Abstract
An asymmetric hetero-Diels-Alder cycloid duct (III) is synthesized and isolated. The 1H-1H distance between a proton on the C12 chiral center and an ortho phenyl proton is measured by NMR spectral studies (ROSEY, NOESY, TOCSY) of the reaction product of 2,4-penanedienoic acid -(-)-menthol ester with 4,4′-dimethoxy-diphenythione. The experimentally determined value is compared to the distance computed by molecular modeling software (Sybyl). The agreement between experiment and computation is only fair indicating that the use of such measurements for small molecules of uncertain geometry must be approached with care. The results indicate that the distance of closest approach between two protons in a molecule is more consistent with the NMR determined distance than is the equilibrium, lowest energy form of the molecule.
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