bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractStandard 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.
Determination of the Charge Distribution in Nonmetallic Crystals II. Compounds with d‐orbitals. Corundum
Authors: Julg A. , Pellegatti A. , Marinelli F. 
Published: November 2013

AbstractA 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

AbstractWe 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

AbstractStarting 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractSolutions 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

AbstractIn 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

AbstractIn 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

AbstractThis 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

AbstractThe 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

AbstractStarting 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.
ESR and NMR Studies on the Effects of Magnesium Ion on Chloroplast Manganese
Authors: Khanna Rita , Rajan S. , Steinback K. E. , Bose S. , Govindjee  , Gutowsky H. S. 
Published: November 2013

AbstractThe addition of 1–50 mM MgCl, to “low salt” thylakoid membranes causes a monotonic decrease in the transverse, aqueous proton relaxation rate (R2 = 1/T2) and an increase in the 6‐line ESR spectrum characteristic of free Mn(II) but does not affect the oxygen evolution rate. These results suggest that magnesium ion at low concentrations replaces Mn(II) from a very loosely bound pool which is not involved in oxygen evolution. The decrease of R2 is probably due mainly to the smaller molar relaxivity of free compared with bound Mn(II). R2 can be affected by conformational and structural changes involving the Mn(II) as well as by the amount of Mn(II) and the nature of its binding. However, MgCl2 causes the same decrease in R2 for trypsin treated thylakoids, which do not undergo the gross structural changes, e.g. grana stacking, that it produces in untreated membranes. R2 measurements of isolated light harvesting complex preparations indicate the presence of bound Mn in it; neutron activation analysis of these samples shows that they have about one‐third of the functional manganese bound in thylakoid membranes—this may be the tightly bound pool of Mn, but the results are not conclusive.
Circular Dichroism and Other Optical Properties of Antenna Chlorophyll Proteins from Higher Plants
Authors: Shepanski John F. , Knox Robert S. 
Published: November 2013

AbstractWe report the measurement of the room‐temperature optical properties of antenna chlorophyll proteins (prepared with sodium dodecyl sulfate membrane solubilization) from six plant species of five different orders: pea (Pisum sativum), soy (Glycine max), barley (Hordeum vulgare), spinach (Spinacea oleracea), yew (Taxus canadensis), and fern (Onoclea sensibilis). All six species' antenna protein preparations exhibit optical spectra which are similar in great detail, implying similar internal chromophore arrangements from species to species. Features of the spectra thought due to chromophore interactions disappear upon heat denaturation. A model proposed by Van Metter for spinach chlorophyll protein has been revised and is consistent with all the data presented here.
The Reaction Center and Antenna Pigments of Green Photosynthetic Bacteria
Authors: Swarthoff T. , Amesz J. , Kramer H. J. M. , Rugersberg C. P. 
Published: November 2013

AbstractExperiments are reported on the optical properties and orientation of reaction center pigments of the green photosynthetic bacterium Prosthecochloris aestuarii. Analysis of the light‐induced absorption difference spectra of P840, the primary electron donor, and of reaction center triplet formation indicates that the bleaching of the P840 band at 836 nm is accompanied by band shifts of bacteriochlorophylls absorbing at 797, 816 and 833 nm at 80 K. The Qy transitions of the long‐wave bacteriochlorophylls were found to be oriented more or less parallel to the membrane, the Qx transitions were more or less perpendicularly oriented. Fluorescence emission spectra of bacteriochlorophyll a in intact cells and isolated pigment‐protein complexes are presented for the temperature range 295‐4 K. Experiments with different wavelengths of excitation indicate that in the PP and RCPP complexes light absorbed by bacteriochlorophyll a produces mainly emission by light‐harvesting bacteriochlorophyll, whereas light absorbed by pigments absorbing at 670 nm (bacteriopheophytin c or a possibly related pigment) predominantly excites long‐wave fluorescence, which appears to be emitted by pigments more closely associated with the photochemical reaction center. The emission spectra of the light‐harvesting bacteriochlorophyll a complex at various temperatures indicated temperature equilibrium between the emitting species. In intact cells, an increase in bacteriochlorophyll c fluorescence upon cooling indicates a decrease in the efficiency of energy transfer between the chlorosome and bacteriochlorophyll a.