Conformational isomerism in 3,5,8-trioxabicyclo[5.1.0]octane and its diastereomeric 4-methyl derivatives. A combined IR, X-ray and ab initio study

IR spectroscopy and ab initio calculations have been applied to the title compounds. Bicyclic acetals were found to exist as mixture of chair and twist-boat conformations, a parent epoxide being in ternary equilibrium. X-ray data on 4-methyl (exo) derivative display a twist-boat form.