bluuebunny/crossref_metadata_2025 huggingface dataset:
The molecular conformations of the stereoisomers of 4-methyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin and of the 4,7-dimethyl derivative
Authors: Lachapelle A. , St-Jacques M. , Guimaraes A. C. , Almeida P. De
Published: May 2006

The conformational and dynamic properties of the stereoisomers of 4-methyl-5,6-benzo-2-oxo-1,3,2-dioxathiepin (5) and of the 4,7-dimethyl derivative (6) have been investigated by 1H and 13C dnmr methods, as well as by ir spectroscopy. Analysis of the nmr spectra at low temperature (−125 °C), together with the conformational interpretation of the stretching vibration bands of the S = O bond in the ir spectra, indicate that the most stable conformations detected for solutions in CHF2Cl are C-a (82%) and TB-t-Mec (18%) for 5a, TB-c-Mec, (96%) and TB-c-Mea, (4%) for 5b, C-a for 6a, TB-t-Mec, c-Mec, for 6b and C-e for 6c. The substituent effects of a methyl group at the benzylic position on both the conformational and dynamic properties of the seven-membered sulfite are discussed.
Novel gas-phase ions. The radical cations [CH2XH]+• (X = F, Cl, Br, I, OH, NH2, SH) and [CH2CH2NH3]+•
Authors: Holmes John L. , Lossing F. P. , Terlouw Johan K. , Burgers Peter C.
Published: May 2006

The title ions have been generated by dissociative ionisation of appropriate precursor molecules and have been unequivocally identified by collisional activation and collisional ionisation mass spectrometry. Their heats of formation, [Formula: see text], have been measured and were found to be similar to those for their ionic isomer of conventional structure, [CH3X]+•. The exception is [CH2NH3]+• whose [Formula: see text], is ca. 30 kcal mol−1 higher than that of [CH3NH2]+•. The shapes and appearance energies of metastable peaks in conjunction with isotopic labelling experiments, show that these novel ions do not interconvert with their conventional isomer at internal energies below the threshold for their fragmentation of lowest energy requirement, namely, loss of H•. However, unimolecular H• loss from all [CH2XH]+• ions is preceded by a rate determining isomerisation to [CH3X]+•, followed by fast dissociation. The results are generally in good agreement with recent abinitio calculations. Also described are the properties of the homologous ion [CH2CH2NH3]+•.
The synthesis of primary, secondary, and tertiary ferrocenylethylamines
Authors: Butler Ian R. , Cullen William R.
Published: May 2006

A simplified procedure for the preparation of α-N,N-dialkylaminoethylferrocenes R2NR′ (R = Me, C6H11, CHMe2; R′ = CH(CH3)C5H4FeC5H5) from the alcohol R′OH by treatment with HBr and R2NH is described. Use of ammonia results in the isolation of R′NH2, R′2NH (major product) and R′3N and use of the optically active amine d-(+)-H2NCH(CH3)C6H5 gives rise to diastereomers R′NHCH(CH3)C6H5 which are separable. When diphenylphosphine is substituted for an amine the oxide R′P(O)Ph2 is obtained in low yield. The secondary amine R′2NH reacts with n-butyllithium and chlorodiphenylphosphine to afford R′2NPPh2.
Optically active 1-aminoalkanephosphonic acids. Dibenzoyl-L-tartaric anhydride as an effective agent for the resolution of racemic diphenyl 1-aminoalkanephosphonates
Authors: Kafarski Pawel , Lejczak Barbara , Szewczyk Jerzy
Published: May 2006

Optically active phosphonic analogues of alanine, valine, leucine, phenylalanine, and phenylglycine were obtained by resolution of diphenyl 1-aminoalkanephosphonates with dibenzoyl-L-tartaric acid anhydride.
An abinitio study of the A2A′—X2A″ vibronic transition in the free radical HNF
Authors: Perić Miljenko , Peyerimhoff Sigrid D. , Buenker Robert J.
Published: May 2006

Potential energy curves for the two lowest electronic states X2A″ and A2A′(2Π in linear geometry) of HNF are calculated employing configuration interaction. A vibrational analysis of the A2A′—X2A″ transition is undertaken; stretching and bending modes are treated separately but vibronic coupling and large-angle bending is taken into consideration explicitly. The various vibronic levels including their K-type structure are compared with measured data wherever available and the results indicate that the prediction of vibronic spectra in small molecules on the basis of purely abinitio data is now within reach.
Kinetics and mechanism of the bromination of 4-pyridone and related derivatives in aqueous solution
Authors: Tee Oswald S. , Paventi Martino
Published: May 2006

The kinetics of bromination of 4-pyridone and selected derivatives have been measured in aqueous solutions in the pH range 0–9, at 25 °C. The tautomeric system 4-pyridone [Formula: see text] 4-hydroxypyridine [Formula: see text] reaets with bromine via the predominant (pyridone) tautomer at pH < 6 and via the conjugate anion at pH > 6. 3-Bromo-4-pyridone behaves similarly. The kinetics also reveal that the facile dibromination of 4-pyridone occurs because at most pH's the monobromo derivative is actually more reactive towards bromine by virtue of its lower pKa values. From the point of view of reactivity the 4-pyridones and their anions behave as substituted phenoxide ions. 4-Methoxypyridine does not undergo bromination under comparable conditions, but rather forms a complex with bromine.
The crystal structure of potassium 1-(N,N-diphenylhydrazono)-2,4,6-trinitrobenzenide
Authors: Gopal Ramanathan , Robertson Beverly E. , Weil John A.
Published: May 2006

Crystals of potassium 1-(N,N-diphenylhydrazono)-2,4,6-trinitrobenzenide, C18H12N5O6K, are monoclinic, P21/c, a = 9.871(2), b = 12.940(3), c = 16.754(4) Å, β = 118.31(1)°, Z = 4, T = 22 °C. Diffraction data were collected on a modified Picker FASC-1 diffractometer. The structure was solved by direct methods and refined by full-matrix least-squares to R = Rw = 0.056 using the 2627 independent reflections with [Formula: see text]. The benzenide ring shows a significant puckering toward the boat conformation. Some important canonical structures contributing to the average geometry of the molecule are discussed. The bonding sphere of the K+ cation contains all of the oxygen atoms and the hydrazine nitrogen atom bonded to the trinitrobenzenide group. Two phenyl carbon atoms also have short contact distances to the cation.
A relationship between some long-range 2H/1H isotope shifts in 13C nuclear magnetic resonance and long-range spin–spin coupling constants for toluene, ethylbenzene, and isopropylbenzene
Authors: Schaefer Ted , Peeling James , Wildman Timothy A.
Published: May 2006

A very good correlation exists between long-range spin–spin coupling constants involving the α-protons in toluene, ethylbenzene, and cumene, and the changes in the chemical shifts of the para and α carbons caused by deuterium substitution at the α carbon. The coupling constants depend on sin2 θ, where θ is the angle by which the α C—H bond twists out of the ring plane, and can be used to find the expectation value of sin2 θ. Consequently the observed correlation provides quantitative support for the hyperconjugative model employed by Wesener and Günther.
A total synthesis of (±)-triophamine
Authors: Piers Edward , Chong J. Michael , Gustafson Kirk , Andersen Raymond J.
Published: May 2006

Treatment of ethyl 2-pentynoate (14) with lithium (phenylthio)(tri-n-butylstannyl)cuprate (12) afforded, in 76% yield, ethyl (Z)-3-(tri-n-butylstannyl)-2-pentenoate (15). On the other hand, when compound 14 was allowed to react with the (tri-n-butylstannyl)copper reagent 13, ethyl (E)-3-(tri-n-butylstannyl)-2-pentenoate (21) was produced in 83% yield. Reduction (diisobutylaluminum hydride, ether) of the esters 15 and 21 gave the alcohols 16 and 22, respectively. Treatment of each of the latter substances with pyridine – sulfur trioxide complex, followed by further reduction of the resultant intermediates with lithium aluminum hydride, provided the geometrically isomeric alkenylstannanes 17 and 23. Conjugate addition of (E)-3-lithio-2-pentene (18) (formed by transmetalation of 17) to compound 19 produced the olefinic trimethylhydrazide 20, which was converted (diisobutylaluminum hydride, ether; pyridinium dichromate, dimethylformamide) into the corresponding carboxylic acid 2. Subjection of compound 23 to a sequence of reactions identical with that used for the conversion of 17 into 2 provided the isomeric acid 3, which was identical (infrared, 1H nmr) with the natural acid derived from triophamine (1). Conversion of 3 into the p-nitrophenyl ester 26, followed by condensation of the latter substance with guanidine, afforded a chromatographically separable mixture of (±)-triophamine (1) and the corresponding diastereomer.
Comparison of photoconductivity and optical absorption spectra of trapped electrons in γ-irradiated 2,2,4-trimethylpentane/2,2-dimethylbutane/2-methyltetrahydrofuran mixture glasses at 77 K
Authors: Kimura Toyoaki , Hirao Kazunobu , Okabe Naoto , Fueki Kenji
Published: May 2006

Optical absorption and photoconductivity spectra of trapped electrons in -γ-irradiated 2,2,4-trimethylpentane (TMP)/2,2-dimethylbutane (DMB)/2-methyltetrahydrofuran (MTHF) mixture glasses at 77 K have been measured. It is found that the magnitude of the photocurrent increases with decreasing MTHF concentration, which is ascribed to the increase in electron mobility with decreasing MTHF concentration in TMP/DMB/MTHF systems. It is also found that the photoconductivity spectra shift to the lower energy side with decreasing MTHF concentration. Although the photoconductivity spectrum in the neat MTHF system is separated from the corresponding optical absorption spectrum, the spectrum becomes closer to the latter with decreasing MTHF concentration in TMP/DMB/MTHF systems. This result indicates that the extent of bound–free transitions increases relative to bound–bound transitions with decreasing MTHF concentration for the photon absorption process of trapped electrons in TMP/DMB/MTHF systems.
Kinetics of the reaction H + C2H6 → H2 + C2H5 in the temperature region of 1000 K
Authors: Cao J.-R. , Back M. H.
Published: May 2006

A system for the measurement of rate constants for elementary reactions of hydrogen atoms in the temperature region of 1000 K is described. The concentration of hydrogen atoms is controlled by the equilibrium constant for dissociation of hydrogen molecules. The kinetics of the rate of conversion of ethane to ethylene in this system has been studied over the temperature range 876–1016 K. The results show that the rate-controlling step is[Formula: see text]and the value obtained for the rate constant is[Formula: see text](R = 1.987 cal mol−1 deg−1). This value is compared with values obtained from other methods over the temperature range 300–1400 K. Combination with a recent measurement of the rate constant for the reverse reaction yields an experimental value for the equilibrium constant for the reaction.
A Fourier transform infrared study of the electrophilic attack at the N7-site of guanosine-5′-monophosphate
Authors: Tajmir-Riahi H. A. , Theophanides T.
Published: May 2006

Fourier transform infrared spectra of several N7-bound cations of guanosine-5′monophosphate disodium salt (5′-GMPNa2), such as N7-H+GMP, N7-MeGMP, and N7-MGMP, where Me = CH3+ and M = divalent metal ions, Cd, Mn, Co, Ni, Cu, Pt, and Mg, have been recorded and a correlation between the spectral changes and the nature of the electrophile (H+, CH3+, and M2+) bound has been established. Spectroscopic evidence shows that methylation of the N7-position of 5′-GMPNa2 causes larger perturbation on the guanine ring system than protonation or metalation, in the order Me+ > H+ > M2+. The effect of an N7-electrophilic attack on the vibrational frequencies of the purine, the sugar, and the phosphate group is discussed.
Electrochemical oxidation of 4-substituted N,N-dimethylaniline in the presence of silyl enol ether. Effect of the substituent on the formation of Mannich bases. II.
Authors: Renaud Roger N. , Stephens Campbell J. , Brochu Gaétan
Published: May 2006

The formation of Mannich bases from the electrochemical oxidation of 4-substituted N,N-dimethylaniline in the presence of silyl enol ether was studied. The yield of bases obtained depended on the relative oxidation potentials of the starting amine compound and the base formed. An electron-donating substituent on the amine showed a large difference in the oxidation potentials and gave the highest yield of product. On the other hand, the oxidation potentials were very close with an electron-withdrawing substituent and the yield in base was relatively much lower. Furthermore, the main product in the case of an electron-withdrawing group in the presence of 1-trimethylsilyloxy-1-cyclohexene was 4-substituted 2-(2-oxocyclohexyl)-N,N-dimethylaniline. Some side products were also isolated and were identified as N,N-diketonic compounds.
Formation and spectra of flavin radicals in the presence of β-mercaptoethanol at pH 9 and 10
Authors: Surdhar Parminder S. , Ahmad Rizwan , Armstrong David A.
Published: May 2006

Spectral changes and rates of reaction of flavins and several radical species have been investigated at pH 7, 9, and 10 in the presence and absence of β-mercaptoethanol. The radicals •CO2−, eaq−, and [Formula: see text] reacted with FAD at pH 10 to give a spectrum of FAD •Fl− with rate constants of 7 ± 1 × 108 and 4 ± 1 × 108 M−1 s−1 for •CO2− and [Formula: see text] respectively. At pH 7 only •FlH was observed and at pH 9 a mixture of •FIH and •Fl−.Interactions between flavin radicals and sulphydryl at 10−4 M concentration did not cause perturbations in the uv–visible spectra until either the radical and/or the sulphydryl were ionized. With FAD at pH 9 or 10 and LFl at pH 10 the 370 nm peak of •Fl− was enhanced by about 15% and a second larger growth occurred near 450 nm in the presence of 10−4 to 10−2 M sulphydryl. We attribute this to the formation of labile intermediate RSHFl•−, which must also be involved in the reduction of Fl by [Formula: see text] at pH 9 or 10.The second order rate constant k13 for reaction of [Formula: see text] with FAD at pH 9 and 10 was found to be 4.2 ± 0.5 × 108 M−1 s−1 and 2.0 ± 0.4 × 108 M−1 s−1 respectively. The rate constant for the reaction between [Formula: see text] and LFl at pH 10 was slightly faster, 7 ± 1 × 108 M−1 s−1, probably reflecting the fact that LFl lacks the bulky negatively charged adenine dinucleotide group of FAD.
Alkaloids of Aconitumcolumbianum Nutt•
Authors: Boido Vito , Edwards Oliver E. , Handa Kashmiri L. , Kolt Ralph J. , Purushothaman Koziparambil K.
Published: May 2006

The most abundant readily isolated alkaloids of the aerial portion of Aconitumcolumbianum Nutt• were found to be talatisamine and cammaconine. New spectral data for known derivatives of these alkaloids and descriptions of new derivatives are presented. Less abundant alkaloids identified included the known ones sachaconitine, talatizidine, isotalatizidine, and 14-O-acetyltalatisamine, and the new ones 8-O-methyltalatisamine and a tetrahydroxymonomethoxy alkaloid, columbianine, with the same oxygenation pattern and stereochemistry as cammaconine.
The preparation, spectral properties, structures, and base-induced cleavage reactions of some α-halo-β-ketosulfones
Authors: Grossert J. Stuart , Dubey Pramod K. , Gill Glen H. , Cameron T. Stanley , Gardner Patrick A.
Published: May 2006

The halogenation of β-ketosulfones such as α-methylsulfonylacetophenone (1) and benzenesulfonylacetone (10) can be effected with sulfuryl chloride or pyridinium bromide perbromide. Regiochemical control can be achieved by control of stoichiometry and/or the reaction conditions. Detailed 1H and 13C nmr, and mass spectra are recorded for a series of halogenated β-ketosulfones, together with structures by X-ray crystallography for 1, 2-chloro-2-methylsulfonyl-1-phenylethanone (2), chloromethyl methyl sulfone (4), and α-chloroacetophenone (21). Results from these studies are used to suggest a reason for the difficulty associated with substitution reactions of α-halosulfones.
Vapor-phase charge-transfer complexes. 12. Dimethyl ether – iodine
Authors: Lo S. J. , Tamres M.
Published: May 2006

Both a modified Benesi–Hildebrand method and the constant activity method were used to study the spectral and thermodynamic properties of the dimethyl ether – iodine complex in the vapor phase and in n-heptane solution. Comparison is made of these results with those for the diethyl ether – iodine complex. The solvent effects on ether – iodine, a relatively weak complex, are compared with those on stronger complexes.
An infrared study of water–ion interactions in perfluorosulfonate (Nafion) membranes
Authors: Quezado Sylvio , Kwak Jan C. T. , Falk Michael
Published: May 2006

We have studied the infrared spectra of Nafion membranes in twenty different cationic forms, in order to characterize the water–anion–cation interactions at low water contents. Spectra in the OH stretching region and in the H—O—H bending region allow the distinction between hydrogen-bonded and non-hydrogen-bonded water molecules, and yield information on the mode of attachment of water molecules to the anion–cation pairs. When there is a good match between the Lewis acid strength of the cation and the Lewis base strength of the anion, ion pairs are relatively stable and water molecules tend to attach on the outside. When the acid strength of the cation and the base strength of the anion are mismatched, as is the case for small cations of high charge or for large cations of low charge, water molecules tend to be inserted between the ion pairs even at the lowest water contents.
Vibrational spectral studies of solutions at elevated temperatures and pressures. VI. Raman studies of perchloric acid
Authors: Ratcliffe C. I. , Irish D. E.
Published: May 2006

Raman spectra of perchloric acid in water have been measured for solutions spanning a wide concentration range and, for two specific concentrations, a wide range of temperatures. The acid is completely dissociated down to a water:acid mole ratio of about 1.8 at room temperature. At elevated temperatures it is still a very "strong" acid. As the concentration increases the apparent symmetry of the ClO4− ion decreases and a small amount of a new species assigned as associated ClO4−•(Haq)+ can be detected. The effects on the OH stretching bands of water, of temperature, ClO4−, and the excess acid protons are discussed.
Structural studies of organoboron compounds. XX.(Salicylaldoximato-O,N)diphenylboron
Authors: Kliegel Wolfgang , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of (salicylaldoximato-O,N)diphenylboron are triclinic, a = 10.125(2), b = 10.797(1), c = 14.760(2) Å, α = 89.05(1), β = 86.98(1), γ = 83.18(1)°, Z = 4, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.048 for4145 reflections with I ≥ 3σ(I). The structure consists of two crystallographically independent, but essentially identical, molecules linked by strong [Formula: see text] hydrogen bonds to form continuous spirals along the a axis. The Ph2B moiety is chelated by the phenolic oxygen and oxime nitrogen atoms of the ligand resulting in the formation of a non-planar six-membered chelate ring. Important libration-corrected mean bond lengths are O—B = 1.516(1), N—B = 1.609(2), and C—B = 1.613(2) Å.
Synthesis and structural characterization of bis(tropolonatodimethylgallium), [(C7H5O2)Ga(CH3)2]2
Authors: Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Details of the synthesis, physical properties, and solid-state structure of [(C7H5O2)Ga(CH3)2]2 are reported. Crystals of bis(tropolonatodimethylgallium) are monoclinic, a = 10.2669(9), b = 9.3237(3), c = 10.8671(10) Å, β = 112.896(4)°, Z = 2, space group P21/n (22°C, λ = 0.70930 Å). The structure was solved by conventional heavy-atom techniques and was refined by full-matrix least-squares procedures to R = 0.034 and Rw = 0.037 for 1746 reflections with I ≥ 3σ(I). The centrosymmetric binuclear dimer features five-coordinate gallium atoms having irregular trigonal bipyramidal coordination geometry and a planar four-membered Ga2O2 ring. Important bond lengths (corrected for libration) are Ga—O(equatorial) = 1.972(2), Ga—O(axial) = 2.025(2) and 2.551(2) Å, and Ga—C = 1.951(4) and 1.954(4) Å.
The gas-phase photolysis of 2-methyl-1,3-butadiene at 123.6 nm
Authors: Lang Valerie I. , Doepker Richard D.
Published: May 2006

The gas-phase photolysis of 2-methyl-1,3-butadiene has been investigated using krypton (123.6 nm) resonance radiation. The observed neutral products of the primary decomposition were vinylacetylene, ethylene, acetylene, methylacetylene, propylene, allene, 2-methy-1-buten-3-yne, pentatriene/1-penten-3-yne, 1,3-butadiene, 2-butyne and butatriene, listed in decreasing order of concentration. There was also evidence of the presence of several radical fragments: CH2/CH3, C2H3, C3H3, and C4H5. Quantum yields for each of the products were determined in the photolysis of 2-methyl-1,3-butadiene, performed both in the presence and the absence of additives. Nitric oxide and oxygen were employed as radical scavengers, while hydrogen sulfide and hydrogen iodide were used as radical interceptors. Twelve primary, neutral molecule, reaction channels were proposed and the quantum efficiency assigned for each. The ionization efficiency of 2-methyl-1,3-butadiene was established as n = 0.55 at 10.03 eV. No products formed exclusively via an ion–molecule pathway were identified and therefore the fate of the C5H8+ ion was not determined.
Aliphatic diazo compounds. XIV. The synthesis of 7-substituted 3-diazo-2-norbornanones and the infrared and proton and carbon-13 nuclear magnetic resonance spectra of these diazo ketones and their precursors
Authors: Yates Peter , Kronis John David
Published: May 2006

syn- and anti-7-Isopropyl-2-norbornanone (5 and 6) were prepared by catalytic hydrogenation of 7-isopropylidene-2-norbornanone; syn- and anti-7-benzhydryl-2-norbornane (9 and 10) were prepared in analogous fashion. Ketones 5 and 6 and syn- and anti-7-tert-butyl-2-norbornanone (7 and 8) were converted to the corresponding 3-diazo-2-norbornanones 1–4 via the monotosylhydrazones 44–47 of the corresponding α-diketones 40–43. The 1H and 13C nmr spectra of 1–10, 40–47, and their precursors have been analyzed. The 1H nmr spectra of the diazo ketones 1–4 have their C-1 and C-4 bridgehead proton signals shifted to higher and lower field, respectively, relative to the bridgehead signals of the corresponding diketones. The 13C nmr spectra of all pairs of bicyclic epimers shown γ-gauche shielding effects by the 7-substituent at (sp3) C-3 in the syn compounds and at C-5 and C-6 in the anti compounds. A converse effect is found at (sp2) C-2 (and C-3 in the diketones). Comparison of the magnitude of the shielding effects of C-7 methyl, isopropyl, benzhydryl, and tert-butyl substituents gives evidence of δ deshielding effects at C-3 in the syn compounds and at C-5 and C-6 in the anti compounds by methyl substituents on C-8.
Synthèse de méso-α,γ bis(diamino-2,6 phényl) porphyrines
Authors: Lecas-Nawrocka Alexandra , Levisalles Jacques , Mariacher Claire , Renko Zafiarisoa , Rose Eric
Published: May 2006

The syntheses of α,γ-meso-bis(2,6 diaminophenyl) octaalkyl-porphyrins are described starting from 2,6-diacetamidophenyl-bis(2′-benzyloxycarbonyl, 3′,4′-dialkyl, 5′-pyrryl) methanes. The synthesis of such double-picket-fence porphyrins enables the four amino groups to function in such a way as to protect both faces of these porphyrins.
Synthesis of 18F-labelled 2-fluoroethyl-nitrosoureas
Authors: Farrokhzad Simin , Diksic Mirko , Yamamoto Lucas Y. , Feindel William
Published: May 2006

18F-labelled 1,3-bis-(2-fluoroethyl) nitrosourea (18F-BFNU) (9) and 1-(2-chloroethyl)-3-(2-fluoroethyl) nitrosourea (18F-CFNU) (isomeric mixture, 11,12) were synthesized by nucleophilic attack of 18F-labelled tetra-n-butylammonium fluoride on the aziridine ring of 1,3-substituted ureas. Diethyleneurea (DEU) (5), 1-(2-fluoroethyl)-3-ethyleneurea (FEU) (7), and 1-(2-chloroethyl)-3-ethyleneurea (CEU) (14) were used as starting materials in the synthesis. Nitrosation of 18F-labelled 1,3-bis-(2-fluoroethyl) urea (18F-BFU) (6) produced 18F-BFNU with a radiochemical yield of 5–10%. Nitrosation of 18F-labelled 1-(2-chloroethyl)-3-(2-fluoroethyl) urea (18F-CFU) (15) gave 18F-CFNU as a mixture of two isomers. Geometrical isomers of CFNU were separated by hplc, and the radiochemical yield of the two isomers ranged from 8% to 15%, with a radiochemical purity exceeding 96%. Syntheses, which took about 60 min, yielded products with specific activity of 680 mCi/mmol when n-Bu4N+F− was used, or 300 mCi/mmol when HF was used to complete the opening of the aziridine ring.
Photochemistry of 2-phenylbenzophenone. An unusual bichromophoric molecule
Authors: Scaiano J. C. , Nicodem David E.
Published: May 2006

2-Phenylbenzophenone is proposed to have two nearby triplets, a low lying π,π* state similar to that of biphenyl and a benzophenone-like triplet lying ~4 kcal/mol higher. The triplet lifetimes of this photostable ketone are extremely short, e.g. 0.56 and 2.5 ns at 300 K in toluene and isooctane, respectively, and are believed to be controlled by population of the benzophenone-like triplet and decay from this state via interaction of the carbonyl chromophore with the phenyl ring in the ortho position. The two triplets interconvert via ring rotation. The Arrhenius parameters for triplet decay in five solvents show some dependency with the temperature dependence of the solvent viscosity.
A calorimetric study of trimethylene oxide and its structure I and structure II clathrate hydrates in the temperature range 85 to 270 K
Authors: Handa Y. P.
Published: May 2006

Heat capacities and dissociation properties of trimethylene oxide and its structure I and structure II clathrate hydrates in the temperature range 85 to 270 K were determined using a Tian–Calvet heat flow calorimeter. The hydrates dissociate incongruently. The heat capacities of the hydrates are similar in magnitude to those observed for other structure I and structure II hydrates. For the structure I hydrate two thermal anomalies were observed. The one centered at 107 K can be identified as due to ordering of the trimethylene oxide dipoles along the [Formula: see text] axes of the cages as suggested by the previous dielectric and nmr relaxation studies. The second centered at 168 K is interpreted as due to trimethylene oxide rich eutectic rather than due to some restructuring of the host lattice as has recently been suggested.
Picosecond measurements of geminate charge pair recombination in photoionized liquids
Authors: Scott T. W. , Braun C. L.
Published: May 2006

The recombination dynamics of geminate cation–electron pairs in liquid hexane is studied by combining picosecond photoionization and infrared-stimulated charge dissociation measurements. The observed yield of free charge is determined by the product of the charge pair survival probability and the probability for infrared-stimulated charge dissociation. Experimental results are compared with transient solutions of the Smoluchowski equation governing diffusive recombination in a Coulomb well. Reasonable agreement with experiment can be reached by allowing for a radial distribution of initial pair separations. However, the stimulated dissociation yield exhibits a functional dependence on pair separation which complicates the analysis. A simple model of geminate charge pair dissociation by infrared stimulation is presented and its implications for these experiments are discussed.
Brown algal polyphenols: synthesis of "fucophlorethol A" octamethyl ether (2,2′,4,6,6′-pentamethoxy-4′-(2,4,6-trimethoxyphenoxy)biphenyl)
Authors: Ragan Mark A.
Published: May 2006

Vanadium tetrachloride-catalyzed dimerization of 3,5-dimethoxyphenol yields the key intermediate 2,2′,6,6′-tetra-methoxy-4,4′-dihydroxybiphenyl, from which the octamethyl ether of the brown algal metabolite "fucophlorethol A" (2,2′,4,6,6′-pentamethoxy-4′-(2,4,6-trimethoxyphenoxy)biphenyl, 6) is synthesized by Ullmann condensation and Hakomori methylation.
Enthalpies of transfer of alkane solutes from the vapor state to organic solvents
Authors: Fuchs Richard , Stephenson W. Kirk
Published: May 2006

Heats of solution of 5 – 8 C5–C16 alkane liquids have been determined in each of 19 organic solvents covering the Taft–Kamlert π* (dipolarity-polarizability) range −0.08 to 1.00. Enthalpies of alkane transfer from vapor to solvents have been calculated (ΔH(v → S) = ΔHs − ΔHv). The methylene increments in (ΔH(v → S) in the 19 solvents and water (−1.18 to −0.67 kcal/mol) are not well correlated with the Hildebrand solubility parameter δ, but an empirical correlation exists with solvent π* and polarizability:[Formula: see text](n = 20, r = 0.977, see = 0.032). By this criterion the small methylene increment in water appears to be associated with the high dipolarity and low polarizability of water.
Synthesis of derivatives of isoindole and of pyrazino[2,1-a]isoindole
Authors: Ferland Jean-Marie , Demerson Christopher A. , Humber Leslie G.
Published: May 2006

Amines were reacted with lactones 7 or with unsaturated nitro derivatives 8 to give isoindole and pyrazino[2,1-a]isoindole derivatives. The mechanisms of formation, proofs of structure, and stereochemistry are presented.
On the mechanism of disproportionation reactions of 1,2-dihydroquinolines
Authors: Forrest T. P. , Dauphinee G. A. , Deraniyagala S. A.
Published: May 2006

The commonly accepted mechanism for the acid-catalyzed disproportionation of 1,2-dihydroquinolines involves a hydride transfer from C-2 of one dihydroquinoline molecule to C-4 of another molecule which has already been protonated at C-3. This mechanism is shown to be incorrect. The proposed intermediate is shown to react by solvent addition and not by reduction under the conditions of the reaction. Evidence has been obtained which shows that the reaction proceeds by way of a 3,4-dihydroquinoline intermediate. A possible mechanism for the formation of the intermediate is discussed.
Infrared spectra of the ammonium ion in crystals. Part XIII. Crystal structure of (NH4)2[AlF5(H2O)] and NH3D+ probe-ion spectra in (NH4)2[AlF5(H2O)], NH4AlF4, and (NH4)3ZnCl5, with remarks on structural filiation of AMF4 fluorides
Authors: Knop Osvald , Cameron T. Stanley , Deraniyagala S. P. , Adhikesavalu D. , Falk Michael
Published: May 2006

The crystal structure of (NH4)2AlF5•H2O = (NH4)2[AlF5(H2O)] (Pbcn, a = 10.192(4) Å, b = 8.037(2) Å, c = 7.844(1) Å, Z = 4) consists of isolated [AlF5(H2O)]2− octahedral and NH4+ ions. The octahedra are linked by [Formula: see text] bonds to form zigzag chains parallel to c and the chains are cross-linked by normal [Formula: see text] hydrogen bonds to the NH4+ ions. The ir characteristics of the hydrogen bonds in this and the other two title compounds were probed with the NH3D+ ion between 10 and 293 K. The probe-ion spectra confirm the C1 symmetry of the ammonium ion in (NH4)2[AlF5(H2O)] and point to [Formula: see text] bonding of moderate strength. For NH4AlF4 the spectra agree with the expectation from the known crystal structure of both the ordered and the disordered phase, but the transition at ~150 K is not evident in the evolution of the spectra with temperature. Detailed assignment of the ND stretching and bending component absorptions of NH3D+ is not possible for (NH4)3ZnCl5 = (NH4)3(ZnCl4)Cl. However, the unusually low frequencies of two of the components of the ND stretching absorptions in this crystal indicate the existence of [Formula: see text] bonds stronger than those in NH4Cl. The filiation of the known AMF4 structures deriving from TlAlF4 is presented in terms of two-colour space groups.
Synthesis and thermolysis of 2-(phenylthio)ethanesulfonyl chloride. The absence of a reported "rearrangement of radicals with migration of the chlorine atom from sulfur to carbon"
Authors: King James Frederick , Khemani Kishan Chand
Published: May 2006

2-(Phenylthio)ethanesulfonyl chloride (1) is the major product of the reaction of (a) lithium 2-(phenylthio)ethanesulfinate (6) and chlorine, and, notwithstanding contrary reports, also of (b) benzenethiol (3) and ethenesulfonyl chloride (4), and (c) sodium 2-(phenylthio)ethanesulfonate (5) and phosphorus pentachloride. The rearrangement referred to in the title, which was proposed to account for the isolation of 2-(phenylthio)ethyl chloride (2) rather than 1 from 3 and 4, therefore does not occur. Desulfonylation of 1 to form 2, however, readily takes place thermally and, in accord with a rate-determining internal displacement of the chlorosulfonyl group with formation of the episulfonium ion, shows a substantial increase in rate with increase in solvent polarity.
Intramolecular Michael-type additions. IV. Synthesis of 2-azabicyclo[3.2.1]oct-3-enes from 4-chloroalkyl-1,4-dihydropyridines
Authors: Gregory Brian , Bullock Eric , Chen Teng-Song
Published: May 2006

2-Azabicyclo[3.2.1]oct-3-enes, including examples having a spiro centre at C(8), may be obtained by the reaction of anions derived from 1,3-diketones or cyclopentadiene with 4-chloroalkyl-1,4-dihydropyridines or with azepines. Intermediate 4,5-dihydro-1H-azepines have been isolated under milder conditions. The structures of the bicyclic compounds were established using infrared, ultraviolet, nuclear magnetic resonance, and mass spectrometry. Pharmacological examination of selected compounds revealed low antimicrobial and hypotensive activity.
The crystal and molecular structure of syn-[4.4.3]propella-2,4,12-trien-11-ol 3,5-dinitrobenzoate
Authors: Gallucci Judith C. , Ohkata Katsuo , Paquette Leo A.
Published: May 2006

The crystal structure of syn-[4.4.3]propella-2,4,12-trien-11-ol 3,5-dinitrobenzoate, 2, has been determined by single crystal X-ray diffraction and refined to an R value of 0.051. The crystal structure is triclinic with a = 10.208(2), b = 13.355(2), c = 7.068(1) Å, α = 99.35(1)°, β = 100.63(1)°, γ = 100.79(1)°, and the space group is [Formula: see text] with two molecules per cell, D(calcd) = 1.39 g cm−3. The unsaturated five-membered ring resides in an envelope conformation with C6—C11—C12—C13 lying essentially in a plane. The fifth atom, C1, is positioned 0.47 Å out of this plane on the side opposite O1. The latter is situated 1.38 Å away and projects the 3,5-dinitrobenzoate group above the central portion of the cyclohexadiene unit. Four contiguous carbon atoms in the latter ring are mutually coplanar and the fused cyclohexane ring adopts a chair conformation. The overall molecular geometry is reconcilable with its solvolytic behavior in aqueous acetone.
The preparation of some fused isothiazole derivatives
Authors: McKinnon David M. , Duncan K. Ann , McKinnon Aileen M. , Spevack Perry A.
Published: May 2006

The treatment of di(2-amino-5-methylphenyl)methane with N-sulfinylmethanesulfonamide gives two materials, 3-(2-amino-5-methylphenyl)-5-methyl-2,1-benzisothiazole and what appears to be its tautomer, a 2,1-benzisothiazolo[2,3-b]-2,1-benzisothiazole derivative. Reaction of the former with methyl iodide gives mono-, di-, and trimethyl derivatives. The second of these also possesses the symmetrical 2,1-benzisothiazolo[2,3-b]-2,1-benztsothiazole structure. The structure of the other methylation product and of the acetylation products are discussed. Some 1,2-dithiol-3-ylidene-2-pyridylmethanes were made by condensation of 3-alkylthio-1,2-dithiolium salts with methyl 2-pyridylacetate. These demonstrate little sulphur–nitrogen interaction. 3-Methylthio-4-phenyl-1,2-dithiolium iodide reacts anomalously with methyl 2-pyridylacetate to form a quinolizinethione. 1,2-Benzisothiazolo[2,3-a]pyridintum triiodide was made by iodine oxidation of 2-(2-mercaptophenylpyridine).
L'isomérisation de radicaux insaturés. II. Les radicaux α-éthallyles et α,γ-diméthallyles formés dans la photolyse de l'hexène-3 et du méthyl-4-pentène-2 à 147,0 et 184,9 nm
Authors: Collin Guy J. , Deslauriers Hélène
Published: May 2006

The photolysis of cis-3-hexene and 4-methyl-cis-2-pentene has been studied at 147.0 and 184.9 nm. The fragmentation pattern of the photoexcited molecule is normal: it requires, mainly, the split of a C—C bond located in the β position relative to the double bond [Formula: see text]. Some α(C—C), β(C—H), and α(C—H) primary splits complete this mechanism. The formation of α-ethallyl and α,γ-dimethallyl radicals is important in 3-hexene and 4-methyl-2-pentene, respectively. An isomerization process, involving these two radicals, is necessary to explain the formation of part of the 1,3-pentadiene in the 3-hexene system and of all the 1,3-butadiene in the 4-methyl-2-pentene system. This process involves a 1,4-hydrogen atom transfer.
Dipole moments of some aromatic and aliphatic aldehydes. Their dependence on the solvent and the atomic polarization
Authors: Grosse Constantino , Mechetti Magdalena , Brito Pedro
Published: May 2006

The dipole moments of 21 aromatic and aliphatic aldehydes were determined. Permittivity measurements were performed on highly diluted cyclohexane solutions at 20 °C. The limiting forms of Debye's, Onsager's, and Bordewijk's expressions were used. The influence of the solvent on the dipole moment values was studied using decalin and heptane mixtures. Only the Debye's values presented an apparent solvent effect while the Onsager's and Bordewijk's values remained independent of the solvent. Dipole moment values obtained using the refractive indexes of the components were also compared with those derived using the refractive indexes of the mixtures. This permitted one to estimate in 0.07 the relation between atomic and electronic polarization.
Protonation of purines and related compounds in dimethylsulfoxide and water
Authors: Benoit Robert L. , Boulet Danielle , Séguin Luc , Fréchette Monique
Published: May 2006

The ionization constants of the conjugated acids BH+ of purine, adenine, 9-methyladenine, adenosine, guanine, and hypoxanthine, and of the related compounds imidazole, N-methylimidazole, benzimidazole, and 4-amino-2,6-dimethylpyrimidine have been determined potentiometrically in Me2SO. The heats of solution and the heats of protonation of most of these bases have been obtained by calorimetry. Some additional determinations were carried out in water so that thermodynamic data in Me2SO and in water could be compared. Our discussion of the solvent effect on these data is largely based on a consideration of the enthalpies of transfer of B and BH+ and emphasizes the contrasting H-bonding properties of the solvents and of the functional groups on the solutes B and BH+.
The multiphoton spectra of all-trans 1,3,5-hexatriene in the region of 6.0 eV
Authors: Nascimento Marco Antonio Chaer
Published: May 2006

The multiphoton spectra of all-trans 1,3,5-hexatriene, in the region of 6.0 eV, is investigated using highly correlated wavefunctions. On the basis of the computed transition energies, intensities, and polarization ratios, an attempt is made to explain the experimentally observed spectra.
The search for fluorescence and the study of radiationless transitions of electronic excited states of NH3+
Authors: Dujardin Gérald , Leach Sydney
Published: May 2006

Photoion – fluorescence photon coincidence experiments were carried out in order to detect the fluorescence of NH3+ which is expected to occur from that part of its Ã electronic state that lies below the lowest dissociation limit. Hel and Nel sources were used to produce the ions. No NH3+ fluorescence was detected and upper limits for its quantum yield under our experimental conditions are given. We show that the lifetime of the Ã state is probably very long, making it difficult to observe fluorescence. Furthermore, we argue that the molecular parameters and potential energy surfaces of the Ã and [Formula: see text] states are such that resonance limit nonradiative coupling to high rovibrational levels of the [Formula: see text] state could be an efficient process for apparent intramolecular quenching of NH3+Ã state fluorescence.
La mécanique de la liaison hydrogène: résultats de spectroscopie infrarouge
Authors: Maréchal Y.
Published: May 2006

We review the mechanics of H-bonds as revealed by ir spectroscopy and show how the various (strong) anharmonic couplings of the νs vibrations [Formula: see text]of H-bonds may be treated so as to eliminate the irrelevant features of the spectra and keep only those features which may give information on the still unknown dynamical quantities of the H-bonds, such as the transfer of protons through H-bonds or the mechanism of rupture of H-bonds. We also describe the possibilities offered by vibrational spectroscopy for studying these dynamical quantities, which may be important in biology.
Infrared spectra of some matrix isolated organoisothiocyanate molecules
Authors: Durig J. R. , Sullivan J. F. , Durig D. T. , Cradock Stephen
Published: May 2006

The infrared (3500 to 300 cm−1) spectra of methylisothiocyanate, ethylisothiocyanate, isopropylisothiocyanate, and cyclopropylisothiocyanate isolated in argon and nitrogen matrices have been recorded. In general, the spectra were more complex in the nitrogen matrices and, for ethylisothiocyanate, nearly all of the fundamentals appeared as doublets in the nitrogen matrix but for the most part as single bands in the argon matrix. No evidence could be found for a second conformer for either ethylisothiocyanate or isopropylisothiocyanate. Even though cyclopropylisothiocyanate has been shown to exist as the cis and trans conformers at ambient temperature, little conclusive evidence could be found for two isomers in the infrared matrix material. The complex spectra observed in the NCS antisymmetric stretching region as well as in the 520 cm−1 region appear to arise in part from combinations involving the low-frequency large amplitude CNC bend or asymmetric torsion of these organoisothiocyanate molecules. It appears that the vibrational spectra of these molecules are not sensitive to the orientation of the NCS moiety.
A model for the geometries of Van der Waals complexes
Authors: Buckingham A. D. , Fowler P. W.
Published: May 2006

Structures of Van der Waals complexes are predicted by a simple model based on electrostatic interaction between the monomers. Point multipoles are assigned to the atoms and embedded in hard spheres to represent short-range repulsions. Structures deduced for some 29 complexes are in agreement with experiment, and numerous predictions are made.
Synthèse d'aryl nitronorbornènes par cycloaddition de Diels–Alder entre les aryl-nitroéthylènes et le cyclopentadiène. Justification de la stéréochimie et de la réactivité relative observées par la méthode CNDO/II. Obtention d'aryl aminonorbornènes
Authors: Bourguignon Jean , Nard Gilles Le , Queguiner Guy
Published: May 2006

Syntheses of numerous 2-aryl nitroethylenes (nitrostyrenes) have been optimized. The nitrostyrenes have been reacted with cyclopentadiene in Diels–Alder cycloadditions and the 3-aryl 2-nitronorbornenes obtained have been reduced into 3-aryl 2-aminonorbornenes. These compounds are potentially dopaminergic molecules. The stereochemistry of the adducts obtained in the Diels–Alder reaction has been determined by 1H nmr. The stereochemistry and the relative reactivity of the nitrostyrenes versus cyclopentadiene have been confirmed by theoretical calculations based on the CNDO/II method.
Cyclic voltammetric study of acid hydrolysis of tris(bipyridine) chromium(II): a critical appraisal of CV determination of kinetic parameters
Authors: Nadler Shachar D. , Dick James G. , Langford Cooper H.
Published: May 2006

Cyclic voltammetry has been exploited to reinvestigate discrepancies in the reported rate constant for the reaction:[Formula: see text]which follows electrode reduction of the substitution inert [Formula: see text]. It is shown that the problems arise from oversimplified treatment of residual currents when estimating the anodic peak current, ia. A "two scan" procedure for estimating the background currents is introduced which appears to resolve discrepancies. The kinetic studies were extended to a methyl-substituted bipyridine. Since ring methylation has very little effect on kf, it appears that the aquation reaction is initiated by a rate-determining step which requires a minimum of bipyridine rearrangement.
The two liquid phase system NaAl(ethyl)4 – benzene–HMPA
Authors: Medley James H. , Ahmad Naseer , Day Marion C.
Published: May 2006

A detailed study of complexation of the sodium ion by HMPA2 has been made using the system[Formula: see text]where HMPA is observed to be a strong donor towards Na+ but does not complex AlEt4−. This system forms two liquid phases at low HMPA:Na+ molar ratios with the salt and the HMPA, up to a 4:1 HMPA:Na+ ratio, occurring only in the lower phase. Based on a variety of experimental techniques, reasonable proposals of the solute species in the lower phase as a function of HMPA:Na+ ratio are presented. A 2.5:1 ratio of HMPA:Na+ is observed to be particularly significant. This ratio is rationalized in terms of a bridging HMPA molecule resulting in a cationic species with the stoichiometry [2Na•5HMPA]2+. It is found that the 27Al and 1H nmr spectra are determined primarily by quadrupole relaxation of the 27Al nucleus rather than by exchange.
Syntheses and reactivity of square-planar Rh(I) complexes, LRh(CO) (L = unsymmetric tridentate chelating pyrazolylgallate ligand). X-ray crystal structures of [Me2Gapz(OCH2CH2NH2)]Rh(CO) and [Me2Gapz(OCH2CH2NMe2)]Rh(COMe)I (pz = pyrazolyl, N2C3H3)
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The syntheses and characterization of a number of square-planar Rh(I) monocarbonyl complexes incorporating un-symmetrical, tridentate, pyrazolylgallate ligands in a meridional coordination mode are described. Oxidative addition reactions of these complexes are detailed and a facile migratory insertion reaction, following the addition of methyl iodide, has resulted in a five-coordinate square-pyramidal Rh(III) acetyl complex. Crystal structures of two compounds are presented, [Me2Gapz(OCH2CH2NH2)]Rh(CO) and [Me2Gapz(OCH2CH2NMe2)]Rh(COMe)I, and confirm the molecular arrangements predicted on the basis of other physical measurements. Crystals of the former are monoclinic, a = 10.212(2), b = 7.8484(5), c = 16.733(2) Å, β = 105.133(6)°, z = 4, space group P21/c; and those of the latter are monoclinic, a = 10.0960(11), b = 11.5352(8), c = 15.871(2) Å, β = 105.764(6)°, z = 4, space group P21/n. Both structures were solved by conventional heavy atom methods and were refined by full-matrix least-square procedures to R = 0.026 and 0.036, respectively, for 2142 and 2941 reflections with I ≥ 3σ(I).
Synthesis, base strength, and prototropic behaviour of a number of alkyllumazines
Authors: Stewart Ross , Gumbley S. J.
Published: May 2006

A number of lumazines and 5-deazalumazines containing a methyl group at C-7 have been prepared, their pKBH+ values determined, and measurements made of the rates at which the hydrogen atoms of their 7-methyl groups undergo isotopic exchange in aqueous sulfuric acid. The presence of an alkyl group at N-8 in the protonated forms of these compounds activates the neighbouring methyl group at C-7; the effect is considerably larger than that previously observed for a methyl group at C-6, which is the other neighbouring position. The comparison of methyl and hydrogen at N-8 can be made only for the acid-catalyzed reaction because the structures of the neutral compounds, which take part in the base-catalyzed reaction, are not analogous.