Figure 2.

Generic mechanism for glycosidic bond cleavage of ribofuranosides. In the upper pathway, attack from the nucleophile (Nu) displaces the leaving group (LG) in a concerted bimolecular process (A_ND_N). In the lower pathway, departure of LG occurs in an independent step (D_N) from attack of the 2-deoxyribosyl oxocarbenium ion by Nu (A_N). In a D_N^‡*A_N mechanism, the D_N step is rate-limiting. In a D_N*A_N^‡ mechanism, the A_N step is rate-limiting, and the glycosidic bond cleaves and reforms many times before nucleophilic capture.