29Si NMR chemical shifts in pertrimethylsilylated 1,6-anhydro-β-D-glucopyranose derivatives. Empirical assignment from Hammett type dependence of the chemical shifts

1983 ◽  
Vol 48 (9) ◽  
pp. 2503-2508 ◽  
Author(s):  
Jan Schraml ◽  
Jaroslav Včelák ◽  
Miloslav Černý ◽  
Václav Chvalovský
Keyword(s):  
Chemical Shift ◽  
Carbon Atom ◽  
Silicon Atom ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Polar Effect ◽  
29Si Nmr ◽  
Nmr Chemical Shifts ◽  
Trimethylsilyl Groups

29Si chemical shift of Si-3 silicon atom of the trimethylsiloxy group attached to C(3) carbon atom in 1,6-anhydro-β-D-glucopyranose derivatives correlates linearly with the sum of Taft polar constants σσ of substituents R2 and R4 on C(2) and C(4) carbon atoms. Quality of this correlation allows assignment of Si-3 line in the spectra of derivatives containing two or three trimethylsilyl groups in the molecule. The shielding order δ(Si-4) < δ(Si-3) found in 1,6-anhydro-2,3,4-O-tris(trimethylsilyl)-β-D-glucopyranose is the same as recently found in other pyranose derivatives with the same configuration of substituents but the order is reversed by strong polar effect of the substituent in 1,6-anhydro-2-O-p-toluenesulphonyl-3,4-O-bis(trimethylsilyl)-β-D-glucopyranose. This finding warns against indiscriminate use of empirical assignment rules based on simple shielding order without considering possible substituent effects.

Origin of the 29Si NMR chemical shift in R3Si–X and relationship to the formation of silylium (R3Si+) ions

2020 ◽  
Vol 49 (45) ◽  
pp. 16453-16463 ◽  
Author(s):  
Winn Huynh ◽  
Matthew P. Conley
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
29Si Nmr ◽  
Surface Oxygen ◽  
Nmr Chemical Shift ◽  
Dft Methods ◽  
Nmr Chemical Shifts

The origin in deshielding of 29Si NMR chemical shifts in R3Si–X, where X = H, OMe, Cl, OTf, [CH6B11X6], toluene, and OX (OX = surface oxygen), as well as iPr3Si+ and Mes3Si+ were studied using DFT methods.

scholarly journals Is hydrogen electronegativity higher than Pauling’s value? New clues from the 13C and 29Si NMR chemical shifts of [CHF3] and [SiHF3] molecules

2019 ◽  
Vol 91 (10) ◽  
pp. 1679-1686
Author(s):  
Michele Benedetti ◽  
Federica De Castro ◽  
Antonella Ciccarese ◽  
Francesco Paolo Fanizzi
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
29Si Nmr ◽  
Nmr Chemical Shift ◽  
Nmr Chemical Shifts

Abstract We previously demonstrated that the δ NMR chemical shift of central NMR active atoms (A), in simple halido [AXn] (A=C, Si, Ge, Sn, Pb, Pt; Xn = combination of n halides, n = 4 or 6) derivatives, could be directly related to X radii overall sum, Σ(rL). Further correlation have also been observed for tetrahedral [AX4] (A=C, Si; X4 = combination of four halides) compounds where the X Pauling electronegativities sum, $\Sigma (\chi _L^{{\rm{Pau}}}),$ exceeds a specific value (≈12.4). In this work, we focused on these latter systems considering the H vs. X substitution. The analysis of the literature reported δ(13C) and δ(29Si) NMR chemical shift for the mono hydrogenated derivatives and in particular for [CHF3] and [SiHF3], characterized by the lowest Σ(rL) and the highest $\Sigma (\chi _L^{{\rm{Pau}}}),$ suggests a revised value for the H electronegativity ranking with respect to Pauling’s.

NMR spectra (13C and 29Si) as a probe into the electronic structure of cyclopropylsilanes

1983 ◽  
Vol 48 (12) ◽  
pp. 3396-3401 ◽  
Author(s):  
Jan Schraml ◽  
Micheline Grignon-dubois ◽  
Jacques Dunoguès ◽  
Harald Jancke ◽  
Günter Engelhardt ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Silicon Atom ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Cyclopropane Ring ◽  
Substituent Effects ◽  
Nmr Chemical Shifts ◽  
Back Bonding ◽  
C Nmr

29Si and 13C NMR chemical shifts are reported for cyclopropyl derivatives with the structure (CH3)3-nRnSiC3H5 where R = OSi(CH3)3 and OCH3. He carbon chemical shifts show substituent effects which are intermediate between those found in the corresponding vinyl and ethyl silanes. The 29Si chemical shifts, however, do not provide any evidence for back bonding between the cyclopropane ring and the silicon atom.

scholarly journals 29Si NMR Chemical Shifts in Crystalline and Amorphous Silicon Nitrides

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1646 ◽  
Author(s):  
Ilia Ponomarev ◽  
Peter Kroll
Keyword(s):  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Density Functional ◽  
Chemical Shifts ◽  
29Si Nmr ◽  
Hydrogenated Silicon ◽  
Nmr Chemical Shifts ◽  
Nmr Data ◽  
29Si Nmr Spectra ◽  
The Impact

We investigate 29Si nuclear magnetic resonance (NMR) chemical shifts, δiso, of silicon nitride. Our goal is to relate the local structure to the NMR signal and, thus, provide the means to extract more information from the experimental 29Si NMR spectra in this family of compounds. We apply structural modeling and the gauge-included projector augmented wave (GIPAW) method within density functional theory (DFT) calculations. Our models comprise known and hypothetical crystalline Si3N4, as well as amorphous Si3N4 structures. We find good agreement with available experimental 29Si NMR data for tetrahedral Si[4] and octahedral Si[6] in crystalline Si3N4, predict the chemical shift of a trigonal-bipyramidal Si[5] to be about −120 ppm, and quantify the impact of Si-N bond lengths on 29Si δiso. We show through computations that experimental 29Si NMR data indicates that silicon dicarbodiimide, Si(NCN)2 exhibits bent Si-N-C units with angles of about 143° in its structure. A detailed investigation of amorphous silicon nitride shows that an observed peak asymmetry relates to the proximity of a fifth N neighbor in non-bonding distance between 2.5 and 2.8 Å to Si. We reveal the impact of both Si-N(H)-Si bond angle and Si-N bond length on 29Si δiso in hydrogenated silicon nitride structure, silicon diimide Si(NH)2.

Solid State NMR Analysis for Hide Powder Tanned by Aluminum, Silicon and Phosphorus Tanning Agents before and after Hydrothermal Denaturation

2021 ◽  
Vol 116 (10) ◽  
Author(s):  
Jun Liu ◽  
Da-hai He ◽  
Hua-lin Chen ◽  
Ke-yi Ding
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
High Field ◽  
Chemical Shifts ◽  
Covalent Bond ◽  
29Si Nmr ◽  
Before And After ◽  
Collagen Molecules ◽  
Field Area ◽  
Aluminum Silicon

In order to investigate the change of chemical bonds between tanning agents and collagen molecules directly, hide powder tanned by aluminum, silicon and phosphorus tanning agents were prepared. The chemical shifts of Al, Si and P in tanned hide powder were analyzed by solid-state 27Al NMR, 29Si NMR and 31P NMR. The results showed that, the chemical shift of Al in aluminum tanned hide powder which interacted with collagen molecules through coordination bond could be regarded as unchanging after hydrothermal denaturation (only slightly moved to high field area). The chemical shift of Si in silicon tanned hide powder which interacted with collagen molecules through hydrogen bond did not change after hydrothermal denaturation. The chemical shift of P in phosphorus tanned hide powder, which interacted with collagen molecules through covalent bond, was obviously shifted to the high field area after hydrothermal denaturation.

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