Correlation table proton chemical shift values

Most chemical shifts have 8 values between 0 and 15. A small 8 value represents a small downfield shift, and vice versa. A simplified correlation chart for proton chemical shift values is shown in Table 2 [37]. 

Bisalkyne d4 monomers, with N = 3 by symmetry, exhibit proton and carbon chemical shifts at higher fields than those of monoalkynes with N = 4. The proton chemical shift of 10.45 ppm for Mo(PhC=CH)2-(S2CNEt2)2 (52) falls nicely between the four-electron donor Mo(CO)-(PhC=CH)(S2CNEt2)2 case (12.6 ppm) and the two-electron donor (7r-C5H5)2Mo(HC=CH) case [7.68 ppm (Table II)]. Additional data for bisalkyne complexes, including pyrrole-N-carbodithioate derivatives, support a correlation of H chemical shifts with alkyne ttj donation, with three-electron donors typically near 10.0 0.5 ppm. Similar H values are found for cyclopentadienyl bisalkyne complexes with terminal alkyne ligands. Chemical shifts between 8.5 and 10.5 ppm characterize all the neutral and cationic bisalkynes listed in Table V except for [CpMo-(RC=CH)2(MeCN)]+ where one isomer has S near 11 ppm for the acetylenic proton (72). 

An electronic measure, the NMR chemical shift values of the amide proton in coil conformations (Table 3) also show a high degree of correlation (r = 0.70-0.89) with hydrophihcity scales and with strand versus coil conformations (Table 4). NMR studies reveal that the amide proton is shielded to a greater extent in coil conformations as compared with extended ( 3) structures (37) increased electron density exists at this atom in the coil conformation. Taken together, the data suggest strong interactions between hydrophihcity and electronic parameters in folding and provide support for additional refinement of the Hp index. 

The proton chemical shifts of representative acyclic and cyclic dienamines are collected in Tables 14-16. Examination of the Tables show that alkenyl substitution at C(l) or C(2) of an enamine produces also deshielding of the olefinic protons, as seen by comparing the <5H(2) values of compound 149 (3 3.75, 3.85 ppm Table 11) with those of the analogous cross-conjugated dienamine 105 ( 3.85, 4.05 ppm Table 14). The chemical shift of the vinylic protons of dienamines correlate only partially with the charge calculated for the corresponding olefinic carbons . In the linear conjugated... 

Next, one should consider the line width of the one-dimensional spectra of both nuclei. The detected nucleus should be the one with the smaller linewidth, since a short T2 leads to signal losses during the pulse sequence. Compared with metal nuclei usually has the smaller linewidth. Because of the chemical shift anisotropy and the temperature dependence of the chemical shift of heavy nuclei, the measurement of is therefore favoured in these cases. For detection, in addition, the large NOE enhancement caused by proton irradiation has to be taken into account. Heteronuclei usually have no directly bound proton their NOE factors are therefore lower. To facilitate further discussion, the y values and the natural abundances of the nuclei used for C-X correlation are given in Table 1. 

Thiazole exhibits a H NMR spectrum of first order. Table 3 lists the relevant chemical shifts for which a relationship exists with the calculated 7t-electron densities on the respective carbon atoms (to which the protons are bonded). Simple correlations were observed in other cases. For instance, a satisfactory linear relationship between the experimental S values and the calculated 7t-electron densities was found for bromothiazoles <84H(22)1077>. Correlations between the experimental d values of some substituted thiazoles and the Cp Hammet constants have been also reported <85SUL17>. 

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