/deprotonation energetics of uracil, thymine, and cytosine in water from e.m.f./spectrophotometric measurements
Authors: Ganguly Sonali , Kundu Kiron K.
Published: May 2006

The protonation/deprotonation constants for uracil (U) (pK1 and pK2), thymine (T) (pK1) and cytosine (C) (pK1 and pK2) in water have been determined from emf measurements of Harned–Ehler type cells comprising H2 and Ag–AgI electrodes at five equidistant temperatures ranging from 15–35 °C. The pKa values were fitted in the temperature equation pKa = AT−1 + B + CT by the method of least squares and the standard free energies (ΔG0), entropies (ΔS0), and enthalpies (ΔH0) of protonation/deprotonation processes in water were evaluated using the values of the coefficients A, B, and C of the respective acids. The second step deprotonation constant for T was determined using precise spectrophotometric method. The results have been duly compared with the existing literature data and are also shown to derive important reflections on the sites of protonation/deprotonation in the light of pK values of some acids and bases of comparable functional groups and especially the entropies of protonation/deprotonation of the key DNA–RNA base molecules.
Facial selective Diels–Alder reactions of (1R,5R)-(+)-3-carbomethoxy-6,6-dimethylbicyclo[3.1.1]hept-3-en2-one. Unusual ketalization–fragmentation reaction of adducts
Authors: Liu Hsing-Jang , Chew Sew Yeu , Browne Eric N. C. , Kim Jeung Bea
Published: May 2006

The stereofacially differentiated enone ester 5 has been used to study the effects of steric influence on the Diels–Alder reaction. In general, under Lewis acid catalysis, 5 adds to dienes at low to ambient temperatures in a reasonable rate. Yields of predictable chiral adducts are moderate with the unexpected exception of zinc chloride catalyzed reactions, which provide good to high yields. In all cases only products of addition to the Si face of general type 21 were observed. The regiochemistry of the adducts is exclusively that predicted by the ortho and para rules. The stereochemistry shows a high selectivity in favor of ester-endo transition state products. Rationales for the observed stereoselectivities are discussed. The fragmentation of adducts of 5, in particular keto ester 9, has been briefly examined. Olefins 30 and 46 derived from 9 have been converted to ring-opened cadinane skeletons 31 and 47, respectively, by conditions we have previously reported. In an entirely new and unexpected reaction, simultaneous ketalization and fragmentation of the cyclobutane ring of ketones derived from 9 gave ring-opened ketals 34 + 35 (from 29), 36 + 37 (from 9), 39 (from 38) and 42 + 43 (from 40).
Solid state and solution stereochemistry of crown ethers and models. ortho-Dimethoxydiphenyl ether and related dibenzo-15-crown-5 and tetrabenzo-30-crown-10 ethers as studied by X-ray crystallography and 1H and 13C NMR spectroscopy
Authors: Buchanan G. W. , Rodrigue A. , Bourque K. , Chiverton A. C. , Castleden I. R. , Fortier S.
Published: May 2006

Solid phase 45.3 MHz 13C NMR spectra of ortho-dimethoxydiphenyl ether, 1, dibenzo[b,e]-15-crown-5- ether, 2, and tetrabenzo[b,e,q,t]-30-crown-10 ether, 3, have been obtained. Chemical shift trends are discussed in terms of the asymmetric units and structural features available from X-ray crystallographic data. Comparison with solution 13C spectra are made. The crystal structures of 1 and 3 were determined by X-ray diffraction at room temperature. 1 crystallizes in space group P21/a with a = 13.366(1), b = 8.230(1), c = 12.303(1) Å, β = 116.63(1)°, Z = 4. 3 crystallizes in space group P21/c with a = 7.903(1), b = 26.337(2), c = 7.852(1) Å, β = 97.28(1)°, Z = 2. The structures were solved by direct methods and refined by full-matrix least squares to residuals of 0.055 using 1727 reflections for 1 and of 0.042 using 2590 reflections for 3.
Ab initio study on the thermal decarboxylation of but-3-enoic acid and its derivatives
Authors: Wang Youliang , Poirier Raymond A.
Published: May 2006

The mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives HXC=CYCH2COOH (X, Y=H, F, CH3, C2H5, and Cl) leading to carbon dioxide and olefins has been studied from the theoretical point of view by ab initio MO calculations. The transition states obtained by our ab initio calculations are completely consistent with the experimental data, and support the "synchronous" mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives via a "twisted chair" six-membered cyclic transition state. The effects of β- and γ-substituents on the activation energy (Ea) can be explained in terms of electronic charge distribution. β-Substitution decreases the activation energy, while γ-substitution increases it. Changes in the activation energy are related to changes in the charges at Cγ(C1) and Cβ(C2) as the substituents are varied. The activation energy decreases with an increase of negative charge at Cγ, while it increases with an increase of negative charge at Cβ. The best estimate of 156.8 kJ/mol for the activation energy with MP2/6-31G*//HF/3-21G(*) is in reasonable agreement with the available experimental values of 164 ± 7 kJ/mol and 160 kJ/mol for decarboxylation of but-3-enoic acid. The calculated primary kH/kD, 2.86, and [Formula: see text] 1.03, for the decarboxylation of but-3-enoic acid, are also in excellent agreement with the available experimental values of 2.7 and 1.035, respectively, supporting the transition state structure obtained.
Comparison of heteroatom-bridged analogues of methylenebisphenols for antioxidant activities
Authors: Nishiyama T. , Kagimasa T. , Yamada F.
Published: May 2006

A series of methylenebisphenols, thiobisphenols, oxybisphenols, and iminobisphenols were evaluated as antioxidants for tetralin at 60 °C by means of an oxygen-obsorption method. It was found that replacement of the bridged methylene group of methylenebisphenols by a nitrogen atom showed considerably better antioxidant effects. The antioxidant effects of these compounds were influenced by the positions of the phenolic hydroxyl groups in their molecules.
Double diastéréosélectivité de la cycloaddition dipolaire-1,3 d'ylures d'azométhine cycliques substitués
Authors: Lakhlifi Tahar , Sedqui Ahmed , Fathi Toufik , Laude Bernard , Robert Jean-François
Published: May 2006

Seven derivatives of methyl 5-phenyl-3,4-dihydro-2H-pyrrole-2-carboxylates 1 were synthetized. These compounds are precursors of pentagonal cyclic azomethine ylids, the two sides of which are diastereotopic. The 1,3-dipolar species react with N-methyl and N-phenylmaleimides diastereospecifically. The approach of the reactant species occurs from the less hindered side of the 1,3-dipole and in endo to lead the thermodynamically stable exo cycloadduct. Moreover, oxidation of the compounds 1 gives the corresponding substituted pyrroles.
Antioxidant activities of tetrakis(4-hydroxyphenyl)pentanes and tetrakis(4-hydroxyphenyl)-p-xylenes
Authors: Nishiyama T. , Shioi H. , Korenaga K. , Tun R. , Yamada F.
Published: May 2006

A series of tetrakis(4-hydroxyphenyl)pentanes and tetrakis(4-hydroxyphenyl)-p-xylenes having relatively high molecular weights (550−810) were prepared and evaluated as antioxidants for tetralin at 60 °C by means of an oxygen-absorption method. Introduction of alkyl groups to the ortho positions of the phenolic hydroxyl group was shown to improve antioxidant activities for both series of compounds.
"UNIFIED" ECO-SYSTEM MODEL OF MACRO- AND MICROEVOLUTION BASED ENERGY
Authors: HE MINGFENG , YU GUOJUN
Published: May 2006

The source-network, the dynamic trophic level and the energy are incorporated into a "unified" model that describes both micro- and macroevolutions within a single theoretical framework. This model describes the microevolution in details by accounting for the birth, ageing, and natural death of individual organisms as prey-predator interactions on a hierarchical dynamic food web. It also provides a natural description of random mutations and speciation of species as well as their extinctions. The distribution of lifetimes of species follows an approximate power law only over a limited regime, and the distribution of trophic level follows an exponential attenuation.
Translating discrete-time simulink to lustre
Authors: Tripakis Stavros , Sofronis Christos , Caspi Paul , Curic Adrian
Published: May 2006

We present a method of translating discrete-time Simulink models to Lustre programs. Our method consists of three steps: type inference, clock inference, and hierarchical bottom-up translation. In the process, we explain and formalize the typing and timing mechanisms of Simulink. The method has been implemented in a prototype tool called S2L, which has been used in the context of a European research project to translate two automotive controller models provided by Audi.
Information systems
Authors: Gorgone John T.
Published: May 2006

The ACM, the IEEE-CS and the Association for Information Systems (AIS) are society members of CSAB, Inc. and are joined together in support of promoting quality assurance of computing programs in the United States. They are interested in the description and defining characteristics of each computing program including information systems. They have a stake in identifying the number IS programs offered, their location within the university structure, and the quality of programs being presented to the public.
What should be in a syllabus?
Authors: Walker Henry M.
Published: May 2006

Students typically receive a syllabus at an early meeting of a course. Sometimes, schools provide faculty with guidelines or a template for the content of these handouts, but more often syllabi may display considerable variation in both the topics covered and the level of detail given. This article presents my perspectives on the purposes of a syllabus and its content. Other documents, of course, might cover some of this content. Traditionally, such syllabi were distributed in paper form, although distribution now may include e-mail or course web pages.
Forthcoming activities in the two-year college setting
Authors: Campbell Robert D.
Published: May 2006

The ACM Two-Year College Education Committee (ACM TYCEC) is actively seeking individuals to participate in several forthcoming initiatives. The following details these activities.
A day for CS education
Authors: Parlante Nick
Published: May 2006

For this column, I'd like to share a few ideas that came out of Bay Area CSE Day 2005. Bay Area CSE day was one-day gathering of CSE people, started with a simple invitation on the SIGCSE list. The event was not elaborately prepared --- I just asked a few people to give 15-minute presentations about topics of interest, and then left a lot of time in between for discussion. The regular SIGCSE conference has a lot of high quality prepared material in the presentations, but there never seems to be enough time discussion and interaction. As a low-effort gathering, CSE Day gave us a few interesting presentations and then lots of time to go around the table and share ideas. At a basic level, I find it refreshing and energizing just to be in a room with other people who care about the same things that I care about, so I encourage others who are thinking about organizing one-day events.
Removing the veil
Authors: Martin C. Dianne
Published: May 2006

This article is a personal reflection on the culture and the education of young women in the United Arab Emirates, a group of seven emirates along the Persian Gulf, which has only been a federated nation since 1971. The rapid pace of development in the UAE and the desire of the rulers to educate women to become leaders in the country's workforce were the impetus for the creation of Zayed University in 1998. The social impact of introducing computer laptops and Internet access for all students is described.