SUBSTITUTION AT A SATURATED CARBON ATOM .X. UNIFICATION OF MECHANISMS SN1 AND SN2

Evidence is presented that the competitive reactions of 2-octyl mesylate with water and added azide ion in both 25 and 30 vol % aqueous dioxane proceed by way of an ion-pair intermediate. Anomalies of “borderline” behavior of secondary halides and sulfonates thus disappear. It is argued that the corresponding competitive reactions of 2-octyl brosylate with water and azide ion in the less aqueous 75 vol % dioxane, which conform to behavior predicted by a traditional Sn2 mechanism, actually react via a reversibly formed ion pair, attack on which by nucleophile is rate determining. It is suggested that, perhaps, all nucleophilic substitutions at a saturated carbon atom proceed via an ion pair, thus making traditional Sn1 and Sn2 reactions extremes of a common mechanism which accommodates borderline behavior as well. © 1969, American Chemical Society. All rights reserved.