To gain further insight into the C-H deprotonation/elimination sequence from aryl thianthrenium and aryl(Mes)iodonium salts, we performed DFT calculations on several different substrates 10 and Figure ). All intermediates and transition state structures were optimized with the M06-2x functional and the Def2-tzvpp basis set with SMD solvation (toluene) using Gaussi-an09. Given the range of solvents used in the experimental methods to access arynes from aryl thianthrenium and aryl(Mes)iodonium salts we survey solvation models (Table ), and ultimately selected toluene as a single and representative solvent for DFT analysis. Our DFT analysis revealed that aryne formation from aryl thianthrenium and aryl(Mes)iodonium salts occur through distinct reaction pathways (Scheme 10). All aryl thianthrenium substrates analyzed by DFT (1b-TT, 1l-TT and 4-chlorophenyl thianthrenium) were found to generate a stable zwitterion (A, Scheme 10) upon deprotonation with tert-butoxide and passing through TS1 (Scheme 10 and Figure ). In the case of A, derived from 1b-TT, protonation (the reverse of the initial step) is lower in energy than elimination of the thianthrenium group through TS2 by 2.5 kcal/mol (Scheme 10, left). Therefore, the C-H deprotonation is reversible and TS2 is the highest energy point on the reaction pathway (Scheme 10, left). Conversely, the computed reaction pathway for all aryl(Mes)iodonium salts analyzed (1m-IMes, 1l-IMes and 4-chlorophenyl(Mes)iodonium) proceed through a single transition state (Scheme 10 and Figure ). In the transition state, epitomized by TS3, C-H and C-I bond cleavage is concerted but asynchronous; the C-H bond is elongated by 30% whereas the C-I bond is elongated by only 5%. Nevertheless, no zwitterionic intermediate could be found as TS3 collapses to the aryne dedihydro-1m as well as tert-butanol and mesityl iodide (Scheme 10, right). With these pathways established, the DKIE were calculated from the optimized geometries of the reactants and transition states for each reaction step. The overall DKIE for the two step aryne formation from 1b-TT was calculated based on equation SF1, and both values were found to be in relatively good agreement (Scheme 10). The DKIE calculated from the DFT data for 1b-TT was 1.0 compared to the DKIE of 1.4 obtained from the wet lab experiment (Scheme 9 and 10, left). The relatively small DKIE reflects the reversible C-H deprotonation followed by rate-limiting thianthrene elimination, and thus the separation of the C-H deprotonation and rate-limiting steps. The DKIE calculated from the DFT data for 1m-IMes was 4.5 compared to the experimental value of 4.9 (Scheme 9 and 10, right). This much larger DKIE reflects C-H bond cleavage in the rate-limiting step of the reaction.