Conformational Analysis of Open-Chain 1,2:3,4-Diepoxides: Comparison of crystal structures,NMR data,and molecular-orbital calculations

Several pairs of diastereoisomeric open-chain 1,2:3,4-diepoxides with different substitution patterns were prepared (see 3–9 ). As far as possible, crystal structures were determined to corroborate the relative configurations and to give insight into the solid-state conformations of these compounds. The comparison with our earlier molecular-orbital calculations and with ¹H-NMR measurements shows that the solid-state conformations of eight out of the nine open-chain 1,2:3,4-diepoxides, whose crystal structures had been determined, correspond to minima on the calculated energy profiles for these compounds or for closely related derivatives. In solution, highly substituted diepoxides of the erythro-series (e- 6 , e- 7 , e- 9 ) seem to prefer the same conformation as in the crystal. The solution conformations of all other diepoxides differ from the arrangement in the solid state.