Keto-Enol Tautomeric Equilibrium in 4-Oxo-1,1,3-Cyclohexanetricarboxylic Acid Trialkyl Esters and 4-Oxo-1, 1, 3-Cyclopentanetricarboxylic Acid Trialkyl Esters

4-Oxo-1,1,3-cyclohexanetricarboxylic acid trialkyl esters in deuterochloroform and dimethylsulfoxide-d⁶ (DMSO) exist exclusivly in the enol form. The keto form is the major component in the analogous compounds of five-membered ring. The 1, 3 interaction between carboalkoxy groups in the six-membered ring should be the reason why the carboalkoxy group at 3-position is in equatorial configuration and engages in the intramolecular hydrogen bond, so that the enol form is dominating.