ENERGETICS AND MECHANISMS OF GAS PHASE IONS SOLVATED BY A SINGLE SOLVENT MOLECULE.

摘要

Fluorinated alcohols are reacted with several anions including fluoride ion. A typical reaction is that of 2-fluoroethanol with F('-). Three possible reaction channels are observed and the relative amount of each is examined as a function of: (1) base strength and size of the attaching anion, (2) fluoride ion binding energies, (3) relative ease of loss of HF from fluoroalkoxide ions, (4) nature of fluorine substitution in the fluorinated alcohol. Gas phase acidity measurements of each of the alcohols are reported and electron affinities of the corresponding fluoroalkoxy radicals are inferred.;KF.;nC(,7)H(,15)Cl + CH(,3)CO(,2)H (--->) CH(,3)CO(,2)(.)nC(,7)H(,15) + KHF(,2) + KCl (1).;Further examples of production of strongly hydrogen bonded species are detailed. The gas phase ion-molecule reactions of (alpha), (alpha), (alpha)', (alpha)' tetrafluorodimethyl ether, both alone and in mixtures with water, are described. The dominant feature of the ion chemistry of these mixtures is the sequential bimolecular production of the hydrated hydronium ion, H(,5)O(,2)('+). That the species at m/e 37 is indeed H(,5)O(,2)('+), is verified by both ICR double resonance and deuterium labelling (D(,2)O) experiments. Two independent mechanistic pathways for production of H(,5)O(,2)('+) are outlined arising from reactions of H(,3)O('+) with (CF(,2)H)(,2)O and from CF(,2)H O CHF('+) with H(,2)O.;Reactions of trifluoromethoxide ion, CF(,3)O('-), with carboxylic acids are studied. Fluoride transfer to the acid occurs and a subsequent fluoride transfer equilibrium is established in the carboxylic acid mixtures. The equilibrium constant is obtained and binding energies calculated. Acetic and propionic acids have near identical fluoride binding energies. Further reactions between the acid solvated fluoride ions and the carboxylic acids result in HF displacement and formation of bicarboxylate anions. An analysis of the energetics reveals that propionic acid binds the carboxylate anions more strongly than acetic acid by 0.1 to 0.2 kcal/mole. Replacing propionic acid from the acetic/propionic mixture with an alkyl halide produces a novel example of nucleophilic attack. The strongly hydrogen bonded CH(,3)CO(,2)HF('-) reacts further with acetic acid to form the acetic dimer (CH(,3)CO(,2))(,2)H('-). The hydrogen bonded dimer attacks the alkyl halide via nucleophilic displacement. If alkyl chlorides are used, CH(,3)CO(,2)HCl('-) is produced along with alkyl acetates. These reactions parallel analogous reactions in solution chemistry, specifically the synthetically important reactions of glacial acetic acid with alkali metal fluorides, reaction (1).;Due to recently reported geometries for H(,3)O('+) and H(,3)S('+) and vibrational frequencies for these ions found from the salts of SbF(,6)('-) and AsF(,6)('-), it is now possible to calculate the entropy change for the important proton transfer reaction H(,3)O('+) + H(,2)S (DBLHARR) H(,3)S('+) + H(,2)O. We have done so using standard statistical thermodynamic equations and a computer program called CFIT. Implications regarding the experimentally determined entropy change for the reaction are discussed.