The role of electronic and steric effects in 29Si-NMR spectra of compounds with Si-O-C group

1981 ◽  
Vol 46 (2) ◽  
pp. 377-390 ◽  
Author(s):  
Jan Schraml ◽  
Václav Chvalovský ◽  
Märt Mägi ◽  
Endel Lippmaa
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
29Si Nmr ◽  
Methyl Group ◽  
29Si Nmr Spectra ◽  
Back Bonding ◽  
Electron Withdrawal ◽  
Electronic And Steric Effects

29Si-NMR chemical shifts are presented for several classes of compounds of general formula (CH3)4-n-mClnSi(OR)m (for n =0 m = 1-4 and for n = 1-3, m = 1). In most of the classes the shifts correlate linearly with polar constants of the substituents R or with Del Re net atomic charges on the silicon. The slopes in these correlations are all positive (i.e. the shielding decreases with electron withdrawal) and decrease with increasing n or m (i.e. the sensitivity of silicon shielding to substituent effects decreases with increasing number of electronegative substituents bonded to the silicon). This finding contradicts the available quantitative theories but can be accounted for by the qualitative model which considers back-bonding to silicon. Each methyl group in the γ position causes' a diamagnetic shift of 2 to 3 ppm, depending on the values of m and n, the effects are additive. Compounds with some heteroatoms in the γ position (R = CH2Cl, CH2Si(CH3)3, but not R = CH2Ge(CH3)3) behave anomalously, the origin of the anomalous shifts could not be ascertained.

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.

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.

Synthetic and Spectroscopic Studies on N-(i,j-Disubstituted Phenyl)-4- Substituted Benzenesulphonamides, 4-X’C6H4SO2NH(i,j-X2C6H3), where X’ = H, CH3, C2H5, F, Cl or Br; i, j = 2, 3; 2, 4; 2, 5; 2, 6 or 3, 4; and X = CH3 or Cl

2005 ◽  
Vol 60 (1-2) ◽  
pp. 113-120 ◽  
Author(s):  
Mahesha Shetty ◽  
B. Thimme Gowda
Keyword(s):  
General Formula ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Spectroscopic Studies ◽  
Methyl Group ◽  
Methods Of Calculation ◽  
Benzene Rings ◽  
Stretching Vibrations ◽  
C Nmr

Fifty four N-(i,j-disubstituted phenyl)-4-substituted benzenesulphonamides of the general formula 4-X’C6H4SO2NH(i,j-X2C6H3), where X’ = H, CH3, C2H5, F, Cl or Br; i,j = 2,3; 2,4; 2,5; 2,6 or 3, 4; and X = CH3 or Cl, are prepared and characterized and their infrared, 1H and 13C NMR spectra in solution are studied. The N-H stretching vibrations νN−H absorb in the range 3305 - 3205 cm−1, while the asymmetric and symmetric SO2 vibrations vary in the ranges 1377 - 1307 cm−1 and 1184 - 1128 cm−1, respectively. The N-(i,j-disubstituted phenyl)-4-substituted benzenesulphonamides show C-S, S-N and C-N stretching vibrations in the ranges 844 - 800 cm−1, 945 - 891 cm−1 and 1309 - 1170 cm−1, respectively. The compounds do not exhibit particular trends in the variation of these frequencies on substitution either at ortho or meta positions with either a methyl group or Cl. The observed 1H and 13C chemical shifts ofare assigned to protons and carbon atoms of the two benzene rings. Incremental shifts of the ring protons and carbon atoms due to -SO2NH(i,j-X2C6H3) groups in C6H5SO2NH(i,j-X2C6H3) and 4-X’C6H4SO2NH- groups in 4-X’C6H4SO2NH(C6H*) are computed and employed to calculate the chemical shifts of the ring protons and carbon atoms in the substituted compounds 4-X’C6H4SO2NH(i,j-X2C6H3). The different methods of calculation lead to almost the same values in most cases and agree well with the observed chemical shifts, indicating the validity of the principle of additivity of the substituent effects with chemical shifts in these compounds.

17O, 13C, and 29Si NMR spectra of some acyloxy- and diacetoxysilanes and acetoxygermanes

1986 ◽  
Vol 51 (11) ◽  
pp. 2582-2589 ◽  
Author(s):  
Antonín Lyčka ◽  
Jaroslav Holeček ◽  
Karel Handlíř ◽  
Josef Pola ◽  
Václav Chvalovský
Keyword(s):  
Periodic System ◽  
Time Scale ◽  
Nmr Spectra ◽  
Group Element ◽  
29Si Nmr ◽  
Carboxyl Group ◽  
29Si Nmr Spectra ◽  
Oxygen Atoms

The 17O, 13C, and 29Si NMR spectra of (CH3)3SiOC(O)R, CH3(XCH2)Si(OC(O)CH3)2, and R3GeOC(O)CH3 compounds are reported. In the 17O NMR spectra at 350 K the only signal is observed with the two latter series, but two well-resolved signals are displayed with the (CH3)3SiOC(O)R compounds. The equivalence of both oxygen atoms in carboxyl group on the NMR time scale is discussed from the viewpoint of a possible coordination of the oxygen atoms to the IVB group element of the periodic system.

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.

13C-NMR-Spektroskopie an polycyclischen Aromaten, IIΙ Die 13C-NMR-Spektren von Amino- und Dimethylaminonaphthalinen /13C NMR Spectroscopy of Polycyclic Aromatics, III The 13C NMR Spectra of Amino- and Dimethylaminonaphthalenes

1975 ◽  
Vol 30 (9-10) ◽  
pp. 794-799 ◽  
Author(s):  
Ludger Ernst
Keyword(s):  
13C Nmr ◽  
High Field ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Double Resonance ◽  
Substituent Effects ◽  
13C Nmr Spectroscopy ◽  
Polycyclic Aromatics ◽  
Electrophilic Reagents ◽  
C Nmr

The 13C NMR spectra of twelve amino-, dimethylamino-, diamino-, and bis(dimethylamino)naphthalenes are completely assigned by selective 13C{1H} double resonance and by interpretation of proton-coupled spectra. Strong substituent effects (Δδ) upon chemical shifts are observed and can largely be accounted for by mesomerism. The pronounced high-field shifts of C-6 in the 2-amino- and 2-dimethylaminonaphthalenes coincide with the enhanced reactivity of this position towards electrophilic reagents. In 1-dimethylaminonaphthalene and even more so in 1-dimethylamino-2-methylnaphthalene, conjugation is inhibited for steric reasons and Δδ’s are greatly diminished, thus giving an estimate for the contribution of resonance to substituent-induced shifts in the unhindered compounds. In two 1,8-disubstituted naphthalenes there are large deviations from additivity of substituent effects.

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