bluuebunny/crossref_metadata_2025 huggingface dataset:
Glaciasterols A and B, 9,11-secosteroids from the marine sponge Aplysillaglacialis
Authors: Pika Jana , Tischler Mark , Andersen Raymond J.
Published: May 2006

The glaciasterols, a family of cytotoxic 9,11-secosteroids, have been isolated from extracts of the northeastern Pacific sponge Aplysillaglacialis. The structures of glaciasterol A (2) and glaciasterol B (3) were elucidated by a combination of spectroscopic analysis and chemical interconversions on the native steroid 2 and the diacetate 5 of glaciasterol B (3).
Enantioselective synthesis of 1-substituted tetrahydroisoquinoline-1-carboxylic acids
Authors: Czarnocki Zbigniew , Suh Dennis , MacLean David B. , Hultin Philip G. , Szarek Walter A.
Published: May 2006

The 3,4-dihydroisoquinolinium salt 1 and its enantiomer have been converted readily and stereoselectively into (+)-and (−)-1,2,3,4-tetrahydro-6,7-dimethoxy-1-methylisoquinoline-1-carboxylic acids. The synthetic route described should be applicable to the enantioselective synthesis of a variety of 1-alkyl- or 1-aryl-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acids. The absolute configuration of the amino acid hydrochloride 11 was established to be as depicted in Scheme 2.
Molecular geometry of M(NO)2 complexes: single crystal X-ray structure of Co(NO)2(C5H5N)2+BF4−, lability of the pyridine ligands of Co(NO)2(C5H5N)2+, and its relevance to the formation of the Co2(NO)3+ bimetallic core
Authors: Roustan Jean-Louis , Ansari Nasrin , Page Yvon Le , Charland Jean-Pierre
Published: May 2006

The BPh4− and BF4− derivatives of Co(NO)2(Py)2+3 (Py = pyridine) have been prepared. In solution, whereas Co(NO)2(L)2+BPh4− (L = phosphane) and 3-BF4− are inert, 3-BPh4− decomposes rapidly in the absence of an excess of Py. Complex 3-BF4− crystallizes in the monoclinic system with two independent molecules, A and B, in the asymmetric unit, space group P21/a, a = 14.7633(6) Å, b = 13.9739(5) Å, c = 15.1667(6) Å, β = 109.334(4)°, 2225 reflections, R = 0.054, Rw = 0.023. The cobalt coordination polyhedron is a distorted tetrahedron. The comparison of the (O)N—Co—N(O) angles of 115.6(3)° (molecule A) and 115.9(3)° (molecule B) with those of other [Formula: see text] pseudotetrahedral dinitrosyl complexes suggests that the lability of the Py ligands of cation 3 reflects the compression experienced by the Co(NO)2+ molecular portion.
Medium effect on the second-stage dissociation constant of N-(2-acetamido)imino diacetic acid (H2ADA)
Authors: Hassan Ahmed , Azab H. A. , Gyar S. A. El , Khafagy Z. A.
Published: May 2006

The second-stage dissociation constant values of N-(2-acetamido)imino diacetic acid (H2ADA) were determined at 25 ± 0.1 °C by potentiometric titration in different mixed-solvent mixtures (methanol, ethanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and dioxane). It was observed that the pKa value is slightly influenced as the solvent is enriched in methanol and ethanol, and remains practically constant in the presence of different amounts of DMF and DMSO. A prounounced change in the pKa value was observed as the solvent is enriched in acetone or dioxane. These results are discussed in terms of various solvent characteristics. It is concluded that the electrostatic effect has only a relatively small influence on the dissociation equilibrium of the imino group [Formula: see text]. Other solvent effects such as solvent basicity, different stabilization of the free base of the conjugate acid by hydrogen bonding interactions in aquoorganic solvent media relative to pure aqueous media, as well as proton–solvent interaction play an important role in the acid dissociation equilibrium.
The solvent dependence of the small internal barrier to rotation in 3,5-dichlorobenzyl fluoride
Authors: Schaefer Ted , Mansfield James R. , Hruska Frank E. , Sebastian Rudy
Published: May 2006

The 1H and 19F nuclear magnetic resonance spectra of 3,5-dichlorobenzyl fluoride, dissolved in solvents of varying polarity, are analyzed to yield precise values of the long-range coupling constants between ring protons and the nuclei in the fluoromethyl group. The conformational properties of these coupling constants, dependent on the angle by which the C—H and C—F bonds of the side chain twist out of the aromatic plane, are used to determine the solvent dependence of the predominantly twofold barrier to rotation about the Csp2—Csp3 bond. In all solvents, the conformer in which the C—F bond lies in the aromatic plane represents the minimum in the internal rotational potential. The magnitude of the twofold potential changes from 3.2(2) kJ/mol in the nonpolar medium, C6D12, to 0.6(2) kJ/mol in the polar solvent, CD3CN. Intermediate magnitudes occur for solvents of intermediate dielectric constant. Comparisons are made with the parent molecule, benzyl fluoride, for which the perpendicular conformer is most stable in the same solvents. Such comparisons indicate that for the free molecules, the in-plane conformer of the dichloro derivative is also more stable than the same conformer of benzyl fluoride. This indication is in qualitative agreement with molecular orbital predictions.
Radical-based syntheses of 5-benzoyl-1,2-dihydro-3H-pyrrolo[1,2-a]pyrrole-1-carboxylic acid (ketorolac)
Authors: Artis Dean R. , Cho In-Seop , Muchowski Joseph M.
Published: May 2006

Short, efficient, and convergent syntheses of ketorolac (1) based on the inter- or intramolecular oxidative addition of malonyl and substituted malonyl radicals to 2-benzoylpyrrole and derivatives thereof are described.
The molecular and electronic structure of 1-pyrazolylphosphazenes
Authors: Gallicano Keith D. , Paddock Norman L. , Rettig Steven J. , Trotter James
Published: May 2006

The nature of the interactions between pyrazolyl and phosphazene rings has been investigated through the study of the structures of bis(1-pyrazolyl)methane, CH2(H2pz)2, 1, bis[1-(3,5-dimethylpyrazolyl)]methane, CH2(Me2pz)2, 2, the pyrazolylphosphazenes N3P3(Me2pz)6, 3, N4P4(H2pz)8, 4, and N4P4(Me2pz)8, 5, and the partially substituted gem-N3P3Ph2(Me2pz)4, 6. Crystal data are as follows: 1, orthorhombic, P212121, a = 7.997(2), b = 9.287(2), c = 10.049(2) Å, Z = 4, R = 0.034 for 647 reflections; 2, monoclinic, C2/c, a = 19.115(4), b = 4.2690(8), c = 14.543(3) Å, β = 98.91(2)°, Z = 4, R = 0.064 for 528 reflections; 3, monoclinic, C2/c, a = 16.778(2), b = 12.1083(9), c = 19.269(4) Å, β = 113.885(6)°, Z = 4, R = 0.039 for 2716 reflections; 4, monoclinic P21/n, a = 10.4223(9), b = 8.1879(7), c = 19.403(2) Å, β = 94.381(7)°, Z = 2, R = 0.059 for 2937 reflections; 5, triclinic, [Formula: see text], a = 11.516(2), b = 13.121(3), c = 18.142(3) Å, α = 77.96(1), β = 79.20(1), γ = 66.54(2)°, Z = 2, R = 0.036 for 5300 reflections; 6, monoclinic, P21/c, a = 10.3598(4), b = 17.8827(4), c = 19.0851(6) Å, β = 94.675(2)°, Z = 4, R = 0.053 for 4867 reflections. Interpretation of the structures through iterative extended Hückel calculations shows that conjugative interactions lead to a quinonoid deformation of the pyrazole ring, similar to that in bis(1-pyrazolyl)carbonyl. π-Electron transfer to the phosphazene ring, facilitated by the use of acceptor d orbitals on phosphorus, is accompanied by a synergic σ transfer to the pyrazole ring. The pyrazolyl group acts both as a strongly electronegative group and as a good potential donor. The calculations account satisfactorily for the bond lengths in the pyrazolyl group, the large bond angles at nitrogen in 4 and 5, the bond length inequalities in the phosphazene ring of 6, and the reactivity of the pyrazolylphosphazenes.
Ground and excited state dipole moments of planar vs. twisted p-N,N-(dimethylamino)benzonitrile systems: maximum charge transfer for minimum overlap
Authors: Sinha Hemant K. , Muralidharan S. , Yates Keith
Published: May 2006

Electric field induced change in the absorption spectrum (electrochromism) has been employed to obtain the ground and excited state dipole moments of planar and sterically hindered (twisted) p-N,N-(dimethylamino)benzonitriles in dioxane solution. These studies support the twisted intramolecular charge transfer (TICT) hypothesis and provide additional insight to the TICT concept. The charge transfer nature of the excited state has been found to directly depend on the torsional angle of the N,N-dimethylamino group with respect to the benzonitrile moiety. It is suggested that solvent coupling is essential to initiate twisting by affecting the intramolecular degrees of freedom and the existence of the highly dipolar excited state is a result of such twisting of the donor–acceptor bond. Theoretical calculations have been performed to explain the observed changes in dipole moment values.
Studies on novel carbacephem analogs: synthesis of 7-methoxy-homo-PS-5 and a 7-methoxy-8-epi-homothienamycin intermediate
Authors: Shakya S. R. , Durst T.
Published: May 2006

The synthesis of two carbacephems bearing a 7-methoxy group and either an additional ethyl (PS-5) or hydroxyethyl (thienamycin) side chain has been completed. Rhodium carbenoid insertion methodology was used to generate the bicyclic ring systems.
Réduction électrochimique régiosélective d'aroyl-2- ou d'acetyl-2 chromones en milieu non aqueux
Authors: Boutoute Patrick , Mousset Guy
Published: May 2006

The electrochemical behaviour of chromones substituted in position 2 by benzoyl or acetyl groups was studied by cyclic voltammetry in a nonaqueous solvent. Self-protonation reactions were observed with compounds possessing a phenol function on the benzoyl group. Macroelectrolyses achieved in the presence of a proton donor afford a regioselective reduction of the carbonyl function in position 2 of the benzoyl-2 chromone and of the double bond for the acetyl-2 chromone. Moreover the further reduction leads to the formation of thermally unstable dimers, which may give homolytic cleavage to free radicals.
Transannular Diels–Alder cyclization of a substituted 13-membered macrocyclic triene. An approach to the A.B.C.[6.6.5] rings of the Veratrum alkaloids
Authors: Quimpère Miguel , Ruest Luc , Deslongchamps Pierre
Published: May 2006

The synthesis and Diels–Alder cyclization of a substituted macrocyclic 13-membered triene 45 is described. Tricyclic compound A.B.C.[6.6.5] 46 having ring junctions of cis-anti-cis (CAC) stereochemistry was used to investigate the possibility of introducing a hemiketal oxygen bridge between positions 9 and 4 of the Veratrum alkaloid skeleton.
1992 CIC Medal Award Address 50 years a spectroscopist—some personal reminiscences
Authors: Ramsay D. A.
Published: May 2006

not available
The metabolites of Trichodermalongibrachiatum. Part 1. Isolation of the metabolites and the structure of trichodimerol
Authors: Andrade Romano , Ayer William A. , Mebe Paul P.
Published: May 2006

Trichodermalongibrachiatum Rifai aggr. is a fungus reported to be antagonistic to the fungus Mycenacitricolor, the causative agent of the American leaf spot disease of coffee. We have investigated the metabolites produced when T. longibrachiatum is grown in liquid culture and have isolated the known compounds sorbicillin (2), bisvertinol (3), and bisvertinolone (4) as well as several new compounds including trichodimerol (1), an interesting new natural product possessing a proper axis of symmetry. The structure of trichodimerol (1) was determined by a combination of spectroscopic techniques, including 1H and 13C nuclear magnetic resonance, infrared, ultraviolet, circular dichroism, optical rotatory dispersion, and mass spectrometry, and by transformation to octahydrotrichodimerol (6) and symmetrical and unsymmetrical derivatives thereof. The relative stereochemistry of bisvertinol (3) and bisvertinolone (4) has been revised. The metabolites described are not biologically active against Mycenacitricolor.
The thermodynamics of the vaporization of liquid indium(I) iodide by modified entrainment
Authors: Gardner Peter J. , Preston Steve R.
Published: May 2006

The transport of gaseous In(I)I in an argon carrier gas was studied in the temperature range 723–887 K by the modified entrainment method. Combination of the entrainment results with a literature equation for the total vapour pressure above the liquid gave the following expressions for the temperature dependence of the vapour pressures of the monomer (InI) and dimer (In2I2) respectively: [Formula: see text] and [Formula: see text]; p0 = 105 Pa. The dimer concentration is ca. 2% and nearly constant from 720 to 810 K.
FT-infrared study of the interaction between all-trans retinylidene isopropylamine and model proton donors
Authors: Migchels P. , Zeegers-Huyskens Th.
Published: May 2006

The interaction between all-trans retinylidene isopropylamine (tRiPA) and phenols covering a large pKa domain is investigated by FT-infrared spectrometry. For phenols having pKa between 10.2 and 8.18, only normal OH … N hydrogen bonds are formed. The thermodynamic parameters (K, −ΔH, −ΔS0) determined in carbon tetrachloride solution show that tRiPA possesses a good proton acceptor ability. The spectral characteristics (frequency and integrated intensity) of the νC=N vibration are also investigated. From a pKa of 6, proton transfer takes place. The proton transfer constants determined in 1,2-dichloroethane are linearly related to ΔpKa (pKa of the protonated base minus pKa of the phenol). Comparison with previously studied imine systems shows that the proton transfer constant increases with the number of C=C double bonds in the base.
Tetrakis(trimethylgermyl)silane and tris(trimethylgermyl)silyllithium
Authors: Baines Kim M. , Mueller Kevin A. , Sham Tsun K.
Published: May 2006

Tetrakis(trimethylgermyl)silane can be synthesized by the addition of four equivalents of trimethylgermyllithium to tetrachlorosilane. Treatment of tetrakis(trimethylgermyl)silane with methyllithium gives tris(trimethylgermyl)silyllithium, which was trapped with aqueous hydrochloric acid, chlorotrimethylsilane or methyl iodide to yield tris(trimethylgermyl)silane, tris(trimethylgermyl)(trimethylsilyl)silane, or methyltris(trimethylgermyl)silane, respectively. Chlorination of tris(trimethylgermyl)silane affords dichlorobis(trimethylgermyl)silane.
Spiro fused β-lactam cyclopropenes
Authors: Zoghbi Michel , Warkentin John
Published: May 2006

Δ3-1,3,4-Oxadiazolines (1) that share their C2 with C4 of a β-lactam ring in a spiro fusion were prepared. The structures were established through single crystal X-ray diffraction of 1a and by infrared, 1H, and 13C nuclear magnetic resonance spectroscopies. Thermolysis of 1 at 100 °C, in benzene containing dimethyl acetylenedicarboxylate, afforded spiro-fused β-lactam cyclopropene 12 in 33% yield. Similar thermolysis of 1b in the presence of ethyl phenylpropiolate gave spiro-fused β-lactam cyclopropene 13 (32%). The molecular structure of 12, determined by single crystal X-ray diffraction, has the two ester carbonyl carbons out of the plane of the cyclopropene ring by about 0.17 Ǻ, indicating substantial nonbonded steric interactions and suggesting unusually high strain energy. At 154.5 °C, 12 underwent isomerization to 19, presumably through a vinyl carbene intermediate.
Électrodes à membrane indicatrices de surfactifs cationiques. Variation des propriétés électriques de la membrane en fonction de sa composition
Authors: Gloton M. P. , Turmine M. , Mayaffre A. , Letellier P.
Published: May 2006

Amphiphilic-cation-specific electrodes most often use, as captor of potential, a specific membrane composed of a mixture of a polymer such as PVC, a plasticizer, and a carrier of the amphiphilic ion. For a given polymer, various plasticizers can be used to make "plastisols" that can be suitable for the preparation of specific membranes. We prepared different membranes using two polymers (PVC: high and low molecular weight), four plasticizers in various proportions, and a carrier of the dodécyltriméthylammonium ion. These membranes were mounted on an electrode support and used as ion-selective electrodes. We show that none of these component mixtures can allow the design of specific electrodes. Only a few of them give a "Nernstian" response. Thus, the mixtures rich in polymer lead to heterogeneous plastisols; the electrode responses cannot be reproduced with different samples of the same mixture. We use a model of ion transport through the membrane that assumes a diffusion by carrier for the amphiphilic ion and nonspecific diffusion of the salt through the flaws created by the heterogeneity of the plastisols. The introduction of this model allows us to explain qualitatively the variation of the slope of the electrode response with the membrane composition.
Preparation and structure of 7-azaindolium salts containing unusual chloro-copper(II) anionic units
Authors: Poitras Jacques , Leduc Martin , Beauchamp André L.
Published: May 2006

Dark-red crystals of (H2aza)5[Cu5Cl14(H2O)4]Cl were obtained by addition of HCl to equimolar amounts of 7-azaindole (Haza) and CuCl2•2H2O in methanol. They were shown by X-ray diffraction (triclinic, [Formula: see text] a = 9.396(1), b = 9.894(1), c = 15.958(1), Å, α = 106.10(1)°, β = 98.25(1)°, γ = 105.56(1)°, Z = 1, R = 0.031) to contain infinite chains in which the basic [Cu5Cl14(H2O)4]4− pattern is built up from trans-CuCl2(H2O)2, [CuCl3(H2O)]−, and dichlorobridged [Cu2Cl6]2− species. In the idealized chain, these units occur in the 1:2:1 ratio, but disorder is present and some of the CuCl2(H2O)2 units are randomly replaced by [CuCl3(H2O)]−. The Cu atoms have a roughly square-planar primary coordination, and connection along the chain is achieved by weaker apical Cu–Cl bridging interactions. All azaindole molecules are present as uncoordinated N7-protonated monocations. A related (H2aza)3[Cu3Cl8(H2O)3]Cl salt was obtained as a side-product of the reaction of 7-azaindole with excess CuCl2•2H2O in methanol without acid. In these brown crystals (triclinic, [Formula: see text] a = 9.308(1), b = 9.964(1), c = 19.212(4) Å, α = 76.67(1)°, β = 79.35(1)°, γ = 75.27(1)°, Z = 2, R = 0.046), the [Cu6Cl16(H2O)6]4− pattern of the chain contains the same three building units as above, but in the 2:2:1 ratio. In both salts, the polymeric chloro-copper chains are parallel and separated by azaindolium cations stacked along the same direction. The structures are stabilized by networks of hydrogen bonds involving the azaindolium cations, the chlorine atoms, and water molecules in the chloro-copper chain, and a noncoordinated Cl− ion. Most of the azaindolium cations are disordered. The influence of N7-protonation on the infrared spectrum of azaindole is discussed.
Electrochemistry and spectroelectrochemistry of substituted tetrabenzotriazaporphine
Authors: Tse Yu-Hong , Goel Alok , Hu Mougang , Lever A. B. P. , Leznoff C. C. , Van Lier Johan E.
Published: May 2006

The spectral and electrochemical properties of tetrabenzo[5,10,15]triazaporphine (TBTAP) and its magnesium derivatives having a long alkyl chain attached to the meso carbon have been studied. Both metal-free and metallated species show typical metal-free phthalocyanine-like spectra. Two reduction and two oxidation redox couples have been observed. The cation, anion, and dianion species of these porphyrin derivatives have been electrochemically generated and their electronic spectra are recorded.
Determination of aluminum in human cerebrospinal fluid through the electrochemical and spectroscopic properties of its complex formed with Solochrome Violet RS
Authors: Johnson Keith E. , Treble Ronald G.
Published: May 2006

Aluminum present in pooled samples of cerebrospinal fluid is essentially uncomplexed since it may be determined by differential pulse polarography of the Al: Solochrome Violet RS (SVRS) complex. The aluminum may also be determined spectrophotometrically through its depression of the SVRS absorbance at 600 nm at pH 8.4. The Al:SVRS ratio in the complex is 1:2.
Photodimerization of α,ω-diarylbutadienes. I. Crystal and molecular structures of trans,trans-1-(2′-methoxyphenyl)-4-(4′-nitrophenyl)-1,3-butadiene and its photodimer
Authors: Capparelli Mario V. , Codding Penelope W.
Published: May 2006

X-ray crystallographic studies showed that orange crystals of the title diarylbutadiene 1 undergo a topochemically controlled [2 + 2] photocycloaddition when exposed to visible light to produce the cyclobutane dimer 2, which is yellow. The conformation of molecule 1 is planar with a maximum deviation from an all-atom mean plane, including substituents, of ≤ 0.28 Å. The crystal structure of 1 displays pairs of molecules packed in a head-to-tail arrangement across inversion centers that allows π orbital overlap between nearest neighbor butadiene double bonds. Intermolecular distances and angles between these photoreactive atoms are [Formula: see text], 3.517(2) Å and [Formula: see text], 92.0(2)°; and the dihedral angle between the plane of the four photoreactive atoms and the plane of the butadiene in one molecule is 72.9°. Molecule 2 lies on a crystallographic inversion centre, which constrains the cyclobutane ring to absolute planarity with C—C distances of 1.558(2) and 1.569(2) Å and C—C—C angle of 90.61(1)°. The dihedral angles between the cyclobutane ring and the two phenyl rings are 81.2° for the p-nitrophenyl and 54.0° for the o-methoxyphenyl. From the crystal structures of 1 and 2, the displacement of each of the four photoreactive atoms during the solid-state dimerization can be estimated to be ca. 1.00 Å. Crystals of 1 are orthorhombic, Pbca, a = 7.471(1), b = 14.283(1), c = 25.940(1) Å, Z = 8, and those of 2 are monoclinic, P21/c, a = 11.5396(5), b = 16.129(1), c = 7.9035(3) Å, β = 90.264(3)°, Z = 4. Both structures were solved by direct methods and refined to final values of R = 0.0481 and 0.0512 using 2788 and 2333 observed (I > 3 σ(I)) reflections, for 1 and 2, respectively.
Ternary complexes of copper(II) and their use in the spectrophotometric determination of copper in alloys and rocks
Authors: Ali Abd-Elhafeez E.
Published: May 2006

Some intensely coloured Cu(II)–L1–2′,7′-dichlorofluorescein ternary complexes were studied. The absorbance characteristics for these ternary complexes were determined. The molar ratio for these complexes is Cu:L1:L2 = 1:2:1 and the formula [Cu(L1)2]2+•[Cl2FlCOO−]− is proposed. The effect of substituent groups of the L1 and L2 ligands on the complexing activity with copper(II) was studied. The interference of some cations and anions in the determination of the Cu(II) by the developed methods was examined. Highly sensitive and selective methods are proposed for the spectrophotometric determination of copper(II) in limestone and copper alloys.
Functionalization of spirocyclopentadienes using organomolybdenum reagents: approaches to the synthesis of (±)-silphinene
Authors: Norris Derek J. , Corrigan John F. , Sun Yan , Taylor Nicholas J. , Collins Scott
Published: May 2006

(η5-Indenyl)molybdenum dicarbonyl complexes of 1,3-dienes, including spirocyclopentadienes, can be cleanly prepared from stoichiometric amounts of 1,3-dienes and [(η5-indenyl)Mo(CO)2(CH3CN)2][BF4] (1) in dichloromethane solution. Nucleophilic addition of lithium dimethylcuprate to the complexed diene occurs in the expected manner to provide η3-allylmolybdenum complexes in high yield. Applications of this chemistry towards the synthesis of (±)-silphinene are described. The allylmolybdenum complexes [(η5-C9H7)(η3-C10H15)Mo(CO)2] (8) and [(η5-C9H7)(η3-C15H23)Mo(CO)2] (33) were structurally characterized by X-ray crystallography. Compound 8: space group P21/n with a = 9.393(1) Å, b = 10.469(2) Å, c = 17.704(2) Å, β = 91.05(1)°, Z = 4, and V = 1770.5(4) Å3. Compound 33: space group P21/c with a = 17.616(4) Å, b = 7.688(2) Å, c = 15.873(2), β = 90.12(2)°, Z = 4, and V = 2149.7(6) Å3.
Helianthoside from Heliaster helianthus, an asterosaponin with a C3′-sulphated pyranose
Authors: Vazquez M. Jesus , Quinoa Emilio , Riguera Ricardo , Martin Aurelio San
Published: May 2006

A new asterosaponin, named helianthoside (1), has been isolated from the butanolic extract of the starfish Heliaster helianthus and its structure established on the basis of extensive spectroscopic experiments and chemical correlations. Helianthoside is the first asterosaponin with a C3′-sulphated xylopyranose. The absolute stereochemistry at C24 was determined by the Trost–Mosher method.
1H and 13C nuclear magnetic resonance studies of the conformational equilibrium of 2-(diphenylphosphino)benzaldehyde in polar and nonpolar solutions. Signs of the proximate coupling constants, 4J(CHO, 31P) and 3(13CHO, 31P)
Authors: Schaefer Ted , Sebastian Rudy , Schurko Robert W. , Hruska Frank E.
Published: May 2006

The analyses of the 1H nuclear magnetic resonance spectra of 2-(diphenylphosphino)benzaldehyde in CS2/C6D12 and acetone-d6 solutions yield stereospecific coupling constants from which the populations of the O-cis and O-trans conformers are derived. The free energy differences favouring the O-trans conformer at 300 K are 2.7 and 0.9 kJ/mol, in the polar and nonpolar solutions, respectively; in the crystal only the O-cis conformer exists. The coupling constant, 4J(CHO, P), is estimated as −7.1(2) Hz in the O-trans confomer and 3J(CHO, P) as +29.4(1.3) Hz. Their magnitudes depend on the proximity of the C—H bond to the lone pair on phosphorus. nJ(C, P) are reported for triphenylphosphine and for the benzaldehyde derivative as dilute solutions in the two solvents, demonstrating a significant solvent dependence for some of these coupling constants. Some simple relationships are proposed between nJ(C, P) and the torsion angle about the C—P bond, estimates of the latter coming from AM1 and STO 3G MO computations. nJ(C, P) are also sensitive to intrinsic ring substituent perturbations, as are the nJ(H, P); for example, 5J(H, P) is negative in the disubstituted ring of 2-(diphenylphosphino)benzaldehyde but positive in the phenyl groups. The nJ(H, P) are also discussed with respect to their dependence on the torsion angles about the C—P bonds. It appears that the conformational properties of the aromatic rings in triphenylphosphine and its formyl derivative are very similar. Further, the phosphorus atom is polarized such that the carbonyl bond is attracted towards the positive region near phosphorus, and the C—H bond of the formyl group more towards the lone-pair region; the actual torsion angles represent a compromise between these attractive forces and the repulsive forces between bonds on neighbouring aromatic moieties. CNDO/2 MO and INDO MO FPT computations of nJ(C, P) and nJ(H, P) are of mixed utility, although the former bear out the idea that the proximate [Formula: see text]lone-pair interaction dominates 3J(CHO,P) and 4J(CHO,P).
Highly stereocontrolled syntheses of 2,3-disubstituted 1,4-butyrolactones using ionic and free radical reactions
Authors: Hanessian Stephen , Vanasse Benoit , Yang Hua , Alpegiani Marco
Published: May 2006

N-Substituted 3-amino-1,4-butyrolactones undergo highly stereocontrolled substitution reactions via anionic and free radical processes.
The a″ vibrations of singlet propynal
Authors: Watson J.K.G.
Published: May 2006

The a″ vibrational frequencies of all possible H and D isotopomers of propynal (HCCCHO) are shown to allow two solutions for the a″ harmonic potential constants. Equations relating the solutions are given. In the [Formula: see text] ground electronic state one solution can be rejected as chemically unrealistic, but in the [Formula: see text] excited electronic state the choice is more difficult. It is shown that a choice can be made on the basis of the observed cross-sequence intensities in the [Formula: see text] band system.
Electronic spectroscopy of yttrium monosulfide: molecular beam studies and density functional calculations
Authors: James Andrew M. , Fournier René , Simard Benoit , Campbell Margot D.
Published: May 2006

The yttrium monosulfide molecule (YS) has been investigated using the techniques of molecular beam fluorescence spectroscopy and density functional theory. Fluorescence spectra in the region of the electronic orgin of the B2∑+ ← X2∑+ system (ν00 = 14 826.07 cm−1) were recorded using a ring dye laser, the experimental resolution being 120 MHz. The B2Σ+ ← X2Σ+ (0,0) band, and a cold band of a hitherto unreported 4Π±1/2 ← X2Σ+ system (νυ′0 = 14 926.02 cm−1) have been rotationally analysed. (The ± 1/2 notation implies that the state has either 4Π1/2 or 4Π−1/2 symmetry.) Improved molecular rotational constants were obtained for the ν = 0 levels of the X2Σ+ and B2Σ+ states (r0(X) = 2.27191(17) Å, r0(B) = 2.32202(19) Å, γ0(B) = −0.15150(14) cm−1 (2σ error bounds)). The magnetic hyperfine and spin rotation parameters determined for the X2Σ+ state were found to be in good agreement with previous work. An accurate bond length has been derived for the upper vibrational level of the 14 926.0 cm−1 band (rυ′ = 2.49510(16) Å). The ν = 1 level of the B2Σ+ state is found to be strongly perturbed by another vibrational level of the 4Π±1/2 state. The spin-forbidden 4Π±1/2 ← X2Σ+ transition gains intensity via spin-orbit mixing between the 4Π state and the B2Σ+ state. Radiative lifetimes of the observed bands were measured by digitizing the fluorescence decay traces obtained upon excitation with a pulsed dye laser. The results of the density functional treatment provide broad confirmation of the experimental measurements. A molecular orbital description of the bonding in the YS molecule is presented.
High-resolution spectroscopy with a CCD array detector: application to the 2880 Å emission band system in I2
Authors: Tellinghuisen Joel
Published: May 2006

The 2880 Å system in the Tesla discharge spectrum of I2 in Ar is reexamined using a CCD array detector to record spectra for both 127I2 and 129I2. This charge-transfer transition terminates on a weakly bound valence state, giving a highly congested spectrum with fine violet-degraded band structure barely perceivable on a pseudocontinuous background. The superior signal-to-noise capabilities of the array detector permit a great improvement in the precision and number of measured bandheads, as compared with previous results obtained from photographically recorded spectra. The new data span a larger range of vibrational levels in the lower state and lead to a change in the previous ν″ numbering by −3 units. Both states can now be located precisely on the absolute energy axis through least-squares fits in which the lower state energy is represented as a near-dissociation expansion. The primary spectroscopic constants (cm−1) are [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] [Formula: see text] The lower state has a dissociation energy of 287.5 cm−1 and supports 35 bound levels, subject, however, to possible further revision due to a remaining uncertainty of 1 unit in the ν″ numbering. The previous tentative electronic assignment of this system remains in effect: The upper state is likely the [Formula: see text] state that correlates with I−(1S) + I+(3P1), while the lower state is the [Formula: see text] component of the lowest valence 3Πu multiplet.
The 353 nm nπ* transition of 4H-pyran-4-one and a deuterated derivative
Authors: Gordon Robert D. , Park William K.C.
Published: May 2006

The 353 nm vapour absorption of 4H-pyran-4-one, and its 3,5-d2 derivative, has been measured and assigned to a forbidden, 1A2 (nπ*)–1A1 electronic transition, with electronic origin near 28 360 cm−1, made allowed by vibrations involving out-of-plane ring and C—H motions. Although the molecule remains planar upon excitation, other effects of conjugation on the nature of the excited state are less marked than in 2-cyclopenten-1-one.
x–y Coriolis interaction in the ν5 and ν8 bands of propyne-d3
Authors: Rajappan Geetha , Job V.A.
Published: May 2006

High resolution Fourier transform spectra of the ν5 and ν8 bands of CD3C≡CH have been recorded and analyzed taking into account the strong x–y Coriolis interaction between these fundamentals. Fermi resonance of the ν8 state with the ν9 + ν10 state, l-type doubling interaction between the ± l components of ν8 and a weak k-type doubling interaction between the ν5 and ν8 states have also been included in the perturbation treatment. The parameters of the ν5 and ν8 states as well as some of the parameters of the unobserved ν9 + ν10 state have been determined. An estimate of the relative value of the transition moments has been obtained from the line intensities, which are strongly affected by the x–y Coriolis interaction.
High-resolution laser spectroscopy of excited bending vibrations (υ2 ≤ 2) of the and electronic states of SrOH: analysis of ℓ-type doubling and ℓ-type resonance
Authors: Presunka P.I. , Coxon J.A.
Published: May 2006

The (0200)Σ+ ← (000)Σ+, (0220)Δ ← (010)Π, (0200)Σ+ ← (010)Π, and (010)Π ← (000)Σ+ bands in the [Formula: see text] electronic system of SrOH have been recorded at Doppler limited resolution using CW dye laser excitation with selective detection. Fluorescence from selected rotational levels of the [Formula: see text] and [Formula: see text] vibronic states has been dispersed, providing access to the (0200)Σ+ and (0220)Δ levels of the ground electronic state. Over 1200 line positions from all transitions were included in a global least-squares fit. The effects of a weak ℓ-type resonance between the ℓ = 0 and ℓ = 2 components of the ν2 = 2 vibrational level were observed in both electronic states and the off-diagonal matrix elements were evaluated in a case (b) basis. A previous analysis of the [Formula: see text] level that attributes the anomalous ℓ-type doubling to an electronic perturbation arising from the [Formula: see text] polyad is inconsistent with our experimental results.
An analysis of the ion-pair state of I2 by a sequential three-photon excitation
Authors: El-Hameed Faten S.M. Abd
Published: May 2006

A three-photon absorption technique that utilizes a visible [Formula: see text] transition followed by two-photon absorption was applied to characterize the high-lying vibrational levels of the [Formula: see text] ion-pair state of I2, which correlates with I−(1S) + I+(1D) at the dissociation limit. The multiphoton spectrum was examined at high resolution using either a single tunable dye laser (3P1C), or two independently tunable pump and probe dye lasers (3P2C), operating in the blue–green region. The one-color spectrum excited by a single laser shows transitions that have not been assigned by previous workers; these rotational lines are interpreted as being due partly to 3P1C transitions to the [Formula: see text] ion-pair state, for which molecular constants are derived to be (for ν′ = 60–74, J′ = 3–100):[Formula: see text](all in cm−1 with one standard deviation in the last quoted digit in parentheses).
Novel [2.2]paracyclophane derivatives via charge-transfer complexation
Authors: Aly Ashraf A. , Hassan Alaa A. , Mourad Aboul-Fetouh E.
Published: May 2006

The transannular electronic interactions in [2.2]paracyclophanes affect the selectivity of the tricyanovinylation reaction with tetracyanoethylene (TCNE). In addition to the normal N-tricyanovinyl product, 4-amino[2,2]paracyclophane reacts with TCNE to give oxaziridine derivatives. In the case of reaction with 4-N-methylamino[2.2]paracyclophane, the unusual N-tricyanovinylated product as well as 4-(N-carbonitrile-N-methyl)annino[2.2]paracyclophane was isolated. The reaction of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) with 4-amino[2.2]paracyclophane results in formation of 2-cyano-3-(4-[2.2]paracyclophanyl)amino-5,6-dichloro-1,4-benzoquinone.
A new synthesis of in situ cyclopropanones and the observation of a thermal cyclopropanone–dienol rearrangement
Authors: Black C. , Lario P. , Masters A.P. , Sorensen T.S. , Sun F.
Published: May 2006

A new in situ low-temperature synthesis of cyclopropanones from α,α′-dibromo ketones is described. The synthetic procedure is particularly well suited to NMR tube-scale experiments, which then easily allows one to spectroscopically characterize low-temperature solutions of these unstable molecules. Nine systems were studied, seven of which give high yields of the cyclopropanones at −78 °C or, in one case, −93 °C. The major rearrangement pathway of these cyclopropanones leads to an α,β-unsaturated ketone. The mechanism of this reaction has been studied in some detail, including deuterium isotope studies, and the direct observation of enols, silyl enol ethers, and dimers. The rearrangement reaction is postulated to involve the intermediacy of an oxyallyl, the transfer of a hydrogen from the anti-alkyl substituent of this oxyallyl to the oxyallyl oxygen atom, which leads to an enol, and then finally tautomerization of the enol to the ketone. The thermal stability of the cyclopropanones is directly related to the ease of this rearrangement and, in two cases studied here, the rearrangement takes place rapidly even at −95 °C and the cyclopropanones could not be observed. There is a remarkably strong correlation between cyclopropanone structure and reactivity, with the main structural factor being the external angles of the cyclopropanone substituents.
Kinetics and mechanism of oxidation of hydroxylamine by hexachloroiridate(IV) ion in buffer solutions
Authors: Rekha Ms. , Prakash Aditya , Mehrotra Raj N.
Published: May 2006

The oxidation of hydroxylammonium ion by [IrCl6]2− ion in acetic acid – acetate buffer solutions, studied by stopped flow, has the stoichiometric ratio Δ[IrCl6]2−/Δ[NH2OH] = 1. The oxidation involves the species [IrCl6]2− and NH3OH+ although spectral analysis of the spent reaction mixture indicates [IrCl5(OH2)]2− to be the main product (almost to the extent of 80%). This anomaly arises because of the aquation of the reduced product [IrCl6]3−. The rate is retarded both by H+ and Cl− ions and the plots of [Formula: see text] against respective concentrations are linear. The proposed mechanism is given by reactions [i]–[v].[Formula: see text]The values of the rate constants at 25 °C are as follows: k1 = 147 dm3 mol−1 s−1 and 102ketKia = 2.8 s−1. The related activation parameters are [Formula: see text], and,[Formula: see text], and [Formula: see text] and [Formula: see text], respectively. The value of Kipd is 2.91 ± 0.03 mol dm−3 and that of Kipa (= 1/Kipd) is 0.344 ± 0.004 dm3 mol−1; both values are almost independent of temperature.
Parvifloracin and parviflorin: cytotoxic bistetrahydrofuran acetogenins with 35 carbons from Asimina parviflora (Annonaceae)
Authors: Ratnayake Sunil , Gu Zhe-Ming , Miesbauer Laura R. , Smith David L. , Wood Karl V. , Evert Dean R. , McLaughlin Jerry L.
Published: May 2006

Using lethality to brine shrimp, activity-directed fractionation of extracts of Asimina parviflora (Michx.) Dunal. (Annonaceae) has led to the isolation of two new and four known acetogenins (1–6). Compound 1, parvifloracin, is the first nonadjacent bistetrahydrofuran acetogenin with 35 carbons. Compound 2, parviflorin, is an unusual adjacent bistetrahydrofuran acetogenin with 35 carbons. Bullatacin (3), molvizarin (4), annonacin (5), and goniothalamicin (6) are also reported for the first time from this plant. Brine shrimp lethality test data and comparative cytotoxicities of 1–6 against three human solid tumor cell lines are presented.
Studies of nonsteroidal anti-inflammatory drugs: azapropazone
Authors: Fauconnier Theresa , Lock Colin J. L. , Bell Russell A. , Britten James F. , Rainsford K. D.
Published: May 2006

The structure of azapropazone, 5-(dimethylamino)-9-methyl-2-propyl-1H-pyrazolo[1,2-a][1,2,4]benzotriazine-1,3(2H)-dione, was determined by single crystal X-ray diffraction. Crystals were orthorhombic (P212121), with a = 5.570(1) Å, b = 14.593(3) Å, c = 19.270(4) Å, and Z = 4. Intensities were measured on a Rigaku AFC6-R diffractometer with Cu-Kα radiation and 2316 reflections were used to determine the structure. Contrary to previous postulates, the tricyclic portion of the molecule is not planar. Azapropazone is a zwitterion with the negative charge delocalized over the β-keto-enol system and with the proton on N(6) of the triazine ring. The nonplanarity of the molecule is caused by steric interaction of a methyl group on the exocyclic dimethylamino group with O(3) of the keto-enol system. Bond lengths and angles are normal. NMR studies showed that at room temperature rapid inversion occurs between the two enantiomers, but this inversion slows at low temperatures with ΔG≠ = 44.9(2) kJ mol−1. The product derived from opening of the pyrazolidine ring of azapropazone by formic acid is not as previously formulated. The compound is 3-dimethylamino-7-methyl-1-valeryl-1,4-dihydro-1,2,4-benzotriazine. Its structure was determined by single crystal X-ray diffraction. Crystals were monoclinic (P21/n), with a = 10.240(2) Å, b = 12.608(3) Å, c = 13.176(3) Å, β = 108.46(3)°, and Z = 4. Intensities were measured on a Rigaku AFC6-R diffractometer with Cu-Kα radiation and 2209 reflections were used to determine the structure. The conformation of the benzotriazine ring system was very similar to that observed in azapropazone and bond lengths and angles were normal.
Basicity, nucleophilicity, and nucleofugality in the elimination–substitution reactions of β-phenylmercaptoethyl phenolates in DMSO–ethanol media
Authors: Xie Hai-Qi , Truong Nguyen , Buncel Erwin , Purdon J. Garfield
Published: May 2006

Kinetic studies have been performed on the base-promoted 1,2-elmination reactions of a series of β-phenylmercaptoethyl phenolates with potassium ethoxide in EtOH–DMSO media, yielding phenyl vinyl sulfide. The E2 mechanism was indicated by the absence of H/D exchange in the substrate when the reaction in EtOD–DMSO-d6 containing EtO− was carried to partial completion. The Brønsted coefficient values (βLG, effect of nucleofugality on reaction rate) of ca• 0.30 and ca• 0.98 were estimated for the reaction in pure DMSO and ethanol, respectively. Comparison of the results with reported reactions of substrates of similar structure revealed the important role of the phenyl group on sulfur, the leaving-group nucleofugality, and the medium basicity, in controlling the reaction pathways (elimination versus substitution).
Gas and solution phase thermochemistry and transition energies of NH2• and NH3•+, and their aquo complexes: an ab initio study
Authors: Yu Dake , Rauk Arvi , Armstrong David A.
Published: May 2006

Ab initio calculations were performed on several aquo complexes of NH2•, and NH3•+, and on monomeric parent species. The geometries were optimized at the HF/6-31 + G* level and the vibrational frequencies were calculated. The total energies and the binding energies of complexes were evaluated at the MP2/6-31 + G* + ZPE level of theory. Gas and aqueous solution phase thermodynamic properites of NH2• and NH3•+ and several other species were calculated. The examination of solution phase properties of the radicals was facilitated by study of the structures and transition energies of aquo complexes. H-bonding interaction energies decreased in the order [Formula: see text] but were generally stronger than σ–σ* interactions involving the unpaired electron. From calculations with the CIS method, the weak absorption observed at 520 nm for aqueous NH2• is confirmed as a 2B1 → 2A1 transition, while the stronger NH2• absorption occurring below 250 nm and the absorption of NH3•+, which rises monotonically below 370 nm, are attributed to solvent-to-solute charge transfer bands. The solution free energies and related E0 values for NH2• and NH3•+ are in agreement with those of Stanbury. The ab initio structure studies show that water protons are bound to N, and proton transfer from solvent in reaction [18], NH2• + e− + H2O → NH3 + OH−, is likely to be the dominant redox reaction of NH2• in alkaline solution. The free energy of solution of NH3•+ is shown to be larger than that of [Formula: see text].
Infrared–ultraviolet double resonance measurements on the temperature dependence of rotational and vibrational self-relaxation of NO(X2Π, υ = 2,j)
Authors: Frost Michael J. , Islam Meezanul , Smith Ian W.M.
Published: May 2006

Infrared–ultraviolet double resonance experiments have been performed to measure the rates of rotational and vibrational self-relaxation in NO at three temperatures: 295 K, 200 K, and 77 K. Pulses of tunable infrared radiation from an optical parameteric oscillator have been used to excite molecules into selected rotational levels (j = 0.5, 6.5, or 15.5) in the [Formula: see text] vibronic component of the X2Π electronic ground state of NO. Loss of population from the initially excited level was observed by making time-resolved laser-induced fluorescence measurements on appropriate lines in the A2Σ+ − X2Π(2,2) band. The rate constants for removal of population from specific rovibronic levels are essentially independent of j and at 295 K agree well with previous direct measurements on a range of υ, j levels. The rotationally thermalized population in υ = 2 relaxes by vibration–vibration (V–V) energy exchange, NO(υ = 2) + NO(υ = 0) → 2 NO(υ = 1), at a rate which is almost independent of temperature and which seems to be uninfluenced by the presence of spin-orbit degeneracy in, and attractive forces between, the NO collision partners.
Non-equilibrium kinetics of bimolecular reactions. Part 6. Transient rate coefficients
Authors: Carruthers Chris , Teitelbaum Heshel
Published: May 2006

The master equation is solved numerically for the time dependence of the vibrational level populations of HCl (treated as a simple harmonic oscillator) during the bimolecular exchange reaction, Br + HCl → HBr + Cl, taking into account the competition between reaction and vibrational equilibration subject to Landau–Teller T–V excitation. Strong deviations from Boltzmann distributions are found. A wide range of reactant concentrations, diluent concentrations and temperatures were explored. It was found that no significant reaction occurs before the establishment of a steady vibrational population distribution, confirming that the rate coefficient for non-equilibrium bimolecular exchange reactions can be determined from a simple analytical steady state treatment (J. Chem. Soc. Faraday Trans. 87, 229 (1991)). The rate of an isolated elementary bimolecular reaction, A + BC → AB + C, under non-equilibrium conditions can deviate seriously from the standard expression, Keq [A][BC], and is better given by the law[Formula: see text]where [R] is the concentration of the collisional equilibrator, R, and a and g are constants depending only on temperature. This generalized rate law describes not only the initial rate but also the rate all the way up to completion, in the absence of the reverse reaction.
Multiple potential surfaces and movable energy barriers in the chemiluminescent reaction Mn + SnCl4
Authors: Herbertson Dale L. , Newnham David A. , Levy Martin R.
Published: May 2006

A laser-ablated pulsed beam of Mn atoms, in various long-lived states, has been employed to determine excitation functions for the reactions Mn + SnCl4 → MnCl* ("blue," "green," "red") + SnCl3. The data all show a sharp rise at low energies, followed by an equally rapid fall, but they differ in the initial thresholds and the rate at which σ(ET) approaches zero. Analysis in terms of a multiple line-of-centres model (Levy, Res. Chem. Kinet. 1, 163 (1993)) indicates that each excitation function is unique, and is due to reaction of only one Mn reagent state — most probably the first metastable state, a6DJ. This suggests a strong symmetry control in the entrance channel of the reaction, at least; that is, the Mn atom approaches along the C3 axis of SnCl4, so that the symmetry corresponding to the spatial configuration of the odd d electron is retained. In two cases, "blue" and "red," if not all, the luminescing MnCl* state seems to be produced on a surface that does not directly correlate with the reagents. As collision energy increases in each case, the reaction transition state seems to shift forward into the entrance valley, a result attributed to restricted access to the exit valley.