Prior computational studies by our group have shown that related mercuronium rearrangements on these substrates proceed with relatively low barriers (~10 kcal/mol) and are under thermodynamic control. Therefore, we sought to understand the selectivity in terms of the relative energies of organomercury ground states. Starting with organomercuric chlorides for computational ease, there was a small ΔG of 0.51 kcal/mol favoring the 5-exo rearranged product 73 over the initial 6-endo intermediate 72 (Figure ). However, for organomercuric triflates, ΔG grew to 1.94 kcal/mol, again favoring 73-OTf over 72-OTf. Note that the mercuric triflate is the more relevant reaction intermediate, whereas the inert mercuric chloride is only present after quenching the reaction with brine. From a ΔG of 1.94 kcal/mol, a Boltzmann population analysis (Equation ) at 0 °C corresponds to a 97.2 : 2.8 (or 34:1) ratio favoring 73. This agrees well with observed selectivity in which 72 is not seen at all, perhaps due to alternative decomposition pathways.