Aldose Alkyl Orthoester

From his studies on models, Brauns arrived at the conclusion that the arrangement of the groups of carbon atoms 1 and 2 in the acetyl-mannosyl halides is such that they can interact to yield derivatives with an orthoacetic acid ring formation. He illustrated with models how the acetyl group on the second carbon is directed to the hydrogen atom of the 

The nucleophilic displacement reaction taking place at a saturated carbon atom is either a bimolecular substitution, Sv2 type, with complete Walden inversion, or a solvolytic reaction, characterized as a nucleophilic substitution of the first order, S l type, with predominant inversion. 

In the first case, the nucleophilic displacing ion or molecule, Y , must approach the CR1R2R3X tetrahedron in the direction of the center of the face opposite the vertex occupied by the X atom, or group of atoms  

The attack is on the carbon atom the driving force is the affinity of the nucleophilic reagent, Y , for carbon. In the transition state the R groups lie in a plane with the central carbon atom, and in the final product, on the opposite side of the carbon atom. The result is complete inversion, the rate of which is proportional to the concentration of the displacing ion or molecule, Y . 

In the second case the reaction consists of two steps, the rate-determining step being the formation of a carbonium ion intermediate (A), and the second step, the reaction of this carbonium ion with a solvent molecule  

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