Pure rotational spectrum of 2-pyridone⋯water and quantum chemical calculations on the tautomeric equilibrium 2-pyridone⋯water/2-hydroxypyridine⋯water

The free-jet millimeter-wave spectrum of the complex 2-pyridone⋯water has been measured. The water is strongly linked to the partner group through a double hydrogen bond. We could not observe the spectrum of 2-hydroxypyridine⋯water (2-hydroxypyridine is more abundant than 2-pyridone in the tautomeric mixture). This failure is explained by density functional and ab initio calculations on the relative stability of the two 1:1 complexes with water. Estimates of the dissociation energy have been obtained both from the centrifugal distortion effects and from quantum chemical calculations.