A TOPOLOGICAL ANALYSIS OF BOND ACTIVATIONS IN ALCOHOLS AND FLUOROALKANES BY PROTONATION IN THE GAS-PHASE

The structures of a set of alcohols (R-OH) and fluoroalkanes (R-F) (R = Me, Et, Pr, i-Pr, But or t-But) and their protonated forms were compared by carrying out ab initio molecular orbital studies at the 3-21G, 6-31G* and, in some cases 6-31 + G(d), levels of theory. A topological analysis of the charge density offers quantitative information on the bond activation upon protonation, confirming some preliminary results. For both homologous series of compounds, bond activation follows the sequence Me < Et < Pr almost-equal-to But < i-Pr < t-But, with the result that protonation of tert-butylfluoride breaks the C-F bond. We also show that there is a direct relationship between bond activation and intrinsic basicity. We conclude that the intrinsic basicity of these systems depends on their ability to withdraw electronic charge from the C-O or C-F bonding regions, respectively. A preliminary study, at the semiempirical level of the potential surface corresponding to the C-O bond-breaking reaction of isopropyl and tert-butyl alcohols is presented.