Properties of the 2' and 2” states in 106, 112, 114Cd

Angular correlations have been measured between γ-rays from the 2 → 2 → 0 cascades in ^106,112,114Cd and the beam of 11.0 MeV α particles effecting Coulomb excitation. Multipole admixtures for the 2 → 2 transitions, as deduced from these correlations, when combined with earlier results establish their B(E2) and B(M1) values. For the transitions from the 1312 and 1208 keV states in ^112,114Cd the B(E2) values in single-particle units are 18±4 and 24±7. These values are typical for transitions from “two-quadrupole-phonon” states in this mass region whereas that of the 1718 keV transition in ¹⁰⁶Cd has the smaller value of 7.0±2.3. The B(E2) values of the 2 → 2 transitions in ^112,114Cd from the 1468 and 1363 keV states are < 0.3 single-particle units. The B(M1) values of all five transitions are ≈ 10^?2$\text{(}\text{e}\text{h}\text{?}\text{2Mc}\text{)}{}^2$.     

Total synthesis of (-)-senepodine G and (-)-cermizine C

An efficient, stereospecific synthesis of the alkaloids senepodine G (2) and cermizine C (1) has been completed using the BF3.Et2O-promoted stereospecific addition of Me2CuLi to alpha,beta-unsaturated lactam 6 to provide lactam 3, the addition of MeMgBr followed by HCl to convert 3 to senepodine G (2) (six steps, 40% overall yield), and the stereospecific NaBH4 reduction of 2 to give cermizine C (1) (seven steps, 40% overall yield).     

Hydrogen bonds with pi and sigma electrons as the multicenter proton acceptors: high level ab initio calculations

Pi-electrons of acetylene and sigma-electrons of molecular hydrogen were investigated as Lewis bases in different complexes. Hence high level ab initio calculations were performed up to the MP2/6-311++G(3df,3pd) level of approximation. It was found that species analyzed possess characteristics typical for H-bonded systems. The Bader theory was additionally applied; bond paths between proton and pi-electrons of acetylene or sigma-electrons of molecular hydrogen were detected with the corresponding bond critical points attributed to the proton-acceptor interactions. Numerous correlations between topological, geometrical and energetic parameters were also found. For example, the H...pi or H...sigma interaction is stronger for the shorter corresponding distance between the proton and the middle of C[triple bond]C or H-H bond. It is connected with the greater elongation of C[triple bond]C or H-H bonds and the greater transfer of electron charge from the Lewis base to the Lewis acid.     

Halogen bond and its counterparts: Bent's rule explains the formation of nonbonding interactions

Ab Initio calculations were carried out on complexes of F(3)CCl. The Cl center may act as the Lewis acid as well as the Lewis base. Hence various interactions are analyzed for several complexes of F(3)CCl: halogen bond, dihalogen bond, halogen-hydride bond, hydrogen bond, and others. It was found that Lewis acid-Lewis base interactions lead to the electron charge redistribution being in agreement with Bent's rule. This rule explains the formation of nonbonding interactions. For example, if the C-Cl bond acts as the Lewis acid thus the increase of the s-character in C-orbital of C-Cl is observed as a result of complexation. However, if the C-Cl bond acts as the Lewis base thus the mentioned above s-character decreases. Numerous analogies between the halogen bond and the hydrogen bond are analyzed and various relationships between energetic, geometrical and the natural bond orbitals method (NBO) parameters are shown.     

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...     

The exchange-correlation potential in ab initio density functional theory

From coupled-cluster theory and many-body perturbation theory we derive the local exchange-correlation potential of density functional theory in an orbital dependent form. We show the relationship between the coupled-cluster approach and density functional theory, and connections and comparisons with our previous second-order correlation potential [OEP-MBPT(2) (OEP-optimized effective potential)] [I. Grabowski, S. Hirata, S. Ivanov, and R. J. Bartlett, J. Chem. Phys. 116, 4415 (2002)]. Starting from a general theoretical framework based on the density condition in Kohn-Sham theory, we define a rigorous exchange-correlation functional, potential and orbitals. Specifying initially to second-order terms, we show that our ab initio correlation potential provides the correct shape compared to those from reference quantum Monte Carlo calculations, and we demonstrate the superiority of using Fock matrix elements or more general infinite-order semicanonical transformations. This enables us to introduce a method that is guaranteed to converge to the right answer in the correlation and basis set limit, just as does ab initio wave function theory. We also demonstrate that the energies obtained from this generalized second-order method [OEP-MBPT2-f] and [OEP-MBPT2-sc] are often of coupled-cluster accuracy and substantially better than ordinary Hartree-Fock based second-order MBPT=MP2.     

210Pb and 210Po radionuclides in the urban air of Lodz, Poland

The concentration of two important radionuclides: ²¹⁰Pb and its decay product ²¹⁰Po in the urban air in the center of the Polish city of Lodz were measured during the winter and spring seasons of 2008–2009. Urban airborne particulate matter was collected using two methods: an Anderson 9-stage impactor, and a high-volume aerosol sampler type ASS500 working in the frames of the aerosol sampling network in Poland, established for radionuclide monitoring. Average concentrations for 10 months sampling period for ²¹⁰Pb and ²¹⁰Po were 0.556 and 0.067 mBq/m³, respectively. However remarkable fluctuations due to meteorological condition were observed: from 0.010 to 0.431 mBq/m³ for ²¹⁰Po and from 0.167 to 1.847 mBq/m³ for ²¹⁰Pb. The highest concentrations, almost 60% of the total activities, of both radionuclides were found in the first two fine aerosol fractions with particle diameters below 0.36 μm. The aerosol residence times calculated from the ²¹⁰Po/²¹⁰Pb ratio ranged from 7 to 120 days.