bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbonyl stretching frequencies in acyl- and aryl-substituted phenyl benzoates
Authors: Shawali Ahmad Sami , Eweiss Namek Farahat
Published: May 2006

The infrared carbonyl stretching frequencies of acyl-substituted p-tolyl, phenyl, and p-chlorophenyl benzoates, XC6H4COOC6H4Y, have been determined in carbon tetrachloride. Each of the substituted phenols generated an independent [Formula: see text] plot which was correlated precisely with the Hammett equation (r = 0.999–0.998). The values of ρX so obtained show no tendency to vary with the structure of the parent phenol and are all within ± 0.202 of the mean value of 13.899. Similar correlations were obtained with the Hammett plots made by varying the aryl moieties of the esters while holding the acyl portions constant. For the four sets (4–8) studied, the mean value of ρY is 8.964 ± 0.266. Using the slopes of [Formula: see text] vs. σ correlations in the series studied, the transmissive factor for the ether bridge in carbon tetrachloride was calculated (π′ = 0.64). An expression relating substituents in both acyl and aryl moieties to the mono-substituted compounds suggests that substituents on the two different groups act reasonably independently of each other; [Formula: see text] For all esters studied the equation [Formula: see text] was found to hold with r = 0.998.
The stereochemistry of conjugate addition of lithium dialkyl cuprate reagents to some carbohydrate α-enones
Authors: Yunker Mark Bernard , Plaumann Dieter Ernest , Fraser-Reid Bert
Published: May 2006

Conjugate addition-alkylation reactions of lithium dialkyl cuprates to hex-2-enopyrano-4-ulosides (1), hex-3-enopyrano-2-ulosides (2), and hex-1-enopyrano-3-uloses (3) have been investigated. Extensive studies with 1 show that the homogeneous system using the soluble tri-n-butylphosphine copper(I) complex is less satisfactory than the heterogeneous medium in which copper(I) iodide is used. The use of Grignard reagents versus alkyl lithiums has also been investigated, the latter being found preferable. 1,2-Addition was observed in some cases, but conditions were developed to avoid formation of these side products.With α-enones 1 and 2 alkylation is completely stereoselective, the newly introduced alkyl group being in axial orientation. With 3 a complex mixture is obtained from which equatorial and axial adducts can be isolated in approximately equal amounts.
Pyrrole chemistry. XVI. Acylation of the pyrrolyl ambident anion
Authors: Wang Nam-Chiang , Anderson Hugh J.
Published: May 2006

An investigation of the acylation of the pyrrolyl ambident anion has been carried out. The results have been rationalized in terms of the 'principle of hard and soft acids and bases.' The metal cation, solvent or complexing agent, halide of the pyrrole Grignard reagent, and temperature were varied. As well, the reactions of acylating agents of the carbonyl, cyanide, and carbimine type with the pyrrole Grignard reagent were studied to determine N/C acylation ratios under the same conditions. Several new products were isolated and identified.
An explanation of reported participation of hydrated electrons as intermediates in electrochemical reduction reactions
Authors: Duncan John R. , Wright Graham A.
Published: May 2006

Suggestions that e−(aq) is involved as a reactant in reduction reactions at metal electrodes are examined. It is shown that an experimental test of the participation of e−(aq) can be devised. The results of this test show that the conventional theory, involving electron transfer directly from the electrode to the species being reduced, provides a better explanation of the reduction process in aqueous solution.
The cyclopentadienide anion and tropylium cation analogs of triptycene
Authors: Butler Douglas N. , Gupta Indranil
Published: May 2006

The cyclopentadienide analog of triptycene 1 and the tropylium cation analog of triptycene 2 have been synthesized. Some comparative spectroscopic data of these ions relative to triptycene are discussed.
Crown ether catalysis of decarboxylation: a general survey of reactivity and detailed analysis of the triphenylacetate anion
Authors: Hunter D. H. , Hamity M. , Patel V. , Perry R. A.
Published: May 2006

The effect of 18-crown-6 ether 3 on the decarboxylation rate in THF of sodium salts of carboxylic acids formally derived from hydrocarbons has been investigated and these acids include 9-phenylfluorene-9-carboxylic acid, fluorene-9-carboxylic acid, phenylacetylene carboxylic acid, triphenylacetic acid, and diphenylacetic acid. Addition of equimolar 3 resulted in an increase in decarboxylation rate of 13- to 500-fold and there was a correlation between the decarboxylation rate and the pKa value of the product hydrocarbon.The decarboxylation of triphenylacetate was investigated in detail. The effect on reaction rate of cation (Li+, Na+, K+), crown ether concentration, water concentration, and solvent polarity has provided information as to optimum reaction conditions and has helped to clarify the reaction mechanism.
Absolute rate constants for hydrocarbon autoxidation. 24. Rate constants and Arrhenius parameters for reaction of tert-butylperoxy radicals with 3-methylpentane
Authors: Howard J. A. , Chenier J. H. B. , Holden D. A.
Published: May 2006

Autoxidation of 3-methylpentane in the presence of tert-butyl hydroperoxide gives, after reduction with triphenylphosphine, 3-methyl-3-pentanol and 3-methyl-2-pentanol as the major reaction products. The overall rate constant for reaction of (CH3)3COO· with this substrate at 30 °C is 0.008 ± 0.001 M−1 s−1 which consists of k/tertiary C—H = 0.007 ± 0.001 M−1 s−1 and k/secondary C—H = 0.0002 ± 0.0001 M−1 s−1. The products from cooxidation of cumene and 3-methylpentane in the presence of tert-butyl hydroperoxide are formed in yields which are consistent with these rate constants relative to a value of 0.16 M−1 s−1 for cumene. The Arrhenius equations for reaction of (CH3)3COO• with the t-C—H and s-C—H of 3-methylpentane relative to the Arrhenius equation for reaction of (CH3)3COO• with cumene (log (k10/M−1 s−1) = (8.7 ± 0.3) − (13.2 ± 0.4)/θ) are[Formula: see text]respectively, where θ = 2.303 RT kcal mol−1.
Comparison of orbital symmetry allowed and forbidden ring opening of aziridines
Authors: Oehlschlager A. C. , Yim A. S. , Akhtar M. H.
Published: May 2006

The rates of reactions of N-aryl-cis-2,3-diphenyl aziridines (4a–d) with dimethyl acetylenedicarboxylate (DMAD) are dependent only on aziridine concentration suggesting slow conversion of aziridines to azomethine ylides which subsequently react in 1,3-dipolar cycloadditions to yield Δ3-pyrrolines. The Hammett reaction constant (−0.80) determinee for the N-substituents in the slow ring opening further suggests direct generation of azomethine ylides from these aziridines. The stereochemistry of the cycloaddition products derived from cis-1,2,3-triphenylaziridine with DMAD, maleic anhydride, dimethyl maleate, and dimethyl fumarate is consistent with the conrotatory generation of the ylides followed by their stereospecific cis-cis cycloaddition to the dipolarophiles.Similarly, cycloaddition of 7-aryl-6a,7a-dihydroacenaphtha-[1,2]-aziridines (5a–f) with DMAD yields bicyclic Δ3-pyrrolines and the rate is dependent only on aziridine concentration. This suggests the reaction proceeds via a slow disrotatory cleavage of the aziridine rings producing azomethine ylides which undergo subsequent addition to DMAD. The Hammett reaction constant for the ring opening step is +0.74 suggesting that the transition state for the ring cleavage is electron deficient in the aziridinyl ring but the cycloaddition reactions of 5a with isomeric dipolarophiles as well as several dienes and cycloheptatriene reveal only stereospecific 1,2-cycloadditions expected of an azomethine ylide intermediate.
α-Pyrones. V. The synthesis of bufadienolides. Part IV
Authors: Engel Ch. R. , Dionne Gervais
Published: May 2006

Additions of preformed enolate ions, derived from esters, to α-methylene carbonyl compounds, the methylene group of which carnes in the terminal position a leaving group, were studied. The reaction of steroidal 20-chloromethylene 21-aldehydes with preformed diethyl sodiomalonate results in a Michael addition which allowed an efficient synthesis of a 23-alkoxycarbonyl bufadienolide. In contrast, the reactions of the same chloromethylene aldehydes and of an analogous 20-methoxymethylene 21-aldehyde with ethyl lithioacetate give rise to 1,2-additions. The reaction of lithioacetate with the methoxymethylene aldehyde was used for the most efficient bufadienolide synthesis yet realized. Treatment with lithioacetate of 20-acetoxymethylene and 20-hydroxymethylene 21-aldehydes gave no addition products. The reactions of preformed sodiomalonate and lithioacetate with α-chloromethylene and α-methoxymethylene cyclohexanones proceeded analogously to those of the steroidal aldehydes.
Vinyl ether hydrolysis. XI. The effect of α-phenyl substitution
Authors: Chiang Y. , Chwang W. K. , Kresge A. J. , Robinson L. H. , Sagatys D. S. , Young C. I.
Published: May 2006

The unexpected inability of an α-phenyl group to accelerate the rate of vinyl ether hydrolysis more strongly than an α-methyl substituent, k(CH2=CPhOEt)/k(CH2=CMeOEt) = 0.2 for catalysis by H3O+ at 25 °C, is examined and is found to be the result of two effects: (i) preferential initial state stabilization by phenyl and (ii) weak resonance interaction with the developing alkoxy carbonium ion in the transition state induced by the reactant-like character of the latter. A curved Brønsted relation for the hydrolysis of 3-methoxyindene catalyzed by carboxylic acids and monohydrogen phosphonate anions gives the Marcus theory parameters ΔG0≠ = 3 ± 1 kcal/mol and wr = 12 ± 1 kcal/mol.
Vinyl ether hydrolysis. XII. Use of cis–trans isomerism to probe the reaction mechanism
Authors: Chiang Y. , Kresge A. J. , Young C. I.
Published: May 2006

Rates of hydrolysis of cis- and trans-β-phenylvinyl methyl ethers, cis- and trans-β-(p-nitrophenyl)vinyl methyl ethers, and cis- and trans-β-cyanovinyl ethyl ethers were measured in concentrated (10–55 wt%) aqueous perchloric acids. The results show that these cis and trans isomers do not interconvert under the hydrolysis reaction conditions, and that formation of the alkoxy carbonium ion intermediate in these reactions is therefore not reversible.
Synthesis of dehydrocycloroyleanone
Authors: Burnell Robert H. , Ringuet Michel
Published: May 2006

A degradation product (14) obtained during the elucidation of the structure of lycoxanthol has been synthesized from podocarpic acid. Several model series of experiments are also described, leading to quinones and furan derivatives.
X-ray photoelectron spectra of C6F5X compounds (X = CH3, CF3, CN, CHO, OH, OCH3, NH2, NO2)
Authors: Trudell Barry C. , Price S. James W.
Published: May 2006

The gas phase photoelectron spectra, XPS, were observed for the series C6F5X (X = CH3, CF3, OCH3, OH, CHO, NO2, NH2, CN). Binding energies were determined from the spectra by using computer curve fitting. Charge calculations were carried out using CNDO/2 and ACHARGE techniques. The CNDO/2 analysis led to the following correlation for the C 1s binding energies and the atomic charges, qi[Formula: see text]Correlations were also obtained for O 1s and N 1s:[Formula: see text]These equations are based on only four and three points respectively. However, the N 1s values cover a wide range (Ei, 402 to 419 eV; qi, −0.2 to 0.5) and show a better correlation than those for oxygen.
Biosynthetic studies of stress metabolites from potatoes: incorporation of sodium acetate-13C2 into 10 sesquiterpenes
Authors: Stoessl A. , Stothers J. B. , Ward E. W. B.
Published: May 2006

The results of incorporation studies of doubly-labelled sodium acetate-13C2 into the stress metabolites produced by fungal invasion of potato tubers are presented. The 13C-labelling patterns for 10 sesquiterpenes have been determined by 13C nmr. Two of these products have not been described previously and their structural elucidation is discussed. The biosynthetic interrelationships of these compounds are considered in detail.
Reorientation of thiophene molecules in a benzene lattice
Authors: Sanford William E. , Boyd Robert K. , Ripmeester John A.
Published: May 2006

Benzene and thiophene are known to form solid solutions over the entire composition range; the present work demonstrates the orientational freedom of thiophene molecules in solid solution with excess perdeuterobenzene, through measurements of spin–lattice relaxation times. In addition, the atom–atom approximation to intermolecular forces yielded a potential energy profile for in-plane rotation of a thiophene molecule, embedded in a benzene lattice, which is consistent with the experimental activation energy for the relaxation. The second moment of the absorption signal for thiophene in perdeuterobenzene at 80 K was determined to be 0.66 G2, compared with a value of 0.42 G2 computed as the intramolecular contribution only for in-plane rotation
Carbon-13 nuclear magnetic resonance spectra of N-, O-, and S-methylated uracil and thiouracil derivatives
Authors: Still Ian W. J. , Plavac Nick , McKinnon David M. , Chauhan Mohinder S.
Published: May 2006

13C nmr chemical shifts have been recorded for a number of uracil, thiouracil, and pyrimidine derivatives. These data are discussed in relation to what is known of the lactam–lactim tautomerism in such systems and possible correlations of chemical shifts with normal aromatic substituent chemical shift parameters. The chemical shifts for the CH3 groups in simple methylated derivatives of uracil are very characteristic of the site of methylation and should prove useful as a tool for assigning structures to alkylated derivatives of this general type.
Mechanism of borohydride reductions. Evidence for lack of disproportionation in the reduction of ketones
Authors: Wigfield Donald C. , Gowland Frederick W.
Published: May 2006

Examination of unreacted sodium borohydride after reduction of ketones by mixtures of NaBH4 and NaBD4 shows that it is still isotopically pure and that no detectable species NaBHnD4−n have been formed. Disproportionation of intermediates back to NaBH4 therefore plays no significant role in the reduction.
A vapor pressure method for the simultaneous determination of standard thermodynamic functions of both solutes in a ternary dilute solution
Authors: Treiner Claude , Tzias Pierre , Chemla Marius
Published: May 2006

It is shown that from vapor pressure measurements on dilute solutions of ternary mixtures with one nonvolatile component, the standard free energy of transfer (ΔGt0) of both solutes from water to aqueous binary solvents can be determined simultaneously. The method is most useful in the case of volatile components. ΔGt0 values are discussed in particular in the case of the transfer of tetrahydrofuran, acetone, and acetonitrile from water to aqueous tetrabutylammonium bromide and urea solutions and compared to the case of the transfer of nonpolar solutes to the same aqueous solution. In each case, the free energy of transfer from water to an aqueous solution of a nonpolar molecule was negative, and introduction in that molecule of a polar group caused the free energy of transfer to be considerably less negative.
Significance of effects of pressure on electrode reactions. Part III. Equilibrium processes at reference electrodes and the volume of H in Pd
Authors: Conway Brian E. , Currie J. C.
Published: May 2006

For studies on effects of pressure on kinetics of electrode processes (Parts I, II), reversible reference electrodes suitable for use in a completely enclosed high-pressure bomb are required. The electrodes must exhibit reversible behaviour over the pressure range employed in the experiments, i.e., their changes of emf with increasing and decreasing changes of pressure must be reproducible and correspond to the respective volume changes in the reactions.A series of reversible reference electrodes is examined over a range of pressures up to ca. 2500 bars. The Pd–H/H+ and Ag, AgCl/Cl− reference electrodes are found to behave very satisfactorily at elevated pressures; the Pt,H2/H+ electrode is, however, less satisfactory, due to problems associated with dissolved H2.The results enable the volume of Pd–H and of H sorbed into Pd to be evaluated, together with estimates of the partial molar volume of H2 in aqueous HCl. These data enable the pressure-coefficients of metal–solution potential differences at individual reference electrodes to be evaluated. Such information is required for interpretation of effects of pressure on kinetics of electrode processes.
Etude des interactions des oxirannes et thiirannes avec les α,β,γ,δ-tétraphénylporphyrines au cadmium, zinc et magnésium
Authors: Dumas Philippe , Guerin Philippe
Published: May 2006

1/1 adducts from oxiranes or thiiranes and cadmium, zinc, or magnesium α,β,γ,δ-mesotetra-phenylporphyrins were obtained in benzene and complexation constants determined. Results agree with the theory of 'hard and soft' acids and bases.Demetallation of the metaloporphyrins of Cd, Zn, and Mg is achieved with thiols. The cadmium porphyrin reacts with sulfur heterocycles which contain a β hydrogen to yield the free porphyrin and a thiolate of cadmium. If this heterocycle is methylthiirane, the organocadmium compound formed may initiale the subséquent in situ stereospecific polymerization of methylthiirane.
The hydrolysis of thioacetic, thiobenzoic, and three substituted thiobenzoic acids in perchloric and sulfuric acids
Authors: Edward John T. , Welch Graeme , Wong Sin Cheong
Published: May 2006

The rates of hydrolysis of thioacetic, thiobenzoic, and three substituted thiobenzoic acids increase with concentration of solvent sulfuric or perchloric acid to a maximum in 30–40% acid and then decrease. Yates–McClelland r, Bunnett–Olsen [Formula: see text], and Hammett ρ parameters, and entropies of activation indicate an AAC2 mechanism over this range of acid concentrations. In acid concentrations above 50–60% the rates increase sharply and the same mechanistic criteria now indicate an AAc1 mechanism. The difference between the rate–acidity profile of thiobenzoic acid and that of ethyl thiolbenzoate can be explained by the different response of the activity coefficients of their transition states to increase in sulfuric acid concentration.
Local anisotropic contributions to 1H nuclear magnetic resonance shifts in alkynes
Authors: Agarwal Arvind , McGlinchey Michael J.
Published: May 2006

Local anisotropic contributions to chemical shifts of protons sited near an alkyne moiety have been calculated using a classical model previously applied to aromatic systems. The results are presented in terms of an isoshielding contour map. The upfield shifts of ethyne and propyne and also the downfield shifts of the γ-protons of cyclooctynes are well accounted for by this theory.
Chemistry of chelocardin. IV. C(2)-acylation and alkylation of 2-deacetylchelocardin
Authors: Chu Daniel T. W. , Bernstein Edith , Huckin Stuart N.
Published: May 2006

The properties of the 1,3-cyclohexanedione system in 2-deacetylchelocardin (2) and N-carbobenzoxy-2-deacetylchelocardin (3) are found to be significantly different from those of ordinary 1,3-cyclohexanediones. Acylation and alkylation of (2) or (3) generally gives O-acylation or O-alkylation products. However, reaction of N-carbobenzoxy-2-deacetylchelocardin (3) with methyl orthoformate or N,N-dimethylformamide dimethyl acetal leads exclusively to C-acylation products.
The crystal structure of RbCdCl3 and the polarized Raman spectra of RbCdX3 (X = Cl, Br)
Authors: Natarajan Mahadevan , Howard-Lock Helen Elaine , Brown Ian David
Published: May 2006

The polarized Raman spectra of single crystals of RbCdCI3 and RbCdBr3 (isostructural with NH4CdCl3) have been measured and analysed by comparison of the frequency shifts. The crystal structure of RbCdCl3 refined by X-ray diffraction is also reported.
Methods for the comparison of fulvic acid samples: the effects of origin and concentration on acidic properties
Authors: Burch R. Douglas , Langford Cooper H. , Gamble Donald S.
Published: May 2006

The principles according to which the acidic properties of fulvic acid solutions should be compared are demonstrated. An equilibrium function defined and measured for any mixture, including fulvic acid functional groups, will be a weighted average. A concentration change will generally affect this average by changing the relative values of the statistical weights. Concentration corrections are therefore required for the comparison of two fulvic acid solutions. A Chernozem Ah fulvic acid and the previously described Armadale fulvic acid Batch FA1 were examined in this way. They were found to have the same general chemical characteristics, but with somewhat different numerical values. The implications of these results for the definition of fulvic acid are considered.
The chiroptical properties of the strychnine alkaloids: strychnine, β-colubrine, brucine, and their dihydro derivatives
Authors: Show Julian W. , Hooker Jr. Thomas M.
Published: May 2006

Ultraviolet absorption and circular dichroism spectra of the strychnine alkaloids strychnine, β-colubrine, brucine, dihydrostrychnine, dihydro-β-colubrine, and dihydrobrucine have been investigated under various experimental conditions. It appears that at least five electronic transitions are required to account for the spectroscopic properties of these molecules in the ultraviolet region above 190 nm. Transitions, which are tentatively assigned as the 1Lb, 1La, 1Bb, and 1Ba in the notation due to Platt, and an n → π* transition apparently make significant contributions to the spectra of ail of the molecules studied.
Nuclear analogs of β-lactam antibiotics. VIII. Synthesis of 3-acetoxymethyl-Δ3-O-2-isocephems
Authors: Conway Terry Thomas , Lim Gary , Douotas James Leslie , Menard Marcel , Doyle Terrence William , Rivest Pierre , Horning Donald , Morris Leeson R. , Cimon Denis
Published: May 2006

The synthesis of 7β-(-2′-thienylacetamido)-3-acetoxymethyl-Δ3-O-2-isocepheni-4-carboxylic acid (17) is described. Thus treatment of enol mesylate 3a or triflate 3b with triethylamine gave the allene 4 which gave the diiodide upon treatment with iodine. The diiodide gave benzyl 7β-azido-3-acetoxymethyl-Δ3-O-2-isocephem-4-carboxylate (12) on treatment with potassium acetate in DMF. Hydrogenolysis of 12 gave the amino acid 16 which was converted to 17 upon treatment with 2-thienylacetyl chloride. Resolution of 17 into its optical antipodes was carried out. The antibiotic activities of racemic 17 and each antipode is compared to that of cephalothin. Antibiotic activity was found to reside in the dextrorotatory isomer.
Nuclear magnetic resonance studies. XXXII. Rearrangement, isomerization, and deuterium exchange via β-enolization in bicyclooctenones. A 2H nuclear magnetic resonance study
Authors: Cheng A. K. , Stothers J. B.
Published: May 2006

The equilibration of the α,α -diniethyl derivatives of bicyclo[2.2.2]octenone, bicyclo[3.2.1]-oct-2-en-6-one, and its Δ3 isomer has been examined at 155 and 185 °C in tert-BuO−/tert-BuOH. Using 2Hmr spectroscopy the rates and stereoselectivity of hydrogen–deuterium exchange in each of these ketones have been determined for equilibrations with tert-BuOD as solvent. The relative reactivities for exchange at the allylic and vinylic sites compared to the analogous results for the corresponding olefins reveal a significant activating effect of the carbonyl group. Comparison of the data with those for the corresponding saturated ketones shows that the double bond enhances the rate of isomerization appreciably and increases the bias of the equilibrium toward the [3.2.1] skeleton.
Field desorption mass spectrometry of carboxylic acids: characteristic spectra and analysis of mixtures and impure samples
Authors: Wooo Gordon Walter , Oldenburg Emily Jane , Lau Pui-Yan , Wade Donna Lee
Published: May 2006

Field desorption mass spectra were obtained for a variety of saturated and unsaturated carboxylic acids containing 12 or more carbons. At best anode temperature molecular ions were dominant and small peaks representing [M + 1]+, [2M + 1]+, [M − 17]+, and [Formula: see text] were present in several compounds. At higher temperatures several novel ions were found, including one corresponding to [2M + 1 – 18]+ which may represent anhydride formation. In a mixture of cis-5-eicosenoic and elaidic acids each molecular ion desorbed as expected but at higher temperatures the three possible anhydride ions appeared, with the cross product [M1 + M2 + 1 − H2O]+ as the base peak. Isomeric hydroxystearic acids (2-OH, 12-OH, 17-OH) gave predominantly ions in the molecular ion region with some differences in spectra which may relate to structure. Apparent polyester formation has been observed in 3-hydroxypropanoic acid where ions of the general formula [xM − (x − 1)H2O + H]+ with x = 2, 3, … 13 were found. Several other hydroxyacids show dimer formation and lactic acid has ions up to x = 5 in the above formula. Two of four technical grade dicarboxylic acids tested were seriously contaminated by sodium ions and gave useful spectra only after extraction by dibenzo-18-crown-6 ether. After this treatment both adipic and azelaic acid have [M + 1]+ as base peak, although adipic acid decarboxylates readily ([Formula: see text] = 74%) Other technical grade acids showed the presence of homologues and related structures as impurities.
A new stereospecific total synthesis of chasmanine and 13-desoxydelphonine
Authors: Wiesner Karel , Tsai Thomas Y. R. , Nambiar Krishnan P.
Published: May 2006

A simple synthesis of the title compounds, which is more than 10 steps shorter and an order of magnitude more efficient than our recent photochemical synthesis of chasmanine, is described. The main feature of the new process is a stereo- and regiospecific addition of benzyl vinyl ether to an o-quinone intermediate masked by a spirolactone group according to the method of Deslongchamps.
A study of the ion [Ta2OF10]2−
Authors: Sala-Pala J. , Calves J. Y. , Guerchais J. E. , Brownstein S. , Dewan J. C. , Edwards A. J.
Published: May 2006

Hydrolysis of (Et4N)[TaF6] with Et4NOH in organic medium gives (Et4N)2[Ta2OF10]. The Ta—O—Ta infrared and Raman frequencies reflect the linearity of the bridge, in agreement with a previous X-ray study. The 19F nmr spectrum is of the type AA′E4E4′. Chemical shifts are compared with other pseudo-octahedral species of tantalum with formula [TaF5L].
Decomposition of tetramethyl-2-tetrazene under acidic conditions
Authors: Madgzinski Leon J. , Pillay K. Somasekharen , Richard Hervé , Chow Yuan L.
Published: May 2006

Decompositions of tetramethyl-2-tetrazene (TMT) under acidic conditions were investigated by product analysis and by nmr and esr spectroscopic monitors. Photolysis in acetonitrile containing trifluoroacetic acid generated the dimethylaminium radical which added efficiently to an olefinic double bond. Some adducts contained a (CH3)2NCH2— moiety, the immediate precursor of which could be CH2=N(CH3)2+ species. Photolytic addition of TMT to nor-bornenes generated 2-norbornyl radicals that underwent coupling through the exo or endo side to give the dimers. Thermal decomposition in sulfuric acid in the presence of toluene gave N,N-dimethyltoluidines, N-methylphenethylamine, benzyltoluenes, and a plethora of other minor products in addition to a large amount of formylidene methylamine. The last compound was the major product when thermal decomposition of TMT was carried out in trifluoroacetic acid in the presence of toluene or anisol; amination products of aromatic substrates were low and contained only ortho and para isomers. TMT dissolved in these solvents exhibited the esr signal of the stable [Formula: see text] (the tetrazene cation radical) which did not react with cyclohexene. In concentrated sulfuric acid, TMT was decomposed in less than 15 min giving formylidene methylamine and dimethylamine as shown by nmr. In trifluoroacetic acid, the esr signal of tetramethylhydrazine cation radical [Formula: see text] emerged after the TMT solution was irradiated; no dimethylaminium radical signal could be detected. The relationship of [Formula: see text] and [Formula: see text] with formation of the observed products remains unclear.
Long-range 1H, 19F spin–spin coupling constants in benzenesulfonyl fluoride and some of its derivatives. Insensitivity of 19F shifts to ortho substituents
Authors: Schaefer Ted , Parr William J. E.
Published: May 2006

The proton and 19F high resolution nuclear magnetic resonance spectra of benzenesulfonyl fluoride and of some derivatives are analyzed to yield spin–spin coupling constants between 19F and the ring protons. These parameters display a marked dependence on the ring substituents and it is not clear how their conformational behaviour can be distinguished from intrinsic substituent perturbations. The large magnitudes of the couplings over six bonds to the para protons, relative to those in benzoyl fluoride, strongly indicate the importance of conformations in which the S—F bond does not lie in the benzene plane. The methyl group replacement technique suggests that the six-bond coupling contains contributions in addition to that from a σ–π mechanism. The chemical shift of the para proton yields a π electron density at the contiguous carbon atom which is considerably smaller than in nitrobenzene, for example. The 19F shifts are much less sensitive to ortho substituents than are the 19F shifts in benzoyl fluoride derivatives, implying much smaller intramolecular van der Waals interactions in the sulfonyl compounds.
A novel acid-catalyzed isomerization of the adducts of 1,4-dimethyl-2,3-diphenyl-cyclopentadiene and dialkyl azodicarboxylates
Authors: Dao Lê H. , Mackay Donald
Published: May 2006

The adduct (4a) of 1,4-dimethyl-2,3-diphenylcyclopentadiene with dimethyl azodicarboxylate is isomerized by one or more equivalents of trifiuoroacetic acid to the exocyclic alkene 5a. The di-tert-butyl analogue 4b is isomerized by limited amounts of trifluoroacetic acid to a mixture of 5b and the oxadiazine 10, the latter being the only product with 1 equiv. of acid; 5b can be made more efficiently from 4b by the action of pyridine or triethylamine. Excess acid converts 4b, 5b, or 10 to the oxadiazinone 7. A protonated intermediate derived from 4b is postulated as the precursor to both 5b and 7 in acid, a view supported by deuterium labelling studies.
Pyrones. III. The alkylation of pyronones. Preferential formation of 2-alkoxy-4-pyrones
Authors: Cyr Terry Donald , Poulton Gerald Arthur
Published: May 2006

2-Alkoxy-4-pyrones and 2-alkoxychromones were prepared in high yield from 4-hydroxy-2-pyrones (2,4-pyronones) and 4-hydroxycoumarin, respectively. The products of diazomethane methylation of dehydroacetic acid (3-acetyl-4-hydroxy-6-methyl-2-pyrone) were identified.
Synthèse et caractérisation des oxypentafluorouranates(VI) NH4UOF5, KUOF5, RbUOF5 et CsUOF5
Authors: Joubert Philippe , Bougon Roland , Gaudreau Bernard
Published: May 2006

The oxypentafluorouranates(VI) MUOF5, where M = NH4, K, Rb, Cs, have been synthetized from reaction of UOF4 with the ammonium or corresponding alkali metal fluoride in liquid SO2. According to X-ray diffraction, Raman and infrared spectroscopy, and from an isomorphism with the corresponding hexafluorouranates(V) MUF6, two different environments around the uranium atom are observed. In CsUOF5 the five fluorine atoms and the oxygen around the uranium result in a pseudo-octahedral surrounding whereas for the other complexes (M = NH4, K, Rb) each uranium is surrounded by eight light atoms forming a dodecahedron. In this structure the dodecahedra are linked together by fluorine atoms to form infinite chains. The UOF5− ion has been characterized by vibrational spectroscopy in the solid state. The proposed assignment, which was made with the assumption of a C4v symmetry of the UOF5− ion, was confirmed by a force constant calculation. From these data and contrary to the values reported for comparable oxypentafluoroanions, the axial fluorine is found to be less ionic than the equatorial ones.
A new route to 5-bromo-5′-bromomethylpyrromethenes
Authors: Rowold Arend , MacDonald S. Ferguson
Published: May 2006

Esters of hitherto inaccessible 5-bromo-5′-bromomethylpyrromethenes, with alternating acetic acid (or methyl) and propionic acid groups in the (β positions, are obtained by brominating the appropriate 5-acetoxymethylpyrrole-2-carboxylic acids in ethanol-free chloroform at ≤10 °C. The bromomethylpyrromethenes give the corresponding methoxymethylpyrromethenes in methanol at room temperature.
Synthèse et propriétés chimiques du phényl-5-octahydro-1,2,3,4,6,7,8,9-dibenzophosphole
Authors: Mathey François , Thavard Daniel
Published: May 2006

5-Phenyl-1,2,3,4,6,7,8,9-octahydrodibenzophosphole (L) has been synthesized by reacting DBU with the PhPBr2-1,1′-bicyclohexenyl cycloadduct. Its chemical properties have been compared with those of more classical phospholes. Its P-oxide and P-sulfide are monomeric. A double ring-expansion reaction is observed with benzoyl chloride as with simple phospholes. On the contrary we met a limited success with the P—Ph bond cleavage by K in THF and we did not succeed at all when attempting a P—Ph → P—tBu exchange by reaction with tBuLi. The corresponding phosphacymantrene has been obtained with Mn2(CO)10. σLFe(CO)4, σ,ηLFe2(CO)7 ans ηLOFe(CO)3 complexes have been obtained from the reactions of L or its P-oxide with Fe3(CO)12.
Reaction of 1,1-diphenylpropene with stannic chloride and hydrogen chloride
Authors: Bywater Stanley , Worsfold Denis J.
Published: May 2006

SnCl4 and HCl have been found to react with 1,1-diphenylpropene to form a small equilibrium amount of the diphenylethylcarbenium ion. No further reaction is detectable, and the equilibrium between the three reactants may be determined from the uv absorption of the ion. The electrical conductances of the solutions have also been measured. The results are consistent with the formation of the salt of this carbenium ion with the SnCl5− anion. The salt in the concentrations formed in these experiments (ca. 10−5–10−4 M) was nearly all dissociated into free ions in methylene chloride solution. The equilibrium constant for formation of the salt was 2.0 M−2 at −30 °C, and the dissociation constant into ions 4.4 × 10−4 M. The overall heat of reaction to the carbenium ion salt was 8.8 kcal, most of which is attributed to the initial formation of the undissociated salt.
Approaches to the synthesis of triterpenoids. IV. The ABC + E ring approach to the pentacyclic triterpene skeleton. Synthesis of a pentacyclic compound suitable for triterpene synthesis
Authors: Apsimon John W. , Badripersaud Satyanand , Hooper John W. , Pike Richard , Birnbaum George I. , Huber Carol , Post Michael L.
Published: May 2006

Studies on the ABC + E ring construction of the pentacyclic triterpene skeleton are described. Acid-catalysed cyclisation of the mixture of diastereoisomers 11 led to preferential cyclisation of one isomer to 10-methoxy-2,2,4aβ,6aβ, 12bβ -pentamethyl-1,2,3,4,4a,5,6,6a, 6bα,7,8,12b,13,14-tetradecahydro-1-picenone (12). An X-ray analysis was performed on this compound which crystallizes in the monoclinic space group P2/c. There are four molecules in the unit cell which has dimensions a = 6.456(2), b = 42.518(6), c = 8.519(2) Å, β = 100.92(3)°. The structure was solved by direct methods and refined by block-diagonal least-squares to a final R value of 0.042 for all 3234 observed reflections. The molecular structure found by X-ray diffraction confirms the stereochemical reasoning used in the synthetic steps.
The nonstereospecific addition of benzeneselenenyl chloride to 3,4-dihydro-2H-pyran
Authors: Garratt Dennis G.
Published: May 2006

The addition of benzeneselenenyl chloride to 3,4-dihydro-2H-pyran in methylene chloride at 25 °C gives 65% of the trans and 35% of the cis Markownikoff adduct: 2-chloro-3-phenylseleno-tetrahydropyran under conditions of kinetic control. The above reaction was observed to be reversible, the adducts subsequently reacting with the benzeneselenenyl chloride under conditions similar to those used for the reaction with 3,4-dihydro-2H-pyran to give diphenyl diselenide and 2,3-dichlorotetrahydropyran in good yield. There was no evidence for the formation of 3-chloro-2-phenylselenotetrahydropyran under conditions of either kinetic or thermodynamic control. Kinetic studies support a mechanism involving a seleniranium ion that opens to an oxacarbonium ion before the product determining step.
The preferred conformations in solution and rotational barriers of the phenyl moiety in 3,5-dichlorobenzyl derivatives of ammonia, dimethylamine, and dimethylarsine
Authors: Schaefer Ted , Danchura Werner , Niemczura Walter
Published: May 2006

The long-range spin–spin coupling constants between methylene protons and ring protons are measured in 3,5-dichlorobenzylamine, 3,5-dichlorobenzyldimethylamine, and in 3,5-dichlorobenzyldimethylarsine. The couplings over six bonds are used to derive internal barriers to rotation about the carbon–carbon bond to the phenyl ring. In the above order, they are 0.3 ± 0.3, 0.8 ± 0.2, and 3.0 ± 0.5 kcal/mol. The conformation of lowest energy in the arsine is that in which the CH2—X bond lies in a plane perpendicular to the benzene plane.
On spin trapping hydroxyl and hydroperoxyl radicals
Authors: Janzen Edward G. , Nutter Jr. Dale E. , Davis Edward R. , Blackburn Barry J. , Poyer J. Lee , McCay Paul B.
Published: May 2006

The assignments of the hydroxyl, hydroperoxyl, and alkylperoxyl radical spin adducts of α-phenyl N-tert-butyl nitrone (PBN) are discussed. Results of new experiments designed to test the assignments of the first two are described. It is concluded that the hydroxy adduct assignment is correct. The relationship between aβH and aN is[Formula: see text]This equation gives a good fit for the seven pairs of constants reported for the hydroxy adduct. The assignments for the hydroperoxy adduct may be correct but no proof is yet available for this assignment.
Hydrolyse des sels de phospholium monomères: Préparation et propriétés des oxydes de 1,3-diénylphosphines
Authors: Mathey François , Muller Georges
Published: May 2006

The hydrolysis of 3,4-dimethylphospholium salts by thallium ethylate in alcohol yields exclusively the corresponding dienylphosphine oxides by ring opening in the general case. However when one of the phosphorus substituents is benzyl, the dienylphosphine oxide becomes the minor product of the hydrolysis, the major product being the 3-methyl-4-methylene-2-phospholene oxide which results from the cleavage of the P—CH2Ph bond with isomerization of one of the double bonds of the phosphole ring. Deuterolysis of benzylphospholium salts shows that the isomerization does not take place before the hydrolysis. Attempted reduction of the P=O bond of dienylphosphine oxides by phenylsilane yields hydrogenated products. On the contrary, the P=O → P=S conversion by P4S10 occurs without destruction of the dienic system. High yields of diene–Fe(CO)3 complexes are obtained by reaction with Fe3(CO)12. When the two phosphorus substituents are different, two diastereoisomeric complexes are obtained.
An electron spin resonance study of organomercury adducts of phenanthroquinont
Authors: Chen Kuang S. , Smith Richard T. , Wan Jeffrey K. S.
Published: May 2006

The exchange reaction between M+PQ−• ion-pairs and MeHgCl leads to the formation of MeHgPQ• adduct with a characteristic low g-factor of 2.00052 and a small methyl proton splittings of 0.16 G. The dynamic and equilibrium aspects of the exchange depend upon the alkali cation, the concentration of MeHgCl, and for M+PQ−• also on temperature. The MeHgPQ• is found to be relatively stable at room temperature and in the presence of water. These results may be of potential value to toxicology studies of methylmercury.
Electromotive force measurements of the cell: In/InCl3/In—Hg, together with the derived thermodynamic quantities
Authors: Campbell Alan N.
Published: May 2006

Amalgams containing up to 60 wt.% indium are liquid and homogeneous at room temperature. The emf's of liquid amalgams containing from 10 to 50 wt.% of indium in the cell In/InCl3/amalgam have been determined and from these the quantities ΔG, ΔH, and ΔS for the process In + Hg → amalgam.
The radical addition of N-haloamides to 1,6-heptadiene: The transfer step in the photochemical and chromous chloride promoted addition of N-haloamides to olefins
Authors: Mondon Martine , Lessard Jean
Published: May 2006

A study of the photochemical addition of N-haloamides (ZCONHX) to 1,6-heptadiene shows that the reactivity of ZCONHX as an halogen-atom donor to an alkyl radical increases with Z in the order CH3 < ClCH2 < OC2H5 ≤ CCl3 ∼ CF3 which indicates a polar character of the transition state. An N-bromoamide is shown to be more reactive than an N-chloroamide as expected. The chromous chloride promoted addition of N-chlorochloroacetamide and N-chlorotrichloroacetamide to 1,6-heptadiene is compared with the photochemical addition under similar conditions of solvent and temperature. The better interpretation of the results, for the chromous chloride promoted additions, is in ternis of a classical chain mechanism rather than a redox chain mechanism; the latter mechanism cannot be excluded however.
Stereospecific synthesis of (−)-α-multistriatin from D-glucose
Authors: Sum Phaik-Eng , Weiler Larry
Published: May 2006

A totally stereospecific synthesis of the insect pheromone, (−)-α-multistriatin, is reported starting from D-glucose.
Field desorption mass spectrometry of carboxylate salts: characteristic spectra and effects of added complexing agents
Authors: Wood Gordon Walter , Oldenburg Emily Jane , Lau Pui-Yan
Published: May 2006

Field desorption mass spectra are reported for a series of sodium carboxylates. Above 20 mA the major ions in the spectra belong to the series [xNa+ + (x − 1)RCOO−]+ with values of x normally extending throughout the measurable mass range. Desorption characteristics and spectral composition have been shown to be strongly modified by the addition of fructose and other polyhydroxy compounds. Thus, the sodium acetate spectrum is more intense and contains higher aggregates when 0.1–0.2 mol of fructose is added. With further additions the ionized free acid, AcOH+•, becomes the base peak in a low intensity spectrum recorded at 17–18 mA. The main ion from fructose is the sodium complex which does not exceed 20% of the base peak. Added fructose also has a beneficial effect on sodium 12-hydroxystearate but the improvement is less dramatic and there are some complications in the interpretation. A sample of technical lithium stearate contains the usual complexes up to [Li4(RCOO)3]+ and the presence of important amounts of palmitate gives rise to all possible combinations of the two carboxylate anions in these complexes. Smaller amounts of Li2Na, Li3Na, and Li3K complexed with the appropriate number of anions give evidence of alkali metal impurity.
Factor analysis as a complement to band resolution. V. Complexing of pentachlorophenol and acetone in carbon tetrachloride solution
Authors: Korppi-Tommola J. , Shurvell H. F.
Published: May 2006

Complex formation between pentachlorophenol and acetone and acetone-d6 in carbon tetrachloride solution has been studied in both the hydroxyl and carbonyl stretching regions of the infrared spectrum. Factor analysis of the digitized spectra indicates three absorbing components for each set of solutions in the hydroxyl stretching region. Concentration studies revealed roughly linear relationships between the areas of the 'free' ν(OH) band and both of the resolved complex bands, suggesting that two different 1:1 complexes occur in CCl4 solution. In the ν(CO) region only one band due to complex formation was detected. Equilibrium constants for the isotopically different complexes at about 30 °C are reported. In the hydroxyl stretching region, band resolution was also carried out using four components which gave a better fit to the observed spectrum. A set of equilibrium constants were then obtained. However, considerable difficulties were met in the calculations and in the interpretation of these results, so that the three band, two complex model is preferred.
13C-nuclear magnetic resonance spectra of oxiranes. Configuration of 1,2-epoxypropyl side chains in fungal metabolites
Authors: Lesage Suzanne , Perlin Arthur S.
Published: May 2006

13C nmr data indicate that the epoxypropyl side chain of 'asperlin' (1) has a trans configuration. This assignment follows from associated measurements on model compounds, showing that the 13C chemical shift of an epoxypropyl CH3 group is close to either 17 ppm (trans isomers) or 13 ppm (cis isomers). Synthesized as oxirane derivatives related to 1 are diastereomeric pairs of 8-deoxy-6,7-cis- and -trans-epoxy-1,2:3,4-di-O-isopropylidene-α-D-galacto-octopyranoses.
Milieux hyperbasiques: Synthèse de cyclariones α-cyanées par cyclisation anionique d'amides-nitriles
Authors: Larcheveque Marc , Mulot Patrick
Published: May 2006

ω-Cyano N,N-disubstituted amides are conveniently prepared from halogenated amides by treatment with alkaline cyanides. By reacting them with powerful bases such as lithium dialkylamides in ether, these cyano amides may be metallated in α position to the cyano group only. When they are warmed up, the anions react with the amide group to afford α-cyano cyclanones by an intramolecular cyclisation.
Fumaritine N-oxide, an alkaloid of Fumaria kralikii Jord.
Authors: Klryakov H. G. , Hughes Donald W. , Nalliah Bala C. , MacLean David B.
Published: May 2006

Alkaloid Fk-5, isolated from F. kralikii, has been shown to be fumaritine N-oxide. The structure was established by 1H and 13C nmr and by mass spectrometry and confirmed by reduction of Fk-5 to fumaritine. The 13C spectra of fumaritine and its N-oxide are discussed.
Molecular reorieentation in solid sym-triazine
Authors: Ripmeester J. A. , Boyd R. K.
Published: May 2006

Molecular motion in solid sym-triazine was investigated using continuous wave and pulsed 1H nmr methods between 290 and 350 K. In addition, the potential energy profile of the sym-triazine molecule as a function of orientation in the crystal lattice was calculated. From the nmr results, only one motional process was identified, in-plane reorientation of sym-triazine molecules with an activation energy of 15 kcal/mol. This is in agreement with the potential energy calculation which also shows that the reorientation takes place between equivalent sites.
The preparation and characterisation of 1,1,2,2-tetramethyl-1,2-diacyloxyditin(IV) compounds
Authors: Birchall Thomas , Johnson James P.
Published: May 2006

Reaction of hexamethylditin with haloacetic acids results in the production of 1,1,2,2-tetramethyl-1,2-diacyloxyditin(IV) compounds in good yield. Infrared, Raman, 1H and 13C nmr, and 119Sn Mössbauer data have been interpreted in terms of a tetramethylditin species asymmetrically bridged by two acyloxy groups to give each tin a five-coordinate environment.
Nuclear analogs of β-lactam antibiotics. X. Synthesis of 2-substituted desthiocephalosporins
Authors: Doyle Terrence William , Conway Terry Thomas , Casey Michael , Lim Gary
Published: May 2006

The syntheses of the desthiocephem system from the enol 2 is described. Thus conversion of 2 to its triflate 3 followed by treatment with the sodium salts of malonate esters gave the cyclized products 4a–c. Azide reduction followed by coupling of phenoxyacetic acid and hydrogenolysis gave the acids 7 and 8. Compound 15 was also prepared.
Nuclear analogs of β-lactam antibiotics. XI. Synthesis of 3-methyl-7-β-(phenoxyacetamido)-Δ3-desthiocephem-4-carboxylic acid
Authors: Doyle Terrence William , Conway Terry Thomas , Lim Gary , Luh Bing-Yu
Published: May 2006

Treatment of the acid 3 with triethylamine in refluxing tert-butyl alcohol gave the decarboxylated product 4 which was isomerized to the desired Δ3 isomer 5 using DBN. Reduction of the azido functions in 4 and 5 followed by coupling to phenoxyacetic acid and debenzylation gave the acids 11 and 8, respectively. Attempts to prepare dienic cephalosporins failed. The halogenation of 4 and 5 was studied and is discussed.