Chemical shift values

However, one of the most successfiil approaches to systematically encoding substructures for NMR spectrum prediction was introduced quite some time ago by Bremser [9]. He used the so-called HOSE (Hierarchical Organization of Spherical Environments) code to describe structures. As mentioned above, the chemical shift value of a carbon atom is basically influenced by the chemical environment of the atom. The HOSE code describes the environment of an atom in several virtual spheres - see Figure 10.2-1. It uses spherical layers (or levels) around the atom to define the chemical environment. The first layer is defined by all the atoms that are one bond away from the central atom, the second layer includes the atoms within the two-bond distance, and so on. This idea can be described as an atom center fragment (ACF) concept, which has been addressed by several other authors in different approaches [19-21]. 

In Table III a comparison is made between calculated and observed chemical shift values of a variety of allenes that were not included in the data set of Table I,... 

Section 13 15 C signals are more widely separated from one another than proton sig nals and C NMR spectra are relatively easy to interpret Table 13 3 gives chemical shift values for carbon in various environments... 

TABLE 7.69 Fluorine-19 Chemical Shifts Values given in ppm on the 5 scale, relative to CCI3F. 

A study of H NMR spectra of monosubstituted pyrazines in DMSO has been reported and the assigned chemical shift values of protons located ortho or para relative to the substituent correlate well with Hammett or Taft tr-substituent values. meta-Piotons did not, however, give good correlations (72JOC1H). 

The negative sign indicates a chemical shift value numerically smaller than that of pyrazine itself. 

The NMR spectrum of quinoxaline has been measured in CDCI3 and the chemical shift values are as shown in (16) (69JA6381). Curiously, C NMR spectra of phenazine and its derivatives have been recorded in benzene solution and the chemical shift values quoted relative to benzene however, for consistency the values in (17) are quoted relative to TMS. 

This index lists the text pages on which quantitative information can be found relating to over 4000 specific heterocyclic compounds. In general the technique used (eg. H NMR) to measure the information has been given and not the type of information provided (eg. chemical shift values). The latter details may be found on the text pages themselves. 

In the following 55 problems, the chemical shift value (ppm) is given in the scale below the spectra and the coupling constant (Hz) is written immediately above or below the appropriate multi-plet. Proton NMR data are italicised throughout in order to distinguish them from the parameters of other nuclei ( C, N). 

The empirical formula contains five double-bond equivalents. In the H NMR spectrum a doublet signal at Sh = 9.55 stands out. This chemical shift value would fit an aldehyde flinction. Since the only oxygen atom in the empirical formula is thus assigned a place, the methyl signal at Sh = 3.80 does not belong to a methoxy group, but rather to an /f-methyl group. 

Part structure A is recognised to be a 2,5-disubstituted cyclohexa-1,3-diene on the basis of its chemical shift values. The ethyl group is one substituent, the other is a carboxy function judging by the chemical shift value of 8c = 174.1. The CH multiplicities which follow from the DEPT subspectra, 2C, 4CH, 5CH2 and CHj, lead to the CH part formula C2 + C4H4 + CsHw + CH3 = C12///7. Comparison with the given molecular formula, Ci2/7j 03, indicates an OH group. Since... 

The CH fragment which is linked to the OH group (Sh = 5.45 ) can easily be located in the H and NMR spectra. The chemical shift values Sc =74.2 for C and Sh = 3.16 for //are read from the CH COSY plot. The H signal at S,i = 3.16 splits into a triplet (11.0 Hz) of doublets (4.0 Hz). The fact that an antiperiplanar coupling of 11 Hz appears twice indicates the diequatorial configuration (trans) of the two substituents on the cyclohexane ring 5. If the substituents were positioned equatorial-axial as in 4 or 5, then a synclinal coupling of ca 4 Hz would be observed two or three times. 

The keto-carbonyl C signal at 5c = 200.9 would only fit the aflatoxins B, and M,. In the C NMR spectrum an enol ether-C// fragment can also be recognised from the chemical shift value of 5c = 145.8 and the typical one-bond coupling constant Jch = 196 Hz the proton involved appears at Sh = 72, as the CH COSY plot shows. The H triplet which belongs to it overlaps with a sing-... 

The assignment of all of the chemical shift values and coupling constants as derived from the measurements can be checked in structural formula D. 

Table 47.3. Relative configurations of the protons between Sh = 7.23 and 3.42 from the HH coupling constants of the expanded proton multiplets. Chemical shift values (Sh) of the proton multiplets are given as large numerals in boldface and coupling constants (Hz) are as small numerals...

The typical chemical shift values and CH coupling constants in the one-dimensional NMR spectra reveal three functional groups ... 

First the five protons (integral) of the //NMR spectrum (Sfj = 7.50 - 7.94) in the chemical shift range appropriate for aromatics indicate a monosubstituted benzene ring with typical coupling constants 8.0 Hz for ortho protons, 1.5 Hz for meta protons.). The chemical shift values especially for the protons which are positioned ortho to the substituent Sn = 7.94) reflect a -M effect. Using the CH COLOC plot it can be established from the correlation signal hclS = 66.AI7.94 that it is a benzoyl group A. 

Typical chemical shift values for XPS core levels. 

NMR Chemical Shift Values" of the Ring Carbons OF Representative 1,2-Dithietes... 

TABLE 5.3 The Chemical Shift Values, in Parts per Million (ppm) from for the Charged Carbon Atom of Some Carbocations in SO2CIF—SbFs, SOj-FSOaH-SbFft, or SOz-SbFj... 

Fig. 2. H NMR spectra of (A) oxidized spinach Fe2S2 ferredoxin (33) (B) reduced spinach Fe2S2 ferredoxin (5f) (C) oxidized Desulfovibrio gigas Fe3S4 ferredoxin (138) (D) oxidized ectothiorhodospira halophila HiPIP iso-II (23) (E) reduced Chromatium vinosum HiPIP (14) (F) fully reduced Clostridium pasteurianum 2(Fe4S4) ferredoxin (139). Chemical shift values are in ppm.

In this case, Sy is the best, theoretical, C chemical-shift value, 5b is the chemical shift of the di[ C]methylamino group in the nonprotonated form, and A is the chemical-shift difference between the di[ C]methylamino group in the protonated and nonprotonated forms. The best fit was obtained when E, [ST(i) 5obs(i)] was minimized Sobs is the chemical-shift value observed at that given pH value. 

The GASPE spectrum of podophyllotoxin is shown. The signals at 8 56.0,108.6, and 152.0 each represent two carbons in identical magnetic environments, while the signal at 8 147.6 also represents two carbons that accidentally appear at the same chemical shift. Assign chemical shift values to various protonated and quaternary carbons in the structure. 

The GASPE spectrum of vasicinone is shown. The peak at 8 126.5 is a cluster of three peaks at 8 126.3 and 126.7 representing methine carbons. Similarly, the signal at 8 160 on the positive phase of the spectrum represents two close singlets at 8 160.4 and 160.5. Predict the chemical shift values of various protonated and quaternary carbons in the structure. 

The one-bond HETCOR spectrum and C-NMR data of podophyllo-toxin are shown. The one-bond heteronuclear shift correlations can readily be made from the HETCOR spectrum by locating the posidons of the cross-peaks and the corresponding 5h and 8c chemical shift values. The H-NMR chemical shifts are labeled on the structure. Assign the C-NMR resonances to the various protonated carbons based on the heteronuclear correlations in the HETCOR spectrum. 

Two possible structures, A and B, were initially considered for a naturally occurring coumarin isolated from Murraya paniculata. Its nOe difference and H-NMR spectra are presented. The relevant H chemical shift values are given around structure A. On the basis of the nOe data, identify the correct structure of the coumarin. 

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