Carbon chemical shifts unshared electron pairs

Since it is clear that the presence of an unshared pair of electrons on the sulfur of the sulfoxide group leads to no special instability in the case of the known thiirene oxides (i.e., 18a, 28a,b and the first alkyl-substituted thiirene oxide 30 recently synthesized60), the reduced antiaromatic properties of the thiirene oxides relative to that of thiirenes have been manifested experimentally. As far as the possibility of electron-attracting conjugative stabilization involving the sulfur atom in thiirene oxides is concerned, the experimental evidence accumulated so far is not decisive. Thus, the chemical shift of the vinylic carbon of... 

Lest we take this analogy with carbon too far, we must remember that nitrogen is unique and has chemical shift features peculiar only to nitrogen. The two most important ones are both due largely to the unshared pair of electrons found on nitrogen. 

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