Conformational behaviour enantiomers

X-ray structure analysis may offer one explanation as to why we observe the change in the major enantiomer of epoxide formed (Fig, 5.9). A comparison of catalyst (24) and the sulphone catalyst (36) shows that in the case of (24), the iminium carbon atom sits above 0(1), and the re face is blocked by the phenyl ring. In the case of the sulphone catalyst (36), the iminium carbon faces away from the dioxane ring, and so the re face is now open to attack from the oxidant, therefore producing an oxaziridinium unit of the opposite configuration. These solid-state conformations, however, may well not be representative of the behaviour of the compoimds in solution. 

As in solution only the cone conformation occurs, which is the intermediate form, between the two enantiomers observed in the crystal, calculations were performed on the different molecular forms in order to understand the molecular behaviour. The strain eneigy of the cone form is 128 instead of 125 kcal/mole for both enantiomorphous pinched-cone forms. The pinched-cone forms are the most stable forms, which explains why they are observed in the solid state (the state always corresponding to an eneigy minimum). 

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