Structural Dynamics of C(2)F(4)I(2) in Cyclohexane Studied via Time-Resolved X-ray Liquidography

The halogen elimination of 1,2-diiodoethane (C(2)H(4)I(2)) and 1,2-diiodotetrafluoroethane (C(2)F(4)I(2)) serves as a model reaction for investigating the influence of fluorination on reaction dynamics and solute–solvent interactions in solution-phase reactions. While the kinetics and reaction pathways of the halogen elimination reaction of C(2)H(4)I(2) were reported to vary substantially depending on the solvent, the solvent effects on the photodissociation of C(2)F(4)I(2) remain to be explored, as its reaction dynamics have only been studied in methanol. Here, to investigate the solvent dependence, we conducted a time-resolved X-ray liquidography (TRXL) experiment on C(2)F(4)I(2) in cyclohexane. The data revealed that (ⅰ) the solvent dependence of the photoreaction of C(2)F(4)I(2) is not as strong as that observed for C(2)H(4)I(2), and (ⅱ) the nongeminate recombination leading to the formation of I(2) is slower in cyclohexane than in methanol. We also show that the molecular structures of the relevant species determined from the structural analysis of TRXL data provide an excellent benchmark for DFT calculations, especially for investigating the relevance of exchange-correlation functionals used for the structural optimization of haloalkanes. This study demonstrates that TRXL is a powerful technique to study solvent dependence in the solution phase.