bluuebunny/crossref_metadata_2025 huggingface dataset:
A carbon-13 nuclear magnetic resonance study of benzyl cyanide
Authors: Wasylishen Roderick E. , Pettitt Brian A.
Published: May 2006

Spin–lattice relaxation times are reported for the cyano, methylene, and ring carbons in liquid benzyl cyanide at selected temperatures between 215 and 406 K. The rotation of the molecule is modelled on the diffusion of a prolate spheroid and the following features are deduced: (1) rotation of the aromatic ring about the long axis of the molecule is about 3 times faster than rotation of this axis, (2) rotation of the —CH2CN group about the long axis is about 1.5 times faster than the aromatic ring, and (3) activation energies associated with the temperature dependence of the 13C—1H dipolar relaxation rates agree with the hydrodynamical prediction of 3.6 kcal/mol associated with the temperature dependence of the ratio shear viscosity–temperature.Linewidths of the cyano carbon resonance are shown to result from scalar coupling with 14N.Spin–spin coupling constants involving the cyano and methylene carbons are reported and compared with those calculated at the INDO level of molecular orbital theory.
Stereocontrolled Diels–Alder reactions with a bifunctional dienophile
Authors: Kakushima Masatoshi , Scott Daniel G.
Published: May 2006

In the Diels–Alder cycloaddition of electron-rich dienes to methyl E-4-oxobutenoate, the formyl group controls both regio- and stereoselectivity. Secondary overlap considerations are used to explain these results.
Ring expansion of cyclic ketones: The reliable determination of migration ratios for 3-keto steroids by 13C nuclear magnetic resonance and the general implications thereof
Authors: Dave Vinod , Stothers J. B. , Warnhoff E. W.
Published: May 2006

Several ring-expansion reactions (diazomethane, diazoacetic ester, Tiffeneau–Demjanov, Baeyer–Villiger, and Schmidt) of 3-keto steroids have been reexamined to determine the true migration ratios for C-2 and C-4 in these unsymmetrical cyclohexanones. Migration ratios were measured to ±3% accuracy by integration of baseline-separated signals in the proton-decoupled 13Cmr spectra of total reaction products. This underexploited method provides for the first time a way to get accurate migration ratios without loss of components during separation and without interference from excess starting material under conditions minimizing side reactions. In contrast to numerous literature reports, all but one of the 16 reactions studied were found to give nearly the same amount of both possible A-homo products. (The single exception was the only reaction in which the A-homo product reacts markedly faster than the starting material.) This simple, consistent ∼1:1 pattern is that expected if migration is governed mainly by the electronic effect of the α- and α′-carbon atoms and not by any conformational or near-by-to-remote substituent effect.
Microbial hydroxylation of steroids. 6. Hydroxylation of C-6-substituted androst-4-ene-3,17-diones by Rhizopusarrhizus ATCC 11145
Authors: Holland Herbert L. , Diakow Peter R. P.
Published: May 2006

The products arising from the incubations of C-6α and C-6β chloro-, fluoro-, and methyl-substituted Δ4-3-keto steroids with the C-6β hydroxylating fungus Rhizopusarrhizus ATCC 11145 have been identified, and their formation rationalised in terms of Δ3,5 enolic intermediates. The incubations of C-6 chloro and methyl Δ3,5 enol acetates with R. arrhizus, and the oxidations by m-chloroperoxybenzoic acid of the corresponding enol ethyl ethers have also been described. The relevance of the results so obtained to the mechanism of C-6β hydroxylation of Δ4-3-keto steroids by R. arrhizus is discussed.
The biosynthesis of the Lythraceae alkaloids. I. The lysine-derived fragment
Authors: Gupta Ram Nath , Horsewood Peter , Koo Swe Hoo , Spenser Ian D.
Published: May 2006

The biosynthesis of decodine (7) and decinine (9), Lythraceae alkaloids containing a trans-fused quinolizidine nucleus, was studied in intact plants of Decodonverticillatus (L.) Ell. Nonrandom incorporation of radioactivity from 14C-labelled samples of lysine, cadaverine, and Δ1-piperideine was demonstrated by partial degradation. Pelletierine did not serve as a precursor of the alkaloids. It was also shown, by means of 3H,14C-labelled tracers, that the alkaloids are derived from L-lysine whereas pipecolic acid, which is present in the plant, is derived from D-lysine.
Total synthesis of indole and dihydroindole alkaloids. XVII. The total synthesis of catharine and vinamidine (catharinine)
Authors: Kutney James P. , Balsevich John , Worth Brian R.
Published: May 2006

Oxidation of 16,18-dicarbomethoxycleavamine gave the epoxide (6) and the enamide (9). Similar oxidation of 3′,4′-dehydrovinblastine (8) or leurosine (7) gave the natural product catharine (3). Potassium permanganate oxidation of 7 or 8 gave 3R-hydroxyvinamidine (19) whereas similar oxidation of 4′-deoxyleurosidine (29) gave the alkaloid vinamidine (4).
Crystal and molecular structure of bis[methyltris(1-pyrazolyl)gallato]nickel(II)
Authors: Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Crystals of bis[methyltris(1-pyrazolyl)gallato]nickel(II) are rhombohedral, a = 9.6670(5), c = 23.893(1) Å, Z = 3, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R of 0.030 and Rw = 0.035 for 925 reflections with I ≥ 3σ (I). The crystal structure consists of well separated molecules of [MeGa-(N2C3H3)3]2Ni having exact [Formula: see text] (S6) symmetry and approximate D3d symmetry. The coordination geometry about the nickel atom is octahedral with Ni—N = 2.109(2) Å, N—Ni—N = 90.65(6) and 89.35(6)°. The gallium atom has distorted tetrahedral coordination geometry with Ga—N = 1.939(2), Ga—C = 1.940(4) Å, N—Ga—N = 99.55(6), and N—Ga—C = 118.16(5)°.
Aminocyclitols. III. Synthesis of diaminocyclohexanediols
Authors: Kavadias Gerry , Droghini Robert
Published: May 2006

Reaction of N,N′-diethoxycarbonyl-2,5-dideoxystreptamine (1b) with thionyl chloride produced the iminoether dihydrochloride 8 which, upon simple treatment with water gave the di-N,O-carbonyl compound 9. Acidic hydrolysis of 9 yielded the aminocyclitol 2a. Alternatively, 2a was prepared from N,N′-dibenzoyl-2,5-dideoxystreptamine (1c) via the oxazoline 10 followed by acidic hydrolysis. Treatment of 1c with triethyl orthoacetate in the presence of boron trifluoride etherate produced the oxazoline 11 and the latter product was hydrolyzed to give 3a. By the same reaction sequence, 1e and 1h were converted to the oxazolines 12 and 13 which upon acidic hydrolysis provided the enantiomeric aminocyclitols 4 and 5. Ring-opening reactions of cis- and trans-1,4-diepoxycyclohexanes (14 and 16) with sodium azide to the diazido compounds 15 and 17, followed by reduction, afforded the aminocyclitols 6 and 7.
Carbon-13 nuclear magnetic resonance spectral study of some isomeric derivatives of 2-methoxytropone. Troponoid-II
Authors: Bagli J. F. , Bogri T. , Palameta B. , St-Jacques M.
Published: May 2006

The 13C nmr spectra of several isomeric monosubstituted derivatives of 2-methoxytropone together with some dibromo derivatives have been obtained and analysed. Substituent parameters were defined and shown to exhibit additivity. Differences with corresponding parameters for monosubstituted benzene analogs suggest proximity interactions between the 3-substituents and the 2-OCH3 group as well as between 7-substituents and the adjacent carbonyl group. The data indicates that the OCH3 group is a convenient probe to investigate the orientation of mesomeric electronic charge transfer to the various carbons of the tropone seven-membered ring. Finally, it is demonstrated that 13C nmr is quite useful to distinguish between the various substituted 2-methoxytropones.
Synthèse et réactivité des halogéno-2 sulfonyl-2 aziridines
Authors: Gaillot Jean-Marc , Gelas-Mialhe Yvonne , Vessiere Roger
Published: May 2006

Carbon tetrahalide reacts rapidly with 2-phenylsulfonyl aziridines in the presence of KOH, leading to 2-phenylsulfonyl 2-haloaziridines.Starting with 2-isopropylsulfonyl aziridines, a monochloro and a dichloroaziridine are produced; the Ramberg–Bäcklund reaction is not observed.These halo compounds decompose either thermally or in acidic medium leading to N-substituted α-haloacetamides and α-phenylsulfonylacetamides. 2-Phenylsulfonyl 2-haloaziridines are unreactive toward potassium cyanide or sodium thiophenoxide. Sodium methoxide, sodium ethoxide, or sodium thioethoxide reduce them to 2-phenylsulfonyl aziridines; the reaction depends upon the solvent.
Effects of organic cosolvents on enzyme stereospecificity. The enantiomeric specificity of α-chymotrypsin is reduced by high organic solvent concentrations
Authors: Jones J. Bryan , Mehes Mladen M.
Published: May 2006

The influence of a range of protic and aprotic solvents of varying polarities on the enantiomeric specificity of α-chymotrypsin has been examined using methyl (2S)- and (2R)-2-acetamido-2-phenylacetate (1) as representative L- and D-substrates. The rates of hydrolysis were determined in solutions containing up to 30% organic solvent. The addition of organic solvent reduced the overall rates of hydrolysis of (2S)- and (2R)-1 in each case, with those of the L-enantiomer (2S)-1 being affected more than those of the D-stereoisomer (2R)-1. However, the enzyme overwhelmingly retains its normal L-enantiomeric preference under all conditions surveyed. It is concluded that α-chymotrypsin, and possibly other strongly stereospecific enzymes, can be used with confidence for asymmetric synthesis or resolution purposes in aqueous solutions to which moderate (up to 40%) proportions of organic cosolvents have been added to increase solubility of hydrophobic organic substrates.
Comment: Ultrasonic velocities for deuterium oxide – water mixtures at 298.15 K
Authors: Ernst Stefan , Glinski Jacek
Published: May 2006

The results of highly precise measurements of ultrasonic velocity in mixtures of deuterium oxide with water by Kiyohara et al. were used to calculate and discuss the excess velocity of sound in this system.
On the reliability of the inversion of the Arrhenius rate law
Authors: Yau Andrew W. , Pritchard Huw O.
Published: May 2006

A numerical test of the reliability of the Slater–Forst procedure for the inversion of the Arrhenius rate law is presented using the theoretical data for the reactions N2O → N2 + O and CO2 → CO + O reported previously: the test results are positive. The sensitivity of the procedure to variations in the Arrhenius parameters is also examined.
Ab initio configuration interaction study of the A2A1–2B1 transition of PH2 and PD2
Authors: Peric Miljenko , Buenker Robert J. , Peyerimhoff Sigrid D.
Published: May 2006

The potential surfaces for the X2B1 and A2A1 states of PH2 are calculated by means of an ab initio CI method. These results are then used to obtain vibrational levels and wavefunctions for each electronic state in both PH2 and PD2, whereby a two-dimensional treatment of the associated bending modes is carried out; the resulting vibrational frequencies are found to agree with the corresponding experimental findings (where available) to within 25 cm−1 in each case. The discrepancy in the calculated 0–0 transition energy is 0.06 eV and the variation in [Formula: see text] values parallels quite closely that obtained experimentally. Finally the electronic transition moment is calculated as a function of the internuclear angle and this information is combined with the above vibrational wavefunctions to describe the intensity distribution in this electronic system; a maximum intensity is obtained for v2′ = 4 in the bending mode for PH2, in agreement with the observed findings, and is predicted to occur for v2′ = 6 in PD2.
The normal and the retro-Boulton–Katritzky rearrangement of hydroxy- and nitro-substituted benzofuroxans
Authors: Buncel Erwin , Chuaqui-Offermanns Noemi , Norris Albert R.
Published: May 2006

The demethylation of 7-methoxy-4-nitrobenzofuroxan by aqueous KOH gives rise to 7-hydroxy-4-nitrobenzofuroxan as well as 5-hydroxy-4-nitrobenzofuroxan, the latter being formed via a retro-Boulton–Katritzky rearrangement. The retro rearrangement also occurs on heating the potassium salt of 7-hydroxy-4-nitrobenzofuroxan in the solid state. In basic aqueous solution 5-hydroxy-4-nitrobenzofuroxan undergoes the normal Boulton–Katritzky rearrangement to yield 7-hydroxy-4-nitrobenzofuroxan. These processes are rationalized on the basis of a balance between electrostatic and steric interactions in the reactants and the products of rearrangement.
The occurrence of ergosterol and (22E,24R)-24-ethylcholesta-5,7,22-trien-3β-ol in the unicellular chlorophyte Dunaliellatertiolecta
Authors: Wright Jeffrey L. C.
Published: May 2006

Using 13C nuclear magnetic resonance spectroscopy the major sterols of the unicellular chlorophyte Dunaliellatertiolecta were found to be ergosterol and a closely related C29 trienol. Apparently the absence of a cell wall in D. tertiolecta does not significantly affect the type of sterol produced since other unicellular chlorophytes which possess a cell wall produce similar sterols containing an unsaturated side chain and a 24[R]-alkyl substituent.
Polar radicals XIII. A reinvestigation of the polar effects reported for the hydrogen transfer reactions of the 1-ethylpentyl radical
Authors: Tanner Dennis D. , Henriquez Roberto , Reed Darwin W.
Published: May 2006

The relative kinetics obtained from the decomposition products of tert-butyl-2-ethylperhexanoate, BEPH, (0.1 M) in mixtures of toluene and carbon tetrachloride were reinvestigated. Relative reactivities calculated from the ratios of heptane to 3-chloroheptane formed from BEPH decompositions in a variety of substituted toluenes, with added carbon tetrachloride, gave a similar Hammett correlation to that previously reported, but with a rather poor correlation coefficient (r = 0.88, ρ = 0.68).From a material balance of the products formed it was determined that very few if any of the 1-ethylpentyl radicals formed ultimately abstract a benzylic hydrogen from toluene or a substituted toluene. The small amounts of heptane found (<0.7%) at any of the kinetically meaningful ratios of substrates, ArCH3/CCl4 2.1 to 16.3, could have potentially arisen from radical disproportionation. No appreciable amount of aromatic substitution product could be detected under these conditions.Decompositions of BEPH carried out in neat toluene only yielded small amounts (∼0.4%) of addition product; however, the absolute amounts of heptane produced in reactions run in p-cyanotoluene were less than those formed in reactions carried out in toluene. These observations do not argue strongly for the authenticity of a relatively large positive ρ value (previously reported, +0.7) arising either from benzylic abstraction, or from addition to the aromatic ring.
Characterization of autohydrolysis aspen (P. tremuloides) lignins. Part 2. Alkaline nitrobenzene oxidation studies of extracted autohydrolysis lignin
Authors: Wayman Morris , Chua Miranda G. S.
Published: May 2006

Alkaline nitrobenzene oxidation of the lignins extracted from extractive-free aspen wood meal after autohydrolysis at 195 °C for periods varying from 5 min to 2 h indicated that these lignins were structurally more condensed in terms of an increase in new carbon–carbon bonds than aspen milled wood lignin. The degree of condensation generally increased with longer autohydrolysis times. It is postulated that condensation involved materials from both the carbohydrate and lignin components of the wood which were generated during the autohydrolysis. The molar ratio of syringaldehyde to vanillin of extracted lignin on oxidation was observed to decrease with increasing autohydrolysis time. It is suggested that syringyl units are preferentially extracted as low molecular weight material.
Substituent effects on the zero-field splitting parameters of diarylmethylene. Evidence for merostabilization in appropriately substituted diphenylmethylenes
Authors: Humphreys Robert W. R. , Arnold Donald R.
Published: May 2006

An analysis of the temperature dependence (4–30 K) of the electron spin resonance (esr) spectra of substituted diphenylmethylenes (e.g. para-, para′-; methoxy, cyano, dimethylamino, and nitro) indicates all of these species have a triplet ground state. The variation in the zero-field splitting parameter D for this series of methylenes provides evidence that the average separation of the unpaired electrons is greatest for the unsymmetrically substituted derivatives, those having a strong para-electron-withdrawing substituent and a strong para′-electron-donating substituent. This result is explained in terms of a favourable contribution of charge-separated valence-bond structures, i.e., merostabilization.
Photochemical ring expansion of a bridged cyclobutanone. Crystal and molecular structure of the photoproduct acetal
Authors: Greenhough Trevor J. , Scheffer John R. , Trotter James , Walsh Leueen
Published: May 2006

The photochemistry of the bridged cyclobutanone system 1,3,4,6,8,9-hexamethyltricyclo-[4.4.0.03,10]decane-2,5-dione has been studied. Irradiation in methanol leads to a single ring-expanded cyclic acetal whose structure was determined by X-ray crystallography. The reaction represents the first example of oxacarbene formation in a bridged cyclobutanone. Rationalization of the observed regioselectivity on the basis of alkyl substitution effects on radical stability following α-cleavage is inappropriate since the starting cyclobutanone bears equal α and α′ substitution. An alternative explanation involving alkyl radical angle strain and hyperconjugation effects is advanced.
Phase transformation studies on K2Cr2O7
Authors: Natarajan Mahadeva , Secco Etalo A.
Published: May 2006

The phase transformations occurring in K2Cr2O7 have been examined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), specific heat measurements, electrical conductivity technique, and X-ray diffractometry. The results show that the polymorphic behavior of K2Cr2O7 is very sensitive to the thermal and preparative history of the sample.
The commutative property of strong-transition rate matrices
Authors: Pritchard Huw O. , Lakshmi Arunachalam
Published: May 2006

The (n − 1)-fold degenerate set of transition probabilities used in our recent reformulation of unimolecular reaction theory is operationally equivalent to the set of effective strong-transition probabilities introduced recently by Nordholm. We have found that the relaxation matrix corresponding to these transition probabilities commutes with any other relaxation matrix which will drive the same system to a Boltzmann distribution at infinite time. Some useful results stemming from this commutative property are presented; we expect that these results will help to clarify further the nature of the assumptions underlying strong- and effective strong-collision theories.
Molecular and group relaxation studies in parasubstituted benzenes in various media
Authors: Crossley J. , Shukla J. P. , Tay S. P. , Walker M. S. , Walker S.
Published: May 2006

Dielectric absorption studies have been made on molecules of the type [Formula: see text][Formula: see text] where X—Y is —OCH3, —COCH3, —CH2Cl, and —CH2CN. The molecules have been dissolved in (a) a polystyrene matrix and (b) in the viscous liquid o-terphenyl. For 1,4-dimethoxybenzene the group process dominates in both media, and estimates have been made of the activation enthalpy for group relaxation. For 1,4-dimethoxybenzene in benzene, decalin, Nujol, and o-terphenyl solutions, however, there appears to be a small contribution from the molecular process. No such contribution was detected in the matrix studies on this solute molecule. For 1,4-diacetylbenzene, 1,4-bis(chloromethyl)benzene, and 1,4-bis(cyanomethyl)benzene in o-terphenyl solution it again seems that the group and molecular processes overlap. However, in polystyrene the enthalpies of activation which emerge are characteristic of the group relaxation process as determined by the nmr approach. Altogether, the work illustrates that o-terphenyl may be a useful solvent in helping to decide whether a solute has contributions from an intramolecular motion.
The synthesis of bicyclo[2.2.2]octenones via intramolecular Diels–Alder reactions of modified Wessely oxidation products
Authors: Yates Peter , Auksi Hillar
Published: May 2006

"Modified" Wessely oxidation of 2,6-dimethylphenol with lead tetraacetate in the presence of acrylic acid, cinnamic acid, cis-β-bromoacrylic acid, trans-β-bromoacrylic acid, methyl hydrogen maleate, methyl hydrogen fumarate, and tiglic acid followed by intramolecular cycloaddition gives exo-6-hydroxy-4,6-dimethyl-5-oxobicyclo [2.2.2]oct-7-ene-exo-2-carboxylic acid lactones. Analogous products have been obtained from o-cresol. Structural assignments have been made on the basis ofthe ir, uv, and 1H nmr spectra of the products; analysis of the last shows that the geometry of the bicyclo[2.2.2]octenone system is distorted by the presence of the lactone ring. Chemical transformations of two of the products from the "modified" Wessely oxidation–intramolecular cycloaddition sequence have demonstrated that this route may be used to prepare regioisomers or stereoisomers of products obtained by the conventional Wessely oxidation–intermolecular cycloaddition sequence.
Partial molal volumes of organic compounds in carbon tetrachloride. V. Cyclic alkanes, ethers, alcohols, ketones, and bromides
Authors: Edward John T. , Farrell Patrick G. , Shahidi Fereidoon
Published: May 2006

The partial molal volumes [Formula: see text] or 47 mono- or polycyclic alkanes, ethers, alcohols, ketones, and bromides have been determined in carbon tetrachloride at 25 °C. [Formula: see text] of most of these compounds can be calculated with moderate (±1–2%) accuracy using an equation containing parameters previously developed for acyclic compounds, and an additional cyclization parameter C, which is roughly linear with the number n of atoms in the ring, from n = 3 (C = +5.3 mL mol−1) to n = 10 (C = −21.0 mL mol−1). Substituted cyclohexanols and some polyfunctional compounds had [Formula: see text] considerably lower than calculated.
Kinetic equations for reactions in concentrated aqueous acids based on the concept of "excess acidity"
Authors: Cox Robin A. , Yates Keith
Published: May 2006

Kinetic equations, applicable to A-1, A-SE2, and A-2 reactions in concentrated aqueous acids, are derived. The variation in reaction rate with varying acid concentration is treated in terms of the "excess acidity" of the medium (X-function), rather than in terms of Hammett-type acidity functions or the water activity. The parameters obtained are the medium-independent rate constant k0, in the aqueous standard state, as an intercept, and a slope parameter m≠ hydration parameters (r-values) are also obtained, for A-2 reactions. The equations derived are shown to apply to A-1 acetal hydrolyses, A-SE2 electrophilic aromatic substitutions, and mixed A-2/A-1 ester hydrolyses. In a general discussion of available methods for analyzing rate data in these media, it is shown that the X-function method encompasses most, if not all, of the others, and that classical acidity functions are no longer necessary.
The hydrolyses of some sterically crowded benzoate esters in sulfuric acid. The excess acidity method at different temperatures
Authors: Cox Robin A. , Goldman Malcolm F. , Yates Keith
Published: May 2006

The excess acidity method has been used to analyze the observed acid-catalyzed hydrolysis rate constants for methyl benzoate, methyl para-toluate, methyl ortho-toluate, and methyl 2,6-dimethylbenzoate, over a wide sulfuric acid concentration range, at several different temperatures. Enthalpies and entropies of activation in the aqueous standard state are reported, with slope parameters m≠ also given are the [Formula: see text] and m* values found for the protonation of these compounds. The mechanistic changeover from AAc-2 to AAc-1 hydrolysis occurs at lower acidity with increasing methyl substitution, mainly due to the decrease in activation enthalpy in the transition state for the AAc-1 process, caused by release of steric strain and increased mesomeric interaction. The AAc-2 hydrolysis involves two water molecules, and is energetically favourable and entropically unfavourable. The AAc-1 reaction is difficult energetically, but this is offset by the large positive activation entropies found.
Stereochemical analysis of exo-methylenebenzocycloalkanes: evidence from carbon-13 nuclear magnetic resonance chemical shifts, 13C–13C nuclear spin couplings, and force field calculations
Authors: Buchanan Gerald W. , Selwyn Jocelyn , Dawson Brian A.
Published: May 2006

A series of exo-methylenebenzocycloalkanes with ring sizes 5–8 have been prepared, enriched with 13C and also deuterated at the exocyclic position. 13C chemical shifts are found to be influenced by the degree of planarity between the aromatic ring and the exocyclic methylene function. 13C–13C couplings through one, two, and three bonds have been measured. The 1JCC values correlate very well with %S character calculations. Values of 3JCC are found to be influenced by both dihedral angle and valence angle. The relative propensity for these compounds to isomerize to endocyclic material is discussed. Some earlier spectral assignments for the indene derivative are shown to be in error.
Substituent and solvent effects on Lewis acidity of p-substituted anilines: symmetry of interactions
Authors: Launay G. , Wojtkowiak B. , Krygowski T. M.
Published: May 2006

Symmetrical influences of the solvent and the substituent on NH2-Lewis acidity of six p-substituted anilines studied in a series of six solvents were found. The sensitivity parameter (Hammett reaction constant) estimated for various solvents correlated well with basicity of solvents. The sensitivity parameter of the regression of NH2-acidity vs. basicity parameters of solvents (slope in eq. [5]) correlated with electron attraction or repulsion as measured by substituent constants σ.
The synthesis of oligoribonucleotides V. The stepwise synthesis of the 3′-terminal heptanucleotide sequence of tRNAfMet from E. coli
Authors: Ogilvie Kelvin K. , Theriault Nicole Y.
Published: May 2006

The stepwise synthesis of a heptaribonucleotide GpCpApApCpCpA corresponding to the 3′-terminus of tRNAfMet from E. coli is described. The procedure takes advantage of the ease of obtaining ribonucleoside units bearing a tert-butyldimethylsilyl group on the 2′-position. These units, bearing a 5′-methoxytrityl group are phosphorylated at the 3′-position and coupled to the free 5′-position of the growing nucleotide chain using the chlorophosphite coupling procedure. Yields varied from 87 to 50% over the entire sequence.
The chemistry of thujone. II. Insect juvenile hormone analogues via acid dianion coupling. The β lactone route
Authors: Kutney James P. , McGrath Michael J. , Young Robert N. , Worth Brian R.
Published: May 2006

Several stereoselective syntheses of (E)-2-ethyl-6-methyl-5-octenoic acid (17) are described. The dianion of pure 17 was subsequently coupled with (E)-β-thujaketonic acid methyl ester (5), derived from thujone (1), to give the β-lactones 45 and 46 which were then epoxidized and pyrolyzed exemplifying a route to juvenile hormone analogues such as 51 and 54.
Total synthesis of barbatane sesquiterpenes: α- and β-barbatenes, gymnomitrol, and isogymnomitrol
Authors: Kodama Mitsuaki , Kurihara Toshio , Sasaki Jinko , Itô Shô
Published: May 2006

A total synthesis of the barbatenes and a formal total synthesis of gymnomitrol and isogymnomitrol were achieved through a common intermediate utilizing a cycloaddition reaction and skeletal rearrangements.
A proton magnetic resonance relaxation time study of several vitamin D derivatives
Authors: Kotowycz George , Nakashima Tom T. , Green M. Kirk , Aarts Gerdy H. M.
Published: May 2006

Proton magnetic resonance relaxation time studies at 200 and 400 MHz have been measured for vitamins D2, D3, as well as the biologically active 1α,25-(OH)2D3. A comparison of these relaxation times at the two frequencies allows the evaluation of the dipolar correlation times for the different protons in the molecule. These are very short, and range from < 0.7 × 10−10 s to 1.2 × 10−10 s. Application of the Solomon equation to the relaxation times of the 19Z and 19E protons allows a calculation of the internuclear distance since these two geminal protons relax each other predominantly by the dipolar mechanism. Using the T1 values, the calculated distances are 1.98 ± 0.10 Å for 1α,25-(OH)2D3, 2.01 ± 0.10 Å for D3, and 1.95 ± 0.10 Å for D2. The calculated distance based on a neutron diffraction distance for the C—H bond is 1.91 Å. The measurement of the relaxation times also allows a definitive spectral assignment of the 21- and 28-methyl protons for vitamin D2.
N-(tert-Butyldimethylsilyl)imidazole and related heterocycles: 13C nuclear magnetic resonance study and reaction with dimethylsulfoxide
Authors: Janzen Alexander F. , Lypka Gerald N. , Wasylishen Roderick E.
Published: May 2006

N-tert-Butyldimethylsilyl derivatives of imidazole, 2-methylimidazole, 4-methylimidazole, benzimidazole, pyrazole, 1,2,4-triazole, and benzotriazole were prepared from tert-butyldimethylsilyl chloride and the corresponding heterocyclic compound. The products were identified by carbon and proton nmr, mass spectrometry, and elemental analysis. The carbon nmr spectra confirmed the absence of intermolecular silyl exchange at ambient temperature. Silyl exchange did occur at elevated temperatures, 130–160 °C.Reaction of N-tert-butyldimethylsilyl or N-trimethylsilyl heterocycles with dimethylsulfoxide gave N-(methylthio)methyl derivatives of imidazole, 2-methylimidazole, 4-methylimidazole, benzimidazole, pyrazole, and 1,2,4-triazole. The products were characterized by carbon and proton nmr, mass spectrometry, and elemental analysis. A mechanism involving a Pummerer rearrangement is proposed to account for the results.
Studies on the rearrangement of (trichloromethyl)carbinols to α-chloroacetic acids
Authors: Reeve Wilkins , McKee James R. , Brown Robert , Lakshmanan Sitarama , McKee Gertrude A.
Published: May 2006

Phenyl(trichloromethyl)carbinol undergoes an unimolecular, predominantly intramolecular conversion into potassium α-chlorophenylacetate on stirring with 10 % aqueous potassium hydroxide at 0 °C for several days. Besides providing an interesting example of a 1–2 chlorine shift, the reaction is of potential importance for the synthesis of α-chloro acids. The study of a variety of (trichloromethyl)carbinols shows the reaction is general for secondary (trichloromethyl)carbinols as well as trichloroethanol. The mechanism of the reaction involves the preliminary formation of an epoxide. Several mechanisms are considered for the conversion of the epoxide to the α-chloroacetate anion, but none accounts for all of the experimental facts. Tertiary carbinols break down at the epoxide stage into a ketone and carbon monoxide.
The conformations of oligosaccharides related to the ABH and Lewis human blood group determinants
Authors: Lemieux R. U. , Bock K. , Delbaere L. T. J. , Koto S. , Rao V. S.
Published: May 2006

Nuclear magnetic resonance properties are shown to be in good accord with those that are expected for synthetic oligosaccharides in the conformations which are predicted by hard-sphere molecular modelling and taking into consideration the important contribution by the exo-anomeric effect. The studies involve first a comparison of the βDGal(1 → 3)βDGlcNAc (Type 1) and βDGal(1 → 4)βDGlcNAc (Type 2) disaccharide structures based mainly on 13Cmr and then an examination of the relationships between the calculated conformations and 1Hmr and 13Cmr parameters for human blood group determinants which are derived from the Type 1 core disaccharide. Among the structures examined are the di-, tri-, and tetrasaccharides for the ABH and Lewis antigenic determinants. Certain immunological–conformational relationships are noted.
Linnett double quartet theory in organic chemistry: structure, reactivity and resonance
Authors: Langler Richard Francis , Trenholm June Ellen , Wasson John Spencer
Published: May 2006

A reexamination of Linnett's nonpairing spatial orbital theory, as it is qualitatively employed, has led to a number of conclusions. Firstly, in our view the theory has been inconsistently applied to the prediction of molecular geometries and may be ambiguous in dealing with saturated systems. Secondly, it does not provide a guide to chemical reactivity, in contrast to claims made for it. Finally, NPSO theory does provide a useful extension of resonance theory as it is qualitatively employed in organic chemistry, contrary to an existing claim that NPSO theory makes resonance theory obsolete.
The X-ray crystal structures of SeBr3SbF6 and TeBr3AsF6
Authors: Passmore Jack , Richardson E. Keith , Whidden Tom K. , White Peter S.
Published: May 2006

The crystal structures of SeBr3SbF6 and TeBr3AsF6 were determined by X-ray diffraction methods. Single crystals of SeBr3SbF6 are orthorhombic, space group P21212, with a = 9.454(5) Å, b = 12.623(6) Å, c = 8.272(4) Å, and Z = 4. Single crystals of TeBr3AsF6 are monoclinic, space group P21/c, with a = 7.994(3) Å, b = 10.118(3) Å, c = 12.306(3) Å, β = 99.66(2)°, and Z = 4. The cations in each salt have essentially C3v symmetry and the average Se—Br distance in SeBr3SbF6 is 2.269(8) Å and the average Br—Se—Br angle is 100.9(3)°. Analogous data for TeBr3AsF6 are: Te—Br = 2.432(3) Å; Br—Te—Br = 97.92(9)°. Anions in each salt are essentially octahedral. The bond angles in isoelectronic Group V and Group VI trihalide molecules and cations are compared and found to be very similar. However, those found for Group VI trihalide cations are greater than (5 pairs) those observed in isoelectronic Group V molecules determined in the solid state, and angles estimated for Group VI cations in gas phase are greater (8 pairs) than those found for the related gas phase Group V trihalide partners. This result implies that geometries, at least in part, are determined by the relative sizes of the constituent atoms. The crystallography of the related salts SeBr3AsF6 and SBr3MF6 (M = As, Sb) was studied by single crystal and powder diffraction methods. Salts containing the same anion were found to be isostructural.
Pseudozoanthoxanthins from gold coral
Authors: Schwartz Robert E. , Yunker Mark B. , Scheuer Paul J. , Ottersen Tor
Published: May 2006

not available
Synthesis and physical studies of pyridine and imidazole containing tridentate metal binding ligands
Authors: Brown R. S. , Huguet J.
Published: May 2006

Several tridentate ligands incorporating pyridine and substituted imidazoles were prepared and their physical properties studied as models for the enzyme carbonic anhydrase (CA). The H+ and M2+ binding abilities (pKa and [Formula: see text]) were determined. In the case of the imidazole ligands, N-methylation reduces the metal binding ability of the ligand by some 3–4 [Formula: see text] units over the analogues in which the imidazole has N—H. 1H-nmr studies of the simple ligands as a function of [Zn2+] show that the ligands are bound symmetrically as 1:1 and 2:1 complexes depending upon the ligand/metal ratio. Increasing the steric bulk of the ligands by introduction of 4,5-diisopropyl substituents on the imidazole inhibits the 2:1 (ligand/metal) complex. Titration experiments of several ligands bound to equimolar Zn2+ and Co2+ are described and analysed.
Thermodynamic and transport properties of binary liquid systems
Authors: Prakash Sheo , Sivanarayana Kandimalla , Prakash Om
Published: May 2006

Densities, viscosities, and sound velocities were determined for the system o-chlorophenol + acetone and o-chlorophenol + ethyl methyl ketone at 25 °C. From the experimental results, the deviation in isentropic compressibility KS, excess molar volume VE, excess viscosity ηE, and excess molar free energy of activation of flow G*E were calculated. The deviations from ideality of the thermodynamic and transport functions are explained on the basis of molecular interactions between the components of the mixture.
Preparation and structure of mer-trichloro(acetonitrile)bis-(triphenylphosphine)osmium(III)
Authors: Parkes R. L. , Payne N. C. , Sherman E. O.
Published: May 2006

An air-stable, red, crystalline, N-bonded acetonitrile complex of Os(III), OsCl3(NCCH3)(P(C6H5)3)2, has been prepared and characterized by elemental analysis, magnetic susceptibility, and a single crystal X-ray structure determination. Crystals are monoclinic, space group P21/c, cell dimensions a = 10.029(2), b = 15.233(2), c = 25.246(4) Å, β = 113.65(1)°, and Z = 4. Three dimensional X-ray diffraction intensity data were collected on an automatic four circle diffractometer using Cu radiation. Full-matrix least-squares refinement on F converged at R = 0.038 for 4384 unique observations. The Os atom has a slightly distorted octahedral coordination geometry, with trans phosphine ligands, mean Os—P 2.406(2) Å. The acetonitrile ligand is σ-bonded through the N atom, Os—N 2.038(6) Å. The bond trans to the acetonitrile ligand. Os—Cl(1) 2.364(2) Å, is not significantly different from the mean of the cisOs—Cl bonds, 2.361(2) Å.
The mechanism of oxidation of acetals by ozone. I. Stoichiometry, order of the reaction, solvent effects, and substituent effects
Authors: Taillefer Roland J. , Thomas Shirley E. , Nadeau Yves , Fliszár S. , Henry Hervé
Published: May 2006

A systematic investigation of the reaction between ozone and acetals to form acetal hydrotrioxides A has been undertaken. The stoichiometry of the reaction has been shown to be 1:1 in each reactant and the order of the reaction was also one in each reactant. Substituent effects measured in a variety of systems and under several conditions of temperature and solvent were found to be small (ρ = −1.10 to −1.58). Solvent polarity was also found to have little effect on the rate of the reaction. Mechanistically, these facts are interpreted in terms of a 1,3-dipolar insertion of ozone into the C—H bond of the acetal function.
Air oxidation of Reissert compounds
Authors: Rozwadowska Maria D. , Brózda Danuta
Published: May 2006

Reissert compounds undergo autoxidation in basic solution giving rise to isoquinaldo- or quinaldonitriles. Under the same reaction conditions, dihydroisoquinoline Reissert compounds undergo oxidative decyanation to dihydroisocarbostirils. The intermediacy of α-peroxycyanides is proposed in this transformation.
1,2-Diphenyl-3,5-dimethyl-4-oxo-6,7-diazabicyclo[3.2.0]hept-2-ene, a nitrogen unsubstituted diazetidine with an unusually unreactive nitrogen
Authors: McIntyre Deane D. , Mackay Donald , Wong Lichin L.
Published: May 2006

In the title ring System, the benzylic nitrogen (N7), whether substituted or not, is abnormally unreactive. Hydrolysis of the di-urethanes 3a or b occurs readily at N6 to give 10a or b, but not at all at N7. In 3d Pd—H2 removes very rapidly the benzyloxycarbonyl group at N6 but only very slowly the one at N7. The product 7 is the first example of a diazetidine unsubstituted on nitrogen which has been fully characterized.N6 in 7 or in 10a or b can be readily acylated (products 24, 13, 14), acyloxylated (23a–c, 3a, 3b, 11, 12), or methylated (25). All efforts to induce similar reactions at N7 in 7 or in its monosubstituted derivatives 23 or 24 failed.Diazetidine 7 is thermally very stable, but it is rapidly oxidized by a wide variety of reagents to 2,5-diphenyl-3,4-dimethylcyclopentadienone and nitrogen. There is no evidence for the intermediacy of the cyclic azo compound 19, even when the oxidation is carried out at −50 °C.
The reaction of potassium iodide in polyhydrogen fluoride – pyridine with two cage diols. A simple synthesis of tetracyclo[6.3.0.04,11. 05,9]undeca-2,6-diene ("homohypostrophene")
Authors: Dong Dao Cong , Edward John T.
Published: May 2006

The diol 2 was converted by treatment with potassium iodide in polyhydrogen fluoride – pyridine into a mixture of the diiodide and homohypostrophene 6. The diol 10 under the same conditions gave the ether 14. Treatment of the mixture of 5 and 6 with sodium in boiling tetrahydrofuran gave an easily-separable mixture of 6 and 7.
Amide hydrogen bonding in organic medium
Authors: Spencer J. N. , Garrett Robert C. , Mayer Fred J. , Merkle Johanna E. , Powell Carla R. , Tran Mai T. , Berger Scott K.
Published: May 2006

Thermodynamic parameters for the self-association of N-methylformamide and N-methylacetamide in CCl4 solvent have been determined by infrared spectroscopy. The pure base calorimetric method was used to determine the enthalpy of hydrogen bond complex formation of N-methylformamide and N-methylacetamide with N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, and dioxane. Comparison of the calorimetric and spectroscopic results show that the dimers of N-methylformamide and N-methylacetamide are linear with hydrogen bond enthalpies of −2.9 and −3.9 kcal mol−1 respectively. The carbonyl group of N-methylacetamide was found to be a better proton accepter than the carbonyl of N-methylformamide in agreement with theoretical predictions. N-methylacetamide was found to be a better proton donor than N-methylformamide in disagreement with theoretical predictions. The dimer self-association constants appear to be larger than previously reported.
Aromatic fluorination with xenon difluoride: L-3,4-dihydroxy-6-fluoro-phenylalanine
Authors: Firnau Gunter , Chirakal Raman , Sood Sudesh , Garnett Stephen
Published: May 2006

L-3-Methoxy-4-hydroxyphenylalanine was fluorinated directly with XeF2 in CH2Cl2 at −60 °C invacuo. After hydrolysis with 48% aqueous HBr, L-6-fluorodopa was obtained. The yield, based on XeF2, was 25%. This reaction might be applied when chiral biomolecules are to be tagged with fluorine-18.
Disc micelles in type II DM phases: short chains in long chain host bilayers
Authors: Acimis Mahmut , Reeves Leonard W.
Published: May 2006

Host bilayers of the large disc shaped micelles in type II DM phases have been prepared with two detergents having a 16 carbon chain. Studies of small quantifies of 10 carbon guest amphiphiles have been made using deuterium magnetic resonance. The host bilayer solution is only slightly perturbed by changes in simple counter and co-ions. The only major change in host chain order profiles is obtained when its pyridinium head groups are changed for N-trimethyl head groups. The guest chain motions near the non-polar chain terminus are considerably more restricted than in bilayers prepared from hosts of shorter chain length conforming closely to the guest chain length. The small changes observed in motion behaviour of the chains as a function of simple counter and co-ions can be a standard to test the effect of specific complexing agents on guest chain motions in the present System.
The enthalpy of solution of NaI, NaCl, NaClO4, and urea in water–tetrahydrofuran mixtures at 298.15 K
Authors: Taniewska-Osińska Stefania , Piestrzyńska Bożena , Łogwinienko Roman
Published: May 2006

The integral enthalpy of solution of NaI, NaCl, NaClO4, and urea was measured in the concentration range 0.01–0.5 mol/kg in mixtures of water and 2.5, 5, 7.5, 10, and 20 mol% of tetrahydrofuran at 298.15 K.
An X-ray crystallographic, Raman, and infrared spectral study of crystalline potassium uranyl carbonate, K4UO2(CO3)3
Authors: Anderson Anthony , Chieh Chung , Irish Donald E. , Tong James P. K.
Published: May 2006

X-ray diffraction studies have revealed that K4UO2(CO3)3 is isostructural with (NH4)4UO2(CO3)3; the crystal is monoclinic with a = 10.247(3), b = 9.202(2), c = 12.226(3) Å, β = 95.11(2)°, Z = 4, and space group C2/c. Three carbonate anions are arranged in bidentate fashion in the equatorial plane of UO22+; one of these occupies a C2 site and the other two occupy C1 sites. All carbonates are significantly distorted from D3h symmetry. The binding of carbonates to uranyl is strong and thus the lattice can be considered to be composed of [UO2(CO3)3]4− anions and K+ cations. The Raman and infrared spectra exhibit fewer lines than predicted for such a crystal. Tentative assignments are suggested for the more prominent bands of the constituent polyatomic species.
Fourier transform carbon-13 spin–lattice relaxation study of motion of cyclic hydrocarbons
Authors: Axelson David E. , Holloway Clive E.
Published: May 2006

The molecular dynamics in solution for a series of cyclic and bicyclic hydrocarbon derivatives has been investigated by C-13 pulsed Fourier Transform nuclear magnetic resonance spin–lattice relaxation experiments. Molecular motion has been analysed in terms of an anisotropic rotational diffusion model, and an attempt has been made to assess the effects of structure on the observed rotational diffusion constants. Errors in the diffusion constants are discussed, and some of the other problems inherent in the use of these parameters to obtain structural information are outlined.
Solvolysis of specifically deuterated 7-chloro- and 7-bromo-exo-2-norbornyl brosylates; unusually large γ-kinetic isotope effects in the absence of σ-participation
Authors: Werstiuk Nick Henry , Timmins George , Cappelli Frank Peter
Published: May 2006

A series of specifically deuterated syn-7-chloro-, anti-7-chloro-, syn-7-bromo-, and anti-7-bromo-exo-2-norbornyl brosylates have been prepared and solvolyzed in NaOAc-buffered 80:20 EtOH–H2O. For solvolysis at 25 °C the γ-kinetic isotope effects (KIE's) for syn-7-chloro-exo-2-norbornyl brosylate-endo-6-d (1e), anti-7-chloro-exo-2-norbornyl brosylate-endo-6-d (2c), syn-7-bromo-exo-2-norbornyl brosylate-endo-6-d (1f), anti-7-bromo-exo-2-norbornyl brosylate-endo-6-d (2d), syn-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (1g), anti-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (2e) are 1.125 ± 0.007, 1.128 ± 0.005, 1.063 ± 0.008, 1.149 ± 0.020, 1.119 ± 0.011, and 1.115 ± 0.013, respectively. There is no detectable γ-kinetic isotope effect for solvolysis of anti-7-chloro-endo-2-norbornyl brosylate-endo-6-d(3a) and the β-KIE for anti-7-chloro-exo-2-norbornyl brosylate-exo-3-d(4a) is 1.111 ± 0.011. From a consideration of the possible sources of the unusually large secondary KIE's, we conclude that the exo-6-d and endo-6-d γ-KIE's likely are derived from a combination of effects rather than from participation of the C1—C6 bond in the ionization step.
Oxidation products of arachidonic acid II. The synthesis of methyl 8R,9S,11R-trihydroxy-5Z,12E,14Z-eicosatrienoate
Authors: Just George , Luthe Corinne
Published: May 2006

A stereospecific total synthesis of the title compound, 37, starting from diacetone glucose (9), is described. Key intermediates in the synthesis are 3-deoxy-5,6-anhydro-1,2-O-isopropylidene-glucofuranose (15), obtained in 55% yield from 9, and methyl 8-tert-butyldiphenylsilyl-9,11-O-isopropylidene-8R,9S,11R-trihydroxy-12-oxo-dodeca-5Z-enoate (33), an important intermediate in the synthesis of other oxidation products of arachidonic acid.
Synthesis and stereochemistry of hydrogenated 1,1,4,4,7a-pentamethylindenes
Authors: Thomas Alan Francis , Ozainne Michel , Guntz-Dubini Renée
Published: May 2006

Ease of methylation of hydrogenated 2H-inden-2-ones depends on the presence of a double bond in the cyclohexane ring, and occurs readily with compound 20 but not with 10. Differences of reactivity are also noted in Wittig reactions. Most reactions of the system are highly stereoselective, and the stereochemistry of hydrogenated indenes is discussed.
Reactions of the Lythraceae alkaloids. Regio and stereoselective methoxylations and hydroxylations of lythrine
Authors: Lantos I. , Razgaitis C. , Loev B. , Douglas B.
Published: May 2006

Mercuric acetate assisted methoxylations and hydroxylations of lythrine resulted in a regio and stereoselective introduction of the substituent at the benzylic position with S-stereochemistry. The compounds obtained are thus epimeric at C13 with the naturally hydroxylated alkaloid lythridine and its derivatives. The implications of the results in planning the total synthesis of lythrine is discussed.