bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Resonance Studies of the Solution Chemistry of Metal Complexes. XIII. The Lability of the Metal–Nitrogen Bonds in the Cadmium, Zinc, and Mercury Complexes of Selected Polyaminocarboxylic Acids
Authors: Rabenstein Dallas L. , Blakney George , Fuhr Bryan J.
Published: May 2006

The lability of the metal–nitrogen bonds in the Cd(II), Zn(II), and Hg(II) complexes of (HO2CCH2)2N(CH2)nN(CH2CO2H)2 (n = 2, 3, 4) has been investigated by proton magnetic resonance spectroscopy. The acetate methylenic protons of each of the complexes give rise to AB multiplet patterns, indicating the metal–nitrogen bonds to be inert on the n.m.r. time scale. From the temperature dependence of the multiplet patterns, the relative lability of the metal–nitrogen bonds in each series of complexes has been established. In the Cd(II) and Zn(II) complexes, the metal–nitrogen bonds become more labile as the size of the internal chelate ring increases whereas it becomes more inert in the Hg(II) complexes. Also, the mercury–proton coupling constants increase as n is increased from two to four, which is interpreted as evidence that the increased kinetic stability results from structural changes to a more linear N—Hg—N arrangement. The metal–nitrogen bonds in the Cd(II) complexes having n = 3 and 4 is more labile than in the corresponding Zn(II) complexes. The thermodynamic stability patterns of the complexes are discussed in terms of their relative kinetic stabilities.
Synthesis and Characterization of Some Dibasic Tridentate Schiff Base Ligands
Authors: Alyea Elmer C. , Malek Abdul
Published: May 2006

The synthesis and characterisation of several dibasic tridentate Schiff base ligands (H2SB) are described. Structural formulas for the isolated ligands are suggested on the basis of infrared, nuclear magnetic resonance, and mass spectral data.
Variable Temperature Nuclear Magnetic Resonance Studies of Some Five-Membered Ring Chelate Complexes
Authors: Cullen William R. , Hall Laurance D. , Ward John E. H.
Published: May 2006

The temperature dependence of the n.m.r. spectra of nine ditertiary arsine chelate complexes of formula (CH3)2AsC(3)(3′)C(4) (4′)As(CH3)2M(CO)3X has been studied (M = Mo, Cr; X = CO; M = Mn; X = halogen; (3), (3′), (4), (4′) = H, F, Si(CH3)3, CN; but not all combinations ). Significant variation in coupling constants, indicating a shift in the conformer populations, was found only for the CHFCF2 bridged Mn(CO)3Cl complex, the CH2CF2 bridged Mn(CO)3Cl complex, and the CHFCHF bridged Mo(CO)4 complex. In the last case the 3JHH coupling constants were used to estimate ΔH ∼ 1 kcal/mol and ΔS ∼ 3 e.u for the conformational equilibrium.
The Activity of AgCl in AgCl–LiCl–KCl Melts
Authors: Gruner Anthony C. , Thompson William T.
Published: May 2006

Thermodynamic properties of silver chloride in molten silver chloride – lithium chloride – potassium chloride melts were studied using a silver chloride formation cell employing a chlorine electrode of novel design which facilitated measurements in ternary melts. The data were treated by analytical methods resulting in the generation of activity and the partial molar excess free energy at 500 °C.The measured properties were interpreted with the aid of a model which presupposed the existence of free silver ions as well as those "bonded" to adjacent chloride ions. With three adjustable parameters it was possible to account for the thermodynamic behavior of silver chloride.
Oligoribonucleotide Synthesis. VIII. Insertion of Terminal 5′-Phosphate Groupings
Authors: Neilson Thomas , Deugau K. V. , England T. E. , Werstiuk E. S.
Published: May 2006

General oligoribonucleotide synthesis using phosphotriester protection has been extended to allow insertion of terminal 5′-phosphates. Selective removal of 5′-triphenylmethoxyacetyl groups allow phosphorylation by TPS-activated mono-2,2,2-trichloroethylphosphate on protected oligomers.
On the π-Donating Abilities of Sulfur and Oxygen. A Comparative Quantum Chemical Investigation of the Static and Dynamic Properties and Gas Phase Acidities of and
Authors: Bernardi Fernando , Csizmadia Imre G. , Schlegel H. Bernhard , Wolfe Saul
Published: May 2006

Nonempirical SCF-MO computations have been performed on CH2O, CH2S, and their protonated derivatives [Formula: see text] and [Formula: see text]. The methylene group of CH2O is strongly positive and that of CH2S is slightly negative, because oxygen in CH2O behaves towards carbon as a π-donor and σ-acceptor, but sulfur in CH2S behaves as both a π- and σ-donor. The total π-overlap in CH2O is greater than that in CH2S.The stable conformations of [Formula: see text] and [Formula: see text] correspond in each case to a structure in which all atoms lie in the same plane. In this conformation, both the C—O and C—S bond lengths are substantially shorter than those of methanol and methanethiol, indicative of conjugative interaction between the cationic center and the adjacent heteroatom. From the results of a Mulliken-type population analysis it is found that, relative to hydrogen, OH and SH behave towards an adjacent [Formula: see text] group as electron-withdrawing and electron-releasing ligands, respectively. When [Formula: see text] is considered to form from [Formula: see text] and OH fragments, π-donation from O to C amounts to 0.38 electron, but σ-donation in the opposite direction amounts to 0.35 electron; the π-overlap population is 0.1496. A similar analysis of [Formula: see text] reveals π- and σ-donation from S to C of 0.53 and 0.15 electron, respectively, and a π-overlap population of 0.1734, so that sulfurformsastronger π-bondtotheadjacentcationiccenter.Geometrical isomerization of [Formula: see text] proceeds by linear inversion at oxygen, with a barrier of 13.98 kcal/mol; but that of [Formula: see text] proceeds by rotation about the C—S bond, with a barrier of 36.47 kcal/mol. This latter value is substantially higher than that (23 kcal/mol ) computed for [Formula: see text] with a rigid rotor model, and reflects the greater strength of the π-bond between sulfur and the adjacent cationic center.
Nucleic Acid Related Compounds. 16. Direct Fluorination Of Uracil Nucleotides Using Trifluoromethyl Hypofluorite
Authors: Robins Morris J. , Ramani G. , MacCoss Malcolm
Published: May 2006

Treatment of commercially available uracil nucleotides and dinucleoside phosphates in methanolic solutions with trifluoromethyl hypofluorite in trichlorofluoromethane (Freon 11) gave adducts which were converted into the corresponding 5-fluorouracil nucleotides in basic solution. This procedure circumvents certain problems involved in phosphorylation of the rather inaccessible and expensive 5-fluorouracil nucleosides.Salts of both 5-fluorouridine-5′-monophosphate (5′-FUMP) and 5-fluorouridine-3′,5′-cyclic monophosphate (cFUMP) were crystallized and fully characterized. The procedure is not readily applicable to dinucleoside phosphates.
The Extraction of Mercury and Methylmercury by Diphenylthiocarbazone-treated Polyurethane Foams
Authors: Chow Arthur , Buksak Daniel
Published: May 2006

Dithizone-treated polyurethane foams which are easily prepared in the laboratory, are shown to efficiently extract mercury(II) and methylmercury(II) chloride from aqueous solution over a wide pH range for mercury concentrations below 10 p.p.m. The mercury is firmly held but can be recovered for analysis by eluting with acetone if desired. The extraction of both forms of mercury from domestic water, river water, raw sewage, and secondary-treated sewage is shown to be acceptable.
Carbon-13 Chemical Shifts of Furanosides and Cyclopentanols. Configurational and Conformational Influences
Authors: Ritchie R. George S. , Cyr Natsuko , Korsch Brian , Koch Hans J. , Perlin Arthur S.
Published: May 2006

Assignments for the 13C chemical shifts of methyl aldopento- and hexofuranosides and of cyclopentane polyols are reported, and these chemical shifts are evaluated with respect to all combinations of configurational arrangements of the ring substituents. A cis configuration of vicinal substituents is generally associated with a substantial increase in shielding, as compared with the trans analog. Among the furanosides, however, changes in configuration involving O-3 and C-5 are accompanied by a complex shielding pattern: e.g., effects on C-3 are minor, C-4 is more shielded in cis than in trans isomers, and C-4 and C-5 of hexosides are more shielded than those of pentosides. Variations in shielding attributable to cis or trans arrangements of substituents in a 1,3-relationship are encountered in only a few instances; however, it is noteworthy that C-4 is less shielded when O-l and O-3 are cis than when trans. These diverse effects are considered also in relation to steric interactions and to conformational influences on 13C chemical shifts in the five-membered ring series.
The Rearrangement of Aryl Thiohydrazonates
Authors: Elliott Arthur J. , Callaghan Patrick D. , Gibson Martin S. , Nemeth Steven T.
Published: May 2006

Rearrangement and cyclization of a series of p-nitrophenyl and heteroaryl thiohydrazonates ArSCAr′ = NNHC6H3XY(2,4), where the displaced substituent X is Br or F and the remaining substituent Y is Br or NO2, occurs under suitable basic conditions to the corresponding 7-substituted 2-aryl-4-p-nitrophenyl- and -4-heteroaryl-4H-1,3,4-benzothiadiazines, e.g. 13 → 19. Under these or suitable acidic conditions, the 4,6-dimethyl-2-pyrimidinyl thiohydrazonate rearranges to the thiohydrazide Ar′CSNHNArC6H3XY(2,4), apparently the first case of thiohydrazonate thiohydrazide rearrangement; such acidic treatment produces cleavage of some other heteroaryl thiohydrazonates.Independent syntheses of two of the 4-heteroaryl-substituted benzothiadiazines are reported.
Radiolysis of Liquid Nitrous Oxide: Alcohol and Carbonyl Additives
Authors: Sambrook Terance E. M. , Freeman Gordon R.
Published: May 2006

Methanol, ethanol, acetaldehyde, and acetone were added separately over wide concentration ranges to liquid nitrous oxide at 183 K. The oxygen and nitrogen dioxide yields were reduced from their G values of 2.7 and 5.6, respectively, to 0 by < 8 mol% organic solute. The nitrogen yield decreased from 13.1 to about 11 over the same concentration region, but continued to decrease as the nitrous oxide was progressively diluted by the solute. The results are consistent with the previous mechanism II. The nitrogen yields from dilute solutions of nitrous oxide in the carbonyl compounds are smaller than those from similar solutions in the alcohols. The smaller yields are attributed to electron scavenging by the carbonyl compounds in competition with the nitrous oxide.
Nuclear Magnetic Resonance Studies of Enantiomeric Internal Rotational Isomers of 1- and 3-Arylhydantoins in Achiral and Chiral Solvents
Authors: Colebrook Lawrence D. , Icli Siddik , Hund Frank H.
Published: May 2006

1H and 13C n.m.r. spectra have been determined for a number of 1- and 3-arylhydantoins in achiral and chiral solvents. These compounds, which have enantiomeric rotational isomers, show restricted internal rotation about the aryl C—N bond at normal probe temperatures. Chemical shifts between corresponding protons on the pairs of rotamers, induced by diastereomeric solute–solvent interactions in the chiral solvent, are strongly dependent on the location of the protons in the solute molecules. In conjunction with 1H and 13C chemical shifts, these data provide information on the geometry of the solvated species. No splitting of signals resulting from the presence of diastereomeric solvates was observable in the 13C spectra. Activation parameters for hindered internal rotation, determined by complete p.m.r. line shape analysis using signals of the diastereotopic methyl groups in the 5-position, show some solvent dependence.
13C Chemical Shifts of Quinolizidines. 2. 13C Spectra of Some Nuphar Alkaloids
Authors: LaLonde Robert T. , Donvito Thomas N. , Tsai Amy I-M.
Published: May 2006

The 13C n.m.r. spectra of nine Nuphar alkaloids: deoxynupharidine, 7-epideoxynupharidine, nupharidine, 7-epinupharidine, nupharolutine, 7-epinupharolutine, thiobinupharidine, thionu-phlutine B, and neothiobinupharidine, have been determined. Also examined were the spectra of five model compounds, 2,2,4,4-tetramethylthiolane, 3(a)-methyl-3(e)-methylthiomethylquinolizidine, 3(e)-methyl-3(a)-methylthiomethylquinolizidine, 3(e)-methylthio-3(a)-methylquinolizidine, and 3-methylfuran. This latter group of spectra were used to assist the chemical shift assignments of the Nuphar alkaloids. The most significant findings of this study are: (i) axial methyl and thiomethylene groups are shielded more than their equatorial counterparts in all cases; (ii) axial and equatorial hydroxyl groups substituted at C-7 of deoxynupharidine and 7-epideoxynupharidine give α-, β-, and γ-effects in ring B similar to those in carbocyclic systems but also produce small upfield shifts in ring A especially at the carbons α to nitrogen; (iii) the effect of a 3-furyl group located at C-4 appears to have nearly the same effect on quinolizidine ring carbons as a methyl group in the same position, the effects being shielding and deshielding at the various ring carbons; (iv) N-oxide formation results in α-, β-, γ-, and δ-shielding and deshielding effects consistent with the incorporation of an axial oxygen into a trans-fused system or the formation of a cis-fused quinolizidine N-oxide; and (v) methylene or methyl groups attached to C-2 and C-4 of a thiolane, including that in the skeleton of the C30 thiaspirane alkaloids, experience deshielding δ-effects.
Synthetic Studies in the Veratrum Alkaloid Series. II. The Total Synthesis of Verarine, Veratramine, Jervine, and Veratrobasine
Authors: Kutney James P. , Cable John , Gladstone William A. F. , Hanssen Harald W. , Nair G. Vijay , Torupka Edward J. , Warnock William D. C.
Published: May 2006

Coupling of 3β-acetoxy-5α-etiojerv-12(13)-en-17-one (1) with the lithio derivative of 2-ethyl-5-methylpyridine provides the crucial intermediate (3) for the subsequent elaboration to verarine. Aromatization of 3 to 4 and reduction of the latter provides a mixture from which N-acetyl-5α,6-dihydroverarine (11) was isolated. Subsequent introduction of the 5,6-double bond in the latter and removal of the N-acetate function completed the synthesis of verarine (31). In a similar sequence of reactions employing 1 and the lithio derivative of 2-ethyl-3-methoxy-5-methyl-pyridine, the resultant intermediate (54), was elaborated to 5α,6-dihydroveratramine (56). Due to known conversions of the latter to veratramine (14), jervine (32), veratrobasine (33), and 11-deoxojervine (34), the formal total synthesis of these natural products is complete.
Predicting the Most Favored Path and the Overall Rate of Multistep: 2-Norbornyl Cation Rearrangements. The Assignment of a Trial Activation Energy for Each Unique Step
Authors: Haseltine R. , Huang E. , Ranganayakulu K. , Sorensen T. S. , Wong N.
Published: May 2006

Observable 2-norbornyl cations undergo at least five different rearrangement reactions, all of which are known from previous work on this system. In this paper, these rearrangement categories have been subdivided to reflect secondary–tertiary energy and rate differences and a trial set of activation free energies ΔG≠ is derived for each subdivided step. The most important of these parameters is the energy difference between secondary and tertiary (methyl) systems which was estimated as 5.5 kcal/mol. These parameters allow one, for the first time, to make a rational assessment of the overall reaction course of multistep rearrangement reactions in this system, for example, those observed in a number of bicyclo[2.2.1]heptyl(norbornyl) terpene systems.
A Kinetic and Thermodynamic Behavioral Comparison of Observable Secondary and Tertiary 2-Norbornyl Cations
Authors: Haseltine R. , Wong N. , Sorensen T. S. , Jones A. J.
Published: May 2006

By analyzing various rearrangement processes, one can deduce the relative stabilities of the following 2-norbornyl cations (kcal/mol): 1,2-dimethyl, 0; 2-methyl, 1; 1-methyl, 6.5; and the parent 2-norbornyl, 8.5. Secondary 2-norbornyl cations have been assigned a "carbonium ion" structure and tertiary a "carbenium ion" structure. Using suitable model systems, an absolute rate comparison has been made of all three common rearrangement processes in the tertiary systems ("carbenium") with those already measured for the 2-norbornyl cation ("carbonium"). The activation free energies, ΔG≠, (in kcal/mol) were: Wagner–Meerwein (WM) shift: tertiary, < 4; secondary, < 4; endo-6,2-hydride shift: tertiary, 7.2; secondary, 5.8; exo-3,2-hydride shift: tertiary, 6.6; secondary, 11.4. A discussion of the structure of tertiary and secondary 2-norbornyl cations emphasizes the following points: (i) a rationalization of the rapid endo-6,2-hydride shift observed in norbornyl cations does not necessitate a protonated nortricyclene ("carbonium ion") postulate; (ii) on the basis of the results for acyclic cations and the 1,2-dimethyl-2-norbornyl cation, one would not expect to "freeze out" the WM shift in an equilibrating 2-norbornyl cation structure; (iii) the formation of nortricyclenes may be related to a partial C6—C2 bond in the ions; and (iv) the structure of the observable secondary 2-norbornyl cation probably involves partial C6—C2 bonding but, in our opinion, this does not require a symmetrical static formulation.
13C Nuclear Magnetic Resonance Studies of Methylated Anthracenes
Authors: Caspar Myron L. , Stothers J. B. , Wilson Nancy K.
Published: May 2006

The 13C n.m.r. spectra of anthracene and 11 methylated anthracenes have been examined. Analysis of the 1H spectra allowed unequivocal assignments for most of the protonated carbons by selective proton decoupling. Parameters describing the methyl substituent effects on the aryl carbon shieldings were defined and refined by regression analysis so that the 13C shieldings were predicted for 67 independent aryl positions in anthracenes without peri-methyls with a standard deviation of 0.12 p.p.m. Peri methyl-methyl interactions cause considerable deviations from the predicted substituent effects. The relationships of the 13C shieldings to charge densities calculated by the CNDO/2 method were briefly examined. Syntheses of 2,7,9-trimethyl-, 1,4,5,8- and 1,4,5,9-tetramethyl-, and 1,4,5,8,9-pentamethylanthracene are described.
Bridged Xanthenes. I. An Intermolecular Cycloaddition Route
Authors: Yates Peter , Bichan D. J.
Published: May 2006

Condensation of o-hydroxybenzyl alcohol (4) with 1,3-cyclohexanedione (7) in hexamethylphosphoramide gives 3,4-dihydro-l(2H)-xantnenone (9). Treatment of the tosylhydrazone of 9 with methyllithium gives 3,4-dihydroxanthene (12), which undergoes Diels–Alder reactions with dimethyl acetylenedicarboxylate and propiolonitrile to give the bridged xanthenes 15 and 17, respectively. Condensation of o-hydroxybenzyl alcohol (4) with 4-carboxamido-1,3-cyclohexanedione (29) and 4-carbomethoxy-1,3-cyclohexanedione (38) gives 2-carboxamido-(30) and 2-carbomethoxy-3,4-dihydro-l(2H)-xanthenone (39), respectively.
Refinement of the Crystal Structure of the Low-quartz Modification of Ferric Phosphate
Authors: Ng Hok Nam , Calvo Crispin
Published: May 2006

The structure of ferric phosphate at room temperature was refined on a Dauphiné-twinned crystal using full-matrix least-squares methods. The final R value was 0.078 for 487 symmetry-independent reflections whose intensities were corrected for twinning. The structure was found to be isotypic with AlPO4 (berlinite) with the space group P3121 and four formula units in a unit cell defined by a = 5.036(2) and c = 11.255(4) Å. The structure is also closely related to that of α-quartz with a nearly doubled c-axis because of the ordering of Fe and P atoms. The PO4 tetrahedron is almost regular with a mean P—O distance of 1.526 Å. The Fe3+ ion is tetrahedrally coordinated with an average Fe—O distance of 1.853 Å.
1,4-Dioxane Hydrate: Dielectric Absorption by a Nondipolar Enclathrated Molecule
Authors: Gough S. R. , Ripmeester J. A. , Davidson D. W.
Published: May 2006

X-Ray, continuous-wave and pulsed n.m.r., and dielectric relaxation studies show the hydrate of 1,4-dioxane (D) to be a normal clathrate hydrate of von Stackelberg's structure II with composition D·∼17H2O. The reorientation rate of the relatively large D molecule is slower and the effective activation energy(l.6 kcal/mol) larger than for other guest molecules previously studied in hydrates of the same structure. Weak dielectric absorption associated with reorientation of nondipolar D molecules is attributed mainly to the induction of a total dipole moment of ∼0.2 D in the 28 water molecules of the large structure II cage by two equal and opposed dipoles in the chair form of D.
A Micrometer Syringe Dilatometer: Application to the Measurement of the Excess Volumes of some Ethylbenzene Systems at 298.15 K
Authors: Tanaka Reiji , Kiyohara Osamu , D'Arcy Patrick J. , Benson George C.
Published: May 2006

A dilatometer using a micrometer syringe to measure small changes in volume at constant pressure is described. Excess volumes determined for cyclohexane + benzene at 298.15 K are in reasonable agreement with values from the literature. Results are also reported for the excess volumes of mixtures of ethylbenzene with benzene, toluene, and the isomeric xylenes.
2-Hydroxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline. Novel Induced Decomposition by Radical Attack at the Hydroxyl Group
Authors: Knittel Peter , Warkentin John
Published: May 2006

Synthesis of 2-hydroxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline (3) is described. It decomposes readily in solution at moderate temperatures, forming nitrogen and isopropyl acetate. Evidence for a concerted, radical-chain, induced decomposition by attack at hydroxyl hydrogen includes trapping of 2-acetoxy-2-propyl radicals by nitrosobenzene and by alkenes, inhibition of decomposition by (C6H5)3SnH, and initiation of decomposition by 'stable' free radicals. The novel chain decomposition of 3 is attributed to a concerted mechanism, which brings the heats of formation of nitrogen and of a carbonyl group into play to lower the free energy of activation.Synthetic utility of 3 is discussed together with a general principle pointing to new reagents for radical-chain additions to unsaturated systems.
The Infrared Spectrum and Force Field of Matrix Isolated cis-Thionylimide (HNSO)
Authors: Tchir Peter O. , Spratley Richard D.
Published: May 2006

Infrared spectra of cis-HNSO and several deuterium, 15N, and 34S isotopically substituted homologs have been obtained in argon and nitrogen matrices. The Fermi resonance between ν4 and 2ν5 is discussed. A force field has been calculated.
The Photolyses of Fully Aromatic Amides
Authors: Carlsson D. J. , Gan L. H. , Wiles D. M.
Published: May 2006

The 254 nm photolyses of ethanol solutions of four fully aromatic amides were followed by liquid chromatography and u.v. spectroscopy, and quantum yields for the major products calculated. The photolysis of benzanilide was examined in detail at various wavelengths and in several solvents, both in the presence and absence of oxygen. Quantum yields for 2- and 4-aminobenzophenones and products from free radical precursors decreased with increasing solvent polarity and with increasing incident wavelength of irradiation. Oxygen had no affect on aminobenzophenone formation but produced benzoic acid from free radical fragments which escaped the solvent cage. The results are tentatively interpreted in terms of an energy dependent radiationless conversion to a reactive 1π*-carbonyl which then cleaves the N—C bond to give caged free radicals, rather than by a concerted, nonradical rearrangement.
The Crystal and Molecular Structure of the Dihydrochloride of 2-trans-6-Diethyl-2,4,4,6,8,8-hexamethylcyclotetraphosphazene
Authors: Calhoun Harry P. , Oakley Richard T. , Paddock Norman L. , Trotter James
Published: May 2006

Octamethylcyclotetraphosphazene is deprotonated by methyllithium to form carbanions, which react with methyl iodide to give ethyl derivatives N4P4Me8−nEtn, [Formula: see text] the structure of the dihydrochloride of the diethyl derivative, N4P4Me6Et2•2HCl has been determined. Its crystals are monoclinic, a = 9.928(5), b = 15.482(6), c = 6.329(2) Å, β = 103.29(2)°, space group P21/n. The structure was determined from diffractometer X-ray data and refined by full-matrix least squares methods to R 0.079 for 715 observed reflections. The N4P4Me6Et2H22+ ion lies on a crystallographic center of symmetry and the eight-membered phosphazene ring has the "chair" conformation. There are two significantly different P—N bond lengths, 1.665(6) and 1.572(7) Å, and two significantly different P—N—P angles, 126.7(6) and 139.8(6)°. The mean P—C bond length is 1.801(7) Å, and the mean N—P—N and C—P—C angles are 112.2(4) and 107.6° respectively. Bond lengths and angles in the phosphazene ring show the characteristic effects of π-electron localization found in other protonated phosphazene derivatives. The two ethyl groups are in tran-antipodal positions, corresponding to the least intramolecular electrostatic repulsion in the carbanion.
Synthesis of cis-9-Cyano-l,10-dimethyl-6-ethylenedioxy-1-octalin and its Conversion into an Intermediate for a Synthesis of Thelepogine
Authors: Kelly Ronald B. , Alward Sandra J. , Zamecnik Jiri
Published: May 2006

The synthesis of cis-9-cyano-1,10-dimethyl-6-ethylenedioxy-1-octalin, the structure of which has been determined by X-ray crystallography, is described. Also described is the conversion of this compound into an octalone having the functionality and stereochemistry appropriate to its use as an intermediate in a total synthesis of thelepogine.
Conformational Analysis of N-Nitrosopiperidines by 13C Nuclear Magnetic Resonance. The Orientation Preference of an α-Methyl Group
Authors: Fraser Robert R. , Grindley T. Bruce
Published: May 2006

The 13C shielding parameters for N-nitroso-4-phenylpiperidine and four α-methyl derivatives have been measured. From these data a number of methyl substituent parameters have been obtained. A comparison of the observed spectra of syn- and anti-N-nitroso-2-methylpiperidines with those calculated from the substituent parameters and the shieldings in N-nitrosopiperidine established the syn isomer to exist exclusively in the conformation having the methyl group axial; the anti isomer has the methyl group predominantly axial (59%). It is proposed that the large differential shielding between α carbons syn and anti to the nitroso group is caused by steric compression at the syn carbon. Large dilution effects on the carbon shieldings (up to 1.3 p.p.m.) have been encountered in these nitrosamines.
Total Synthesis of Monosaccharides. Synthesis of Methyl DL-Pentopyranosides with α- and β-lyxo, β-ribo, α-xylo, and α-arabino Configurations from Furfuryl Alcohol
Authors: Achmatowicz Jr. Osman , Bukowski Pawel
Published: May 2006

Hydroxylation and epoxidation, followed by the oxirane ring opening, of methyl 2,3-dideoxy-α and β-DL-pent-2-enopyranosides, readily available by the transformation of furfuryl alcohol, afforded the title compounds. Steric course of hydroxylation and epoxidation reactions were examined. The p.m.r. data of methyl 4-O-acetyl-2,3-anhydro-DL-pentopyranosides are reported.
Recherches sur les composés éthyléniques. V. Liens entre la structure des akènes et leur fréquence de vibration νC = C influence des effets structuraux et établissement d'une relation de topo-information
Authors: Basso J. H. , Delattre S. , Lanteri R. , Luft R.
Published: May 2006

An examination of spectroscopic data for 43 alkenes reveals the influence of increasing substitution at the carbon atoms α or β to the ethylenic bond. The presence of a particularly large steric constraint requires that there be a single preferred molecular conformation: in such a case the frequency of the νC = C vibrator is strongly decreased (10 cm−1).A quantitative analysis of the phenomenon can be achieved using the "topological-chemical method D.A.R.C.". Topologic-information relationships could be developed for the two series 2-alkylethylenes and 2,2-dialkylethylenes. These permit the calculation of the contribution of each topological site to the frequency νC = C. For the first series, the relationship, based on 9 compounds, permits predictions about 30 others. For the second series, deductions are made concerning 159 compounds from a relationship established on a base of 13 compounds. [Journal translation]
The Calculation of Effective Pair Potentials in Solution from Activity Coefficient Data: Nitrobenzene in Benzene
Authors: Goldman Saul
Published: May 2006

The stoichiometric activity coefficients of nitrobenzene in benzene at low concentrations over the range 5.5–25 °C were represented by a temperature-dependent dimerization constant. Constant Pressure Solution Theory was used to derive a relationship between this dimerization constant and the sum of two cluster integrals. One of these integrals involves an effective nitrobenzene–nitrobenzene pair potential in benzene, and the other, an effective nitrobenzene-benzene pair potential in benzene. Two approximate mathematical models, each involving dipole–dipole and square-well potentials were used to evaluate the cluster integrals. The resultant expressions were fitted to the data. It was found that unique expressions for the pair potentials could not be obtained, and therefore ranges of solutions were reported. These solutions indicated (i) that the effective pair potentials in solution were of the same order of magnitude as those determined for comparable systems from gas-phase second virial coefficient data and (ii) that there existed a relatively short-range stabilizing effect in the nitrobenzene–benzene pair potential that was absent in the nonelectrostatic part of the nitrobenzene–nitrobenzene pair potential. This was explained in terms of a charge-transfer interaction between nitrobenzene and benzene, an explanation that is consistent with n.m.r. shift data.
Synthesis and Characterization of Cu(I) Complex Compounds With Methyl Isonicotinate
Authors: Goher Mohamed A. S.
Published: May 2006

The preparation of Cu(I) complexes of methyl isonicotinate, MeIN, of the formula (MeIN)nCuX, in which n = 1,2, 3, and 4 and X is Cl, Br, I, CN, SCN, and ClO4, has been described. The isolated complexes are characterized by their analytical data, diamagnetism, and conductivity measurements. The M → L charge transfer bands in the visible spectra and the i.r. spectra of these complexes are discussed.
The Initial Stages of the Pyrolysis of Dimethyl Ether
Authors: Pacey Philip D.
Published: May 2006

Dimethyl ether was pyrolized in a flow system at 782–936 K and 25–395 Torr with conversions from 0.2–10%. Product analyses were consistent with a simple Rice–Herzfeld mechanism with most chain termination by the recombination of CH3 radicals. The rate coefficients for both the initiation and termination reactions appeared to be slightly pressure dependent. The first-order rate constant for the initiation reaction,[Formula: see text]calculated from the rate of C2H6 formation, was k1 = 1015.0±0.5exp (−318 ± 8 kJ mol−1/RT) s−1, corresponding to ΔHf0(CH3O) = −5 ± 8 kJmol−1. Comparison of CH4 and C2H6 yields enabled calculation of the rate constant for the reaction of CH3 with dimethyl ether. From 373−936 K, the Arrhenius plot for this reaction is a curve.
Mechanisms of Acylal Hydrolysis in Sulfuric Acid Solutions
Authors: McClelland Robert Allan
Published: May 2006

The acid-catalyzed hydrolysis (in aqueous H2SO4) of acylals ArOCH2OAc is reported, and compared with that of normal acetate esters. On the basis of r plot behavior and the effects of the aromatic substituents, an AAc-2 ester hydrolysis mechanism is shown to occur in dilute acids, with a changeover to a mechanism analogous to AA1-1 ester hydrolysis (intermediate cation ArOCH2+) in more concentrated acids, the position of the changeover being dependent on the substituent. Methylene diacetate is also investigated and shown to display the same behavior, with an A-1 mechanism involving an intermediate CH3COOCH2+ becoming important at about 75% H2SO4. The relative AA1-1 reactivities for acetates ROAc, R = CH3OCH2, tert-butyl, C6H5OCH2, C6H5CH2, 4-NO2C6H4OCH2, CH3COOCH2, isopropyl, are 6 × 103, 5 × 102, 1, 7 × 10−2, 4 × l0−2, 1.1 × 10−2, 1.3 × 10−4 respectively.
Substituted 5-Allyl-9-oxobenzomorphans. Versatile Intermediates for Investigations in the Field of Analgesics and Narcotic Antagonists. Part 1
Authors: Monković Ivo
Published: May 2006

not available
Synthèse et réactions d'une bis(α-dicétone) carboranique. Explication par la méthode CNDO/2
Authors: Rabilloud Guy , Sillion Bernard , Rossarie Jean , Blain Monique , Odiot Simone
Published: May 2006

1,7-Bis(phenylglyoxyloyl)-m-carborane has been prepared by different methods but the best yield was obtained with 1,7-dilithio-m-carborane and 2,2-dimethoxyphenylglyoxal. Mixed with o-phenylenediamine this new compound failed to yield the expected quinoxaline but afforded m-carborane, 3-phenyl-2-quinoxalinone, and 2-benzoylbenzimidazole. Moreover, under the action of bases, we observed a cleavage of the carbon–carbon bond giving m-carborane and phenylglyoxylic acid. A theoretical study of the molecule by CNDO/2 indicated a significant difference between chemical reactivities of the α and β carbonyl groups.
The Systems Indium Trichloride – Pyridine and Indium Trichloride – Pyridine – Water: Equilibrium Diagrams and Heat of Formation of Incl3.3C5H5N
Authors: M. Kartzmark Elinor
Published: May 2006

The equilibrium diagram of the system indium trichloride–pyridine–water, at 25°C, shows the existence of two compounds, InCl3. C5H5N.2H2O and InCl3.3C5H5N. The melting point diagram shows that the compound InCl3. 3C5H5N melts incongruently at 242°C. The heat of the reaction[Formula: see text]is ΔH = −34.6 kcal/mol and the heat of formation of InCl3.3C5H5N is −137.0 kcal/mol.
A Correlation between Bond Length and Ionic Bond Order. Application to the Ylide–Ylene Problem
Authors: Whangbo Myung-Hwan , Wolfe Saul , Bernardi Fernando
Published: May 2006

The C—O and C—S bond lengths of the cations, radicals, and anions CH3O, CH3S, CH2OH, and CH2SH have been found not to correlate with the overlap populations of the C—X bonds. On the other hand, very satisfactory linear relations are observed with the ionic bond orders of the C—X bonds. It is suggested that, in certain molecular systems, it may be more meaningful to associate shortening of a bond A—B with greater coulombic attraction (or smaller coulombic repulsion) between the two point charges represented by the net atomic charges on the atoms A and B than with an increase in the overlap population between these atoms. It is noted that such an interpretation can account for the short C—P bond in a phosphonium ylide without resort to (p → d)π conjugation.
Mössbauer and Related Studies of Complexes of R2 Sn(NCS)2 with Neutral Ligands Containing Oxygen Donor Atoms
Authors: Mullins F. Patricia , Curran Columba
Published: May 2006

Mössbauer, infrared, and electric dipole moment data are reported for several complexes of the type (i) R2Sn(NCS)2L2 and (ii) R2SnX2B (where R = C4H9, C2H3, C6H5; X = Cl, NCS; L = monodentate ligands with O, S donor atoms; B = bidentate ligands with O, P, As donor atoms). Quadrupole splittings indicate trans C—Sn—C bonds in octahedral complexes of divinyl-and diphenyltin diisothiocyanate with bidentate oxygen-donor ligands, in contrast to a cis configuration for complexes with bidentate nitrogen-donor ligands. Data indicate that the 1:2 complex of 2,2-bipyridyl-N,N′-dioxide with Bu2Sn(NCS)2 is polymeric, with octahedral monomer units having one bridging and one terminal NCS group, a bridging bipyO2 ligand and trans butyl groups. [Ph2Sn(NCS)2]2•bipyO2 appears to be a dimer with a bridging bipyO2 ligand and five-coordinate tin atoms. Mössbauer parameters for R2SnX2L2 and R2SnX2B complexes having oxygen donors are similar.
Reaction of Hydrazonyl Halides with Derivatives of Thiourea and Thiosemicarbazide; A New Source of C-Amino- and C-Hydrazino-1,2,4-triazoles
Authors: Wolkoff Peder , Nemeth Steven T. , Gibson Martin S.
Published: May 2006

Reaction of hydrazonyl halides with (substituted) thioureas and thiosemicarbazides gives mainly 1,3,4-thiadiazolines, the stronger base being preferentially eliminated in the process. Similar reactions in presence of triethylamine give C-amino- and C-hydrazino-1,2,4-triazoles, respectively, together with the hydrazonyl sulfide.Potassium cyanide cleavage of a hydrazonyl disulfide gives the corresponding 1,3,4-thiadiazoline and thiohydrazide.
Synthèse et propriétés des pentaméthyl-2,3,3,5,5 et tétraméthyl-3,3,5,5 N-pipéridinométhyl-2 cyclohexanones et de leurs dérivés
Authors: Richer Jean-Claude , Arlotto Raphael
Published: May 2006

The preparation is reported of 2-methylene- and of 2-butylthiomethylene-3,3,5,5-tetramethylcyclohexanone as is their transformation into 2,3,3,5,5-pentamethylcyclohexanone. The synthesis of 2-N-piperidinomethyl-3,3,5,5-tetramethylcyclohexanone is described. The properties of the ketones as well as the stereochemistry of their reduction by complex hydrides was examined. [Journal translation]
Stereochemistry of the Bucherer–Bergs and Strecker Reactions of 4-tert-Butylcyclohexanone
Authors: Edward John T. , Jitrangsri Chote
Published: May 2006

The spirohydantoin (α-isomer) obtained from 4-tert-butylcyclohexanone by the Bucherer–Bergs reaction has been shown by n.m.r., u.v., and considerations of steric hindrance to have the tert-butyl group and 1′-nitrogen atom cis; the β isomer obtained via the Strecker reaction, or via modified Bucherer–Bergs reactions employing carbon disulfide or carbon oxysulfide, has these groups trans. The differing stereochemical courses of the various reactions can be explained by a detailed consideration of their mechanisms.
On the Alkaline Degradation of 2-Furfurylidene-10-methyl-trans-1-decalone
Authors: Stoessl A. , Stothers J.B.
Published: May 2006

The reaction of 2-furfurylidene-10-methyl-trans-1-decalone with base (NaOH – aqueous HOCH2CH2OH) has been reinvestigated and found to give nine products. Elucidation of the structures of eight of these products, which accounted for ca. 80% of the process, was accomplished from their spectroscopic data and confirmed by chemical interconversions. The product mixture obtained shows that the reaction involves competition between the retroaldol process and various hydride reductions with some allylic isomerization.
Crystal and Molecular Structure of Dithiocyanato(triphenylarsine)mercury(II)
Authors: Hubert Joseph , Beauchamp André L. , Rivest Roland
Published: May 2006

The crystal and molecular structure of dithiocyanato(triphenylarsine)mercury(II) has been determined from X-ray diffraction data. The crystals are monoclinic, space group P21/c, with a = 10.290(7), b = 21.199(23), c = 10.719(7) Å, β = 112.00(2)°, and Z = 4. The structure has been solved by the heavy-atom method and refined by block-diagonal least-squares calculations. The agreement factor R obtained for 2607 'observed' reflections is 0.030. The crystal consists of single molecules. The 'characteristic' coordination number of mercury is three, with two sulfur and one arsenic atoms at the apexes of a triangle. The nitrogen atoms of the thiocyanate groups are at 2.67 and 2.74 Å from the adjoining mercury atoms and therefore link the different molecules together.
Acid-catalyzed Reactions of 3β-Acetoxy-9α-hydroxy-11-keto-5α-lanostane: 19(10→9β) abeo-lanostenes
Authors: Edwards Oliver E. , Paryzek Zdsislaw
Published: May 2006

Acid-catalyzed dehydration of 3β-acetoxy-9-hydroxy-11-keto-5α-lanostane gave under varying conditions 3β-acetoxy-11-keto-14(13→12)abeo-lanost-12-ene, or the two cucurbitanes 3β-acetoxy-11-keto-19(10→9β)abeo-lanost-1(10)-ene and the corresponding 5(10)-ene.
On the Preparation of MoS2 Catalysts from MoS3
Authors: Furimsky E. , Amberg C. H.
Published: May 2006

We have examined the effect of reducing MoS3 in hydrogen in the range 450–800 °C on the properties of the resulting MoS2 catalyst. The appearance of rhombohedral MoS2 at 800 °C is disputed. Instead, an 'overreduced' catalyst containing some Mo metal and hexagonal MoS2 was formed. Catalytic activity in thiophene hydrodesulfurization was insensitive to pretreatment.
Derivatives of 2-Pyrazolin-5-one. III. The Preparation and Properties of Some 1′-Phenylspiro[indoline-2,4′-[2]pyrazoline]-5′-ones
Authors: Coutts Ronald T. , El-Hawari Abdel-Monaem , Biggs David F.
Published: May 2006

The choice of solvent has a great influence on the nature of the products obtained when suitably substituted aromatic nitro-compounds are reduced by means of sodium borohydride in the presence of palladium–charcoal. When derivatives of 4-(2-nitrobenzylidene)-1-phenyl-2-pyrazolin-5-one are reduced by this reagent in dioxane, three products are obtained. They are identified as derivatives of 1′-phenylspiro[indoline-2,4′-[2]pyrazoline]-5′-one, of 1-hydroxy-1′-phenylspiro[indoline-2,4′-[2]pyrazoline]-5′-one, and of 4-(2-aminobenzyl)-1-phenyl-2-pyrazolin-5-one. The 1-hydroxyspiro[indolinepyrazolones] are very reactive compounds. The products of their oxidation, reductions with various reagents, and reactions with chemical nucleophiles have been isolated and identified. Some preliminary pharmacological properties of four of the synthesized compounds are reported.
Chromic Acid Esters as Corrosion Inhibitors
Authors: Ghali Edward L. , Girard Bertrand , Hachey Jean-Marie
Published: May 2006

The hydrolysis of the chromate ester, derived from 1-methylcyclohexanol, was studied by electrochemical methods. Progressive and complete hydrolysis in an open or closed system yields chromic acid and 1-methylcyclohexanol. No evidence of the presence of monoester was detected. In a closed system, where most of the hydrolyzed alcohol is retained in solution, a side reaction between chromic acid and the alcohol has been detected and followed by conductivity measurements.Electrochemical characteristics of pure iron immersed in aqueous solutions containing hydrolyzed ester were found to be identical to those in aqueous solutions containing equivalent quantities of CrVI as CrO3. Sulfuric acid additions to the above solutions still give comparable electrochemical characteristics; however, the anodic current in the passive region was found to be less for solutions containing hydrolyzed ester than for solutions containing equivalent quantities of CrVI as CrO3.
4-Methylene-1,2,3-benzotriazines
Authors: Fong Handrick , Vaughan Keith
Published: May 2006

Diazotization of 2′-aminoacetophenone, followed by coupling with primary aliphatic amines, affords unstable triazenes which readily undergo cyclodehydration over neutral alumina to give 3-alkyl-4-methylene-1,2,3-benzotriazines (5a-d). 3-Aryl-4-methylene-1,2,3-benzotriazines (8a-c) are likewise obtained by cyclodehydration of the stable 1-(ortho-acetylphenyl)-3-aryltriazenes (7a-c). Attempted synthesis of the unsubstituted 4-methylene-1,2,3-benzotriazine (5e), by the same method, did not succeed. 4-Hydroxy-1,2,3-benzotriazines (4) are postulated as intermediates in the cyclodehydration; this hypothesis is supported by the isolation of the stable 4-hydroxy-1,2,3-benzotriazine (12) from the coupling reaction of methylamine with the diazonium salt derived from ortho-aminobenzophenone. An account of a preliminary study of the thermolysis of 3-methyl-4-methylene-1,2,3-benzotriazine (5a) is included.
Characterization of S1P1 and S1P2 receptor function in smooth muscle by receptor silencing and receptor protection
Authors: Hu Wenhui , Mahavadi Sunila , Huang Jiean , Li Fang , Murthy Karnam S.
Published: May 2006

Sphingosine-1-phosphate (S1P) induces an initial Ca2+-dependent contraction followed by a sustained Ca2+-independent, RhoA-mediated contraction in rabbit gastric smooth muscle cells. The cells coexpress S1P1 and S1P2 receptors, but the signaling pathways initiated by each receptor type and the involvement of one or both receptors in contraction are not known. Lentiviral vectors encoding small interfering RNAs were transiently transfected into cultured smooth muscle cells to silence S1P1 or S1P2 receptors. Phospholipase C (PLC)-β activity and Rho kinase activity were used as markers of pathways mediating initial and sustained contraction, respectively. Silencing of S1P1 receptors abolished S1P-stimulated activation of Gαi3 and partially inhibited activation of Gαi1, whereas silencing of S1P2 receptors abolished activation of Gαq, Gα13, and Gαi2 and partially inhibited activation of Gαi1. Silencing of S1P2 but not S1P1 receptors suppressed S1P-stimulated PLC-β and Rho kinase activities, implying that both signaling pathways were mediated by S1P2 receptors. The results obtained by receptor silencing were corroborated by receptor inactivation. The selective S1P1 receptor agonist SEW2871 did not stimulate PLC-β or Rho kinase activity or induce initial and sustained contraction; when this agonist was used to protect S1P1 receptors so as to enable chemical inactivation of S1P2 receptors, S1P did not elicit contraction, confirming that initial and sustained contraction was mediated by S1P2 receptors. Thus S1P1 and S1P2 receptors are coupled to distinct complements of G proteins. Only S1P2 receptors activate PLC-β and Rho kinase and mediate initial and sustained contraction.
Hypotensive hypovolemia and hypoglycemia activate different hindbrain catecholamine neurons with projections to the hypothalamus
Authors: Dinh Thu T. , Flynn Francis W. , Ritter Sue
Published: May 2006

To better understand the involvement of hindbrain catecholamine neurons in hypovolemia-induced secretion of AVP, we injected antidopamine β-hydroxylase saporin (DSAP) or unconjugated saporin (SAP) control solution into the hypothalamic paraventricular nucleus (PVH) of anesthetized rats to retrogradely lesion catecholamine neurons innervating magnocellular areas of the hypothalamus. Subsequently, hypotensive hypovolemia was induced by remote blood withdrawal (4.5 ml, 1 ml/min) using an intra-atrial catheter. Blood was sampled at 2, 5, 20, and 50 min after onset of blood withdrawal. The AVP response was severely impaired by DSAP. Peak responses at 50 min were 51 pg/ml in SAP control and 17 pg/ml in DSAP-lesioned rats, indicating the importance of catecholamine neurons for this response. We also measured AVP responses to osmotic challenge induced by administration of hypertonic saline (1 M, 15 ml/kg, sc) and to insulin-induced hypoglycemia. Osmotic challenge increased AVP levels, but the response was not impaired by DSAP, indicating that AVP neurons were not damaged by the DSAP injection. Insulin-induced hypoglycemia did not increase AVP levels in either DSAP- or SAP-treated rats. However, the same dose of insulin increased food intake and corticosterone secretion in SAP controls, and these responses were profoundly impaired by DSAP. Thus catecholamine neurons are required for both the AVP response to hypotensive hypovolemia and for feeding and corticosterone responses to hypoglycemia. Lack of an AVP response to insulin-induced hypoglycemia in intact rats therefore indicates that responses to hypovolemia and hypoglycemia are mediated by different catecholamine neurons under distinct sensory controls.