CONFORMATIONAL PREFERENCES OF C1-OXYGENATED ACYCLIC CHIRAL ALKENES - EVIDENCE FOR THE C-C ECLIPSED CONFORMER

Three forms of conformational minima were found for 3-buten-2-ol by ab initio MO methods, including the conformers where the allyl methyl gr oup eclipses the C=C bond. The computational results are corroborated by a VT NMR study of a variety of Cl-oxygenated chiral alkenes. The ex perimental study indicates that chiral allylic alcohols and ethers wit h a formula of (E)-RCH=CHCH(OP)R' can have either two or three stable rotamers depending on the size of the allylic substituent, R'. When R' is a methyl group, the coupling constant, 3J(ab), is smaller than whe n R' is a bulky group, indicating a three-rotamer equilibrium.