Microcanonical variational transition state theory was employed to determine the entropy of activation, DeltaS(double dagger), for the dissociation of a series of acetonitrile-alcohol proton-bound pairs over an internal energy range corresponding to metastable ion decomposition observations on a magnetic sector mass spectrometer. It was found that DeltaS(double dagger) decreases with increasing size of the alcohol chain in the complex. These values ranged from 64 to 75 J K-1 mol(-1) for (CH3CN)(CH3OH)H+, 34-43 J K-1 mol(-1) for (CH3CN)(CH3CH2OH)H+, 6 J K-1 mol(-1) for (CH3CN)(CH3CH2CH2OH)H+, and 11-13 J K-1 mol(-1) for (CH3CN)((CH3)(2)CHOH)H+. The entropy of activation was compared to the thermodynamic AS for the overall reaction, and larger relative changes are observed between AS' values than for AS.