bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aromatic Guest Molecules Enclathrated in Hofmann‐Type and Analogous Clathrates
Authors: Iwamoto Toschitake 
Published: November 2013

AbstractThe structural features of the clathrate compounds with a general formula M(diam)M'(CN)4. 2G (M = a divalent metal in six‐coordination, diam = (NH3)2 or a diamine, M'(CN)4 = a square‐planar or tetrahedral teracyanometallate(II), G = an aromatic guest such as C4H5N, C4H4S, C6H6, C6H5NH2, etc.) are discussed from the viewpoint of the arrangement and orientation of the guest molecules in relation to the structure of the metal complex hosts. The layer structure of the Hofmann‐type host M(NH3)2M'(CN)4 (M'(CN)4 = a square‐planar moiety) enclathrates the guest molecules with a fixed orientation, but the three‐dimensional host structures built up of tetrahedral M'(CN)4 moieties provide considerably flexible and expanded cavities for guest molecules. The cavity in the three‐dimensional host may be seen as a container of a guest molecule with a chemically inactive wall and with a volume slightly larger than that of the molecule; in the container the guest molecule has freedom of motion to a certain extent. It can be expected that appropriate selection of the host constituents will afford the host lattice a stereospecific function and/or a function of keeping chemically‐active species stable in the cavity of the clathrate structure.
Alumina‐Catalyzed Alcoholysis of Cyclohexene Oxide
Authors: Posner Gary H. , Rogers Donald Z. , Romero Arthur 
Published: November 2013

AbstractAlcoholysis of cyclohexene oxide by methanol and allyl alcohol, catalyzed by chromatographic γ‐alumina, was studied. Two procedures were used: (1) passing a mixture of the epoxide and alcohol through a column of alumina at 25° and (2) stirring a mixture of epoxide and alcohol over alumina at 100°. The 25° column procedure allowed conversion of ca 2 mmol of epoxide per 1 g of alumina, and the 100°‐reaction allowed catalytic conversion of ca 100 mmol of epoxide per 1 g of alumina. These results are compared with those reported for zeolite catalysts.
Topotactic and Topochemical Conversions of Distyrylpyrazine
Authors: Nakanishi H. , Parkinson G. M. , Jones W. , Thomas J. M. , Hasegawa M. 
Published: November 2013

AbstractThe γ‐form of distyrylpyrazine, hitherto regarded as photostable, is shown to undergo an unusual, thermally stimulated, topotactic phase transformation \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {(010)_{\rm \gamma } ||(\bar 101)_{\rm \alpha } ;[001]_{\rm \gamma } ||[010]_{\rm \alpha } } \right) $\end{document} into the α‐form which, in turn, undergoes photostimulated topochemical reaction into the single‐crystal polymer.
Liquid Crystalline Solvents as Mechanistic Probes. IV. The Influence of Ordered Media on the Norrish Type II Photoprocesses in α‐Diketones
Authors: Nerbonne Jeanne M. , Weiss Richard G. 
Published: November 2013

AbstractThe Norrish II photoreactions of octane‐4,5‐dione (1) and 1,6‐diphenylhexane‐3,4‐dione (2) have been investigated at several temperatures and in isotropic and ordered (liquid crystalline) media. The sole photoproducts detected in all solvents are 1/1 diastereomeric mixtures of α‐hydroxycyclobutanones. The quantum yields for disappearance of 1 and 2 tend to decrease as the temperature increases in all media investigated. Whereas the quantum yield ratio for disappearance of 1 in cholesteric mesophases and hexane is greater than one, the ratio for disappearance of 2 is less than one. Possible explanations for these observations, based upon the influence of solvent order on solute conformational lability, are advanced.
Synthesis and Reactivity of a Surfactant Ferrocene. Environmental Effects on Oxidation of Ferrocene in Organized Media
Authors: Seiders Reginald P. , Brookhart M. , Whitten David G. 
Published: November 2013

AbstractThis paper reports on the synthesis of a surfactant ferrocene, 16‐ferrocenylhexadecanoic acid, (1), which can readily be incorporated into monolayer films and assemblies, micelles and vesicles. The reactivity of this ferrocene towards potential oxidants and complexing agents has been investigated in the different media under a variety of conditions. In the monolayer assemblies (1) was readily oxidized by I2 but inert towards exposure to aqueous Ag+, aqueous TCNE or TCNO vapor. The inertness of (1) under the latter conditions suggests the chromophore is oriented in a highly hydrophobic site. In contrast, (1) is readily oxidized by I2 and Fe3+ in lecithin vesicles and anionic SDS micelles. In cationic CTAB micelles iodine is reactive as an oxidant but Fe3+ is not, presumably due to charge effects. The results suggest that the ferrocene moiety in (1) is not rigidly oriented in the hydrophobic core of the vesicles or micelles but spends sufficient time near the hydrophobic interface to be oxidized by polar reagents.
Ab Initio Calculation of One‐Center Integrals of Semiempirical Theories of Valence
Authors: Freed Karl F. , Sun Hosung 
Published: November 2013

AbstractIn order to highlight some of the apparent contradictions between semiempirical and ab initio theories of valence, a brief review of some facets of the two approaches is presented. The recently developed effective valence shell Hamiltonian, , is then briefly introduced to bridge the gap. Results of purely ab initio Hv calculations for atoms and simple molecules are mentioned. The ab initio one‐center integrals are quantitatively much different from those of semiempirical theories. However, the exact contains extra terms, three‐ (or higher) electron interactions, which are totally absent in semiempirical theories. This paper shows that the nonclassical, three‐electron terms are incorporated into semiempirical one‐ and two‐electron integrals, and a parametrization scheme illustrating this is presented. As an example, the carbon system is chosen and the one‐center carbon semiempirical integrals are calculated from the results of ab initio calculations for C and CH. This enables discussions of questions of the degree of transferability of semiempirical one‐center integrals. The one‐center one‐ and two‐electron integrals obtained from ab initio calculations by including the effects of three‐electron terms are found to be close to the traditional semiempirical values.
On the Dependence of Total Energy on Occupation Numbers
Authors: Gopinathan M. S. , Whitehead M. A. 
Published: November 2013

AbstractAn equation is developed for describing the pairwise interactions of q electrons, when q is integer or non‐integer. This expression is compared with the usual equation. It is found to give lower total energies, different ionization and transition energies in the Slater Transition State theory, different values for the atomic energies calculated by the Hyper‐Hartree–Fock method, but numerically identical results for the Mulliken Electronegativity.
Approximate Electron Densities for Atoms and Molecules
Authors: Hall George G. , Martin David 
Published: November 2013

AbstractApproximate electron densities for atoms and molecules can be calculated from some given electron density by minimizing the total energy of their error‐fields. Results are presented for some simple systems using one or two term expansions. A conical function and a Gaussian function give comparable results. Electrostatic potentials calculated from the results are of good accuracy while the Coulomb self‐energy begins to converge quickly.
Affinities of Ammonia and Methylamine for H+, Li+, K+ and CH3+ An Ab Initio SCF Study with Large Basis Sets
Authors: Berthod Hélène , Pullman Alberte 
Published: November 2013

AbstractComputations of Li+‐affinities of NH3 and NH2CH3 performed with the SCF ab initio method, using the 4‐31G, 6‐31G*, 6‐31G** basis sets as well as Dunning's (9s, 5p/4s) basis contracted to double‐zeta without and with polarization functions, show that only the last basis is able to reproduce the experimental order of the gas‐phase affinities. A study is made of the evolution of the various components of the binding energy upon methylation, and of the modifications observed upon improvement of the basis sets: reversal of the order of the binding energies to the correct order occurs when the decrease of the Coulomb term becomes smaller than the increase of the delocalization term upon methylation. The best of the previous sets is shown to account in a satisfactory way for the H+ and CH3+ affinities of the same compounds. For K+‐affinities, the same basis still yields an incorrect ordering upon methylation. A further improvement of the basis is seen to work in the right direction. The K+‐affinities of H2O and NH3 computed with the most extended basis are in numerical agreement with the gas‐phase values.
Ab Initio Study of Inner Solvent Shell Reorganization in the Fe2+–Fe3+ Aqueous Electron Exchange Reaction
Authors: Jafri J. A. , Logan J. , Newton M. D. 
Published: November 2013

AbstractAb initio RHF molecular orbital calculations are carried out for several hydrate clusters of Fe2+ and Fe3+, using a double‐zeta valence atomic orbital basis set and an effective core potential for inner shell electrons, and comparison is made with all‐electron results at the monohydrate level. The calculations are shown to give a good quantitiative account of the solvent shell radii and breathing vibration frequencies for the hexahydrates. The large decrease (∼0.15 Å) in going from Fe2+(H2O)6 to Fe3+(H2O)6 is related to the interaction of the ag (4s) and ϵg (3d) Fe valence orbitals with the ligand 2p‐orbitals, with little π antibonding character found for the tg orbitals. The expansion of the 3d orbitals in the Fe2+ ion, relative to the Fe3+, is also noted and discussed in connection with the change in solvent shell size for the two complexes. The charge transfer from the ligands involves mainly a depletion of the hydrogen atom electrons, implying increased acidity for the first‐shell water molecules.
The Conformation of Free and Complexed Oligoethers
Authors: Dale Johannes 
Published: November 2013

AbstractRecent X‐ray and 13C NMR results on macrocyclic compounds containing oxyethylene units (1,4 dioxa groupings) are reviewed. When such “saturated” crown ethers and related compounds form complexes with cations and uncharged protonacidic molecules, they adopt conformations which contain chiefly ag± a units or g± g± a units (genuine corners) and are thus of the types encountered, or conceived for corresponding cycloalkanes. Uncomplexed or incompletely complexed crown ethers, on the other hand, adopt as a rule unusual conformations never encountered in cycloalkanes. These latter crown ethers contain g± g± a units (pseudo corners) characterized by close 1,5 CH … O interactions. Such conformational units are also found in uncomplexed cryptands. In open chains, there is no evidence of this type of chain folding, except in the gas phase for 1,2‐dimethoxyethane. It is concluded that pseudo‐corner formation is resorted to only when solvation of ether oxygen is excluded, such as in the gas phase or in the inaccessible interior of macrocyclic compounds.
Stereochemistry in the Coordination Chemistry of Metal Surfaces
Authors: Muetterties E. L. 
Published: November 2013

AbstractThe stereochemistry of metal surface coordination chemistry is discussed with respect to the chemisorption states of hydrogen, carbon monoxide, nitriles, isocyanides, pyridine, benzene, acetylenes and olefins. A stereochemical comparison is made of the binding of such species on metal surfaces with the binding in discrete molecular clusters.
Stereochemistry of Perhydrocrysene
Authors: Farina Mario , Silvestro Giuseppe Di , Mantica Enrico , Botta Donatella , Morandi Francesco , Brückner Sergio 
Published: November 2013

AbstractThe five most stable stereoisomers of perhydrocrysene were prepared and identified by 13C‐NMR analysis. Their relative stability was determined by epimerization on Pd/C at 508°K and compared with the results obtained by molecular mechanics calculations. As expected, isomer TATAT is the stablest. Of particular interest is the considerable stability of compounds with central cis junction (TACAT and TSCST), practically identical with that of TATAC and TATSC. Both analogies and differences between perhydrocrysene and steroids are briefly discussed from a conformational point of view.
Radical Anions of Some Dehydro[n]annulene‐diones with n = 16 and 18
Authors: Gerson Fabian , Beckhaus Hans‐Dieter , Sondheimer Franz 
Published: November 2013

AbstractRadical anions of 10,15‐dimethyl‐2,4,11,13‐tetrakisdehydro[18]annulene‐1,6‐dione (syn‐18 ), 6,15‐dimethyl‐2,4,11,13‐tetrakisdehydro[18]annulene‐1,10‐dione (anti‐18 ) and 8,13‐dimethyl‐2,9,11‐trisdehydro[16]annulene‐1,4‐dione (syn‐16 ) have been investigated by ESR and, in part, by ENDOR spectroscopy. The hyperfine patterns of these radical anions depend on the rate of intramolecular interconversion between two equivalent ion pairs in which the counterion is associated with one oxygen atom. It is found that the polarity of the solvent, which is an important factor influencing such a rate, does not affect the spectra of syn‐16⊕. quite in the same way as those of syn‐18⊕. and anti‐16⊕. This behavior, together with the lower stability of the former radical anion as compared to the two latter ones, points to substantial differences in physico‐chemical properties. Simple MO models indicate that the electronic structures of syn‐16⊕., syn‐18⊕. and anti‐16⊕. can be related to those of the corresponding 16π‐ and 18π‐perimeters. One is thus tempted to interpret the observed differences in terms of Hückel's rule of “aromaticity” and “antiaromaticity”.
Chemistry of the Homophenalenyl Systems
Authors: Murata Ichiro , Nakasuji Kazuhiro 
Published: November 2013

AbstractThe perturbational molecular orbital theory by Haddon suggested the interesting possibility that introduction of homoconjugate linkages as a perturbation of the parent phenalenyl systems at 1,2‐, 1,10‐, and 10,11‐positions leads to the most unfavorable, medium, and most favorable energy changes, respectively. In order to prove this prediction, formation of 1,2‐, 1,10‐, and 10,11 ‐homophenalenyl systems were examined by employing the possible precursors such as the ketone 5,29, the alcohol 8, as well as the hydrocarbons 16, 22, and 37. In contrast to the prediction by PMO theory, these systems have no homoaromatic stabilization even in the 10,11 ‐homophenalenyl cation and anion. In further extension of this study, the synthesis of the hitherto unknown parent 8,16‐methano[2.2]metacyclophane‐1,9‐diene 45 has been achieved recently.
Structure‐Resonance Theory. A Review of Applications to π ‐Hydrocarbon Systems
Authors: Herndon William C. 
Published: November 2013

AbstractStudies of structure‐resonance theory applied to π‐hydrocarbon systems are reviewed. The theory leads to quickly obtainable quantitative predictions of bond orders, charge distributions, and relative stabilities of ground state species or reaction intermediates. Numerical results correlate precisely with experimental properties, and with results of LCAO‐MO‐SCF calculations.
Structure‐Resonance Theory for π‐Hydrocarbon Iron Tricarbonyl Complexes
Authors: Herndon William C. 
Published: November 2013

AbstractStructure‐resonance theory is applied to transition metal π ligand complexes. This theory leads to specific, quantitative predictions of bond orders, charge distributions in ions, and relative stabilities of ground state species or reaction intermediates. In applications to hydrocarbon systems, numerical results correlate precisely with experimental properties, and with results of LCAO‐MO‐SCF calculations. Initial extensions to iron tricarbonyl derivatives are described herein. A unique advantage of structure‐resonance theory is that it can be applied rapidly by hand calculation, allowing numerous applications with little labor. The orbital basis for describing iron complexes allows one to use graph‐theoretical algorithms to further simplify the theoretical formulism.
Effects on Cyclopropane Geometry of Aromatic Substituents in the Bisected Conformation. The Structures of Spiro[cyclopropane‐1,9′‐[9H]fluorene] and 2,2‐Dichlorospiro[cyclopropane‐1,9′‐[9H]fluorene]
Authors: Jason Mark E. , Gallucci Judith C. , Ibers James A. 
Published: November 2013

AbstractThe structures of spiro[cyclopropane‐1,9′‐[9H]fluorene] (1) and 2,2‐ dichlorospiro[cyclopropane‐1,9′‐[9H]fluorene] (2) have been determined by conventional single‐crystal X‐ray diffraction techniques. Compound 1 crystallizes with 32 molecules in the unit cell in space group C212v–Iba 2 of the orthorhombic system in a cell of dimensions a = 42.228(23), b = 27.318(17) and c = 7.664(8) Å. Compound 2 crystallizes with four molecules in the unit cell in space group C52h–P21/c of the monoclinic system in a cell of dimensions a = 8.451(3), b = 8.960(3), c = 15.882(5) Å and β = 97.31(1)°. The structures of 1 and 2 have been refined by full‐matrix least‐squares techniques to conventional R indices of 0.055 and 0.049, respectively. Relative to the bridgehead position, the cyclopropane ring in 1 contains a short distal bond of average value 1.496(9)Å and lengthened vicinal bonds averaging 1.531(11)Å. This geometry agrees qualitatively with a simple molecular orbital model for charge transfer from cyclopropane to an aromatic π‐system held in the bisected conformation. The cyclopropane ring in compound 2 contains C–C bond lengths of 1.537(3), 1.517(3) and 1.475(3) Å. These values cannot be explained by summing the expected changes induced by the aromatic and halogen substituents.
Small and Strained Ring Compounds via Unsaturated Carbenes
Authors: Stang Peter J. 
Published: November 2013

AbstractUnsaturated carbenes, provide a ready means of entry into numerous, diverse small ring systems. They have been employed to prepare strained alkylidenecyclopropanes that open up to the corresponding trimethylenemethanes or in one case m‐xylylene. Triafulvenes, [3]‐radialenes as well as [4]‐radialenes and cyclynes have been prepared by addition of unsaturated carbenes to appropriate π‐systems. They show great potential for the simple preparation of novel small ring heterocycles. Potential formation of allene oxides, allene episulfides, α‐lactams and heterocumulene oxides are discussed.
The Chemistry of Silylcyclopropanes
Authors: Paquette Leo A. 
Published: November 2013

AbstractThe synthesis and reactions of silylcyclopropanes are reviewed. From the preparative viewpoint, these strained systems can be obtained by the addition of silyl‐substituted carbenes to olefins and of carbenes or carbenoids to vinylsilanes, by condensation of cyclopropyllithiums with chlorosilanes, by ring opening of silyl‐substituted bicyclobutanes and by trimethylsilylmethylenesulfurane addition to α,β‐unsaturated ketones. The susceptibility of this class of molecules to acid‐ and base‐promoted ring openings, electrophilic substitution and thermal rearrangement is detailed. These latter topics and a summary of the use of silylcyclopropanes as cyclopropene precursors are presented in a manner which stresses the unique synthetic utility conveyed by the presence of the silicon atom.
Reactions of 3‐Amino‐2H‐Azirines with NH–Acidic Compounds
Authors: Heimgartner Heinz 
Published: November 2013

Abstract3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) reacts with a number of NH–acidic compounds to give adducts of interesting structural variety. In analogy to the reaction of OH‐acidic substrates, the reaction mechanism can be understood to proceed via initial protonation of the aminoazirine, subsequent attack of the nitrogen nucleophile on the iminiumaziridine and ring expansion of the three‐membered ring to form a zwitterionic intermediate. Depending very much on the charge‐distribution delivered by the variety of substituents, this zwitterionic intermediate is going to be stabilised by different routes, e.g. water elimination, ring enlargement or rearrangement, to yield new N‐heterocyclic compounds.
Thermal Isomerizations of Fluorinated Spiropentanes
Authors: Dolbier William R. Jr. , Sellers Simon F. , Al‐Sader Basil H. , Fielder Thomas H. Jr. , Elsheimer Seth , Smart Bruce E. 
Published: November 2013

AbstractThe syntheses and thermal rearrangements and/or fragmentations of 1,1‐difluorospiropentane, 6, 1,1,4,4‐ and 1,1,2,2‐tetrafluorospiropentanes, 7 and 8, 1,1,2,2,4,4‐hexafluorospiropentane, 9, and perfluorospiropentane, 10, are described., Spiropentanes 6 and 7 undergo only rearrangement to 2,2‐difluoromethylene‐cyclobutane and 1‐(difluoromethylene)cyclobutane and to 2,2,4,4‐tetrafluoromethylenecyclobutane, respectively. Spiropentanes 8 and 9 rearrange and extrude CF2: competitively, while perfluorospiropentane extrudes CF2: exclusively. Activation parameters are presented for all processes and the mechanisms of these thermal processes are discussed in detail.
The Cleavage of Three‐Membered Ring Compounds by Transition Metal Organometallic Complexes
Authors: Alper Howard 
Published: November 2013

AbstractTransition metal organometallic complexes effect a wide range of useful and interesting cleavage reactions of three‐membered ring compounds. This review examines some recent developments in the organometallic chemistry of cyclopropanes, epoxides, episulfides and azirines. Novel synthetic approaches to heterocyclic [e.g., β γ and δ‐lactones, β‐lactams, isoxazoles, pyrazoles, indoles] and acyclic compounds [β‐diketones, vinyl isocyanates] have been achieved by means of these cleavage reactions.
Inhibition of the Primary Photochemical Events in Rhodospirillum Rubrum by Ubiquinone Analogues
Authors: Bering Charles L. , Bustamante Peggy L. , Loach Paul A. 
Published: November 2013

AbstractTwenty‐one quinone compounds have been tested for their ability to inhibit the primary photochemical events when added to R. rubrum chromatophores. This was determined by measuring their effect on the light‐induced absorbance change at 605 nm and their ability to quench the variable portion of fluorescence (Fv). Benzoquinone structures with one or more bromine or iodine substituents and a bulky group (isopropyl, t‐butyl, n‐hexyl) were particularly effective inhibitors. The most potent of these were 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone and 2,3‐diiodo‐5‐t‐butyl‐1,4‐benzoquinone which caused 50% inhibition at less than μM quantities (or about 5 to 10 fold above the phototrap concentrations). From control experiments with egg yolk phosphatidylcholine liposomes containing bacteriochlorophyll, it was shown that although the effective inhibitors also quenched fluorescence when added to this model system, quenching depended on the viscosity of the bilayer and was not very sensitive to structural parameters. In the in vivo system, phototrap activity was inhibited at 77 K to the same extent as room temperature, indicating diffusion was not important. In the control experiments with liposomes, the concentration for which 50% quenching was observed by 2,5‐dibromo‐3,6‐dimethyl‐1,4‐benzoquinone and 2,3,5‐tribromo‐6‐n‐hexyl‐1,4‐benzoquinone only differed by two fold whereas in the chromatophore system, the difference was over 1000 fold; no effect was seen in vivo by the former compound and the latter was the most effective. It is suggested that most of the instantaneous fluorescence (Fo) is from a bacteriochlorophyll component(s) which does not communicate with the reaction center and a higher concentration of added quinone is required before this pigment fluorescence is quenched.