bluuebunny/crossref_metadata_2025 huggingface dataset:
Complexes of lanthanide iodides with 3-methylpyridine-1-oxide
Authors: Ramakrishnan Lakshminarayanan , Soundararajan Sundaresa
Published: May 2006

Complexes of lanthanide iodides with 3-methylpyridine-1-oxide of the formula Ln(3-MePyO)8I3.xH2O where x = 0 for Ln = La and Tb, x = 1 for Ln = Pr, and x = 2 for Ln = Nd, Sm, Dy, Yb, and Y have been prepared and characterized by chemical analyses, conductance, infrared, proton nmr, and DTA data. Infrared and proton nmr data have been interpreted in terms of the coordination of the ligand to the metal ion through the oxygen of the N—O group. Proton nmr spectrum of the Yb(III) complex is indicative of a restricted rotation of the pyridine ring about the N—O bond.
Application of photoelectron spectroscopy to intramolecularly hydrogen-bonded systems. Part IV. π-Systems; the photoelectron spectra of syn- and anti-7-norbornenol
Authors: Brown R. S.
Published: May 2006

In an effort to determine the effect of an intramolecular hydrogen bond on the ionization energy of a simple π-system, the photoelectron spectra of syn- and anti-7-norbornenol have been determined. The difference in the ionization energy of the π(C—C) and nÖH orbitals is 0.30 eV for the former, and 0.85 eV for the latter. The photoelectron spectrum of the syn- isomer shows that the π(C—C) bond is roughly 0.2 eV more difficult to ionize than its counter-part in the non-hydrogen bonded geometric isomer and has been interpreted as arising from hydrogen bond induced stabilization of the π-bond. That the spectral differences in the alcohols is not simply due to differing orbital interactions between the two isomers can be demonstrated by the photoelectron spectra of syn- and anti-7-methoxynorbornene. In these systems which allow no possibility of hydrogen bonding the π(C—C) – nÖR difference is the same for both isomers.
A proton magnetic resonance determination of the rotational barrier in benzyl chloride and of the low energy conformations in benzyl bromide and iodide derivatives based on motionally averaged spin–spin interactions
Authors: Schaefer Ted , Kruczynski Leonard J. , Parr William J. E.
Published: May 2006

The long-range spin–spin coupling constants over six bonds between side-chain and ring protons in benzyl chloride derivatives are combined with solutions to the hindered rotor problem to demonstrate that the twofold barrier to internal rotation in benzyl chloride is 2.1 ± 0.4 kcal/mol. The low energy conformation is that in which the C—Cl bond lies in a plane perpendicular to the aromatic plane. Molecular orbital calculations at the MINDO/3 and STO-3G levels indicate that the conformation in which the C—Cl bond lies in a plane having an angle of 60° to the aromatic plane has a higher energy; comparable to kT at ambient temperatures. The geometry-optimized STO-3G results agree quantitatively with the derived barrier for benzyl chloride. A semiempirical relationship between the long-range couplings over four bonds and the internal barrier for a number of benzyl compounds indicates a barrier of 3.1 kcal/mol for benzyl bromide and of 3.6 kcal/mol for benzyl iodide, these values being lower limits. The observed coupling constants are only consistent with low-energy conformations analogous to that for benzyl chloride, so that they contrast with the low-energy conformation for benzyl fluoride in which the C—F bond lies in the aromatic plane. The present method for the determination of twofold barriers in benzyl derivatives is useful in the range from about 0.2 to 2 kcal/mol.
A proton magnetie resonance and molecular orbital study of the conformational preferences of the vinylic fragment in some 2-vinylfurans and in 2-vinylthiophene
Authors: Parr William J. E. , Wasylishen Roderick E. , Schaefer Ted
Published: May 2006

The stereospecific spin–spin coupling constants over five bonds between the α-proton in the side chain and the protons in the heterocycle in 2-vinylfuran, in its β-nitro and β-aldehydic derivatives, and in 2-vinylthiophene are used to demonstrate the preponderance of the s-trans conformers in polar and nonpolar solutions. These conclusions are compared with predictions made by molecular orbital theory at the STO-3G, INDO, CNDO/2, and MINDO/3 levels. Long-range coupling constants between the protons in the side chain and protons in the heterocycle are calculated by CNDO/2 and INDO–MO–FPT and are compared with experiment. It is concluded that the five-bond couplings involving the α-proton are most sensitive to conformation and that they are transmitted mainly via a σ electron mechanism. The other long-range coupling constants are discussed in terms of σ and π electron mechanisms. The STO-3G calculations yield barriers to internal rotation of greater than 4.8 kcal/mol.
Reaction of dichlorobis(dimethylsulphoxide)platinum(II) with pyridine and isomerization of dichloro(dimethylsulphoxide)(pyridine)platinum(II)
Authors: Kong Pi-Chang , Iyamuremye Daniel , Rochon F. D.
Published: May 2006

The reaction between cis-[Pt(DMSO)2Cl2] and pyridine, picoline, and lutidine has been studied by nmr techniques. The results obtained with 4-picoline are discussed. trans-[Pt(4-pic)-(DMSO)Cl2] is first formed and then isomerizes to a mixture of cis- and trans-isomers.[Formula: see text]An effective method to prepare cis-isomers has been derived from this study. The advantages of the new method are discussed.
Theoretial studies of some nonbenzenoid hydrocarbons. III. Acenaphthylene, fluoranthene, and related compounds
Authors: DasGupta Archana , DasGupta Nanda K.
Published: May 2006

The molecules acenaphthylene, pyracylene, fluoranthene, acefluoranthylene, and indeno[1,2,3-cd]fluoranthene have been studied using the Pariser–Parr–Pople semi-empirical SCF MO method with the core resonance integral value developed by Lo and Whitehead and Dewar etal. It has been found that with this core resonance integral value developed for the prediction of ground state properties, π* ← π spectral transitions can also be predicted with reasonably good accuracy and the results are also compared with those calculated by using the core resonance integral value proposed by Yamaguchi etal. The resonance stabilization of acefluoranthylene and indeno[1,2,3-cd]fluoranthene has been studied. The attachment of a vinyl linkage at the 1,8 centres of naphthalene, or similar attachment to anthracene and phenanthrene, reduces the resonance energy below that of the parent compounds. The resonance stabilization has been predicted for aceanthrylene and acephenanthrylene.All the molecules studied here have acenaphthylene moiety and it would be interesting to see whether there is any similarity in properties between acenaphthylene and other molecules or how the properties change with the introduction of benzene nucleus or ethylinic linkage or both in acenaphthylene moiety.
Confidence in fluorescence lifetime determinations: a ratio correction for the photomultiplier time response with wavelength
Authors: Rayner D. M. , McKinnon A. E. , Szabo A. G. , Hackett P. A.
Published: May 2006

The photomultipliers used in single photon counting fluorescence lifetime Systems have a time response function which varies with wavelength. This variation results in a reduced confidence in the kinetic parameters obtained after deconvolution of the lamp intensity decay profile measured at the excitation wavelength from the sample emission decay profile measured at the emission wavelength. Moreover in the case of multi-component decays, inaccurate kinetic parameters are calculated because of this PMT variation. Using weighted residual plots, we demonstrate how one may make a satisfactory subjective appraisal of the adequacy of the deconvolution and the physical model of the decay processes. We have developed a ratio correction technique which accounts for the PMT time response variation with wavelength. This technique requires no apriori assumption of the nature of the PMT effect. Only when the data are corrected using the ratio correction technique can sufficient confidence in the accuracy of the singlet excited state parameters and the validity of the physical model be obtained.
Monomeric di-oxygen adducts of high spin cobalt(II) complexes
Authors: Khare G. P. , Lee-Ruff E. , Lever A. B. P.
Published: May 2006

The complexes Co(s-R2en)2X2 where R is Me, Et, and X is Cl, Br, I, NCS, or NO3, are shown to reversibly bind di-oxygen in polar solvents. Electron spin resonance and spectrophotometric measurements reveal the formation of 1:1 adducts which are fairly stable towards further reaction. Thermodynamic binding constants are determined and are found to be larger than hitherto reported for such Co(II)–O2 systems. This is ascribed to the high basicity of the amines employed. Conductivity measurements reveal extensive hydrogen bonding for these adducts in butyronitrile.
Metals intercalated in graphite. V. A concentration cell with intercalated bromine
Authors: Lalancette Jean-Marc , Roussel Roger
Published: May 2006

Bromine intercalates can be used as electrodes in concentration cells. Voltages of the order of 50 mV can be obtained with thermal gradients of 60–75 °C, in the range 0–100 °C. The cell can be operated on a continuous basis by allowing the high activity electrode to distill bromine to the low activity electrode.
Through-space or proximate 19F,19F and 19F,1H spin–spin coupling constants in some benzenesulfonyl fluoride derivatives
Authors: Parr William J. E. , Schaefer Ted
Published: May 2006

The analysis of the fluorine and proton magnetic resonance spectra of 2,4,6-trimethylbenzenesulfonyl fluoride and of 2,5-difluorobenzenesulfonyl fluoride yields the signs and magnitudes of the spin–spin coupling constants containing a through-space component. The coupling between the fluorine nucleus and the methyl protons over five bonds is +1.9 Hz, opposite in sign to the −3.1 Hz observed for the corresponding coupling in 2,6-dimethylbenzoyl fluoride. The difference of 5 Hz is possibly a consequence of the different conformational preference of the SO2F and COF substituents. The coupling over four bonds between the fluorine nucleus on the side chain and that on the ring is +11.6 Hz in 2,5-difluorobenzenesulfonyl fluoride. It is argued that this value indicates a preference of the S—F bond for a plane lying, on average, nearly perpendicular to the benzene ring. Similar indications are noted for pentafluorobenzenesulfonyl fluoride and for pentafluorobenzenesulfinyl fluoride.
Optical spectra of electrons solvated in liquid ethers: temperature effects
Authors: Jou Fang-Yuan , Freeman Gordon R.
Published: May 2006

The optical absorption band of electrons solvated in ethers has an approximately Gaussian shape on the low energy side of the absorption maximum. The high energy side is wider and has an approximately Lorentzian shape down to A/Amax ≈ 0.3, then extends into a long tail to high energies. The energy at the absorption maximum EAmax and the Gaussian and Lorentzian dispersion parameters g and l are reported as functions of temperature for electrons in diethyl ether (DEE), di-n-propyl ether (DPE), di-n-butyl ether (DBE), and tetrahydrofuran (THF). The values in eV of the parameters at 180 K are: EAmax = 0.76 in THF, 0.67 in DEE, 0.65 in DPE and DBE; l = 0.32 in THF, DEE, and DPE, 0.39 in DBE; g = 0.19 in all the ethers. The temperature coefficients of EAmax are ∼ −2 × 10−3 eV/K, those of l are −(1 ± 1)10−4 eV/K, and those of g are +4 × 10−4 eV/K. The band becomes less asymmetrical as the temperature increases. To make progress in the theoretical treatment of solvated electron spectra attention should be focussed on the separate values of g and l and their temperature dependences; the width at half height W1/2 thereby loses theoretical significance. The decadic molar absorbancy εmax (M−1 cm−1) is 2.9 × 104 in DEE and DPE, 2.6 × 104 in DBE, and 2.1 × 104 in THF. The oscillator strengths f are 0.7 in the n-alkyl ethers and 0.6 in THF. The value of EAmax in p-dioxane is 0.1 eV greater than that in THF and about 0.2 eV greater than those in the open chain ethers. This agrees with a prediction based upon the relative mobilities of electrons in the ethers.
Charge-transfer interaction of bithienyls and some thiophene derivatives with electron acceptors
Authors: Abu-Eittah Rafie , Al-Sugeir Fakhreia
Published: May 2006

The charge transfer complexes of 2,2′-bithienyl, 5,5′-dimethyl-2,2′-bithienyl, and some thiophene derivatives as donors with tetracyanoethylene as an acceptor have been studied spectrophotometrically. In addition, complexes of the first donor with chloranil and iodine have been studied. The formation constants and extinction coefficients of the molecular complexes formed have been determined by graphical as well as iterative methods. From measurements at different temperatures, the thermodynamic functions of the complex formation have been calculated. The ionization potentials of the donors have been obtained from the energies of the charge transfer transitions.
Studies in the usnic acid series. II. The condensation of (+)-usnic acid with hydroxylamine
Authors: Kutney James P. , Sanchez Ignacio H. , Yee Trevor
Published: May 2006

The results of the reaction of usnic acid (1) with hydroxylamine are presented. Four products, two isomeric isoxazoles (2 and 4), a novel oxazocine structure (3), and Δ2,11-enaminousnic acid (5) were isolated and characterized. These data clarify the earlier published results in this area.
Flash thermolysis: multiple sigmatropic rearrangements in ortho-substituted aromatic compounds
Authors: Champlain Pierre de , Luche Jean-Louis , Marty Robert A. , Mayo Paul de
Published: May 2006

A number of o-disubstituted benzenoid substances on flash thermolysis undergo 1,4-elimination of water or alcohols to yield o-quinonoid derivatives. Those products possessing a pentadienyl hydrogen subsequently undergo a 1,5-sigmatropic rearrangement: in many cases the rearrangement product undergoes yet further transformations, such as addition or hydrolysis, and such reactions have been used for their characterization. Included are: the conversion of N-methyl anthranilate esters to o-aminobenzaldehyde; o-(N-methyl)benzyl alcohol and methyl ether to o-toluidine; o-methoxymethylformanilide to o-tolyl isocyanate; and o-carboxymethylformanilide to o-aminobenzaldehyde.
The use of polymer supports in organic synthesis. VII. Polymer-bound 1,3-diols as monoblocking agents of symmetrical dialdehydes
Authors: Leznoff Clifford C. , Greenberg Shafrira
Published: May 2006

Two different 2% cross-linked divinylbenzene–styrene copolymers incorporating 1,3-diol groups were prepared. The symmetrical dialdehydes terephthalaldehyde and o-phthalaldehyde were attached to these polymers through acetal formation, showing that even hindered o-aromatic dialdehydes can be monoblocked by the use of polymer supports. The free aldehyde group of polymer-bound terephthalaldehyde reacted with Wittig reagents to give 1-p-formylphenyl-4-phenyl-1,3-butadiene and p-formylstilbene. Similarly, polymer-bound o-phthalaldehyde gave o-formylstilbenes. Polymer-bound 1,3- and 1,2-diols did not form acetals of aliphatic dialdehydes and formed ketals of symmetrical diketones in very low yield.
Equilibrium in the formation of barium carbonate from barium sulphate
Authors: Horlings Harry , Scott Donald S. , Wynnyckyj John R.
Published: May 2006

Heat of reaction and free energy of formation at 25 °C were determined from experimental equilibrium yields for the reaction[Formula: see text]in an aqueous solution.The values are 5045 and 1927 cal/mol respectively. Equilibrium constants for the reaction were determined over a temperature range from 20 to 193 °C.
Electrophilic additions of iodonium nitrate to unsaturated substrates
Authors: Lown J. William , Joshua Alummoottil V.
Published: May 2006

Iodonium nitrate (generated by reaction of iodine chloride with silver nitrate in chloroform–pyridine) reacts with a variety of unsaturated substrates to form the following: 1,4-conjugate addition products of the type alkenyl pyridinium nitrates; alkyliodopyridinium nitrates; products of aromatic iodination of both phenols and anilines; substituted benzodihydrofurans; tetrahydrofurans and tetrahydropyrans; polycyclic bridged ethers; lactones; thiazolines.
Hydroxyl proton resonances of methyl 4,6-O-benzyIidene-α- and β-D-glucopyranosides and their derivatives in dimethyl sulfoxide solution
Authors: Kondo Yôtaro , Kitamura Keisuke
Published: May 2006

Proton magnetic resonance spectra of methyl 4,6-O-benzylidene-α- and β-D-glucopyranosides (1 and 10) and their mono-substituted derivatives are determined in dimethyl sulfoxide solution. Assignments of the hydroxyl group resonances of 1 and 10 are confirmed by means of INDOR techniques. It is shown that the position of the hydroxyl substituent of the mono-substituted derivatives of 1 and 10 can be determined by using the coupling constants JH—C—O—H. It is proposed that the vicinal diols of 1 and 10 give 1:1 associations with dimethyl sulfoxide molecules, and the C—H and O—H bonds at position 2 of the mono-substituted derivatives of 1 are approximately anti.
X-Ray diffraction data for β-(1 → 3)-D-glucan
Authors: Marchessault R. H. , Deslandes Y. , Ogawa K. , Sundararajan P. R.
Published: May 2006

The conformation of a bacterial β-(1 → 3)-D-glucan (curdlan) was studied by X-ray diffraction measurements on fiber diagrams. The glucan fiber, prepared by extruding a dimethyl sulfoxide solution of the glucan into methanol and washing in water (A) was of low crystallinity but with a characteristic diffraction and orientation 'as spun'. The same fiber annealed in water, under tension, at 140 °C, in a closed bomb, was of higher crystallinity and occurred as two reversible crystalline polymorphs: one at high relative humidity (B) and the other at relative humidities less than 20% (C). All three X-ray diagrams displayed the X-shaped patterns characteristic of helical conformations; equatorial diffraction corresponded to hexagonal packing. The fiber axis data for B and C coupled with a conformational study and density data leads to a proposed three-stranded helical structure with P63 symmetry.Curdlan in water forms an irreversible gel when a 2–4% solution is heated above 55 °C. The same gel given the annealing treatment described above undergoes syneresis and the gel properties are lost.
The electronic structures, geometries, and relative energies of some N2H2 and N2H2+ systems
Authors: Baird N. Colin , Wernette David A.
Published: May 2006

Ab initio calculations using the 4-31G basis set and extensive configuration interaction are reported for the 1Ag state of trans-diimide (1), the 3A″ and 1A1 states of 1,1-dihydrodiazine (2), and the ground states of the positive ions of these systems and of cis-diimide. In all cases the geometries have been optimized. The relative stabilities of these systems are discussed, with particular reference to the heat of formation of trans-1 and to the ionization potentials of 1 and 2.
Dicyclohexanecarbonylsulphate: a precursor of cyclohexyloxocarbenium ions
Authors: Montoneri E. , Giuffré L. , Cassago M. , Tempesti E. , Fornaroli M.
Published: May 2006

Dicyclohexanecarbonyl sulphate (1) is the prevailing species in the equimolar solution of cyclohexanecarboxylic anhydride and sulphur trioxide in liquid sulphur dioxide. The ionization of 1 to cyclohexyloxocarbenium ions occurs only in the presence of excess sulphur trioxide. Both 1 and C6H11CO+ are stable only in solution and at low temperature.
Nuclear magnetic resonance studies. XXXI. Rearrangement and deuterium exchange through β-enolization in bicyclooctanones. An 2H nuclear magnetic resonance study.
Authors: Cheng A. K. , Stothers J. B. , Tan C. T.
Published: May 2006

The bicyclo[2.2.2]octan-2-one and -[3.2.1]octan-6-one skeletons are interconvertible under strongly basic conditions. Their α,α-dimethyl derivatives in tert-Buo−/tert-BuOH at 185 °C undergo very slow interconversion by β-proton abstraction. Using 2H nmr the stereoselectivity of deuterium incorporation at the β-methylene sites was established. The relative reactivities of β-methyl exchange in the [3.2.1] system were also determined. As models for this process, exchange in the α,α,α′,α′-tetramethyl derivatives of the monocyclic ketones, C5–C8, was also studied.
Ab initio calculations on 4-substituted styrenes: a theoretical model for the separation and evaluation of field and resonance substituent parameters
Authors: Reynolds William F. , Mezey Paul G. , Hamer Gordon K.
Published: May 2006

Ab initio (STO-3G minimal basis set) molecular orbital calculations on 4-substituted styrenes and CH3X–C2H4 pairs indicate that ΔqH (the charge density difference between β-vinyl protons) provides a direct theoretical measure of the field effect of a polar substituent. Σqcπ, the total substituent-induced π electron density change in styrene provides a theoretical measure of the resonance effect of the substituent. ΔqH and Σqcπ provide the basis of a theoretical dual substituent parameter scale, TF and TR0. This scale compares very closely with experimental DSP scales, indicating the latter scales are fundamentally valid. The calculations also indicate that field effects and σ inductive effects do not show parallel trends. It is concluded that field effects are more important than σ inductive effects except at very close range. Individual carbon π electron densities reflect both resonances effects and polar π inductive effects.
Substituent-induced 1H chemical shifts for 4-substituted (2, 2-dichlorocyclopropyl)benzenes: further evidence for intramolecular electric field effects on 1H chemical shifts
Authors: Kohler Robert H. , Reynolds William F.
Published: May 2006

Correlations of cyclopropyl proton chemical shifts for 4-substituted (2,2-dichlorocyclopropyl)-benzenes with σI and σR0 provide evidence that these chemical shifts reflect direct field effects and weak phenyl–cyclopropyl conjugative interactions. Corrections for variable ring current effects due to substituent-induced changes in conformation improve the individual correlations but do not alter the basic pattern of results. Correlation of the β cyclopropyl 1H chemical shift difference with σI with calculated hydrogen electron densities, and with calculated electric field components provides further strong evidence for a field effect on 1H chemical shifts.
13C Chemical shifts for 4-substituted phenylvinyl ethers, sulfides, and selenides: evidence concerning the relative abilities of O, S, and Se to transmit electronic effects
Authors: Reynolds William F. , McClelland Robert A.
Published: May 2006

13C chemical shifts for β carbons of 4-substituted phenylvinyl ethers, sulfides, and selenides plus previous data for styrenes indicate that the relative ability of link groups to transmit electronic effects between conjugative groups is S > Se ≈ — > O (where — refers to no link group, i.e. styrene). However, marked deviations from additivity are noted for C(1) chemical shifts which may indicate that O deactivates the ring to electronic substituent effects while S and Se activate the ring. If this explanation is valid then the actual ability of the link atom to transmit electronic effects is — > O > S > Se.
Proportionality relationships in the carbon-13 nuclear magnetic resonance spectra of para-disubstituted benzenes: a new interpretation of non-additive behavior
Authors: Lynch Brian Maurice
Published: May 2006

The carbon-13 chemical shifts for 214 distinct sites (the 4-carbons) in 24 sets of 1-X,4-Y-disubstituted benzenes and for 270 distinct sites (the 1- and 2-carbons) in 16 of these sets are reproduced with excellent precision (correlation coefficients 0.99 or greater) either by linear proportionality relationships with the appropriate substituent chemical shift (scs) in a mono-substituted benzene (for the 4-carbons), or by simple additivity relationships with the scs (for the 1- and 2-carbons).Inconsistencies are pointed out in a theoretical rationalization of 4-carbon shifts used in discussing the non-additivity of these shifts in terms of a DSP approach, whereas the above one-parameter approach yields sets of proportionality constants (slopes of scs relative to Y = H) following systematic trends which are interpreted as results of changes in the excitation energy term at carbon-4 dependent upon the ionization potential of the group Y. There is no significant association between the scs slopes and sets of calculated CNDO/2 electron densities for these para-disubstituted benzenes.
A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes
Authors: Parr William J. E. , Schaefer Ted
Published: May 2006

The long-range spin–spin coupling constants between protons bonded to silicon and ring protons in C6H5SiH3, C6H5SiH2Cl, C6H5SiH2CH3, C6H5SiHCl2, and C6H5SiH(CH3)2 are determined from the proton magnetic resonance spectra of benzene solutions. A hindered rotor treatment of the barrier to internal rotation about the C—Si bond, in conjunction with the coupling constants over six bonds, allows the deduction of the low-energy conformations for C6H5SiH(CH3)2 and for C6H5SiHCl2, as well as of barriers of 1.0 ± 0.2 kcal/mol. The approach becomes less reliable for C6H5SiH2CH3 and for C6H5SiH2Cl and, particularly for the latter compound, the derived barrier is very likely an upper limit only. Ab initio molecular orbital calculations of the conformational energies are reported for C6H5SiH3, C6H5SiH2Cl, and for C6H5SiHCl2.
The structure of isoflavipucine
Authors: Findlay John A. , Krepinsky Jiri , Shum Anita , Casinovi C. G. , Radics L.
Published: May 2006

The structure of isoflavipucine 2a, a remarkable rearrangement product of the antibiotic flavipucine 1, is proposed on the basis of spectral data and chemical and mechanistic considerations.
The electronic structure of tetraphosphorus trisulphide
Authors: Head John D. , Mitchell Keith A. R. , Noodleman Louis , Paddock Norman L.
Published: May 2006

The electronic structure of P4S3 has been investigated by the Xα scattered wave (XαSW) method as well as by the extended Hückel (EH) and complete neglect of differential overlap (CNDO) molecular orbital methods. The XαSW method gives a particularly good account of the ionization energies determined by HeI photoelectron spectroscopy. The valence shell levels fall into two groups. Those of lower energy are for the most part multicentre orbitals having high s character. The upper occupied levels are non-bonding or weakly bonding, and have a large p component. Contour plots of wave functions and charge distributions emphasize the importance of 'bent bonding' associated with electron density outside the framework of the cage structure, and of multicentre density inside the cage structure. These calculations provide a basis for understanding the relationship between the chemical properties of P4S3 and its electronic structure.
The crystal and molecular structure of lead(II)bromide-bis-dimethylsulphoxide, PbBr2•2[(CH3)2SO]
Authors: Baranyi Anthony D. , Onyszchuk Mario , Page Yvon Le , Donnay Gabrielle
Published: May 2006

The title compound has two PbBr2•2[(CH3)2SO] units, Z = 2, in a cell with a = 11.093(2), b = 12.382(3), c = 4.540(1) Å, belonging to space group Pmmn. The structure was solved by Patterson functions and was refined by full-matrix least-squares calculations to a final R of 0.054 for 348 observed diffractometer intensities. Passing through the unit cell are two antiparallel, infinite polar chains, each with symmetry mm2, extending along z and interacting with each other by weak van der Waals forces. Lead(II) is six-coordinate with a close, covalent hemisphere consisting of two bromine atoms [Pb—BrIBrII 2.93(1) Å], and two oxygen atoms [Pb—O,O′ 2.50(3) Å] which subtend an angle of 157.9(9)° at lead, located at the intersection of the O—Pb—O′ and BrI—Pb—BrII perpendicular mirror planes. The other hemisphere consists of bridging bromine atoms from the neighboring PbBr2•2dmso unit [Pb—BrIII,BrIV 3.24(1) Å], resulting in a rectangle of bromine atoms around lead [BrI—Pb—BrII 90.5(1)°, BrIII—Pb—BrIV 80.2(1)°]. The distortion of the octahedral coordination sphere around lead is discussed in terms of (a) a repulsive effect of the Pb(II) valence lone electron-pair, (b) weak Br—S bonding, and (c) crystal packing forces.
The reactivity of tungsten halides with organic sulfides. Part II. Desulfurization of tetrahydrothiophene
Authors: Boorman P. Michael , Chivers Tristram , Mahadev Kalabeerappa N.
Published: May 2006

WCl6 reacts with tetrahydrothiophene (tht) to yield initially [C4H8SC4H8Cl]2 [W2S2Cl6(tht)2]. The sulfonium ion is slowly degraded at 120 °C in tht and a green, neutral complex [W2S2Cl4(tht)4] is produced. The formation of [C4H8SC4H8Cl]+ occurs through the desulfurization of tht by WCl6 to form Cl(CH2)4Cl, which in turn alkylates a tht molecule. The identity of most of the organic by-products of these reactions has been determined, and on this basis it is suggested that S-chlorination of tht occurs to give [C4H8SCl]Cl. The degradation of this species by various possible pathways may account for the formation of some of the diverse products.
The synthesis of 1,3-diazepine derivatives by the ring expansion of alkyl 4-chloromethyl-1,2,3,4-tetrahydro-6-methyl-2- oxopyrimidine-5-carboxylates
Authors: Bullock Eric , Carter Roger A. , Cochrane Regina M. , Gregory Brian , Shields Douglas C.
Published: May 2006

Alkyl 4-chloromethyl-1,2,3,4-tetrahydro-6-methyl-2-oxopyrimidine-5-carboxylates are obtained from the reaction of 1,2-dichloroethyl ethyl ether with alkyl 3-ureidocrotonates. Reaction of the chloromethyl compounds with basic nucleophilic reagents causes ring expansion and leads, in high yield, to 7-substituted 2,3,6,7-tetrahydro-2-oxo-1H-1,3-diazepine derivatives. In the case of sulfhydryl ion, intramolecular Michael addition follows ring expansion and gives derivatives of 3-oxo-8-thia-2,4-diazabicyclo[3.2.1]octane, whose structures are established by spectroscopic examination and chemical degradation. The alkyl 7-alkoxy-2,3,6,7-tetrahydro-2-oxo-1H-1,3-diazepine-5-carboxylates react rapidly with acid to give alkyl 1-carbamoyl-2-methylpyrrole-3-carboxylates. Mechanisms are suggested for these rearrangement reactions.
3,4-Methylenedioxyphthalide-α-carboxylic acid; its use in the total synthesis of isoquinoline alkaloids
Authors: Nalliah Bala C. , MacLean David B. , Rodrigo Russell G. A. , Manske Richard H. F.
Published: May 2006

3,4-Methylenedioxyphthalide-α-carboxylic acid has been synthesized in four steps from piperonal. From it and phenylethylamines ten phthalideisoquinoline and spirobenzylisoquinoline alkaloids have been synthesized.
Synthetic routes to nucieoside analogs of N-substituted 1-oxa-4-azacyclohexanes and 1-thia-4-azacyclohexanes. 13C nuclear magnetic resonance spectra of six-membered, cyclic amides
Authors: Pinto B. Mario , Vyas Dolatrai M. , Szarek Walter A.
Published: May 2006

Nucleoside analogs, namely 6-chloro-9-(4-benzoyl-1-oxa-4-azacyclohexan-2-yl)-9H-purine 6 and 6-chloro-9-(4-benzoyl-1-thia-4-azacyclohexan-2-yl)-9H-purine 7, were obtained by treatment of 4-benzoyl-2-hydroxy-1-oxa-4-azacyclohexane 13 and 4-benzoyl-2-hydroxy-1-thia-4-azacyclohexane18, respectively, with 6-chloropurine, methyldiphenylphosphine, and diethyl azodicarboxylate in refluxing tetrahydrofuran. Compounds 13 and 18 were obtained by O-deacetylation of the corresponding 2-acetoxy derivatives 11 and 16 with a catalytic amount of sodium methoxide in chloroform. 2-Acetoxy-4-benzoyl-1-oxa-4-azacyclohexane 11 was obtained from 4-benzoyl-1-oxa-4-azacyclohexane 10 by treatment with tert-butyl peracetate, cuprous chloride, and benzene, whereas 2-acetoxy-4-benzoyl-1-thia-4-azacyclohexane 16 was prepared by a Pummerer reaction with 4-benzoyl-1-thia-4-azacyclohexane 1-oxide 15. The13C nmr spectra of all the compounds are reported; the spectra provided unambiguous proof of structure.
Rearrangement of a barrellene oxide to an isocoumarin under flash thermolysis conditions. An apparent series of sigmatropic shifts
Authors: Lewars E. G. , Morrison G.
Published: May 2006

Flash thermolysis of dimethyl 3-oxatricyclo[3.2.2.02,4]nona-6,8-diene-6,7-dicarboxylate (the oxide of barrellene-2,3-dicarboxylic acid dimethyl ester) (2) at 700 °C gave methyl isocoumarin-7-carboxylate (3) as a major component of the thermolysate. The rearrangement is discussed in terms of sigmatropic shifts in cycloheptatrienes and their norcaradiene tautomers.
Products and stereochemistry of thermolysis of some diazenes containing the 2-phenyl-2-butyl group
Authors: Kopecky Karl R. , Mojelsky Thomas W. , Gillan Thomas , Barry James A. , Lopez Sastre Juan A.
Published: May 2006

Thermolysis of (−)-(R)-1-benzyl-2-(2-phenyl-2-butyl)diazene, (−)-R-4, produces (+)-(S)-2-methyl-1,2-diphenylbutane with 12% net retention of configuration at 110 °C in benzene or pentane containing 1 M butanethiol. The ratio of the rate constant for coupling of the initial radical pair to that of rotation of the 2-phenyl-2-butyl radical, kc/kr, is calculated to be ∼0.04–0.08. Thermolysis of (+)-(S-1-(2-phenyl-2-butyl)-2-(2-propyl)diazene at 100 °C in benzene containing 1 M butanethiol produces 2,3-dimethyl-3-phenylpentane with no observable rotation. The product must be less than 15% optically pure. The reaction produces (−)-(R)-2-phenylbutane, (−)-(R)-16, with 0.6–1.3% retention of configuration. The ratio of the rate constant for disproportionation to (−)-(R)-16 to kr is calculated to be 0.02–0.04. Thermolysis of (−)-(R)-1-(4-nitrophenyl)-2-(2-phenyl-2-butyl-diazene, (−)-(R)-12, at 175 °C in diphenylether produced no 2-(4-nitrophenyl)-2-phenylbutane. This product was produced on photolysis of (+)-(S)-12 in hexadecane at 15 °C but had no rotation. Neither (+)-(S)-7 nor (−)-(R)-12 was racemized during thermolysis and (+)-(S)-12 was not racemized during photolysis. Activation parameters for thermolysis of (±)-4 are ΔH≠ = 33 kcal/mol, ΔS≠ = 15 eu and for (±)-12, ΔH≠ = 37.3 kcal/mol, ΔS≠ = 5.5 eu.
Studies in the usnic acid series. V. The base catalyzed usnic acid – isousnic acid rearrangement. Part III. (—)-Usnic acid isomethoxide monoacetate
Authors: Kutney James P. , Sanchez Ignacio H.
Published: May 2006

Further studies on the base catalyzed usnic acid – isousnic acid rearrangement process clarify the situation concerning (−)-usnic acid isomethoxide monoacetate (7). This substance is now shown to be a mixture of the two possible C4a epimers. These and previous data allow a mechanism to be proposed for this interesting rearrangement.
Carbohydrates as chiral intermediates in organic synthesis. Two functionalized chemical precursors comprising eight of the ten chiral centers of erythronolide A
Authors: Hanessian Stephen , Rancourt Georges
Published: May 2006

Two appropriately functionalized branched-chain sugars have been synthesized as potentially useful chemical precursors to erythronolide A, encompassing its C-1–C-6 and C-9–C-15 segments respectively.
The reactions of isothiazolium salts with selected nucleophilic reagents. The preparation of thieno[2,3-c]isothiazolium salts
Authors: McKinnon David M. , Hassan Mohammed E. R. , Chauhan Mohinder
Published: May 2006

Isothiazolium salts react with a number of carbanions by attack on sulfur. Thiophene derivatives, formed by ring opening and recyclization, are often products but with cyclopentadiene, pseudoazulene products are obtained. 3-Amino-2-acylthiophenes, prepared by suitable nucleophilic attack, are synthetic precursors of thieno[2,3-c]isothiazolium salts
The isolation and identification of makisterone A from the yew, Taxus cuspidata
Authors: Burns Brenton Garth , Gilgan Michael Wilson
Published: May 2006

The ecdysteroids were extracted from yew, Taxus cuspidata, needles and twigs and recovered from the aqueous extract by reversed phase adsorption. Purification of the ecdysteroids was achieved by a single solvent partition and a dry column chromatogram followed by fractionation on an adsorptive Porasil A (60) column. Makisterone A was a minor component identified by melting point, liquid chromatography, gas chromatography of the trimethylsilyl ether, mass spectrometry, and nuclear magnetic resonance spectrometry. A second minor component was isolated but not identified.
Some thermodynamic properties of the solutions of ZrCl4 and HfCl4 in CsCl melts
Authors: Asvestas D. A. , Pint P. , Flengas S. N.
Published: May 2006

The binary equilibrium phase diagrams of the systems CsCl—Cs2ZrCl6, CsCl—Cs2HfCl6, and CsCl—KF were established by cryoscopy. A portion of the ternary CsCl—KF—ZrCl4 has also been determined.Equilibrium vapour pressures of the two pure compounds Cs2ZrCl6 and Cs2HfCl6, as well as of mixtures of Cs2HfCl6 with CsCl, have been measured. The equilibrium reaction is given as[Formula: see text]where M represents Zr or Hf.From the results, activities of CsCl, Cs2HfCl6, and HfCl4 were calculated at 825 °C.The low escaping tendency of the MCl4 vapour from the CsCl—Cs2MCl6 type melts makes these solutions suitable as electrolytes for the recovery of Zr and Hf metal by fused salt electrolysis
Crystal structure of a dimeric 1-methylcytosine mercuric chloride complex
Authors: Authier-Martin Monique , Beauchamp André L.
Published: May 2006

Di-μ-chloro-bis[chloro(1-methylcytosine-O,N3)mercury(II)] belongs to space group P21/c with cell dimensions a = 9.932(2), b = 14.051(3), c = 9.198(2) Å, and β = 135.41(2)°. The structure was solved by the heavy-atom method and refined to an R factor of 0.027 for 1271 independent reflections. The crystal is composed of centrosymmetric dimeric molecules in which two mercury atoms are attached by a pair of symmetrical chlorine bridges. The 1-methylcytosine ligand is bidentate via N(3) and O(2). The metal atom has a (2 + 3) coordination with a very distorted trigonal bipyramid geometry. A chlorine atom at 2.322(3) Å and ring nitrogen N(3) at 2.17(1) Å form strong axial bonds with mercury. Two bridging chlorine atoms at 2.719(2) and 2.745(3) Å, and carbonyl oxygen O(2) at 2.84(1) Å form weaker equatorial bonds. The amino group is hydrogen-bonded to a bridging chlorine of the same molecule [Formula: see text] and a carbonyl oxygen of a neighboring molecule [Formula: see text]
Kinetics and mechanism of decarboxylation of some pyridinecarboxylic acids in aqueous solution. II
Authors: Dunn Gerald E. , Thimm Harald F.
Published: May 2006

Six 3-substituted picolinic acids were synthesized and decarboxylated in buffered aqueous solutions of ionic strength 1.0 at 150 and/or 95 °C. 3-Amino- and 3-hydroxypicolinic acids appear to decarboxylate by initial protonation, but the others fit the requirements of the Hammick mechanism for picolinic acid decarboxylation. Both electron-withdrawing and electron-releasing 3-substituents accelerate decarboxylation in picolinic acids but inhibit decarboxylation in their anions. Acceleration in the acids is considered to be the result of interference by 3-substituents with coplanarity of the carboxyl group and the aromatic nucleus. This reduces the order of the bond between the carboxyl group and the ring, thus facilitating bond breaking. In decarboxylation of the anions water appears to play a critical role, since picolinate ions have not been observed to decarboxylate in any other solvent, including ethylene glycol. It is proposed that water forms a hydrogen-bonded bridge between carboxylate oxygen and aromatic nitrogen, so that as the carbon–carbon bond breaks a nitrogen–hydrogen bond is formed. This may provide a lower energy path through an ylide intermediate than would be required if the picolinate ion were to decarboxylate to a 2-pyridyl carbanion.
Synthesis of nor-anatoxin-a and anatoxin-a
Authors: Campbell Henry F. , Edwards Oliver E. , Kolt Ralph
Published: May 2006

The neuro-muscular post-synaptic depolarizing agent anatoxin-a from Anabaena flos-aquae (Lyngb.) de Bréb. has been synthesized from cocaine.
The autoxidation of optically active 1-bromo-2-methylbutane
Authors: Howard J. A. , Chenier J. H. B. , Holden D. A.
Published: May 2006

(+)-1-Bromo-2-methylbutane undergoes autoxidation at 1 atm of oxygen and 30 °C to give, after reduction with triphenylphosphine, 1-bromo-2-methyl-2-butanol with a (+) to (−) enantiomer ratio of 1.9 ± 0.2. The optically active 1-bromo-2-methyl-2-butyl radical is, therefore, partially trapped by oxygen at this pressure before it has time to completely racemize. The half-life for racemization of the preferred conformation is approximately 2 × 10−8 s−1 at 30 °C. At 100 atm of oxygen the yield of (+)-CH3CH2COH(CH3)CH2Br is >90% and the reaction appears to proceed with retention of configuration. A small percentage of (−)-1-bromo-2-methyl-2-butanol is, however, still produced, presumably by inversion of configuration.
The crystal structure and polarised Raman spectrum of Rb2AgI3
Authors: Brown Ian David , Howard-Lock Helen Elaine , Natarajan Mahadevan
Published: May 2006

The crystal structure of Rb2AgI3, space group Pnma, a = 10.258(2), b = 4.886(4), c = 20.063(10) Å, has been refined. It is isostructural with K2AgI3 with chains of corner linked AgI4 tetrahedra (Ag—I(bridge) = 2.881 Å, Ag—I(terminal) = 2.834 Å) running along b. The average bonding distance around the two seven coordinate Rb atoms is 3.722 Å. The polarised Raman spectrum shows the expected 36 modes which are assigned to four different symmetry species. All modes occur with frequencies less than 112 cm−1.
Intermediates in the photolysis of alkyl sulfides and disulfides in dilute glass matrices
Authors: Adam Frank C. , Elliot Allen John
Published: May 2006

Simple alkyl sulfides and disulfides have been photolysed at 253.7 nm in dilute rigid glasses of 3-methylpentane, and the reactions which occur both at 77 K and in the glass at higher temperatures have been studied using epr and optical spectroscopy. The end products of photolysis have been determined using glc at room temperature. In sulfides, C—S bond cleavage leads to 'hot' radical pairs that react with each other giving rise to the main diamagnetic products observed, or react with nearby solvent molecules in the matrix by hydrogen abstraction yielding RSH and the solvent derived radicals (M•) which dominate the initial epr spectrum at 77 K. Thiyl radicals (RS•) are produced in significant amounts only after the sulfide glasses have been warmed slightly to allow the cage reaction,[Formula: see text]to occur. Pethiyl radicals (RS2•) are not ordinarily observed in sulfide photolyses. Photolysis of disulfide-containing glasses gives rise to S—S bond rupture and mainly diamagnetic products, or to C—S bond cleavage resulting in the formation of solvent radicals and RS2. Very little RS• is generated on warming the matrices. As with ethyl mercaptan photolysis, radicals corresponding to α-hydrogen abstraction of the substrate are obtained for both ethyl sulfide and disulfide. The spectral characteristics and photolytic behaviour of the sulfur containing radical species have been investigated where possible.
The perturbation by anesthetics of hydrogen bonds involving water
Authors: Nagyrévi A. , Sandorfy C.
Published: May 2006

It is shown through the measurement of infrared spectra at low temperatures, on the examples of two fluorocarbon anesthetics and a protein denaturing agent, that such compounds shift the association equilibrium in hydrogen bonds involving water in favor of free or less hydrogen bonded species.
Far infrared absorption and rotational vibrations of the guest molecules in structure I clathrate hydrates between 4.3 and 100 K
Authors: Bertie John E. , Jacobs Stephen M.
Published: May 2006

The infrared spectra between 330 and 15 cm−1 of the structure I clathrate hydrates of ethylene oxide, cyclopropane, and trimethylene oxide, at 4.3 K are presented. The spectra have an unusually high signal-to-noise ratio made possible by a Michelson interferometer and a silicon bolometer detector which operates at 1.2 K. Rotational vibrations of the guest molecules were observed at 65.0 and 35.6 cm−1 for ethylene oxide and at 69 and 50 cm−1 for trimethylene oxide. Inter-guest coupling of rotational vibrations is small and the two frequencies are assigned to vibrations about different inertial axes. The resulting force constants are 487 and 264 ferg rad−2 for ethylene oxide and 1190 and 1130 ferg rad−2 for trimethylene oxide and are discussed in relation to the barriers to reorientation of the guest molecule. The bands due to these vibrations are fairly sharp at 4.3 K, but are broad and poorly defined at 100 K. The guest and water vibrations interact predominantly through their transition dipoles, although the main contribution to the force constants of the rotational vibrations is from steric forces. The absorption by the water vibrations above 100 cm−1 is very similar for ethylene oxide and cyclopropane hydrates but significantly different for trimethylene oxide hydrate. Strong objections exist to the obvious interpretations of this difference which remains unexplained.
Effects of phase density on ionization processes and electron localization in fluids
Authors: Jortner Joshua , Gaathon Ariel
Published: May 2006

In this paper we shall be concerned with the energetics of selective ionization processes in simple nonpolar fluids and with the nature of electron localization in polar fluids, studied over a wide density range. The static features of bound Wannier states and of the conduction band in simple solid and fluid insulators were monitored by vacuum-ultraviolet absorption spectroscopy and photoemission studies providing quantitative information concerning the energy of the bottom of the conduction band, impurity ionization potentials, and adiabatic polarization energies. Electron localization in subcritical and supercritical water and ammonia was studied by pulse radiolysis methods. A critical, temperature dependent, density ρC for electron localization in ND3 was observed. The weak density dependence of the maximum of the absorption band of the localized electron in D2O and ND3, and the temperature and density dependence of ρC in ND3, provide compelling evidence for the crucial role of density fluctuations on electron localization in polar fluids.
Electron energy loss processes at subelectronic excitation energies in liquids
Authors: Magee John L.
Published: May 2006

The theory of the processes by which subexcitation electrons lose energy in molecular liquids is considered. It is convenient to classify such losses as resulting from 'indirect' and 'direct' interactions; the former interactions arise from the transient electric field of the electron and the latter from the short range quantum mechanical forces occurring in direct collisions. Indirect processes are considered at some length; Monte Carlo trajectories for electrons are generated and the Fourier spectrum of the electric displacement obtained from which energy loss to dipolar relaxation and infrared-active vibrations are estimated. A tight binding scheme is used to derive an expression for the rate of energy loss to single-phonon excitation in direct collisions; the same theoretical framework is used to discuss electron trapping by the molecules of the liquid. Finally, some attempt is made to relate the loss mechanisms considered to experimentally known facts. It is concluded that the 'direct' processes are probably dominant and that knowledge of elastic scattering is of primary importance for the construction of a satisfactory theory.
Photoelectric determination of V0 values and electron ranges in some cryogenic liquids
Authors: Tauchert Wolfgang , Jungblut Helmut , Schmidt Werner F.
Published: May 2006

Conduction state energies V0 were measured for liquid neon, argon, krypton, xenon, liquid nitrogen, liquid methane and ethane, and mixtures of methane and ethane by means of photo-effect on a metal electrode. A lower limit of V0 for liquid hydrogen was estimated. From the dependence of the photocurrent on the electric field strength electron penetration ranges could be deduced.
Thermal emission of excess electrons from liquid hydrocarbons (Extended Abstract)
Authors: Balakin A. A. , Boriev I. A. , Yakovlev B. S.
Published: May 2006

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