Stepwise solvation of halides by alcohol molecules in the gas phase

The gas phase equilibrium clustering reactions X-(ROH)(n) + ROH reversible arrow X-(ROH)(n+1) (X = F, Cl, Br, I; R = CH3, CH3CH2, (CH3)(2)CH, (CH3)(3)C; n = 0, 1, 2) have been investigated by using pulsed-ionization high pressure mass spectrometry (PHPMS). From the corresponding van't Hoff plots the standard enthalpies (Delta H-n,n+1(o)) and entropies (Delta S-n,n+1(o)) were obtained, which are discussed in terms of the radii of the halides, the geometry of the alcohol molecules, the number of alcohol molecules, and molecular properties such as polarizability and gas phase acidity. The observed enthalpy trends can be explained on the basis of ion-dipole, ion-induced dipole, and dipole-dipole interactions within the clusters. The observed entropy trends are qualitatively discussed in terms of hindered rotations and low frequency intermolecular vibrations. In general, where available, there is good agreement between the present data and literature values obtained by various experimental techniques. In addition to the experiments, both density functional theory (DFT) calculations at the B3LYP/6-311 + G(d,p) level of theory and G2 level calculations have been performed on a number of selected systems to test these methods for obtaining energetic data and to gain more insight into the structures of the investigated clusters. (Int J Mass Spectrom 185/186/187 (1999) 707-725) (C) 1999 Elsevier Science B.V.