Simple Enols. 3. Stereochemistry of Simple Enols in Solution

Article abstract of DOI:10.1021/jo00176a008

The simple enols vinyl alcohol, (E)-prop-1-en-1-ol, (Z)-prop-1-en-1-ol, and 2-methylprop-1-en-1-ol have been generated from reactive precursors in solution in slightly aqueous CD3COCD3 and their 1H NMR spectra measured under conditions where exchange of the OH proton is slow on the NMR time scale.At -80 deg C J(OH-CαH) for vinyl alcohol and (E)-prop-1-en-1-ol is greater than 9 Hz whereas that for (Z)-prop-1-en-1-ol and 2-methylprop-1-en-1-ol is less than 6 Hz.With the former two compounds J(OH-CαH) decreases with temperature whereas with the latter it increases.It is concluded that the former two enols exist mainly in the s-cis-co nformation and the latter mainly in the s-trans conformation.The 13C NMR spectra of these enols in aqueous CD3COCD3 were also measured, and it is concluded that some factor other than a through-space shielding effect is important in determining the relative chemical shifts of the olefinic carbon atoms.