High level ab initio MO calculations have identified two complexes of borane with 2-fluoropropane. In the first, the boron atom is above the small C1,C2,C3 angle ( in complex); in the other, the boron atom is outside that angle ( out complex). The ionization to form the 2-propyl cation and the trihydrofluoroborate ion A was followed by lengthening the C–F bond, d, in each complex and reoptimizing all other geometrical parameters. It was concluded that ionization occurred at d=1.8–2.0 A ̊ . The out ionization pathway was of lower energy (1–2 kcal/mol at MP2(FC)/6-31G ∗∗) at al values of d. A third pathway ( top), in which the F–B bond was held perpendicular to the C1,C2,C3 plane, rather than allowed to tilt, was 8–9 kcal/mol higher in energy throughout. Ionization to the tight ion pair did not require a large energy expenditure (19.0 kcal/mol over the isolated reactants at d=2.00 A ̊ , 30.3 kcal/mol at d=2.20 A ̊ ). A medium of dielectric constant 8.93, in SCRF(IPCM)-MP2(FC)/6-31G ∗∗MP2/6-31G ∗∗ calculations, reduced the ionization energy to 14.2 kcal/mol at d=2.20 A ̊ . The dielectric medium also reorders the relative energy of the three orientations to out< top (1.0 kcal/mol) < in (4.5 kcal/mol), at d=2.20 A ̊ . Changes in bond lengths and angles show hyperconjugative assistance to the ionization by the methyl hydrogens anti to the fluorine along all pathways. As the ions separate, this effect decreases and. the interaction with the anion of one of the hydrogens initially syn to the fluorine becomes important. Along the in pathway, rotation of one of the methyl groups occurred along the in pathway at 2.20 Å and elimination at 2.30 Å; along the top pathway, it occurred at 2.30 and 2.40 Å, respectively. Along the out pathway, methyl group rotation brought a hydrogen in each close to the anion at d=2.50 A ̊ and elimination followed at 2.70 Å. The top orientation had not eliminated at distances about 2.6 Å and higher in our previous work. Both the in and out forms were optimized without elimination at d=2.80 A ̊ with tetrafluoroborate ( C) as anion. The calculations predict features of solvolyses, such as transfer of a nucleophile from the backside of the anion (retentive solvolysis), elimination to olefin within the ion pair, and recombination at the backside of the anion (oxygen scrambling faster than racemization of tosylates and carboxylates).