Structural Assignments of Ethylidene Acetals by NMR Spectroscopy

The ¹H and ¹³C NMR spectra of ethylidene derivatives of simple diols and of carbohydrates were measured to determine whether NMR parameters could be found which could be related to structure. Four NMR parameters were considered; the chemical shifts of the acetal proton and carbon, the ²J_C,H value between the acetal proton and methyl carbon and the ¹J_C,H value of the acetal carbon. The values,.of these parameters were all somewhat related to ring-size; the ²J_C,H value was most closely related. The sign of ²J_C,H was shown to be positive for 2-methy l-l,3-dioxolane and Z-methy l-l,3-dioxane by means of selective population transfer experiments. Comparison of the ¹³C NMR chemical shifts of the acetal with the parent diol was found to give information about acetal location.