A fundamental aspect of any ambient temperature reaction occurring on a relatively short time scale is its energetics. These were addressed as matter arising from the original synthetic report, in which analysis of the computed thermodynamics of this reaction led to the conclusion that the production of free C2 and iodobenzene was likely to be highly endoenergic. The energetics of the equilibrium (Eqn. 1, R=Me,Ph) were in the range of +(43-53) kcal mol -1 using three different estimates, anchored by a calibrated CCSD(T)/Def2-TZVPPD/SCRF=dichloromethane calculation for a simplified model (Eqn. 1, R=Me) for which DG298 +47.1 kcal mol -1 . Eyring theory tells us that at 298K, unimolecular reactions with a half-life of respectively 1 minute and 1 hour correspond to free energy barriers of 20.0 or 22.5 kcal mol -1 , significantly lower than the energy range predicted above.