Deshielded group

Obviously, there are too many possible combinations of groups for us to show a comprehensive collection of them but Spectrum 5.7 shows a nice example of a 1,3 di-substituted pattern featuring two strongly deshielding groups (a nitro group and a methyl ester) and serves to demonstrate the limitations of Table 5.4. 

To estimate the chemical shift of protons that are deshielded by two groups, add the chemical shifts you would expect with each deshielding group individually, and subtract 1.3 (the 8 for an alkane CH2 group) from the result. 

The two signals at 19 and 22 ppm are from carbon atoms that are not directly bonded to any deshielding group, although the carbon at 22 ppm is probably closer to one of the oxygen atoms. These are also triplets in the off-resonance-decoupled spectrum and they correspond to methylene groups. We can propose ... 

The Bromine nucleus is an intermediate deshielding group in relation to both aliphatic and aromatic hydrogens. It does not couple to nearby hydrogens and thus its presence in a molecule must be inferred from the observed chemical shifts. 

The AZO linkage between aromatic rings acts as a strong deshielding group on the ortho hydrogens. Due to the bulk of the aromatic rings, these compounds most likely exist only in the anti- form. 

The effect of the Nitroso group on the chemical shifts of the ortho aromatic compounds is that of a strongly deshielding group. 

The Phosphine Oxide group is a moderately strong deshielding group in its effect on the ortho aromatic hydrogens. Coupling to these hydrogens, when it can be observed, is found to be about 12-13 Hz. 

It is interesting to note that when the sulfonyl chloride undergoes hydrolysis to form the corresponding sulfonic acid, the methyl resonance is converted from the most strongly deshielded (3.65 ppm) to the least deshielded group of this series (2.82 ppm). 

No unusual couplings nor coupling constants have been noted for the esters of sulfurous acid. The aliphatic patterns are similar in appearance to those of similarly strong deshielding groups such as the ether group. 

This section contains the carbon-13 NMR chemical shifts of the primary amines. Other functional groups containing an -NH2 group include the hydrazines, amine salts and primary amides. The additivity effect of the primary amine group on adjacent aliphatic carbon atoms is that of a moderately strong deshielding group, i.e. 

The additivity effect of either side of the -C(=0)-NH- group is that of an intermediate deshielding group as they also are with the adjacent carbons of phenyl groups. 

Deshielded group. A chemical functional group deprived of its normal complement of electron density. 

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