bluuebunny/crossref_metadata_2025 huggingface dataset:
Acceleration and Retardation by Mercaptans of Photoreduction by Amines
Authors: Cohen Saul G. , Rose Anita W. , Stone Paul G.
Published: November 2013

Aromatic mercaptans and disulfides retard photoreduction of benzophenone by amines and are equilibrated to ∼62% thiyl as mercaptan in the process. Racemization of sec‐butylamine and introduction of deuterium into triethylamine indicate that ∼55% of the retardation arises from a hydrogen‐transfer repair mechanism, after correction for light absorption and quenching. The limiting step in the cyclic repair mechanism is reduction by mercaptan of the amine derived radical k10, in competition with oxidation of it by ground state ketone, k9. Ratios of rate constants for these reactions are, with 2‐mercaptomesitylene as retarder, for sec‐butylamine, k10a/k9a = 30 and for triethylamine, k10b/k9b = 310. The latter high value is attributed to low k9b, slow oxidation of this amine‐derived radical by ketone. The similar high value in reduction by 2‐propanol is attributed to rapid reduction of alcohol‐derived radical by the mercaptan. Aliphatic mercaptan, 0.02 M, accelerates photoreduction of 0.4 M benzophenone by 2 M sec‐butylamine in benzene by 50%, Φ = 1.82, and is not oxidized or equilibrated in the process. Acceleration is less efficient in acetonitrile and tert‐butyl alcohol and is not observed in water. Rate of the less efficient reduction by secondary amine is more than doubled by mercaptan. Inefficient retardation is observed in photoreduction by triethylamine in acetonitrile and in all cases at high concentration of aliphatic mercaptan. In retardation by n‐pentyl mercaptan, k10c/k9a = 0.24 in reduction by sec‐butylamine, and k10d/k9b = 0.88 in reduction by triethylamine. Ratios of reactivity toward aromatic and aliphatic mercaptans are k10a/k10c = 125 with sec‐butylamine, and k10b/k10d = 350 with triethylamine, both much higher than with 2‐propanol, suggesting lower reactivity of α‐aminoalkyl than α‐hydroxyalkyl radical toward reduction by mercaptan. Acceleration by aliphatic mercaptan arises from decrease in the quenching component normal in photoreduction by amines, and is attributed to catalysis by mercaptan of proton transfer from amine‐derived radical‐cation to ketyl radical‐anion in a ternary complex. Similar ternary complexes with aromatic mercaptan or thioether may lead to increased quenching and to retardation not accounted for by hydrogen‐transfer repair.
Photochemical Reactions of 2,2,5,5‐Tetramethyltetrahydrofuran‐3,4‐dione, an Unusual α‐Diketone
Authors: Rubin Mordecai B. , Ben‐Bassat Joseph M. , Weiner Moshe
Published: November 2013

Photochemical reactions of the red title compound (TTFD) in the absence of oxygen have been examined. With benzhydrol the α‐diketone was reduced to α‐hydroxyketone. Addition reactions with toluene and xylene afforded α‐hydroxy‐α‐benzyl‐ketones. Cyclopentene and cyclohexene gave α‐hydroxy‐α‐(3‐cycloalkenyl)‐ketones derived from abstraction of allylic H‐atom as major products; in addition [2 + 2] and [2 + 4] cycloadducts were obtained. In spite of the relatively low triplet energy of TTFD, its photochemistry parallels that of other α‐diketones.
Controlled Fragmentation: An Inverse Approach to Synthesis
Authors: Shanzer Abraham
Published: November 2013

Symmetric cleavage of cyclic compounds into identical fission products is introduced as a generally applicable method for synthesis. The usefulness of this approach in the field of fluorine chemistry is discussed and illustrated with representative examples. The scope and limitations of this method are outlined and possible future applications indicated.
Tautomerism in Xenon Hexafluoride: An Investigation of Xenon Hexafluoride and its Complexes by Raman Spectroscopy
Authors: Adams Chris J. , Bartlett Neil
Published: November 2013

Raman spectra are reported for (i) complexes of xenon hexafluoride with the fluoride‐ion acceptors BF3, PdF4, PF5, AsF5, RuF5, PtF5, and AuF5, and (ii) for solutions of xenon hexafluoride in HF and in WF6. Vibrational assignments are made for the cations XeF+5and Xe2F+11, and evoke a normal coordinate analysis for XeF+5. Xenon hexafluoride, present in concentrated solution in HF as [XeF+5F−]4, progressively ionizes on dilution to give Xe2F+11; and XeF+5; on the other hand, in WF6solution [XeF+5F−]4exists in equilibrium only with molecular XeF6.
Organotin Derivatives of Hexafluorobenzene
Authors: Roesky Herbert W. , Ambrosius Klaus
Published: November 2013

Hexafluorobenzene reacts with N[Sn(CH3)3]3 to give C6F5N[Sn(CH3)3]2. Better yields of this compound were obtained either starting from C6F5NH2 and treating this with Li‐butyl and (CH3)3SnCl or reacting C6F5NSO with N[Sn(CH3)3]3. A byproduct of the reaction with C6F5NH2 is C6F5NHSn(CH3)3. The cleavage of the tin‐nitrogen bond in C6F5N[Sn(CH3)3]2 was achieved with the anhydrides (CF3C(O))2O and (CF3SO2)2O resulting in the following products: C6F5NC(O)CF3Sn(CH3)3, C6F5NSO2CF3Sn(CH3)3 and C6F5N(SO2CF3)2. When C6F5N[Sn(CH3)3]2 is treated with S3N2Cl2 a chain‐like compound of sulfur and nitrogen atoms is obtained (C6F5NSN)2S. The mass and NMR spectra of the new compounds are reported.
Mass Spectrometric Analysis of Laser Induced Microplasmas from Organic Samples
Authors: Nitsche R. , Kaufmann R. , Hillenkamp F. , Unsöld E. , Vogt H. , Wechsung R.
Published: November 2013

A Laser Microprobe Mass Analyser (LAMMA) has been developed for the analysis of microscopically small volumes (10−11–10−13 cm3) of thin organic specimens (0.1–1 μm). Detection limits for most of the organic ions are in the range of 10−17–10−20g corresponding to 0.1–10 ppm. The instrument is based on the combination of a light microscope for observation and exact localisation of the sampled volume within the morphological structures of the specimen as well as for focusing the beam of a pulsed laser onto the specimen. The ions of the laser‐generated microplasma are analysed with a time‐of‐flight mass spectrometer. Mass spectra of organic standard samples and heart muscle cells are reported and discussed.
Rapid Analysis of Therapeutic Drugs in Blood by Chemical Ionization Mass Spectrometry
Authors: Lehrer Michael , Karmen Arthur
Published: November 2013

A rapid procedure was devised for analyzing anticonvulsants in serum by chemical ionization mass spectrometry. Samples were volatilized by heat into the ion source of the mass spectrometer and reacted there with CH5+ and other reactant ions produced by ion‐molecule reactions of the methane reagent gas. Increasing the temperature of the probe produced quasimolecular ion peaks of the different drugs, which rose and fell on the oscilloscope tracing at overlapping rates, indicating similar but not identical rates of volatilization. These peaks were recorded by connecting the electron multiplier ion detector output through a voltage to frequency converter to a 200 channel multichannel analyzer (MCA) operated in the multiscale mode. The concentration of the anticonvulsants were then calculated from the ratio of the counts in the channel of the drug to that of the appropriate internal standard. Other drugs present, including barbiturates, carbamazepine, ethosuximide and caffeine were readily identified when present. With one solid probe inlet, an assay could be performed every two minutes.
Use of Polymers as Protecting Groups in Organic Synthesis. VII. Preparation of Monobenzoates of Acyclic Triols
Authors: Fréchet Jean M. J. , Seymour Elizabeth
Published: November 2013

Crosslinked resins containing styrylboronic acid units were used in the protection of 1,2 and 1,3‐diol groupings with several acyclic triols. With 1,2,3‐propanetriol, a five‐membered ring boronate was formed almost exclusively while with 1, 2, 4‐butanetriol a six‐membered ring boronate predominated. The fully recyclable polymer could be used in a fast and efficient synthesis of monobenzoyl derivatives of triols. Macroreticular and 1% crosslinked solvent‐swellable resins were tested and the latter were found to perform better on repeated use.
A Graphite Supported Chiral Catalyst
Authors: Kagan H. B. , Yamagishi T. , Motte J. C. , Setton R.
Published: November 2013

Partially graphitized carbons were functionalized by carboxylic groups which were esterified with 4‐hydroxybenzaldehyde. A chiral diphosphine moiety, analogous to the DIOP framework, was then synthesized from the aldehyde function. The supported chiral diphosphine was transformed into a rhodium catalyst. Preliminary results of asymmetric hydrogenation or asymmetric hydrosilylation are described.
Some Recent Advances in the Study of the Reactivity of Systems Containing Polymers
Authors: Morawetz Herbert
Published: November 2013

Recent studies of reaction rates in polymer systems are reviewed. These involve ionic reactions in polyelectrolyte solutions, kinetic effects due to the nature of the “effective solvent medium” in the polymer domain, neighboring group effects in polysaccharide oxidation, intramolecular polymer reactions involving non‐neighboring groups, the quenching of the fluorescence of groups attached to a polymer by species carried by another polymer chain and the photoisomerization of azobenzene residues in the backbone of polymer chains.
Enzyme–Analogue Built Polymers. IX. Polymers with Mercapto Groups of Definite Cooperativity
Authors: Wulff Günter , Schulze Ilona
Published: November 2013

By copolymerization of bis(p‐vinylbenzyl)disulfide (1) with crosslinking monomers and subsequent reduction of the disulfide bond with diborane, polymers with two closely positioned mercapto groups were prepared. Under comparable conditions polymers with randomly distributed mercapto groups were obtained from (p‐vinylbenzyl)thioacetate (2). The degree of cooperativity of the mercapto groups in polymers of (1) as well as the degree of site separation in polymers of (2) were determined quantitatively by oxidation with I2. The percentage of reoxidation by I2 to disulfide depends on degree of crosslinking of polymer, the concentration of mercapto groups, the degree of swelling and the reoxidation temperature. From these data valuable information on the arrangement of functional groups as well as on polymer structure was obtained.
Synthesis of Potential Biologically Active Polymers Based on Polystyrene
Authors: Gabbay Y. , Zilkha A.
Published: November 2013

Polystyrene was utilized as a polymer backbone on which various potentially biologically active structures were constructed. The polymer was chloromethylated and converted by a series of reactions to polyphenethylamines, polyphenylacetamides and a polybarbiturate.
Impregnated Resins: Metal‐Ion Complexing Agents Incorporated Physically In Polymeric Matrices
Authors: Warshawsky Abraham , Patchornik Avraham
Published: November 2013

Solvent Impregnated Resins (SIR) are prepared by physically impregnating metal‐active compounds in high‐surface area, macroporous, styrene‐divinylbenzene copolymers. Impregnation methods, the structure of the resulting SIR resins, and their metal complexing properties are examined. The interrelationships between complexation efficiency, the nature of the extractant, and its concentration in the polymeric phase is discussed. Three practical examples of ion separation are discussed using solvent impregnated resins incorporating di‐2‐ethylhexylphosphoric acid, tri‐butyl‐phosphate, and 2‐hydroxyaryloximes.
The Effect of Adsorption Conformation of Intermediates on Kinetic Parameters of Electrode Reactions. Mechanism of the Electroreduction of Dihalopyridines on the DME
Authors: Kashti‐Kaplan S. , Kirowa‐Eisner E.
Published: November 2013

The mechanism of reduction of 2,6‐dichloropyridine, 2,5‐dibromopyridine and 2,3‐dichloropyridine in ethanol‐water media was investigated at the DME. The electrode processes were studied by measurements of Tafel slopes, reaction orders and pH effects. The proposed mechanism involves: (i) first protonation and electronation in a quasi‐equilibrium step resulting in an adsorbed pyridinyl radical (intermediate I) parallel to the electrode surface, (ii) Cleavage of the C–X bond in the rate‐determining step, resulting in an adsorbed cation radical (intermediate II), perpendicular to the electrode. The Tafel slope computed via the combined‐adsorption isotherm are in agreement with the experimental values.
Multiscreen Carbon Cloth Electrode
Authors: Sutzkover E. , Zur C. , Ariel M.
Published: November 2013

The current—voltage response of single and multiscreen electrodes for a limited range of electrolyte flow velocities is described. The short and long term stability of the single screen electrodes and their performance under a variety of operating conditions were determined. The multiscreen electrode was next examined to determine resistances within the cell, which were then exploited for the interpretation of current distributions and concentration profiles obtained with the multiscreen electrode operating in the rear or the frontal supply mode.
Anisotropy of the Optical Properties of Electrode Surfaces
Authors: Plieth W. J.
Published: November 2013

Differential reflection spectroscopy of electrode/electrolyte interfaces gives a quantity which in analogy to thermodynamic properties of the surface region shall be called “dielectric surface excess”. The dielectric surface excess has two complex components representing the anisotropy between the dielectric properties tangential and normal to the surface. Methods are described for the experimental determination of the two components. Results for oxide layers on platinum, bromide adsorbed on gold, rhodamin B adsorbed on silver and monomolecular films of lead on silver are discussed.
Study of the Adsorption of Succinic Acid on Platinized Platinum Electrode by Radiotracer Method
Authors: Horányi G. , Rizmayer E. M. , Inzelt G.
Published: November 2013

The problem of the adsorption behaviour of succinic acid has been studied from different points of view. The mobility of adsorbed species, the potential dependence of the adsorption and the effect of different ions and organic species on the adsorption were investigated in M HClO4 supporting electrolyte using platinized platinum electrode. It has been stated that succinic acid does not chemisorb under the experimental conditions studied, and it may be considered as a typical representative of organic compounds which behave like anions with respect to the adsorption properties. An attempt was made to explain the unexpected potential dependence of the adsorption of these species.
Adsorbed Hydrogens and Reduction of Olefins on Platinum in Acid Solution
Authors: Kita Hideaki
Published: November 2013

Platinum electrodes subjected to anodic activation reveal three kinds of adsorbed hydrogen (I, II, and III). These adsorbed hydrogens are interchangeable with each other. The adsorbed hydrogen I (ionization peak at ca. 40 mV, rhe) is the most reactive and responsible for the hydrogen evolution reaction. When C2–C4olefins are reduced by H2, the adsorption layer on Pt drastically changes depending on the composition of olefin and H2in the gas phase. At relatively low pressure of H2(region H), II (ca. 140 mV) takes part in the hydrogenation, whereas III (ca. 290 mV) gradually changes to II. Isotopic study proves that the hydrogenation in region H proceeds by the two Horiuti‐Polanyi type reaction paths, which is common among the olefins studied. The electroreduction gave the same results, where the discharge of H+is always taken to be in equilibrium.
Study of Nonconjugated Bichromophores Linked by a Polyether Chain. I. Photochemical Synthesis of Crown‐Ethers from bis‐(9‐Anthryloxy) Polyoxaalkanes
Authors: Desvergne Jean‐Pierre , Bouas‐Laurent Henri , Sarrebeyroux Roland
Published: November 2013

A series of bisanthracenes (In) linked by a polyoxyethylene chain: 9‐anthryl‐O–CH2–CH2–O–CH2–(CH2–O–CH2)n–CH2–O‐9‐anthryl, where n = 1–4, was synthesized in order to investigate the bichromophoric interactions of the two aromatic rings in connection with the special properties of the chain. UV absorption spectra at room temperature in benzene and ethanol exhibit, in general, a weak hypochromicity compared with other 9–9′ bisanthracenes. Under the same experimental conditions, the fluorescence of In is twofold: (i) an emission from the locally excited state (“monomer fluorescence”) with quantum yield (ΦFM) ca. 0.10–0.17 (benzene) and 0.03–0.08 (ethanol); (ii) an excimer‐type fluorescence centered at ca. 470–515 nm, of which quantum yields (ΦFD) are in the range 0.01–0.025 (benzene) and 0.01–0.012 (ethanol). Of note is the observation of an intramolecular excimer formed from bischromophores linked by long chains (10–19 atoms). Photocyclomerization quantum yields were found to be (365 nm) 0.18–0.26 (benzene and ethanol); closure effiency is almost as high as for bisanthracenes linked by short chains. The photocyclomers, thermally unstable, are readily dissociated to In at room temperature. Several closure and reopening cycles could be observed in degassed diluted solutions. Under our conditions, addition of inorganic salts such as LiClO4 does not distinctly alter closure quantum yields of In. Rather, the complexes formed between the photocyclomers IIn (crown‐ethers) and the cations are thermally stable up to high temperatures and were not observed to revert to In either thermally or by irradiation with a low pressure mercury lamp. But the compounds In were quantitatively recovered with an excess of polar solvents which compete with the crown‐ethers to solvate the cation.
Ligand Structure and Complexation, XLVIII Alkali and Alkaline Earth Metal Ion Complexes of Bipyridine, Phenanthroline and Terpyridine
Authors: Vögtle Fritz , Müller Walter M. , Raßhofer Werner
Published: November 2013

Crystalline alkali and alkaline earth metal ion complexes of 2,2′‐bipyridine and 2,2′:6′,2″‐terpyridine are obtained and compared with known and new alkali and alkaline earth metal salt complexes of 1, 10‐phenanthroline.
Crown Ether Assisted Chemical Reactions, II. Crown Ether Complexes of Potassium Phthalimide, Sodium Saccharinate and Sodium Acetylacetonate: New Reagents Containing Activated Anions
Authors: Raßhofer Werner , Oepen Gerhard , Vögtle Fritz
Published: November 2013

The synthesis of several crown ether and cryptand complexes with potassium phthalimide, sodium saccharinate and sodium acetylacetonate is reported. The anions in the complexes prove to be activated; this has been used to carry out a series of new nucleophilic substitutions with 2,4‐dinitrochlorobenzene, pentachloropyridine and pentafluoropyridine. Without addition of crown ethers these reactions could not be achieved. Only pentafluoropyridine reacts with potassium phthalimide alone, yielding a monosubstituted product. With crown ether assistance threefold substitution could be realized with pentafluoropyridine, whereas pentachloropyridine gave only monosubstitution.
Wrapping of Metal Cations by Linear Polyethers
Authors: Saenger W. , Suh I.‐H. , Weber G.
Published: November 2013

The wrapping of linear polyethyleneglycol ligands around metal cations is dependent on their lengths. Short ligands (containing 5 heteroatoms) form circular complexes; extension by one to five heteroatoms leads to helical structures, and ligands containing 11 heteroatoms are able to bind two cations in an S‐like arrangement. It is remarkable (1) that the longer achiral ligands form chiral complexes, (2) that in general all the heteroatoms are coordinated to the cation, (3) that the cation … heteroatom distance is dependent on the electronegativity of this atom, (4) that the C–C–O–C and C–O–C–C torsion angles are trans while the O–C–C–O are gauche, (5) that while the O–C–C–O torsion angles are always gauche the C–C–O–C and C–O–C–C are more flexible and can adopt a non‐trans form, and (6) that the ligands wrap preferentially in an “equatorial” zone around the cation while the “polar” zones are occupied by one or both ends of the ligands depending on their lengths. In this study we describe the molecular structures of the following complexes as determined by X‐ray crystallographic methods: the RbI‐complexes of α, ω‐bis(8‐quinolyloxy)‐3‐oxapentane, and of the homologous – 3, 6, 9‐trioxaundecane and ‐3, 6, 9, 12, 15, 18‐hexaoxaeicosane; the RbI‐complex of 1, 11‐bis(8‐quinaldyloxy)‐3, 6, 9‐trioxaundecane; the NaSCN‐complex of 1, 8‐bis(2‐methoxyphenoxy)‐3, 6‐dioxaoctane; and the 2 · KSCN‐complex of 1, 5‐bis{2‐[5‐(2‐nitrophenoxy)‐2‐oxypentyloxy]‐phenoxy}‐3‐oxapentane.
Enzyme‐Analogue Built Polymers XII Specific Binding Effects in Chiral Microcavities of Crosslinked Polymers
Authors: Wulff G. , Lohmar E.
Published: November 2013

2,3‐O‐(4‐Vinylphenylboronic)esters (2a–c) of different D‐glyceric esters were copolymerized to macroporous, crosslinked polymers. After the glyceric esters 1a–c, acting as templates, had been split off, chiral microcavities with one boronic acid group per cavity were formed. These polymers were capable of resolving the racemate of the template used. By comparison of resolution‐specificities of polymers prepared from glyceric esters carrying different bulky groups in the ester moiety, the influence of the size of substituents at the asymmetric C could be determined. The polymers showed the most specific racemic resolution for the racemate of the template used. Small differences between the structure of the racemate and that of the template used led to a decrease of specificity; bigger differences resulted in a complete disappearence of specificity. Furthermore, it was investigated whether non‐covalent interactions between the template and added comonomers were strong enough during polymerization to allow the formation of specific structures within the cavities. The directed introduction of charge‐transfer interaction led to a strong increase in specificity for racemic resolution.
Conformational Analysis of Flexible trans‐Dienes by Polarization Spectroscopy
Authors: Sheves Mordechai , Friedman Noga , Levendis Demetrius , Margulies Leon , Mazur Yehuda
Published: November 2013

This paper presents our attempts to utilize polarized (linear dichroic) spectroscopy of compounds oriented in stretched films for the conformational analysis of labile systems.
Monolayer Assemblies of Dyes to Study the Role of Thermal Collisions in Energy Transfer
Authors: Möbius Dietmar , Kuhn Hans
Published: November 2013

The energy transfer from an oxacyanine to a thiacyanine dye was investigated in monolayer assemblies. No temperature‐dependence of the efficiency was observed between 300 K and 20 K in arrangements where the donor molecules were isolated. However, in arrangements where the donor was organized into a large aggregate and the acceptor was highly diluted in the adjacent monolayer, the efficiency of the energy transfer was proportional to the absolute temperature; the spectral distributions of the fluorescence of the donor and the absorption of the acceptor were equally well matched at low and high temperatures. A simple model is discussed based on the idea that the energetic match needed for energy and electron transfer occurs occasionally due to thermal fluctuations and that this match will not be achieved below a certain temperature. A mechanism based on exciton hopping in the aggregate followed by energy transfer from a molecule in the vicinity of the acceptor to the acceptor does not explain the observed temperature‐dependence. However, the present experimental data can be rationalized by assuming that the excitation extends over a certain domain (consisting of about 10 donor dye molecules at room temperature and about 150 molecules at 20 K) which moves over the aggregate, occasionally reaching the vicinity of an acceptor molecule.
The Tetragonal Crystal Structure of 2:3 Deoxycholic Acid–Water Complex
Authors: Tang C. P. , Popovitz‐Biro R. , Lahav M. , Leiserowitz L.
Published: November 2013

The deoxycholic acid (DCA)–water (2:3) complex crystallises in space group P41212. The DCA molecules form hydrogen‐bonded layers which contain channels filled by chains of water molecules. These water molecules are linked by hydrogen bonds with each other and with the DCA molecules on the channel walls. The channel walls are thus hydrophilic unlike the hydrophobic channel walls found in the commonly observed orthorhombic P212121 inclusion complexes of DCA.
The Antisymmetrized Geminal Power, a Simple Correlated Wave Function for Chemical Bonding
Authors: Linderberg Jan
Published: November 2013

The pertinent features of the antisymmetrized geminal power are brought out with a view of describing the chemical bond and the electronic properties of molecules. It is demonstrated that for certain hamiltonians it is consistent with a response function derived from a simple moment expansion characteristic of the random phase approximation. Deficiencies with regard to “size consistency” are pointed out. Simple examples are analyzed in order to familiarize the reader with the nature of the approximations.
The Effect of Intramolecular Interactions on the Transferability Properties of Localized Descriptions of Chemical Groups
Authors: Bonaccorsi Rosanna , Ghio Caterina , Scrocco Eolo , Tomasi Jacopo
Published: November 2013

Starting from a localized description of molecular wavefunctions, approximate descriptions of chemical groups are obtained. The degree of conservation of these representations is verified over a fairly large number of compounds by using different tests, from which it is seen that the influence of intramolecular interactions is strong enough to necessitate the inclusion of these effects in the description of molecular systems in terms of transferable models of groups. Further analyses demonstrate that intragroup interactions can be approximated, to a good degree of precision, by classical interactions only. The usefulness of a zeroth order representation of a group in terms of nonorthogonal transferable models of localized orbitals, coupled to an evaluation of classical intragroup interactions, is discussed, and a simple computational method for the evaluation of the changes in reaction barriers due to substitution of chemical groups in a given molecular framework is briefly outlined.
Walsh's Rules and the Small Bond Angle States of Triatomic Dihydride Molecules
Authors: Casida Mark E. , Chen Maynard M. L. , Macgregor Robert D. , Schaefer Henry F.
Published: November 2013

A series of excited electronic states of AH2 molecules having extremely small bond angles has been discovered theoretically. Systems which have shown this characteristic to date include H2O+, NH2, CH2+, and NH2+. In the present research ab initio studies were carried out using a double zeta plus polarization basis set. Configuration interaction including all Hartree‐Fock interacting single and double excitations was performed. For the 2B2 state of CH2+, the predicted equilibrium geometry is θe(HCH) = 35.2°, re(C‐H) = 1.41 A. This state is bound by 20.3 kcal/mole relative to the separated C+ + H2 ground electronic state. The analogous state of BH2 is not substantially bound, but the neutral C + H2 system shows some very interesting features. All of these results may be qualitatively understood in the context of Walsh's rules.
Bonding in Metal Atom Cluster Compounds from the d‐Orbital Overlap Model to SCF‐Xα‐SW Calculations
Authors: Bursten Bruce E. , Cotton F. Albert , Stanley George G.
Published: November 2013

This paper gives a survey of results pertaining to the electronic structures of metal atom cluster compounds. The development of progressively more complete and accurate calculations, from the simple d‐orbital overlap model of Cotton and Haas (1964) through approximate Hartree–Fock (Fenske–Hall) calculations to recent SCF‐Xα‐SW calculations incorporating corrections for relativistic effects. It is shown that the qualitative essentials of the bonding are apparent even in the simplest treatment but that the more sophisticated methods are required to interpret spectra and other experimental data quantitatively.
On the Quantum‐Mechanical Kinetic Energy as a Measure of the Information in a Distribution
Authors: Sears Stephen B. , Parr Robert G. , Dinur Uri
Published: November 2013

Standard concepts of information theory, including Shannon's entropy, Fisher's information, Jaynes' principle of entropy maximization, Fisher's locality information matrix, and Kullback and Leibler's information measure, are described and extended to many dimensions as appropriate, to establish precise connections between the many body quantum‐mechanical kinetic energy functional T[Ψ] and information measures. Implications for density functional theory of electronic structure are discussed, and elementary examples are displayed to illustrate the argument. Among the several exact relations obtained, one of special interest is the identity

where the first term is the intrinsic accuracy or Fisher's information for locality of the one‐particle density (normalized to 1), \documentclass{article}\pagestyle{empty}\begin{document}$ \rho \left( 1 \right) = \int { \cdot \cdot \cdot \int {|{\rm \psi |}^{\rm 2} d_{{\rm T}_2 } \cdot \cdot \cdot } } \,d_{{\rm T}_{\rm N} ,} $\end{document}, and the second term is the average over the one‐particle density of Fisher's information associated with the conditional density \documentclass{article}\pagestyle{empty}\begin{document}$ f\left( {2,\;3,\; \cdot \cdot \cdot ,\;N|1} \right) \equiv \,|\psi |^2 /\rho \left( 1 \right) $\end{document} that is, the second term is the average over the marginal distribution ρ(1) of the trace of Fisher's information matrix for the distribution f(2,3, …, N|1). Because of this formula, the quantum mechanical variation principle may be precisely stated as a principle of minimal information.
The Persistence of p, d, f and g Orbitals in Compounds
Authors: Jørgensen Christian K.
Published: November 2013

The evidence for a definite number of electrons occurring in a partly filled shell (consisting of f or d‐like orbitals) in gaseous molecules and in condensed matter (including metallic lanthanides) is reviewed, based on the analysis of atomic spectra. Comparison is made with competing descriptions (mainly useful outside the transition‐groups), and inner shells are discussed, accompanied by recent evidence from photo‐electron spectra. The importance of the local kinetic energy, and of the total symmetry of closed shells as the neutral element of Hund vector‐coupling, is emphasized. Critical analysis is made of real angular functions, Schrödinger's equation written on conservative form, and of the cardinal number K of electrons in an atom as an approximate quantum number (like S) in compounds.
Theory of Magnetic Susceptibilities and NMR Chemical Shifts in Terms of Localized Quantities
Authors: Kutzelnigg W.
Published: November 2013

A coupled Hartree–Fock theory for diamagnetic susceptibilities χ and chemical shifts σ in terms of localized MO's and individual gauge origins for the different MO's is derived. The new coupled Hartree–Fock equations and expressions for χ and σ differ from the traditional ones by the presence of “exchange coupling terms” (ECT) and “resonance coupling terms” (RCT). For the ECT, that are expected to be very small, a simple approximation is proposed. Both the ECT and the RCT can be decomposed into “diamagnetic” and “paramagnetic” contributions. Spurious paramagnetic terms due to inappropriate choices of the gauge origin are avoided in the present scheme. The possibility to include correlation effects is discussed.
Quantum Organic Chemistry and the Unitary Group
Authors: Matsen F. A.
Published: November 2013

The unitary group formulation of many‐electron theory provides an accurate and vivid picture of many‐electron states called the Gel'fand label which exhibits both the electron configuration and the spin and which permits a facile correlation of molecular orbital and valence bond states. In addition it provides a convenient method of computation of matrix elements which is competitive with more conventional means.
Generation of Symmetry‐Adapted Wave‐Functions for O2 Using Group Theoretical Projection Operators
Authors: Hurley A. C. , Harcourt R. D. , Taylor Peter R.
Published: November 2013

The simple case of the O2 molecule is used to illustrate the construction and implementation of projection operators for specific symmetry species of infinite continuous groups. The basic theory is quite analogous to that for finite groups, summations over all group elements being replaced by integrations over the group manifold. For linear molecules, with groups C∞v, D∞h, these integrations over the group manifold reduce to simple one‐dimensional integrals of periodic functions. The final wave functions are used to derive a crude estimate of the energy splittings of the multiplets 3Σ−g, 1Δg and 1Σ+g in the π2g ground configuration of O2.
Ab Initio Relativistic Effective Core Potential Studies of Metal–Metal and Metal–Hydrogen Bonding in Pd2, Pt2, PdH and PtH
Authors: Basch Harold , Cohen Drora , Topiol Sid
Published: November 2013

The electronic structure of the palladium and platinum homonuclear diatomics (M2) and diatomic hydrides (MH) have been calculated using relativistic effective core potentials in an ab initio multi‐configuration self‐consistent field framework. Calculated spectroscopic properties (Re and ωe) of the diatomic hydrides are in close agreement with experiment except for the calculated harmonic force constant in PdH. This latter discrepancy is attributed to inaccuracies in the relative energies of the metal atom in the dissociation limit. The calculated M–M and M–H bond strengths follow the expected trend of the Pt atom forming stronger such bonds than Pd. The metal–hydrogen bonding interaction involves primarily the metal nd orbitals for both Pd and Pt, in contrast to NiH where the main metal bonding orbital has been found to be the 4s. On the other hand, as in Ni2, the Pd–Pd bond is essentially a (n + 1)s electron pair bond, while the Pt–Pt bond has a substantial 5d orbital contribution. This quantitative difference between M–M and M–H bonding interactions found for the group VIII transition metals is supported by experimental photoemission energy distribution and difference spectra for the clean metal and hydrogen chemisorbed metal surfaces.
Mulliken Population Analysis and Point Charge Model of Molecules
Authors: Huzinaga S. , Narita S.
Published: November 2013

Essential features of the Mulliken electron population analysis are critically reviewed. Based on theoretical and numerical examination, the method is improved in such a way that the resulting point‐charge model of a molecule precisely reproduces the dipole moment of the molecule calculated by the original molecular wavefunction.
Determination of the Charge Distribution in Nonmetallic Crystals II. Compounds with d‐orbitals. Corundum
Authors: Julg A. , Pellegatti A. , Marinelli F.
Published: November 2013

A S.C.F. method using localized molecular orbitals, previously proposed to determine net charges in zincblende‐ and wurtzite‐type crystals, has been adapted to the corundum case (Al2O3‐α)∞. The presence of d‐orbitals in hybrid atomic orbitals and the difference between coordination numbers give rise to some problems. Then, the choice of Slater‐type orbital exponents, the introduction of corrective factors in the calculation of charges, the molecular orbitals orthogonalization and the introduction of Madelung‐type constants are discussed. The net charge found for A1 atoms magnified image is, given the hypotheses used in the calculation, in good agreement with the one (0.33) determined from an empirical relation connecting hardness and ionicity of a crystal.
The Notion of the Force Analysis of the Non‐Stationary Case
Authors: Srebrenik S. , Pauncz R.
Published: November 2013

We deal with the definition and analysis of the force on a nucleus in a non‐stationary state. The considerations are based on the Ehrenfest theorem and are generalized for an arbitrary model and specifically to the Born‐Oppenheimer approximation. We suggest that the force is given by \documentclass{article}\pagestyle{empty}\begin{document}$ \left\langle {\partial H\,/\partial R} \right\rangle $\end{document} rather than \documentclass{article}\pagestyle{empty}\begin{document}$ \partial E/\partial R $\end{document} and show that this definition is consistent with different physical models and approaches.
A General Definition of Ring Substituent Positions
Authors: Cremer Dieter
Published: November 2013

Starting from the concept of the mean plane of a general nonplanar N‐membered ring, the substituent orientation angles α and β are derived. These angles define the position of a ring substituent in an unambiguous way, the angle α indicating the direction of the ring‐substituent bond relative to the mean plane (perpendicular, inclined or parallel) and the angle β revealing whether the bond vector is directed inward (towards the geometrical center of the ring) or outward (away from the geometrical center). The orientation angle α allows a generalization of the terms “axial” and “equatorial” including Barton's original specification of these terms and vivifying their semantics. Unlike earlier descriptions of ring substituent orientations the new definitions completely avoid terms like “quasi‐axial”, “quasi‐equatorial”, etc. Examples are given which show their usefulness in discussions of steric effects.
The Orbital Interaction Approach to Structural and Conformational Problems in Organic Chemistry
Authors: Whangbo Myung‐Hwan , Wolfe Saul
Published: November 2013

The relationship between the functional group approach to organic chemistry and the group orbital approach to the analysis of molecular orbital results is discussed. The concept of group orbital interactions, within the framework of perturbational molecular orbital theory, leads to a treatment of structural and stereochemical problems that can take both stabilizing and destabilizing effects into account, can be applied either qualitatively or quantitatively and can be done in a manner that is both internally and externally consistent. Certain advantages of these procedures over the classical methods of organic chemistry are pointed out, but it is also recognized that semantic and pedagogical problems must be overcome to make the method generally acceptable.
Circular Dichroism. LXXIV.CD of Benzene Derivatives with Several Identical Chiral Substituents
Authors: Schoenfelder W. , Snatzke G.
Published: November 2013

A comparison of the CD‐ and UV‐spectra of benzene derivatives, which are mono‐, 1,4‐di‐ or 1,3,5‐trisubstituted by (identical) chiral ligands, revealed that the rotational strength within the α‐band of mono‐ and 1,3,5‐trisubstituted benzenes is mainly derived from the magnetic transition moment of the benzene chromophore perpendicular to the ring, and from a corresponding electric transition moment stolen from a ligand transition. For the 1,4‐disubstituted homologues, the main contribution to the rotational strength is associated with the electric transition moment in the plane of the benzene chromophore and with a corresponding magnetic transition moment, stolen from the A1g → E1g (D6b‐notation) transition within the same ring. For the 1,3,5‐trisubstituted compounds, the 0–0‐band is scarcely, or not at all, detectable in the UV‐spectra, but distinctly recognizable in the CD‐spectra. In a few cases Cotton‐effects between the positions of the α‐ and the p‐bands could be detected, which are ascribed to the magnetically allowed A1g → E1g (D6b‐notation) transition.
13C Chemical Shifts — Sensitive Detectors in Structure Determination. 1. 13C NMR Studies of Saturated Heterocycles. 4. Methyl‐Substituted 1,3‐Dioxanes
Authors: Pihlaja Kalevi , Nurmi Timo
Published: November 2013

The 13C chemical shifts for 1,3‐dioxane and 50 methyl‐substituted derivatives are reported. Substituent effects on them are derived and their magnitude shown to be closely related to the exact ring geometry and other conformational aspects. The results confirm the high chair‐twist preference and support the view that 1,4‐twist is appreciably more stable than 2,5‐twist. Only 2,4‐diaxially substituted compounds normally attain a twist form whereas 4,6‐diaxial substitution alone is not enough but deform the chair form. A combination of the detailed knowledge on the stereochemistry of the 1,3‐dioxane ring and on the type of significant shift parameters leads inevitably to the conclusion that a proper understanding of their interdependence offers a useful tool for conformational and configurational analysis.
A Peculiar Substituent Effect Operative in the Ring Inversion of trans‐3,3,7,11‐Tetramethyl‐1,5‐dioxa‐8,9,10‐trithiaspiro[5.5]undecane
Authors: Tavernier D. , Anteunis M. , Becu C.
Published: November 2013

The synthesis of the novel bicyclic spiranes 3,3‐diMe‐ and trans‐3,3,7,11‐tetraMe‐1,5‐dioxa‐8,9,10‐trithiaspiro[5.5]undecane (1 and 2) is reported. In 1, there are four degenerate chair/chair conformers. The rate of the chair‐to‐chair inversion of the constituent 1,3‐dioxane and 1,2,3‐trithiane rings can be measured separately, yielding barriers of Δ G*1.70 = 34.7 and Δ G*2.50 = 52.7 kJ. mol−1, respectively. In 2, however, only one pair of degenerate chair‐chair conformers is observed, and the rate of the chair/chair to inverted chair/inverted chair process yields Δ G*2.50 = 76.5 kJ. mol−1. A mechanism rationalizing the high barrier in 2 is proposed. A geometric definition of “coupled ring inversion” is proposed.
Phytochrome Models. IV. Conformational Heterogeneity and Photochemical Changes of Biliverdin Dimethyl Esters in Solution
Authors: Braslavsky Silvia E. , Holzwarth Alfred R. , Langer Elisabeth , Lehner Harald , Matthews J. Ioan , Schaffner Kurt
Published: November 2013

Solutions of biliverdin dimethyl ester (I) and its monoprotonated form (IH+) exhibit a solvatochromic and thermochromic behaviour. Based on absorption, fluorescence and fluorescence excitation, and solvent‐induced circular dichroism (SICD) data, these properties are interpreted in terms of variations of the relative populations of conformers (including readily interconvertible configurational isomers). Thus, folded helical forms of I and IH+ are more abundant at room temperature in, e.g., ethanol than in ethyl lactate, and stretched conformations other than the already known stable (E, Z, Z) and (Z, Z, E) photoisomers are quite generally favoured with increasing temperature. Irradiation of I in ethanol at 173 K increases the population with stretched, thermally equilibrating conformers. IH+ in ethanol undergoes an irreversible photochemical change at room temperature or below. Its nature has not yet been identified.
The Protonation of Aromatic π Carbocations. The Behavior of 2‐Hydroxy‐ and 9‐Hydroxyphenalenone in Trifluoromethanesulfonic Acid
Authors: Pagni Richard M. , Smith Robert J. , Moore Theresa , Burnett Michael N.
Published: November 2013

In continuation of work on the protonation of aromatic π carbocations, the behavior of 1,2‐dihydroxyphenalenyl cation (7 ) and 1,9‐dihydroxyphenalenyl cation (8 ) in CF3SO3D was investigated. The behavior of carbocation 8 was unexceptional. It underwent a facile exchange at room temperature, with H‐2, H‐5 and H‐8 all exchanging at comparable rates. Carbocation 7, on the other hand, exchanged at an exceptionally slow rate, even at 100°C. The order of reactivity of the various sites on 7 was found to be H‐3 ≫ H‐5 ⪖ H‐4 ≈ H‐6; H‐7, H‐8 and H‐9 did not exchange. These unusual results are best accommodated by assuming that most, if not all, of the exchange actually occurs on 2‐hydroxyphenalenone (9 ) which is present in very low concentration. Hückel calculations support this contention.
Number and Novelty in Approaches to the Calculation of Strainless Group Increments
Authors: van Vechten Deborah , Liebman Joel F.
Published: November 2013

In this paper we show that the large number of approaches using apparently unrelated strainless increments for unsubstituted alicyclic hydrocarbons in the literature are neither mathematically nor conceptually unique. We additionally demonstrate that if the strain energy assigned to a compound by any three sets of increments is known, the strain energy any other approach would assign can automatically be determined without considering any further details of the structure of the compound. Equivalently, there are but three mathematically distinct, i.e. linearly independent, strainless incremental approaches for these compounds. Thus the choice of which method to employ in one's own reasoning relative to a chemical problem must be based on personal, rather than strictly chemical or mathematical criteria. We proceed by presenting our criteria and their molecular realization, the concept of diagonal reference states. Diagonal reference states are defined from hydrocarbons composed solely of the group of interest. In particular, >C<, >CH–, –CH2– and –CH3 are derived from diamond, cubane, cyclohexane and ethane with the accompanying enthalpies of formation, +1.9, –9.7, –20.6. and –42.0kJ mol−1. The virtues and debits of this method are presented in support of our conclusion that this approach is preferable because it is diagonal.
Stereochemistry of Thermally‐Induced Homolytic Fission of C‐C Bonds in Small Rings
Authors: Gajewski Joseph J.
Published: November 2013

This is a review of the pertinent literature on the subject of the stereochemistry of homolytic nonconcerted ring opening of small carbocycles. The data suggests that cyclopropane opens either without bond rotation or with a single rotation or with disrotatory double rotation; conrotatory double rotation has not yet been observed. Cyclobutane and cyclopentane undergo conrotatory ring opening that is coupled with another rotation to cause shearing of the bond to give a gauche 1,4‐ or 1, 5‐biradical. These biradicals apparently undergo bond formation with rearrangement via a least motion stereochemical pathway competitive with rotation around bonds to randomize the stereochemistry of the initially generated biradical.
The Photosensitized Oxidation of Strained Olefins
Authors: Frimer Aryeh A.
Published: November 2013

The effect of strain in determining the rate, mode and direction of singlet oxygen attack is explored using small ring olefins as substrates. The data suggests that1O2is relatively insensitive to strain considerations present in either the starting material or the product. More important factors seem to be the ground state geometry of the olefin, the interatomic distance between the α‐olefinic carbon and the γ‐allylic hydrogen, and the ionization potential of the double bond. Strain does, however, play a crucial and fascinating role in the secondary rearrangements of the primary1O2products.
Synthesis and Properties of Functionalized 2,4‐Ethano‐Bridged Bicyclobutanes
Authors: Hogeveen H. , Zwart L.
Published: November 2013

Starting from 1,2,4,5,6‐pentamethyl‐3‐methylenetricyclo[3.1.0.02.6]‐ hexane (3), a number of functionalized ethano‐bridged bicyclobutanes have been prepared. Ozonolysis of the carbon‐carbon double bond of compound 3 leads to the strained and sterically hindered ketone 4 which can be further transformed into tricyclic alcohols and azines. The formation of the rearranged lactone 19 in the oxidation of ketone 4 with O3 or peracid is in agreement with a mechanism in which the 1,2‐alkyl shift from carbon to oxygen occurs by way of a β‐fission followed by a recombination step. Treatment of the dichlorocarbene adduct of alkene 3 with n‐BuLi afforded allene 7, which on reaction with TCNE yielded a di‐cis‐fused cyclopropane.