Structural and Theoretical Bases

Besides the special reactivity of the OH-2, OH-1, and OH-3 groups lies also the classical relative reactivity between the primary and secondary hydroxyl groups. Depending on the reaction conditions and the nature of the electrophilic species, it may be seen that these two types of possible reactivity can direct the reactivity of sucrose. Of course, the product distribution also depends on whether the transformations are kinetically or thermodynamically controlled. For those reactions under kinetic control, if there is enough difference in the rate of the first substitution at the most reactive hydroxyl group and the second one, then the regioselectivity also monitors the degree of substitution. 

In accordance with all of these structural and electronic considerations, it is shown in the following sections that it would be wrong to simplify our understanding of the selectivity of sucrose transformations to merely the reactivity order of primary versus secondary hydroxyl groups. 

Before going into details in the transformations of sucrose, it should be mentioned that, although sucrose is available in large quantity from plants, its complex structure has been for years a major challenge to synthetic chemists although several syntheses of this disaccharide have been accomplished.51 59 

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