The equilibria RNH3+(H2O)n−1 + H2O = RNH3+(H2O)nwere measured for R = CH3, C2H5, and CF3CH2fromn = 1 ton = 3 with a pulsed electron beam high ion source pressure mass spectrometer. The proton and hydrate transfer equilibria CH3NH3+(H2O)n + C2H5NH2 = CH3NH2 + C2H5NH3+(H2O)nwere measured forn = 0 ton = 3. These data allow the evaluation of ΔH0and ΔG0for the reactions: R0NH3+(H2O)n + RNH3+ = R0NH3+ + RNH3+(H2O)n. ΔH0 = δΔH00,n(RNH3+), ΔG = δΔG00,n(RNH3+). These data are compared with δΔE0,3(STO-3G) evaluated by Hehre and Taft. In general good agreement is observed atn = 3. The δΔH00,3(RNH3+) ≈ δΔE0,3(RNH3+) are also found close to the ion hydration free energy difference in aqueous solution