Search results for "periodic table"
showing 10 items of 262 documents
Über Tetraaryl-methan-analoga in der gruppe 14
1993
The title compounds have been synthesized by Li and Grignard reactions. The crystal structure of Ph3Si-p-Tol has been determined. The substitution of only one phenyl by one p-tolyl group causes only a slight deviation from the ideal S4 symmetry of Ph4Si. Gradual replacement of phenyl by p-tolyl groups leads to increasing low field shifts for all 13C(ipso) atoms. The substitution of the first phenyl group by p-tolyl in Ph4Si and Ph4Sn results in a high field shift both for δ(29Si) (−0.3 ppm) and for δ(119Sn) (−1 ppm). Further replacement shows nearly linear dependencies (Δδ(29Si) = −0.1 ppm, Δδ(119Sn) = + 1.5 ppm per p-tolyl group).
Enhancing performance of α‐diiminonickel precatalyst for ethylene polymerization by substitution with the 2,4‐bis(4,4'‐dimethoxybenzhydryl)‐6‐methylp…
2020
High activities in ethylene polymerization predetermine α‐diiminonickel precatalysts for potential industrial applications. In our study, we have synthesized and characterized a series of unsymmetrical 1‐(2,4‐bis(4,4′‐dimethoxybenzhydryl)‐6‐MeC6H2N)‐2‐arylimino‐acenaphthylene nickel(II) halides. The single‐crystal X‐ray diffraction study of representative compounds reveals distorted tetrahedral geometry. On activation with either Me2AlCl or modified methylaluminoxane, these nickel complexes exhibit high activities of the order of 106 g of PE (mol of Ni)−1 h−1 and produce polyethylene of generic application characterized by high molecular weight, narrow molecular weight distribution, and mod…
Slow and fast methyl group rotations in fragile glass-formers studied by NMR
2000
Abstract The spin-lattice relaxation times of the selectively ring deuterated, fragile glass-formers propylene carbonate and toluene were compared with those measured for species which were specifically labeled at the methyl groups. It was found that the dynamics of the CD 3 group is strongly decoupled from that associated with the primary response of toluene, while for propylene carbonate the degree of decoupling is relatively weak. The experimental results could be described successfully using a model which takes into account the ring dynamics as well as those of the methyl group.
22nd Meeting of the Group of European Charophytologists (GEC)
2019
The 22nd Meeting of the Group of European Charophytologists (GEC) was held from 17 to 21 September 2018 in Palermo. It was convened by the International Research Group on Charophytes (IRGC) and org...
N-Heterocyclic Carbenes with Inorganic Backbones: Electronic Structures and Ligand Properties
2008
The electronic structures of known N-heterocyclic carbenes (NHCs) with boron, nitrogen, and phosphorus backbones are examined using quantum chemical methods and compared to the experimental results and to the computational data obtained for a classical carbon analogue, imidazol-2-ylidene. The sigma-donor and pi-acceptor abilities of the studied NHCs in selected transition-metal complexes are evaluated using a variety of approaches such as energy and charge decomposition analysis, as well as calculated acidity constants and carbonyl stretching frequencies. The study shows that the introduction of selected heteroatoms into the NHC backbone generally leads to stronger metal-carbene bonds and t…
Novel unsymmetrical ortho-metalated dirhodium (II) catalysts: trans influence of the axial ligand
1999
Inductive effects of an X axial group which are transmitted through the RhRh bond influence the reactivity of ortho-metalated dirhodium complexes 3 in the cyclization of 1-diazo-5-penten-2-one (4).
From Masurium to Trinacrium: The Troubled Story of Element 43
2005
The first man-made chemical element was that with atomic number 43. It was produced at the University of Californiaâ€sA„A¬Berkeley (by neutron bombardment of a molybdenum plate and was chemically identified at the University of Palermo (Italy) in 1937 by Segre and Perrier. Previous attempts to identify it in natural ore had been unsuccessful, owing to the short life of its isotopes. Notwithstanding, several claims of its discovery had appeared in the chemical literature. The history of this discovery clearly shows the dramatic improvements of chemical analytical techniques and criteria in the first half of 20th century. In 1949 its discoverers proposed to call it technetium, which means pro…
A Time-Lagged, Actor–Partner Interdependence Analysis of Alliance to the Group as a Whole and Group Member Outcome in Overweight and Obesity Treatmen…
2014
A time-lagged design was used to examine how the perceptions of alliance to the group as a whole by the other group members at an earlier point in the group were related to an individual group member’s perceptions of alliance to the group as a whole at a later point in the group. We also examined how treatment outcome moderated this relationship. Seventy-three patients diagnosed as overweight or obese participating in 10 short-term therapy groups provided data for analyses. Group members completed measures of cohesion to the group and alliance to the group as a whole at the third, sixth, and last session of 12-session groups as well as pre- and posttest ratings on Obesity-Related Well-Being…
Structure of the FeBTC Metal–Organic Framework: A Model Based on the Local Environment Study
2015
The local environment of iron in FeBTC, a metal organic framework commercially known as Basolite F300, is investigated combining XANES and EXAFS studies of the iron K-edge. The building block of the FeBTC can be described as an iron acetate moiety. Dehydration induces a change in the coordination of the first shell while preserving the network. We propose that the local structure around Fe atoms does not undergo a rearrangement, thus, leading to the formation of an open site. The analysis conveys that the FeBTC is a disordered network of locally ordered blocks.
On the impact of linking groups in hydrogen-bonded liquid crystals – a case study
2018
The impact of the linking group in hydrogen-bonded liquid crystals is systematically studied by a modular approach. POM and DSC results exhibited tremendous differences in the mesomorphic behaviour of the assemblies, due to the versatile linkages of the side chains, which were correlated with structural features and the elctronical nature of the side chains.