scholarly journals An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

2014 ◽  
Vol 10 ◽  
pp. 1620-1629 ◽  
Author(s):  
Carla I Nieto ◽  
Pilar Cabildo ◽  
M Ángeles García ◽  
Rosa M Claramunt ◽  
Ibon Alkorta ◽  
...  
Keyword(s):  
Experimental Study ◽  
Solid State ◽  
Proton Transfer ◽  
Chemical Shifts ◽  
Nmr Study

This paper reports the 1H, 13C and 15N NMR experimental study of five benzimidazoles in solution and in the solid state (13C and 15N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d 18.

Synthesis, X-ray crystal structure, and solid-state 13C NMR study of tris(9-crown-3)triphenylene

2001 ◽  
Vol 79 (2) ◽  
pp. 195-200 ◽  
Author(s):  
Gerald W Buchanan ◽  
Majid F Rastegar ◽  
Glenn PA Yap
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Crown Ether ◽  
Chemical Shifts ◽  
Aromatic Rings ◽  
X Ray ◽  
Nmr Study ◽  
Group A ◽  
C Nmr ◽  
Solid State 13C Nmr

Benzo-9-crown-3 ether trimerizes in the presence of FeCl3 and aqueous H2SO4 to produce tris(9-crown-3)triphenylene in 25.4% yield. This compound crystallizes in the monoclinic P21/c space group: a = 13.759(2) Å, b = 13.318(2) Å, c = 13.399(2) Å, β = 96.883(2)°, with Z = 4. The three 9-crown-3 ether units of the trimer possess different geometries and there is substantial deviation from coplanarity in the three aromatic rings. 13C NMR chemical shifts in the solid state are consistent with this lack of symmetry and are discussed in terms of the X-ray crystal-structure data.Key words: crown ether, trimerization, stereochemistry.

Proton transfer in rubazoic acid derivatives in solution and in the solid state. An NMR study

1993 ◽  
pp. 1597 ◽  
Author(s):  
Alejandro C. Olivieri ◽  
Dion�sia Sanz ◽  
Rosa Ma Claramunt ◽  
Jos� Elguero
Keyword(s):  
Solid State ◽  
Proton Transfer ◽  
Nmr Study

scholarly journals 14N, 13C, and 119Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Aleksander Jaworski ◽  
Jędrzej Piątek ◽  
Liuda Mereacre ◽  
Cordula Braun ◽  
Adam Slabon
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chemical Shifts ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Quadrupolar Coupling ◽  
Nmr Study ◽  
Nmr Characterization ◽  
Angle Spinning ◽  
High Level

Abstract We report the first magic-angle spinning (MAS) nuclear magnetic resonance (NMR) study on Sn(NCN). In this compound the spatially elongated (NCN)2− ion is assumed to develop two distinct forms: either cyanamide (N≡C–N2−) or carbodiimide (−N=C=N−). Our 14N MAS NMR results reveal that in Sn(NCN) the (NCN)2− groups exist exclusively in the form of symmetric carbodiimide ions with two equivalent nitrogen sites, which is in agreement with the X-ray diffraction data. The 14N quadrupolar coupling constant | C Q | $\vert {C}_{\text{Q}}\vert $  ≈ 1.1 MHz for the −N=C=N− ion in Sn(NCN) is low when compared to those observed in molecular compounds that comprise cyano-type N≡C– moieties ( | C Q | $\vert {C}_{\text{Q}}\vert $  > 3.5 MHz). This together with the information from 14N and 13C chemical shifts indicates that solid-state NMR is a powerful tool for providing atomic-level insights into anion species present in these compounds. The experimental NMR results are corroborated by high-level calculations with quantum chemistry methods.

ChemInform Abstract: Proton Transfer in Rubazoic Acid Derivatives in Solution and in the Solid State. An NMR Study.

ChemInform ◽  
2010 ◽  
Vol 24 (51) ◽  
pp. no-no
Author(s):  
A. C. OLIVIERI ◽  
D. SANZ ◽  
R. M. CLARAMUNT ◽  
J. ELGUERO
Keyword(s):  
Solid State ◽  
Proton Transfer ◽  
Nmr Study

A solid-state 17O NMR study of platinum-carboxylate complexes: carboplatin and oxaliplatin

2015 ◽  
Vol 93 (9) ◽  
pp. 945-953 ◽  
Author(s):  
Xianqi Kong ◽  
Victor Terskikh ◽  
Abouzar Toubaei ◽  
Gang Wu
Keyword(s):  
Solid State ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Carboxylate Oxygen ◽  
Carboxylate Groups ◽  
Nmr Study ◽  
Nmr Characterization ◽  
Orbital Electron ◽  
Isotropic Chemical Shifts ◽  
Oxygen Atoms

We report synthesis and solid-state NMR characterization of two 17O-labeled platinum anticancer drugs: cis-diammine(1,1-cyclobutane-[17O4]dicarboxylato)platinum(II) (carboplatin) and ([17O4]oxalato)[(1R, 2R)-(−)-1,2-cyclohexanediamine)]platinum(II) (oxaliplatin). Both 17O chemical shift (CS) and quadrupolar coupling (QC) tensors were measured for the carboxylate groups in these two compounds. With the aid of plane wave DFT computations, the 17O CS and QC tensor orientations were determined in the molecular frame of reference. Significant changes in the 17O CS and QC tensors were observed for the carboxylate oxygen atom upon its coordination to Pt(II). In particular, the 17O isotropic chemical shifts for the oxygen atoms directly bonded to Pt(II) are found to be smaller (more shielded) by 200 ppm than those for the non-Pt-coordinated oxygen atoms within the same carboxylate group. Examination of the 17O CS tensor components reveals that such a large 17O coordination shift is primarily due to the shielding increase along the direction that is within the O=C–O–Pt plane and perpendicular to the O–Pt bond. This result is interpreted as due to the σ donation from the oxygen nonbonding orbital (electron lone pair) to the Pt(II) empty dyz orbital, which results in large energy gaps between σ(Pt–O) and unoccupied molecular orbitals, thus reducing the paramagnetic shielding contribution along the direction perpendicular to the O–Pt bond. We found that the 17O QC tensor of the carboxylate oxygen is also sensitive to Pt(II) coordination, and that 17O CS and QC tensors provide complementary information about the O–Pt bonding.

scholarly journals Deuterium Isotope Effects on 14,15N Chemical Shifts of Ammonium Ions: A Solid State NMR Study

2011 ◽  
Vol 2011 ◽  
pp. 1-4
Author(s):  
Poul Erik Hansen
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Natural Abundance ◽  
Ammonium Ions ◽  
Fast Rotation ◽  
Nmr Study ◽  
Ammonium Halides ◽  
Deuterium Isotope Effects

Deuterium isotope effects on N14,15 chemical shifts are measured in ammonium halides in the solid state using both enriched N15 salts and N14 natural abundance materials. The effects are correlated to N15 chemical shifts and to N···X distances. The deuterium isotope effects on N14,15 chemical shifts in the solid state are discussed in relation to effects observed in solution. No NH couplings are seen due to fast rotation in the solid, which leads to self-decoupling, whereas ND couplings are present.

Revisiting B20H16 by means of a joint computational/experimental NMR approach

2010 ◽  
Vol 75 (11) ◽  
pp. 1115-1123 ◽  
Author(s):  
Drahomír Hnyk ◽  
Josef Holub ◽  
Tomáš Jelínek ◽  
Jan Macháček ◽  
Michael G. S. Londesborough
Keyword(s):  
Solid State ◽  
Chemical Shifts ◽  
Molecular Geometry ◽  
Basis Set ◽  
State Structure ◽  
Solid State Structure ◽  
Boron Cluster ◽  
Nmr Study ◽  
New Synthesis ◽  
Good Agreement

A new synthesis of the fused macropolyhedral boron cluster B20H16 is described and its molecular structure in solution discussed, based on multi-nuclear NMR spectra, including COSY measurements, in relation to its previously elucidated solid-state structure. To verify the conclusions from the NMR study, experimentally determined chemical shifts are compared with calculated values at the GIAO-B3LYP level with a TZP basis set by Huzinaga. There is a very good agreement between the experimental and computed δ(11B) values, suggesting that the MP2/6-31G* internal coordinates are a reasonable representation of the molecular geometry of this twenty-vertex cluster in solution that is essentially the same as its solid-state structure. A computational analysis of the FMO orbitals of B20H16, in particular of the LUMO, reveals that the four naked boron atoms, common for two shared icosahedral subclusters, are the reactive sites of this D2d-symmetrical molecule.

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