n→π* Interactions Are Competitive with Hydrogen Bonds.

Because carbonyl groups can participate in both hydrogen bonds and n→π* interactions, these two interactions likely affect one another. Herein, enhancement of an amidic n→π* interaction is shown to reduce the ability of ß-keto amides to tautomerize to the enol, indicating decreased hydrogen-bonding capacity of the amide carbonyl group. Thus, an n→π* interaction can have a significant effect on the strength of a hydrogen bond to the same carbonyl group.