Chemical shift electronegative groups

NMR The electronegative oxygen of an alcohol decreases the shielding of the car bon to which it is attached The chemical shift for the carbon of the C—OH is 60-75 ppm for most alcohols Carbon of a C—S group is more shielded than carbon of C—O... 

The p-carbon signals in heterocyclohexanes 52 (143) respond to the electronegativity of endocyclic substituents similarly to those of carbon atoms in p positions with respect to exocyclic substituents. The slopes of chemical shift vs. electronegativity plots for the p-methylene groups in 52 and 53 are negative (Table 10). For the quaternary P-carbon atom in 53, however, a slight positive slope is observed (164). 

In contrast, the chemical shifts of the axial methyl groups in 53 are nearly independent of X (slope = -0.7) (Figure 4). From that finding these authors (164) concluded tht electronegativity information is transmitted to a y-gauche carbon atom only through a rigid pathway of parallel orbitals and that methyl rotation protects this carbon atom from electronic interaction. 

Any effect which alters the density or spatial distribution of electrons around a nucleus will alter the degree of shielding and hence its chemical shift. H chemical shifts are sensitive to both the hybridisation of the atom to which the H nucleus is attached sp, sp etc.) and to electronic effects (the presence of neighbouring electronegative/electropositive groups). 

The chemical shift is determined by the extent to which a proton is deshielded by the groups to which it is attached. The more a proton is shielded by the electron density around it, the lower its 3 value. If a proton is attached to a system that withdraws electrons from its environment such as an electronegative group or to a group which affects its environment by creating a field opposing the applied... 

A good variety of compounds have been prepared and characterized allowing us to obtain reliable information on the chemical shifts of saturated and unsaturated ring protons. A selection of different structures are shown in Table 4. The thiazine derivatives have been organized in groups for comparison. The effects of saturation (54, 105, 106), substituents of variable electronegativity (107, 108), increasing oxidation state of sulfur (121, 122, 27-29), and deprotonation (109-111) can be observed. 

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