NMR studies of 1-phenylazo-3-substituted-2-naphthols in solution and in the solid state

1990 ◽  
Vol 55 (1) ◽  
pp. 193-201 ◽  
Author(s):  
Antonín Lyčka ◽  
Miroslav Nečas ◽  
Josef Jirman ◽  
Jaroslav Straka ◽  
Bohdan Schneider
Keyword(s):  
Hydrogen Bond ◽  
Solid State ◽  
Nmr Spectra ◽  
Equilibrium Mixture ◽  
Mas Nmr ◽  
Nmr Studies ◽  
Nmr Spectrum ◽  
Cp Mas Nmr ◽  
Hydrazone Form

The 1H and 15Nα-enriched 1-phenylazo-3-X-2-naphthols, where X = COOH (I), X = COOCH3 (II), and X = CONHC6H5 (III), have been measured in various solvents. The values of 1J(15Nα, H) and σ(15N) indicate that in CDCl3, C6D6, CCl4, and CD3NO2 solutions the compounds I and III exist practically completely in their hydrazone forms. The hydrazone form is stabilized by the hydrogen bond of COOH or CONH protons to the C(2)=O group. The compound II represents an equilibrium mixture of azo and hydrazone forms, since it cannot form a similar hydrogen bond. Moreover, the 15N NMR spectra of compounds I-III have been measured in solid state by the CP/MAS technique. The results indicate the existence of two conformers differing by the conformation of COOCH3 group in compound II, which is supported by the 13C CP/MAS NMR spectrum of compound II.

Molecular Structure of Tri(2-thienyl)borane

1996 ◽  
Vol 51 (12) ◽  
pp. 1811-1814 ◽  
Author(s):  
Bernd Wrackmeyer ◽  
Wolfgang Milius ◽  
Elias Molla
Keyword(s):  
Molecular Structure ◽  
Solid State ◽  
Nmr Spectra ◽  
Structural Parameters ◽  
Mas Nmr ◽  
Monoclinic Space Group ◽  
Nmr Spectrum ◽  
Π Interactions ◽  
Cp Mas Nmr ◽  
C Nmr

The molecular structure of tri(2-thienyl)borane (1) was determined [monoclinic, space group P21/ c; a = 12.216(2), b = 7.765(2), c = 12.605(2) Å, β = 93.13(2)°]; two of the three thienyl groups are disordered, as is also indicated by the solid-state 13C CP/MAS NMR spectrum of 1. The 13C NMR spectra of 1 were measured at variable tem perature in solution and the barrier to rotation about the B-C bonds was found to be <35 kJ/mol. Thus, CB(pp)π interactions must be regarded as rather weak, in spite of suggestive δ11 B. δ13C data and structural parameters.

13C solid state CP/MAS NMR studies of EDTA complexes

1987 ◽  
Vol 129 (2) ◽  
pp. L23-L25 ◽  
Author(s):  
Silvio Aime ◽  
Roberto Gobetto ◽  
Rita Nano ◽  
Enrica Santucci
Keyword(s):  
Solid State ◽  
Mas Nmr ◽  
Nmr Studies ◽  
Edta Complexes ◽  
Cp Mas Nmr

Multinuclear Solid-State MAS/CP-MAS NMR Studies of Promoter (Phosphate)-Enhanced Crystallization of Siliceous MCM-41

2003 ◽  
Vol 107 (51) ◽  
pp. 14171-14175 ◽  
Author(s):  
S. C. Laha ◽  
M. D. Kadgaonkar ◽  
A. Anuji ◽  
S. Ganapathy ◽  
J. P. Amoureux ◽  
...  
Keyword(s):  
Solid State ◽  
Mas Nmr ◽  
Nmr Studies ◽  
Cp Mas Nmr ◽  
Mcm 41

scholarly journals 13C CPMAS NMR as a Tool for Full Structural Description of 2-Phenyl Substituted Imidazoles That Overcomes the Effects of Fast Tautomerization

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3770
Author(s):  
Nikola Burdzhiev ◽  
Anife Ahmedova ◽  
Boris Borrisov ◽  
Robert Graf
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Spectroscopic Method ◽  
Mas Nmr ◽  
Structural Description ◽  
Tautomeric Forms ◽  
Cp Mas Nmr ◽  
13C Cp Mas Nmr

Tautomerization of 2-phenylimidazolecarbaldehydes has not been studied in detail so far, although this process is a well-known phenomenon for imidazole derivatives. That is why we focus our study on a series of 2-phenylimidazolecarbaldehydes and their parent alcohols that were synthesized and studied by detailed 1H and 13C NMR in solution and in the solid state. The apparent problem is that the fast tautomerization impedes the full structural description of the compounds by conventional 13C NMR measurements. Indeed, the 13C NMR spectra in solution exhibit poor resolution, and in most cases, signals from the imidazole ring are not detectable. To avoid this problem, we used 13C CP-MAS NMR as an alternative spectroscopic method for unambiguous spectroscopic characterization of the studied series of 2-phenylimidazoles. The data were analyzed in combination with quantum chemical DFT-GIAO methods by considering the tautomerization process and the intermolecular interactions. The DFT (B3LYP/6-31G(d,p)) calculations allowed to identify and suggest the preferred tautomer in the gas phase and in DMSO solvent, which for alcohols are (2-phenyl-1H-imidazol-4-yl)methanol and its analogs, and for the aldehydes are the 2-phenyl-1H-imidazole-5-carbaldehydes. The gas-phase calculated energy differences between the two possible tautomeric forms are in the range 0.645–1.415 kcal/mol for the alcohols and 2.510–3.059 kcal/mol for the aldehydes. In the DMSO solvent, however, for all compounds, the calculated energy differences go below 1.20 kcal/mol. These data suggest that both tautomeric forms of the studied 2-phenylimidazoles can be present in solution at room temperature. Our data from detailed 2D NMR measurements in the solid state (1H-13C HETCOR and 1H-1H double-quantum coherence MAS NMR) suggested that also in the solid state both tautomers coexist in different crystalline domains. This fact does not obscure the 13C CP-MAS NMR spectra of the studied 2-phenyl substituted imidazoles and suggests this spectroscopic method as a powerful tool for a complete structural description of tautomeric systems with aromatic conjugation.

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