Isochroman derivatives and their tendency to crystallize in chiral space groups

In methyl [5‐methoxy‐4‐(4‐methoxy­phenyl)­isochroman‐3‐yl]­acetate, C₂₀H₂₂O₅, (I), and methyl [4‐(2,5‐di­methoxy­phenyl)‐8‐methoxy­isochroman‐3‐yl]­acetate, C₂₁H₂₄O₆, (II), the heterocyclic rings adopt half‐chair conformations. The substituents at the 3‐ and 4‐positions are in a trans configuration in both (I) and (II), being in an axial conformation in (I) and in an equatorial conformation in (II). The crystal structure of (I) is stabilized by weak C—H⋯O hydrogen bonding, leading to the formation of an infinite three‐dimensional network. Compound (II) crystallizes in a chiral space group. This feature, which was also found in previously investigated isochroman derivatives, is related to the arrangement of substituents attached to the isochroman moiety.     

A–X⋯σ Interactions—Halogen Bonds with σ-Electrons as the Lewis Base Centre

CCSD(T)/aug-cc-pVTZ//ωB97XD/aug-cc-pVTZ calculations were performed for halogen-bonded complexes. Here, the molecular hydrogen, cyclopropane, cyclobutane and cyclopentane act as Lewis base units that interact through the electrons of the H–H or C–C σ-bond. The FCCH, ClCCH, BrCCH and ICCH species, as well as the F₂, Cl₂, Br₂ and I₂ molecular halogens, act as Lewis acid units in these complexes, interacting through the σ-hole localised at the halogen centre. The Quantum Theory of Atoms in Molecules (QTAIM), the Natural Bond Orbital (NBO) and the Energy Decomposition Analysis (EDA) approaches were applied to analyse these aforementioned complexes. These complexes may be classified as linked by A–X···σ halogen bonds, where A = C, X (halogen). However, distinct properties of these halogen bonds are observed that depend partly on the kind of electron donor: dihydrogen, cyclopropane, or another cycloalkane. Examples of similar interactions that occur in crystals are presented; Cambridge Structural Database (CSD) searches were carried out to find species linked by the A–X···σ halogen bonds.     

Changes of biodiesel composition after electron beam irradiation

Journal of Radioanalytical and Nuclear Chemistry - The study of the influence of external factors on FAME is increasingly being taken up with research topics. Under natural conditions, they are...     

Analysis of IR and Raman spectra of transition metal telluromolybdates

The work presents the IR and Raman spectra in the range 400–4000 cm^?1 of simple and double salts of hexamolybdotelluric (VI) acid of the general formula M₃[TeMo₆O₂₄]·nH₂O and (NH₄)_2xM_3?x [TeMo₆O₂₄]·mH₂O respectively, and of substitutive telluromolybdates with the wolframite structure MTe_yMo_1?yO₄, where M = Co, Zn, Ni and Mn. In this range the modes have been assigned to stretching vibrations of appropriate Mo-O bonds. Approximate values of force constants for these bonds have been computed and compared with the literature values reported for transition metal molybdates and ammonium heptamolybdate.     

On continuity properties of the entropy of an observable

Let A denote an unbounded self-adjoint operator in Hilbert space with purely point spectrum. The aim of this note is to discuss the continuity properties of the entropy of A in the state ?, H(A, ?), introduced by Ingarden and Urbanik. It is shown that H(A, ?) is lower semi-continuous in both arguments with respect to the generalized operator convergence and to the trace norm, respectively.     

Poisson structures on double Lie groups

Lie bialgebra structures are reviewed and investigated in terms of the double Lie algebra, of Manin- and Gauss-decompositions. The standard R-matrix in a Manin decomposition then gives rise to several Poisson structures on the correponding double group, which is investigated in great detail.     

Three-valence-particle fission product 51 135Sb84

By analysis of fission product γ-ray data measured at Eurogam II using a ₂₄₈Cm source, yrast levels up to about 2 MeV in the N=84 three-particle nucleus ₁₃₅Sb have been identified. These levels are interpreted as π g^7/2ν f^7/2 ₂ and π g^7/2ν f^7/2h^9/2 states with the help of shell model calculations using empirical nucleon-nucleon interactions. Received: 30 July 1998     

Formation and atomic structure of GaSb nanostructures in GaAs studied by cross-sectional scanning tunneling microscopy

GaSb nanostructures in GaAs, grown by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Three different samples were examined, containing a thin quantum well, a quantum well near the critical thickness for dot formation, and finally self-organized quantum dots with base lengths of 5–8 nm and heights of about 2 nm. The dots are intermixed with a GaSb content between 60% and 100%. Also small 3D and 2D islands were observed, possibly representing quantum dots in an early growth stage and quantum dot precursors. All GaSb layers exhibit gaps, which are indications of an island-like growth mode during epitaxy.     

The effective potential and symmetry breaking in theO(N) xO(N) model

We compute the finite temperature effective potential in theO(N)xO(N) symmetric model for largeN in spacetime dimensionsd=4, 3, 2 and discuss the spontaneous symmetry breaking patterns. Ford=3 we find that the symmetry, if broken at zero temperature is restored at arbitrarily small nonzero temperature. Ford=4 the model is plagued by an intrinsic instability; in particular, there is no stable ground state at high temperature.