Dan Johnels

NMR and Raman characterization of pressure polymerized C60

Bulk C60 has been treated at 1.1 GPa and 550–585 K, producing a dense insoluble material which on heating to above 600 K reverts to normal C60. Raman and IR studies on modified material show a larg ...

Clustering of aryl carbon-13 nuclear magnetic resonance substituent chemical shifts. A multivariate data analysis using principal components

A principal component analysis of the 13C substituent-induced chemical shifts of 82 monosubstituted benzenes shows that ca. 90% of the substituents belong to one of four clusters, acceptors, alkyls, donors, or halogens. This grouping is confirmed statistically. The extensions of the subclasses are not parallel. It is also shown that the predictive capability of the single-parameter models for each subclass is better than any multiparameter model applied on the whole data set. The observed grouping of substituents provides an explanation to the apparent correlation frequently found between 13C n.m.r. chemical shifts and dual substituent parameters. The ability of the statistical method to discover incorrect shift data is also illustrated.

Synthesis and Structural Characterization of C70H38

Reference LSMB-ARTICLE-2008-007doi:10.1002/anie.200705450View record in Web of Science Record created on 2008-11-03, modified on 2017-05-12

7LI SOLID-STATE NMR SPECTROSCOPIC STUDY OF CYCLOPENTADIENYLLITHIUM COMPLEXES

Eighteen cyclopentadienyllithium complexes were studied by solid‐state 7Li NMR spectroscopy. It is shown that the chemical shift gives information on the type of complex, i.e. whether the complex is a contact ion pair, a solvent‐separated ion pair, a sandwich structure or a polymeric material. These shift differences are due to the ring current of the aromatic anion. In order to obtain information about the solvation of the lithium cation, the quadrupolar coupling constant χ has to be determined. The χ value depends on the number and type of donor atoms in the ligand, where the nitrogen‐containing ligands give rise to higher χ values than the oxygen analogues.

A solid state 7Li NMR study of phenyllithium aggregates

Abstract A 7 Li MAS and static NMR study of mono-, di-, and tetra-meric phenyllithium aggregates was performed. The chemical shifts and quadrupolar coupling constants obtained are compared to the corresponding values in solution. There is a good agreement between the observed quadrupolar interaction in the solid state and in solution.

7Li Solid-state NMR spectroscopic study of aryllithium complexes: effects of aggregation and solvation

Seventeen aryllithium complexes were studied by 7Li solid‐state NMR spectroscopy. The solid structures of most of the complexes studied are known from x‐ray crystallography and include differently substituted aryllithium complexes in addition to some phenyllithium complexes. It is shown that the quadrupolar coupling constant, χ, is very sensitive to changes in aggregation and solvation. From the magnitude of χ, it is often possible to deduce the aggregation state and also obtain information about the solvation regarding the number and type of donor atoms coordinating the lithium cation. Copyright

Direct NMR spectroscopic evidence for solvated triorganostannyl cations

Abstract Solutions of tributyl- and triphenylstannyl perchlorates have been studied by NMR spectroscopy. Solvent-induced changes in 119 Sn, and 37 Cl line widths as well as SnC scalar couplings indicate the existence of an equilibrium between tetrahedral and trigonal bipyramidal arrangements. Bipyramidal forms are favoured if the solvent donicity is increased, including structures in which the solvent molecules occupy the two axial positions of the five-coordinate trigonal bipyramid. This situation is unequivocally demonstrated by the presence of 119 Sn 31 P coupling using hexamethylphosphoramide- d 18 as solvent.

Structural and physical properties of pressure polymerized C60

We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under t ...

Structural Studies of Fluorenyllithium Complexes Using7Li Solid-State NMR Spectroscopy

The effect on the solid‐state 7Li chemical shifts and quadrupolar coupling constants of different locations of the lithium cation relative to the carbanion framework of delocalized carbanions was investigated. When the lithium cation is situated above the conjugated system, the chemical shift is about ‐7 ppm as expected, and around ‐2 ppm otherwise. The quadrupolar coupling constant is very sensitive to changes in the lithium cation position and to changes in coordination. The value varies between 27 and 262 kHz. A combination of chemical shifts and quadrupolar coupling constants is necessary to retrieve the correct structural information.

Studies of phenyllithium complexes by 13C CP/MAS NMR spectroscopy

Abstract A 13 C CP/MAS study of mono-, di-, and tetrameric phenyllithium complexes was performed. The 13 C CP/MAS data can be used to correlate solution NMR data and X-ray structural data.