Chemical shift of carbon

Table 7.52 Estimation of Chemical Shifts of Carbon Attached to a Double Bond 7.103...

Table 15 contains the C chemical shifts of some selected indazoles. The major difference between indazoles and isoindazoles lies in the chemical shifts of carbons C-3 and C-7a. The substituent chemical shifW (SCS) induced by the substituent in position 3 have been discussed using an empirical model (770MR(9)716). The model that gives the best results, AS = OS + + c and 3i are the Swain-Lupton parameters and 5 is the Schaefer... 

To a large extent the chemical shifts of carbon and silicon run parallel, but the chemistry of the two elements is somewhat different. Thus silicon can have extend its valence shell beyond the coordination number of 4. A few stable or-ganosilicon compounds in which silicon is divalent are known (the silylenes), and compounds with a silicon-silicon double bond also exist (the disilenes). 

Chemical shifts of carbons given next to the structure of 115 differ slightly from those here because they were obtained in CS2-... 

The observed C chemical shifts of carbon atoms in the norbomyl ion are said to rule out the presence of equilibrating ions. In arriving... 

The chemical shifts of the protons in the H NMR spectra of salicylaldoximes are given in Table 7. The hydroxyl proton varies between 11.61 and 10.82 ppm. The chemical shifts of carbon atoms in the C NMR spectra of the salicylaldoximes are given in Table 8. The signal of C7 shifts downfield when the substiment becomes a stronger electron donor (AS = 149.58 — 144.64 ppm = 4.94 ppm). Comparison of the spectra of 50 and 51 shows that the 2-OH group shifts the signal of C7 upheld. Since the most important interactions between the solvent and the aldoxime probably involve the 2-OH group, the solvent chemical shifts in the spectra of 50 and 51 are not parallel. 

Be able to predict the chemical shift of carbon atoms in the NMR spectra of simple molecules... 

The chemical shifts of carbon atoms usually lie between 8 0-220 (with TMS again being used as the reference value of 5 0) (Boxes 4.12-4.14),... 

Table 4.29. 13C Chemical Shifts of Carbons in a,/ -Unsaturated Ketones (<5C in ppm) [291].

There is no indication of any abnormality in the chemical shifts of carbons 11, 12, and 14 shown in Figure 9-48a. Furthermore, there is a downfield resonance 216.5 ppm from the carbons of TMS (not shown in Figure 9-48a) which is typical of a C=0 carbon corresponding to C13. When 14 is treated with acid, we expect the product (warfarin) of structure 15 to be formed, which should have a 13C spectrum much like that shown in Figure 9-48a ... 

Fig. 2.16. 13C NMR chemical shift of carbon 4 (numbering starting from the polar head) in nonylam-monium bromide as a function of the inverse amphiphile concentration. A positive shift is downfield. Solid line calculated with an aggregation number of 33. (After Ref.51))...

The 13C NMR spectra of compounds Via, b, and c were more informative. The chemical shifts of carbon resonances in 13C NMR spectra have been used as a measure of the electron densities of the carbon atoms being studied (55), and so a comparison of the carbinyl carbon resonances of compounds Via, b, and c with those of the alcohols from which they were... 

Table 14.2 Approximate Chemical Shifts of Carbons in l3C-NMR Spectra...

After filling of DMGE-DVB copolymer with methyl,hydride-containing silica, the appearance of a resonance at 39.9 ppm indicated the formation of Si-C bonds between the silica surface and DMGE (Figure 5). Comparison with the chemical shift of carbon in the ester carbonyl... 

Predict the number of signals and approximate chemical shifts of carbon atoms in a given compound. Problems 13-41, 49, 50, 51, 53, and 54... 

The results of two-parameter correlations of the 13C and 15 N NMR chemical shifts of 2-substituted 5(6)-nitrobenzimidazoles with the induction and resonance constants (a, ak) are given in Table 3.26 [688, 689], The electronic influence of substituents on the chemical shifts of carbons (and protons) in positions 4 and 7 are mainly transmitted by a resonance mechanism, C-4 being more sensitive than C-7 to the substituent effect. For positions 5 and 6 a slightly smaller contribution from the resonance component to the total transmission of substituent effects is observed. However, analysis of correlation between 5 15 N and substituent parameters indicates an approximately equal influence of the induction and resonance substituent effects on the nitro group shielding (see Table 3.26) [688, 689], When other sets of substituent constants (F and R, c, and ck, etc.) are used in the correlation the percentage ratios of resonance and inductive contributions remain unchanged. 

Solid-state 13C NMR has been shown to be a more effective analytical tool for demonstrating the formation of P-sheets in polypeptides and proteins, because the isotropic 13C NMR chemical shifts of carbon atoms in proteins are sensitive to the P-sheet s secondary structure. It is well established that SF conformations are dependent upon the species of silkworms and conditions of the sample preparation. In particular, has been reported that fibroin from Bomhyx mori adopts two dimorphic structures, silk I and silk II. The silk II form is identified by the C chemical shifts of glycine (Gly), serine (Ser), and alanine (Ala) that are indicative of P-sheets, while the silk I form produces chemical shifts that are associated with a loose helix or distorted P-tum. However, when compared with silk II, the less stable silk I shows a relatively unresolved structure, and the conformation of the soluble form of SF rapidly undergoes a transition to the insoluble silk II conformation. 

C NMR spectra of five separate series of mono-, di-, and polysubstituted chloro-, bromo-, iodo-, benzoyl-, and nitrocarbazoles substituted at the T,3-, 6-, and 8-positions have been recorded <2005JHC867>. C chemical shifts of carbons ipso, ortho, and para show good linear correlations with net atomic charge density values, suggesting that charge density nicely predicts the substituent effects. 

In the preceding sections the chemical shifts of carbon atoms attached to metals have been reported, but in no case has anything more... 

The chemical shifts of carbon atoms in NMR spectra of the oximes having pyrrolyl, furyl, benzofuryl, thienyl and pyridyl substituents change specifically on going from the E- to the Z-isomer. This makes it possible to use the chemical shifts for assignment of the oximes configuration and studying the special features of their electronic structure (08CHE1238). 

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