N.M.R. Experiments on Ketals IV. P.M.R. Spectra and Conformations of the Dioxolanes of 2,3‐Butanediol and Acetophenone

The dioxolanes of acetophenone and 2,3‐butanediol were prepared and the three possible isomers were separated by GLC. Structural assignment was based on physical and spectral behaviour. The magnetic anisotropy effect between cis ‐1,2‐ and 1,3‐located methylgroups and/or protons is found to be in accordance with previously found values ( 1,6 ). The cis ‐β‐phenyl interaction seems to cause a ca 0.20 ppm downfield shift of the ring proton, while this effect is about 0.06‐0.10 ppm downfield for a methyl group. A cis ‐1,2‐dimethyl interaction on the contrary causes an upfield shift of about 0.12 ppm. The entire X 3 AA'X' 3 patterns were solved using literature data ( 2,3 ). In the erythro compound no AX' coupling was found, while the previously proposed 2 correlation between J AA' and J AX' seems not to be fulfilled.