scholarly journals Solid state NMR study of 1,3imidazolidine-2-thione, 1,3-imidazolidine-2-selenone and some of their N-substituted derivatives

2004 ◽  
Vol 18 (1) ◽  
pp. 113-119 ◽  
Author(s):  
Mohamed I. M. Wazeer ◽  
Anvarhusein A. Isab ◽  
Ali El-Rayyes
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Solid State Nmr ◽  
Nmr Spectra ◽  
Methyl Derivative ◽  
Nmr Spectrum ◽  
Nmr Study ◽  
Molecular Computations

Solid‒state NMR spectra were recorded for 1,3-imidazolidine-2-thione, 1,3-imidazolidine-2-selenone and some of their N-substituted derivatives. Spinning side-bands of thione and selenone carbons were analysed to yield chemical shift anisotropies for these carbons. The NMR spectrum of imidazolidine-2-thione (Imt) showed some evidence for the presence of thiol tautomer. Molecular computations were carried out for Imt and its N-methyl derivative to yield relative energies of various tautomers.

scholarly journals Linear dicoordinate beryllium: a 9Be solid-state NMR study of a discrete zero-valent s-block beryllium complex

2018 ◽  
Vol 96 (7) ◽  
pp. 646-652 ◽  
Author(s):  
C. Leroy ◽  
J.K. Schuster ◽  
T. Schaefer ◽  
K. Müller-Buschbaum ◽  
H. Braunschweig ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Chemical Shift ◽  
Solid State Nmr ◽  
Chemical Shift Tensor ◽  
X Ray Diffraction ◽  
X Ray ◽  
Quadrupolar Coupling ◽  
Nmr Study ◽  
Tensor Data

Beryllium-9 (9Be) quadrupolar coupling and chemical shift tensor data are reported for bis(1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidine-2-ylidene)beryllium (Be(CAAC)2). These are the first such data for beryllium in a linear dicoordinate environment. The 9Be quadrupolar coupling constant, 2.36(0.02) MHz, is the largest recorded in the solid state to date for this isotope. The span of the beryllium chemical shift tensor, 22(2) ppm, covers about half of the known 9Be chemical shift range, and the isotropic 9Be chemical shift, 32.0(0.3) ppm, is the largest reported in the solid state to our knowledge. DFT calculations reproduce the experimental data well. A natural localized molecular orbital approach has been used to explain the origins and orientation of the beryllium electric field gradient tensor. The single-crystal X-ray structure of a second polymorph of Be(CAAC)2 is also reported. Inspection of the powder X-ray diffraction data shows that the new crystal structure is part of the bulk product next to another crystalline phase. Therefore, experimental X-ray powder data for the microcrystalline powder sample and the SSNMR data do not fully match either the originally reported crystal structure (Arrowsmith et al. Nat. Chem. 2016, 8, 890–894) or the new polymorph. The ability of solid-state NMR and powder X-ray diffraction to characterize powdered samples was thus particularly useful in this work.

Cobalt-59 chemical shift and quadrupolar tensors of simple octahedral cobalt(III) complexes

2001 ◽  
Vol 79 (3) ◽  
pp. 296-303
Author(s):  
Christopher W Kirby ◽  
William P Power
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Principal Components ◽  
Solid State Nmr ◽  
Nmr Spectra ◽  
Line Shapes ◽  
Quadrupolar Coupling ◽  
Molecular Frame ◽  
Specific Ligand

Analysis of the solid-state powder 59Co NMR spectra of ten simple inorganic cobalt(III) complexes at 11.75, and in most cases, 4.7 T have permitted the assignment of specific ligand planes to ranges of values of the observed chemical shift principal components. The relevant chemical shift components were determined from the simulations of the powder line shapes. These simulations also provided the relative orientations of the chemical shift (CS) and electric field gradient (efg) tensors, as well as magnitude and asymmetry of the 59Co quadrupolar coupling. Using symmetry arguments and ab initio calculations, as appropriate or necessary, the orientations of the efg tensors in the molecular frame were deduced. This allowed the determination of the CS tensors in the molecular frame and thus assignment of the ligand planes responsible for the observed values of chemical shifts.Key words: cobalt, chemical shift, quadrupolar coupling, solid state NMR.

scholarly journals A phosphorus-31 NMR study of solid carbonylhydridotris(triphenylphosphine)rhodium(I). Unusual MAS sideband intensities in second-order NMR spin systems

1992 ◽  
Vol 70 (3) ◽  
pp. 863-869 ◽  
Author(s):  
Gang Wu ◽  
Roderick E. Wasylishen ◽  
Ronald D. Curtis
Keyword(s):  
Chemical Shift ◽  
Spin System ◽  
Principal Components ◽  
Nmr Spectra ◽  
Magic Angle Spinning ◽  
Chemical Shift Tensor ◽  
Magic Angle ◽  
Nmr Spectrum ◽  
Chemical Shift Tensors ◽  
Nmr Study

The CP/MAS 31P NMR spectrum of carbonylhydridotris(triphenylphosphine)rhodium(I), RhH(CO)(PPh3)3 (1), can be described as a tightly coupled ABMX spin system (X = 103Rh). In contrast to the solution 31P NMR spectrum, the three equatorial phosphorus nuclei are nonequivalent in the solid state and this structural feature allows us to measure the two-bond spin–spin couplings, 2J(31P,31P). A new method is proposed for extracting the principal components of the chemical shift tensor from slow MAS NMR spectra in a tightly J-coupled two-spin system. For compound 1, the principal components of the 31P chemical shift tensors calculated using this method are in good agreement with those obtained from NMR spectra of a static sample. The principal components of the 31P chemical shift tensors determined for 1 are compared with those reported previously for Wilkinson's catalyst, RhCl(PPh3)3. The δ22 component of the 31P chemical shift tensors in 1 shows the largest variation with structure. This is ascribed to differences in the orientation of the P—Cipso bond about the equatorial plane of the trigonal bipyramidal structure. Keywords: rhodium–phosphine compounds, AB spin system, 31P chemical shift tensor, magic-angle spinning, molecular structure.

A solid-state NMR investigation of orexin-B

2004 ◽  
Vol 82 (10) ◽  
pp. 1554-1563 ◽  
Author(s):  
Guy M Bernard ◽  
Mark Miskolzie ◽  
George Kotovych ◽  
Roderick E Wasylishen
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Solid State Nmr ◽  
Dipolar Coupling ◽  
Double Resonance ◽  
Solution Nmr ◽  
Carbonyl Carbon ◽  
Distance Measurements ◽  
Nmr Study ◽  
Amide Carbonyl

Some key aspects of the secondary structure of solid orexin-B, a 28 amino-acid peptide, have been investigated by solid-state NMR spectroscopy. The 13C–15N dipolar coupling between the carbonyl carbon of Leu11 and the nitrogen of Leu15, as determined by rotational echo double resonance (REDOR) experiments, is 35 Hz, indicating that these nuclei are separated by approximately 4.5 Å. This distance is consistent with the α-helical structure determined for this segment of orexin-B by solution NMR measurements. REDOR measurements of the dipolar coupling between the carbonyl carbon of Ala17 and the nitrogen of Ala22 support the contention in an earlier solution NMR study that a bend exists between the two α helices of orexin-B. However, in the solid state the internuclear distance (6.4 Å) is significantly greater than that observed for orexin-B in aqueous solution. In addition to the distance measurements, the principal components of the amide carbonyl carbon chemical shift (CS) tensors for Leu11 and Ala17 and of the amide nitrogen CS tensors for Leu15 and Ala22 are reported. There are only minor differences between the amide carbonyl carbon CS tensors for Leu11 and Ala17 and between the nitrogen CS tensors for Leu15 and Ala22.Key words: orexin-B, solid-state NMR, REDOR, chemical shift tensors.

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