Conformational Studies of Chiral .alpha.,.beta.-Unsaturated Aldehydes

The conformational profiles for chiral α,β-unsaturated aldehydes have been studied by a combination of ab initio MO methods and the variable-temperature NMR technique. The s-trans rotational isomer around the C sp2 -C sp2 single bond is more stable than the s-cis conformer by ∼500 cal/mol in chloroform. This difference is 950 cal/mol according to ab initio calculations at the MP2/6-31G * level of theory. The silyl ethers, 3a-d, prefer the C-0 eclipsed form while the methyl ethers, 6a-d, favor the C-H eclipsed conformation for rotations around the C sp3 -C sp2 bond