13C chemical shifts for

The characteristic II chemical shifts for ArCF2H protons lie between 6.6 and 7.0 ppm, and the characteristic 13C chemical shift for the CF2H carbon of such compounds is -115 ppm (Table 4.7). 

Kajimoto and Fueno66 have reported 13C chemical shifts for 2-substituted 1,3-butadienes at each carbon atom of the dienyl moiety. Their values are X, i1, <52, 8 OEt, —24.5,... 

The 13C chemical shift for the central carbon of the protio-tert-butyl dication (8) has been calculated as 327.5 ppm (IGLO/II//MP2/6-31G(d)).30... 

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

In recent years Pagani and coworkers have made detailed studies of the problem. In the space available we can only outline their work and interested readers should consult the very detailed papers. The authors have developed special scales of substituent constants for dealing with contiguous functionalities 193. These new substituent constants are a (which seems to be related fairly closely to the ordinary a ), aIB (which bears some relationship to o/, but not that close), and (Tr-, a special delocalization parameter. It is claimed194 that these scales are appropriate for describing interactions between contiguous functionalities, as opposed to literature values which account for remote interactions . Various C—H acidities in gas phase and in solution were successfully correlated by means of multiple regressions on am and chemical shifts for the central carbon in the carbanions. 

TABLE 2. 13C chemical shifts for linear and branched dienes7... 

An important tool for the investigation of carbocation structure is measurement of the C nmr chemical shift of the carbon atom bearing the positive charge.66 This shift approximately correlates with electron density on the carbon. 13C chemical shifts for a number of ions are given in Table 5.2.67 As shown in the table, the substitution of an ethyl for a methyl or a methyl for a hydrogen causes a downfield shift, indicating that the central carbon... 

The very upfield 13C chemical shifts for the ylidic carbon are indicative of carbanion character. The JP C coupling constants are large and imply that carbon is sp2 hybridized, a particularly for the stabilized ylides. The values of JP C for the... 

C Chemical Shifts for Ring Carbon Atoms and Substituents in Selected 3//-Pyrazoles... 

Scheme 10 13C chemical shifts for oxygen and sulfur systems... 

The 13C chemical shifts for C-2, C-3 and C-4 in coumarin are at 159.6, 115.7 and 142.7 p.p.m. respectively, and correspond closely to those for pyran-2-one. A good correlation between 13C shifts and charge densities, calculated by the CNDO/2 method, has been established (75JOCH75). 

The proton spectra for the dibenzo derivatives, viz. dibenzo[6,e][l,4]dioxin, phenoxathiin and thianthrene, have been reported in full, as part of a wider survey of heterocyclic compounds structurally related to anthracene. The protons in dibenzo[6,e ][ 1,4]dioxin are the most shielded, and in phenoxathiin the protons ortho and para oriented to the C—O bond are shielded relative to those ortho and para to sulfur <740MR(6)U5). The 13C chemical shifts for phenoxathiin follow a similar pattern, with carbons ortho and para to the C—O bond resonating at 117.5 and 124.2 p.p.m. respectively, and at higher field than those ortho, para to the C—S bond (127.4 and 126.5 p.p.m.), in good agreement with shifts predicted on the basis of additivity effects <73JMR(12)143). 

Figure 1. Hydroxyl PMR signals for a-n-sorbopyranose (upper left) and a-i.-glucoheptulose (lower left) in methyl sulfoxide-6.6. 13C chemical shifts for aqueous solutions of a-v-sorbopyranose (a-S), a-D-xylopyranose (a-X) and their methyl glycosides (Me-a-S and Me-a-X, respectively) (ppm relative to down-...

Figure 3. Hydroxyl PMR signals for p-o-fructopyranose (5) (upper left) and ct-L-gala-heptulose (6) (lower left) in methyl sulfoxide-dtf. 13C NMR spectra of 5 and 6 (in water). The diagonal line relating the 13C-6 resonances of 5 and 6 reflects the large downfield shift attributable to replacement of one H-6 with the 7-carbinol group. 13C chemical shifts for a- and B-o-arabinopyranose (a and b, respectively) (10, 11) are inserted to illustrate the close conformational affinity between 5 and / -, though not a-, d-arabinose (ppm relative to downfield...

The proton NMR spectra for the various naphthyridines have already been listed in Volume 2 of this series.1 The 13C spectra either have since been reported or have since been obtained in the authors laboratory.132133 The data, along with the 13C chemical shifts for quinoline and isoquinoline, are as follows (d ppm, with respect to TMS at 0 ppm) ... 

Figure 11.31 Representative 13C chemical shifts for various classes of organic compounds.

Table A3.15 13C Chemical shift for some hereroaromatic compounds 1434...

Fig.4 Plots of the observed 13C chemical shifts for the carbonyl carbons in Gly, L-Ala, L-Leu and L-Asp residues in peptides and polypeptides in the solid state against the N... O spearation(RN G).

Letourneux et al. (57) have determined the 13C chemical shifts for a series of (22R)- and (22S)-substituted cholesterol derivatives. The magnitudes of the /7-effect are significantly different (2-7 ppm) for the... 

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