17O chemical shift data (natural abundance) for 3-substituted phthalic anhydrides and 4-and 7-substituted phthalides in acetonitrile at 75° C are reported. Steric interactions of substituents ortho to the carbonyl groups result in deshielding effects (9-22 ppm) relative to parent compounds regardless of the electronic character of the substituents. Factors contributing to the deshielding effects are discussed. The relationship between 17O ...
