Monte Carlo determination of the internal energies of hydration for the Ala dipeptide in the C₇, C₅, a_R and P_II conformations Abstract: The internal energies of hydration of the Ala dipeptide in the C₇, C₅, a_R and P_II conformations were computed with the Monte Carlo method. The results indicate that both the a_R and P_II conformations are preferentially stabilized by hydration in general accord with the results of recent experiments described by Madison and Kopple. The major contributing factor to the stability of internal energy if hydration fir these conformation can be traced to the hydration of the carbonyl group.