A self-assembled cylindrical capsule provides a nanoscale environment that affects keto-enol equilibria. The equilibrium constants for encapsulated beta-ketoesters show values that differ by an order of magnitude from that of the free tautomers in solution. For complexes with a single, large encapsulated guest, the inner surfaces of the capsule and the seam of the hydrogen bonds influence the equilibrium between the encapsulated keto and enol forms. For complexes of smaller beta-ketoesters, the coencapsulated solvent influences the equilibria. The solvent reduces the space available and affects the positioning of the ester in the capsule.