Benzylidene acetal structural elucidation by N.M.R. Spectroscopy: Application of carbon-13. N.M.R.-Spectral parameters

The ₁₃C-n.m.r. spectra of 19 2-phenyl-1,3-dioxolane, -1,3-dioxane and -1,3-dioxopane derivatives were examined and it was found that both the ₁₃C-n.m.r. chemical shift for the acetal carbon atom and the one-bond coupling constant between the acetal carbon atom and the acetal proton had values that could be used to distinguish between acetals having different ring sizes. In addition, the presence of axial substituents at positions 4 or 6 in substituted 2-phenyl-1,3-dioxane rings and 4 or 7 in substituted 2-phenyl-1,3-dioxepane rings could be readily detected. The structures of a number of carbohydrate examples were determined by using these two parameters and also the chemical shift of the acetal proton from ₁H-n.m.r. spectra. The use of all three parameters made assignment of benzylidene acetal ring-size unambiguous.