The NMR spectra of cyclic nitrones. 3. Effect of protonation and a hydrogen bond on the chemical shifts in the13c NMR spectra of derivatives of 3-imidazoline 3-oxide

1986 ◽  
Vol 22 (8) ◽  
pp. 861-868 ◽  
Author(s):  
I. A. Grigor'ev ◽  
V. I. Mamatyuk ◽  
G. I. Shchukin ◽  
V. V. Martin ◽  
L. B. Volodarskii
Keyword(s):  
Hydrogen Bond ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Cyclic Nitrones ◽  
Derivatives Of

Routine use of inept technique for measurements of 29Si NMR spectra of trimethylsilyl derivatives

1983 ◽  
Vol 48 (12) ◽  
pp. 3402-3406 ◽  
Author(s):  
Jan Schraml
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
29Si Nmr ◽  
Practical Applications ◽  
Unknown Structure ◽  
29Si Nmr Spectra ◽  
Standard Set ◽  
Trimethylsilyl Derivatives ◽  
Low Sensitivity ◽  
Derivatives Of

Low sensitivity of 29Si NMR, slow 29Si relaxation, and negative Overhauser effect severly limit practical applications of 29Si NMR. The need for the large amount of the sample or of spectrometer time is dramatically reduced if the spectra can be recorded by INEPT technique. It is shown that a standard set of acquisition parameters allows routine measurements of proton decoupled 29Si NMR spectra by INEPT technique in trimethylsilyl derivatives of organic compounds with unknown structure. The INEPT technique makes measurements of 29Si chemical shifts from as litle as 20μmol of compound practical.

Silicon-29 NMR Spectra of Trimethylsilylated Alcohols

1997 ◽  
Vol 62 (5) ◽  
pp. 816-820 ◽  
Author(s):  
Magdalena Kvíčalová ◽  
Jan Čermák ◽  
Vratislav Blechta ◽  
Jan Schraml
Keyword(s):  
Chemical Shift ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Steric Effects ◽  
Almost All ◽  
Derivatives Of ◽  
Related Compounds ◽  
Tms Derivatives

29Si NMR spectra of trimethylsilyl (TMS) derivatives of 26 simple alcohols were measured under standardized conditions (i.e., in sufficiently diluted deuteriochloroform solutions). Due to association with the solvent the chemical shifts are in almost all cases larger than those reported earlier for different solutions. This observation is in agreement with the proposed mechanism of steric effects as being due to sterically controlled association with the solvent. The use of chloroform as a solvent enhances steric effects but at the same time it can reduce small differences due to polar effects in closely related compounds. In the studied class of compounds the gross dependence of the chemical shift on polar effects is not substantially affected by the change of the solvent.

Assignment of the Absolute Configuration of Polyfunctional Compounds

2015 ◽  
Author(s):  
Josi M. Seco ◽  
Emilio Quiqoa ◽  
Ricardo Riguera
Keyword(s):  
Absolute Configuration ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Single Step ◽  
Point Of View ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Polyfunctional Compounds ◽  
The Absolute ◽  
Derivatives Of

From a practical point of view, the assignment of the absolute configuration of sec/sec 1,2- and 1,n-diols does not require the separate derivatization (two different steps with the CDA of choice) of each one of the two hydroxyl groups present in the substrate; on the contrary, it can be carried out by simultaneous derivatization of the two hydroxyls (a single step), leading to the corresponding bis-(R)- and bis-(S)-CDA esters [13, 59–61]. The most used CDAs are 9-AMA and MPA [59, 60], although 1-NMA, 2-NMA, and MTPA are also appropriate [59, 60]. This assignment has an important difference compared to that of monofunctionalized compounds [15]; this is due to the presence in the bis-(R)- and bis-(S)-derivatives of two CDA units that produce distributions of ΔδRS and ΔδSR signs that do not follow the trends found in monoderivatized compounds [13, 15, 82]. This means that the NMR spectra of the bis-CDA derivatives cannot be interpreted as if they had originated from two isolated mono-CDA derivatives [82]. Thus, the correlations described for secondary alcohols [35–39] cannot be applied to diols [59–61] because the chemical shifts and ΔδRS values result from the combination of the anisotropic effects—usually shielding—from the two CDA units and not from a single unit, as happens with monoalcohols. A result of the combination of aromatic shielding effects [59, 60] in diols is that the diagnostic protons/signals for assignment are not always the same as in isolated monoalcohols (i.e., L1/L2). For instance, in acyclic syn-1,2-diols, the diagnostic signals [59, 60] are those corresponding to the protons at the alpha positions of the OH groups (i.e., the hydrogens linked directly to the asymmetric carbons) Hα(R1) and Hα(R2) exclusively. On the other hand, in acyclic anti-1,2-diols, the diagnostic signals are from Hα(R1)/Hα(R2) together with those from R1 and R2. As in the case of monofunctional compounds, the assignment consists [13, 59, 60] in the preparation of two bis-CDA derivatives from the two enantiomers of the chosen CDA, followed by comparison of the corresponding NMR spectra and calculation of the ΔδRS (or ΔδSR in the case of MTPA) signs for Hα(R1), R1, Hα(R2), and R2.

Silicon-29 NMR Spectra of tert-Butyldimethylsilyl and Trimethylsilyl Derivatives of Some Non-Rigid Diols

1997 ◽  
Vol 62 (5) ◽  
pp. 761-768 ◽  
Author(s):  
Magdalena Kvíčalová ◽  
Vratislav Blechta ◽  
Krzysztof Kobylczyk ◽  
Ryszard Piekos ◽  
Jan Schraml
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Independent Study ◽  
Bulky Substituent ◽  
New Correlation ◽  
Proton Donors ◽  
Experimental Errors ◽  
Trimethylsilyl Derivatives ◽  
Intramolecular Hydrogen ◽  
Derivatives Of

29Si NMR spectra of trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBDMS) derivatives of selected diols were measured under standardized conditions (i.e., in diluted CDCl3 solutions). Application of the recently reported correlation between the chemical shifts in TMS and TBDMS derivatives revealed considerable and systematic deviations which exceeded experimental errors and error estimates from the correlation. Two possible explanations of the deviations are considered: interaction between the two bulky substituent groups and invalidity of the reported correlation for simple hydroxy derivatives. An independent study of analogous derivatives of monohydroxy compounds has shown that the linear correlation holds but the slope and intercept are significantly different from those reported previously on the basis of a study of amino acid derivatives. The data obtained for the diol derivatives fit the new correlation very well and no indication of an interaction between the bulky TBDMS groups was noticed. However, deviations do occur in branched diol derivatives in which branching reduces accessibility of the oxygen atoms surface to associate with proton donors. The largest deviation was found when intramolecular hydrogen bond was formed.

29Si (and 13C) NMR spectra of modified silatranyl derivatives of some monosaccharides

1984 ◽  
Vol 49 (12) ◽  
pp. 2897-2902 ◽  
Author(s):  
Jan Schraml ◽  
Aleksandr Mikhailovich Krapivin ◽  
Aleksandr Petrovich Luzin ◽  
Vladimir Mikhailovich Kilesso ◽  
Vadim Aleksandrovich Pestunovich
Keyword(s):  
Molecular Structure ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Distinct Advantage ◽  
13C Nmr Spectra ◽  
Limited Data ◽  
Structural Sensitivity ◽  
Trimethylsilyl Derivatives ◽  
Derivatives Of ◽  
C Nmr

29Si (and 13C) NMR chemical shifts are reported for several 2-carba-3-oxahomosilatranyl (3,9,10-trioxa-6-aza-1-silabicyclo[3.3.4]dodecane-1-yl) and silatranyl (2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecane-1-yl) derivatives of some monosaccharides and other alcohols. The limited data suggest somewhat larger sensitivity of the silicon chemical shifts to molecular structure in 2-carba-3-oxahomosilatranyl derivatives than in silatranyl derivatives. In comparison with trimethylsilyl derivatives homosilatranyl derivatives show lower structural sensitivity of the silicon chemical shift. In some cases, however, larger stability of the silatranyl or 2-carba-3-oxahomosilatranyl derivatives than that of trimethylsilyl derivatives might be a distinct advantage.

Preparation of β-D-Glucopyranosyl Derivatives of 1,6:2,3- and 1,6:3,4-Dianhydro-β-D-hexopyranoses and Their 1H and 13C NMR Spectra

1995 ◽  
Vol 60 (2) ◽  
pp. 311-323 ◽  
Author(s):  
Miloš Buděšínský ◽  
Miloslav Černý ◽  
Ivan Černý ◽  
Stanislav Sámek ◽  
Tomáš Trnka
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
13C Nmr Spectra ◽  
1H And 13C Nmr ◽  
Derivatives Of ◽  
C Nmr

The corresponding acetylated and free 2-O- and 4-O-glucosyl derivatives of dianhydrohexoses Ib - VIIb and Ic - VIIc have been obtained by the reactions of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (IX) with 1,6:3,4- and 1,6:2,3-dianhydro-β-D-hexopyranoses (Ia - VIIa). Structure of the products and the effects of glycosylation upon chemical shifts and conformations of the disaccharides prepared have been studied using 1H and 13C NMR spectra.

Two single-enantiomer amidophosphoesters: a database study on the chirality of (O)2P(O)(N)-based structures

2019 ◽  
Vol 75 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Fahimeh Sabbaghi ◽  
Mehrdad Pourayoubi ◽  
Marek Nečas ◽  
Krishnan Damodaran
Keyword(s):  
Hydrogen Bond ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Two Dimensional ◽  
One Dimensional ◽  
Space Groups ◽  
Structural Database ◽  
Graph Set ◽  
Hydrogen Bonded

The crystal structures of two single-enantiomer amidophosphoesters with an (O)2P(O)(N) skeleton, i.e. diphenyl [(R)-(+)-α-methylbenzylamido]phosphate, (I), and diphenyl [(S)-(−)-α-methylbenzylamido]phosphate, (II), both C20H20NO3P, are reported. In both structures, chiral one-dimensional hydrogen-bonded architectures, along [010], are mediated by N—H...OP interactions. The statistically identical assemblies include the noncentrosymmetric graph-set motif C(4) and the compounds crystallize in the chiral space group P21. As a result of synergistic co-operation from C—H...O interactions, a two-dimensional superstructure is built including a noncentrosymmetric R 4 4(22) hydrogen-bonded motif. A Cambridge Structural Database survey was performed on (O)2P(O)(N)-based structures in order to review the frequency of space groups observed in this family of compounds; the hydrogen-bond motifs in structures with chiral space groups and the types of groups inducing chirality are discussed. The 2,3 JX –P (X = H or C) coupling constants from the NMR spectra of (I) and (II) have been studied. In each compound, the two diastereotopic C6H5O groups are different, which is reflected in the different chemical shifts and some coupling constants.

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