The conformational stabilities of three possible hydrogen bonded complexes of lactonitrile rotamers (A, B, and C) and water have been studied using high-level ab initio calculations. After full geometry optimizations at the second-order Mphiller-Plesset level of theory (MP2), the bimolecular complexes A-(OHOH2)-O-..., B-(OHOHOH2)-O-.-O-...., and C-(OHOH2)-O-... are found to be true energy minima. It is found that rotamers A and B form strongly bonded hydrated complexes with their binding energies calculated between ca. 8.0-9.0 kcal mol(-1), after correcting for BSSE. This is similar to2.0 kcal mol(-1) higher than the calculated binding energy for the complex C-(OHOH2)-O-.... The geometrical parameters and vibrational spectra of the three complexes are determined and compared with their corresponding isolated moieties. In the three species investigated here there exist a Good correlation between the red shift of the OH vibrational stretching mode involved in the hydrogen bonds and the binding energies of the complexes.