| The interactions between halide ions and a variety of organic molecules have been investigated using pulsed-ionization high pressure mass spectrometry (PHPMS), and a variety of ab initio, density functional theory (DFT), and composite quantum chemistry methods. The organic substrates include alcohols, alkyl halides, trifluoromethyl halides, and fluorinated ether and acetones. The computations were performed to get more insight into the structures of the ion-molecule complexes and transition states, to model the experimental thermochemistry and IR characteristics of neutrals and ion-molecule complexes, and to obtain information on the potential energy surfaces for some reactions.; The standard enthalpy (ΔH°) and entropy (ΔS) changes associated with the formation of the halide ion-alcohol complexes, X-(ROH) n (X = F, Cl, Br, I; R = CH3, CH3CH2, (CH3)2CH, (CH3)3C; n = 1, 2, 3), show that observed trends are mainly due to the radius of the halide ion, the alcohol polarizability, and the dipole-dipole repulsion and steric interactions when X, R, and n are the different variables, respectively.; For a series of solvated SN2 complexes, (S)X− (RY) (X, Y = Cl, Br); R = (CH3)2CH; S = CH 3OH, CH3CN, (CH3)2CO, CH3CF 2H), the ΔH° and ΔS° values associated with their formation were determined using PHPMS and solvent effects were observed. In addition, ab initio computations on a series of solvated SN2 reactions confirm solvent effects on the energetics of these micro-solvated systems, as well as different binding characteristics in the solvated SN2 complexes and transition states, indicating solvent reorganization.; Nucleophilic displacement reactions between halide ions and trifluoromethyl halides proceed through a back-side attack SN2 mechanism, while complex formation proceeds through a front-side attack mechanism. For the Cl−(BrCF3), Cl−(ICF 3), and Br−(BrCF3) complexes the ΔH° and ΔS° values associated with their formation were determined by PHPMS.; The thermochemistry measured by PHPMS for the formation of a series of chloride ion-fluorinated ether and acetone clusters shows the distinct influence of the number of fluorine atoms and the substitution pattern. Insights into the structures and thermochemistry was obtained from computations at the MP2/[6-311++G(3df,3dp)/6-311+G(2df,p)]//MP2/[6-31+G(d)/6-31G(d)] level of theory. In general, excellent agreement was obtained. (Abstract shortened by UMI.)... |
