Halogen substituted adamantanones. Structural studies with lanthanide shift reagents

1988 ◽  
Vol 53 (1) ◽  
pp. 97-109 ◽  
Author(s):  
Milan Hájek ◽  
Alena Horská ◽  
Petr Trška ◽  
Luděk Vodička ◽  
Douglas J. Raber ◽  
...  
Keyword(s):  
Bond Length ◽  
Optimization Procedure ◽  
Step Size ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Empirical Force Field ◽  
Lanthanide Shift Reagents ◽  
Shift Reagents ◽  
Empirical Force Field Calculations

Europium shift reagents (both FOD and DPM) have been used to study a series of halogen substituted adamantanones by 1H NMR spectroscopy. Reliable correlations of molecular structure with the lanthanide induced shifts can be obtained only if certain precautions are taken. The source of atomic coordinates used to predict induced shifts with the pseudocontact equation is critical; coordinates by X-ray crystallography can be unreliable for this purpose, while those from empirical force field calculations yield satisfactory results. Determination of the europium-oxygen bond length by optimization of the agreement factor is shown to be inadequate. Even with a restricted Eu-O bond length, calculation of the best lanthanide position is shown to be dependent on the step size by which the lanthanide is moved in the optimization procedure. All of the compounds studied were found to give complexes with approximately linear C-O-Eu arrays, and the distortions from linearity are consistent with steric effects.

The conformational equilibrium of N,N'-bis[(S)-1-phenylethyl]-thiourea and its solvent dependence, studied by NMR and CD spectra and by X-ray crystallography

1998 ◽  
Vol 76 (6) ◽  
pp. 811-820 ◽  
Author(s):  
Knut Rang ◽  
Jan Sandström ◽  
Christer Svensson
Keyword(s):  
Force Field ◽  
Experimental Studies ◽  
Cd Spectroscopy ◽  
Force Field Calculations ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Nonpolar Solvents ◽  
Solvent Dependence ◽  
Empirical Force Field ◽  
Empirical Force Field Calculations

Favoured conformations of N,N'-bis[(S)-1-phenylethyl]thiourea (1) have been predicted by empirical force-field calculations, and the corresponding rotational strengths for the important transitions in the near UV region have been calculated. Experimental studies by 1H NMR, IR, UV, and CD spectroscopy have permitted the assignment of a conformation denoted E,Za to the conformer, which dominates in nonpolar solvents, while hydroxylic solvents were found to favour conformations of Z,Za type. The E,Za conformer is also predicted by force-field calculations to be the most stable one.Key words: circular dichroism, conformation, crystal structure, dynamic NMR spectroscopy, N,N'-bis[(S)-1-phenylethyl]thiourea.

Use of lanthanide shift reagents for the determination of the alkyl conformation in 2-alkyl-2-adamantanols

1977 ◽  
Vol 10 (1) ◽  
pp. 52-55 ◽  
Author(s):  
M. Hájek ◽  
P. Trška ◽  
L. Vodička ◽  
J. Hlavatý
Keyword(s):  
Lanthanide Shift Reagents ◽  
Shift Reagents

1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Part II: Ethosuximide, 3-Ethyl-3-Methyl-2,5-Pyrrolidinedione, and Comparisons with Analogs

1986 ◽  
Vol 40 (4) ◽  
pp. 531-537 ◽  
Author(s):  
John Avolio ◽  
Suzanne Thomson Eberhart ◽  
Robert Rothchild ◽  
Paul Simons
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Shift Reagent ◽  
Ethyl Group ◽  
Molar Ratios ◽  
H Nmr ◽  
Lanthanide Shift Reagents ◽  
Shift Reagents

The 60 MHz 1H NMR spectra of racemic ethosuximide, 1, have been studied in detail with the achiral shift reagent, tris(6,6,7,7,8,8,8-hepta-fiuoro-2,2-dimethyl-3,5-octanedionato)europium(III), 2, and the chiral tris(3-trifluoromethylhydroxymethylene)- d-camphorato]europium(III), 3. Enantiomeric shift differences, ΔΔδ, were clearly observed for the CH3 of the ethyl group of 1 at molar ratios of 3:1 as low as 0.0385, with ΔΔδ valaues of about 12 Hz seen at a 3:1 ratio of 0.340 for CDCl3 solutions at 28°, 0.634 molal in 1. Smaller ΔΔδ values were also seen for the quaternary methyl and for one of the hydrogens at C-4. Parallel studies with 2 were performed to support assignments. Results are compared with a group of important drugs that are structurally related, including ethotoin, mephenytoin, glutethimide, methsuximide, phensuximide, and paramethadione, in terms of steric and basicity effects. Correlations of both lanthanide-induced shift (Δδ) and ΔΔδ could generally be made from simple electronic considerations related to infrared carbonyl stretching frequencies. Of the 28 sets of Δδ values assigned for the substrates, 3 gave significantly larger values than 2 in only two cases.

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