Application of nuclear magnetic resonance spectroscopy in the stereochemical assignment of poly-Z-isomeric conjugated polyene isoprenoids

13 C N.m.r. Spectra of A range of synthetic poly-Z-polyene isoprenoids, i.e. Z-isomers of the tetraenoate (1), the hexaenal (3), and the nonaene (4), are presented and discussed. Carbon-13 magnetic resonance isomerisation shift data for the vinyl methyl and vinyl methylene carbon atoms in Z-E-isomers of (1), (3), and (4) are shown to provide a general protocol for the unambiguous assignment of geometry amongst polyene isoprenoids. 1 H N.m.r. shift data obtained for the vinyl methyl and vinyl methylene groups in isomers of the polyenes (1), (3), and (4) are also discussed and shown to be less useful in determining the structures of poly-Z-polyene isoprenoids.