Proton chemical shift values

Typical Proton Chemical-Shift Values (8) in Dilute CHCI3 Solutions... 

TABLE 6.34 Proton Chemical Shifts Values are given on the 8 scale r = 10.00—5. 

From the H CRAMPS NMR spectra, therefore, it was possible to determine the NH proton chemical shift value for [Ala ]n-2 (a-helix 6 = 8.0) which is identical with that determined using BR-24 (2.0 kHz). Further, it was possible to determine the " NH proton chemical shift for [Ala ]n-1 (/3-sheet, 6 = 8.6) using the MREV-8 pulse sequence at 3.5 kHz. However, unfortunately, the NH proton chemical shift values for [Ala]n-2 and [Ala]n-t could not be determined because the line shapes of the " NH signals exhibit an asymmetric doublet pattern in this system also. Thus, it is found that determination of the true NH chemical shift of poly(L-alanines) can be achieved to measure fully N-labelled samples at higher MAS speed (3.5 kHz) and that these chemical shifts depend on conformation (a-helix 6 = 8.0 /3-sheet S = 8.6). This is the first determination of the true NH proton chemical shifts of poly(L-alanines) by H CRAMPS NMR. 

FIGURE 3.20 A simplified correlation chart for 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]. 

The Lewis acidity order BCIa > CFaiCF-BOa > (CFa CF)2BCl > (CF2 CF)aB > BFa has been established by determination of proton chemical shift values for the 1 1 complexes these boranes form with diethyl ether a relatively linear decrease in acid strength occurs down the series, indicating that electronic factors predominate and steric effects are minimal. ... 

The NMR spectra of NR obtained from the two source plants (Hevea and Goldenrod) are illustrated in Figure 24.6. The structure is very clear from the various proton chemical shift values. ... 

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