An Experimental and Theoretical Study of a Bicyclic Acetal Equilibrium

The position of equilibrium for competitive acetal formation can be hard to predict. This example, the core of zaragozic acid, is finely balanced, but an experimental investigation has proved that the left-hand isomer is preferred. Molecular mechanics force fields are unable to cope with such systems, because there is competition between five- and six-membered rings. Results from these calculations should not be used to estimate the position of equilibrium in such cases.