Oxygen neighboring group

This is consistent with neighboring group participation by the oxygen atom in the separation of the chloride ion. ... 

For a review of neighboring group participation by sulfinyl oxygen, see Montanari221. This special influence of sulfinyl groups on reactivity is, of course, due to the high polarity... 

Neighboring group participation effects appear to play a crucial role in the nucleophilic substitution of chlorine in Michael adducts of 1-R, 2-R, 3-X. Thus, this substitution proceeds very easily in any of the adducts formed with an electron rich nitrogen, sulfur and oxygen Michael donor. For the adducts of nitrogen nucleophiles, the facile substitution of the chlorine has been suggested to occur via formation of intermediate aziridinium ions 103 [8] (Scheme 32), and this postulate was later supported by isolation of azaspiropentane derivatives under appropriate conditions in several reactions (see Sect. 3.2.2) [11b, 53,56]. It is most likely that alkylthio substituents in adducts of type 85 participate in the same way to first form spirocyclopropane-annelated thiiranium ion intermediates which are subsequently opened by attack of the incoming nucleophile. 

The rate of attack of polymer molecules by corrosives may be enhanced or hindered by the presence of neighboring groups. Carbon bonds with oxygen, sulfur, or nitrogen are more readily cleaved by acids, bases, and other corrosive... 

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