Chemical shifts hydrogen values

From these results it was concluded that hydrogen bonds are dominated by polarization, but in general the proton chemical shift is influenced by through-space contributions (see previous chapter) as well. Since through-space contributions affect the anisotropy even more than the chemical shift mean value, no good correlations between distances and proton CS anisotropies are observed. 

The following examples, selected from cyclitols containing four or five hydroxyl groups, Ulustrate many of the approaches already mentioned. In the nine Figures provided for these examples, chemical shift (delta) values in p.p.m. for solutions in chloroform-d are based on an internal reference of tetramethylsilane, and delta values for the solutions in deuterium oxide are approximate figures, based on an external reference of tetramethylsilane or an internal reference of deuterium hydrogen oxide. 

The variations of /uc- h d 7ih-ih acetone and dimethyl sul-phoxide in various solvents show an almost linear relationship with the carbonyl-and chemical shifts/ " Hydrogen bonding with the solvent, or the presence of large solvent dipoles, may increase the relative importance of polar resonance structures of the carbonyl or sulphoxide group (33), and the electron withdrawl experienced by the methyl group will result in increased values of C—H couplings. 

R(CO)-N-H 5.0-9.0 ppm Hydrogens attached to an amide nitrogen are variable in chemical shift, the value being dependent on the temperature, concentration, and solvent. 

The chemical shift (3) value of the peak provides information on the magnetic/ chemical environment of the hydrogens. Hydrogens next to electron-withdrawing... 

In the benzene series, an approximately linear relationship has been obtained between the chemical shifts of the para-hydrogen in substituted benzenes and Hammett s a-values of the substituents. Attempts have been made, especially by Taft, ° to use the chemical shifts as a quantitative characteristic of the substituent. It is more difficult to correlate the chemical shifts of thiophenes with chemical reactivity data since few quantitative chemical data are available (cf. Section VI,A). Comparing the chemical shifts of the 5-hydrogen in 2-substituted thiophenes and the parahydrogens in substituted benzenes, it is evident that although —I—M-substituents cause similar shifts, large differences are obtained for -j-M-substituents indicating that such substituents may have different effects on the reactivity of the two aromatic systems in question. Differences also... 

Carbon-13 chemical shifts of the a- and (8-carbon atoms of various unsubstituted and 3-substituted thietane oxides and dioxides have been recorded and correlated by the equations S = ay + bx and Sf = ax + by where a and b are parameters characteristic of the sulfoxide or sulfone (y) and the substituent (x)216. The values of the substituent parameters were found to parallel those which determine the effect on the 13C chemical shifts when hydrogen is replaced by a substituent224. 

---