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Abstract
The halogen elimination of 1,2-diiodoethane (C2H4I2) and 1,2-diiodotetrafluoroethane (C2F4I2) 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 C2H4I2 were reported to vary substantially depending on the solvent, the solvent effects on the photodissociation of C2F4I2 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 C2F4I2 in cyclohexane. The data revealed that (ⅰ) the solvent dependence of the photoreaction of C2F4I2 is not as strong as that observed for C2H4I2, and (ⅱ) the nongeminate recombination leading to the formation of I2 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.
Highlights
The photoexcitation of haloalkanes at ultraviolet wavelengths induces an electronic transition corresponding to the n → σ* transition of a carbon–halogen bond, leading to the dissociation of halogen atoms [1,2]
The q∆S(q, t) curves exhibit distinct oscillatory features in q-space, which are the signature of structural changes of reacting molecules, and these features which are the signature of structural changes of reacting molecules, and these features change with time, which indicates that reactions occur on the time scales covered by the change with time, which indicates that reactions occur on the time scales covered by the time-resolved X-ray liquidography (TRXL) experiment
We investigated the kinetics and structural dynamics of the photodissociation of C2 F4 I2 in cyclohexane, and compared them with those in methanol
Summary
The photoexcitation of haloalkanes at ultraviolet wavelengths induces an electronic transition corresponding to the n → σ* transition of a carbon–halogen bond, leading to the dissociation of halogen atoms [1,2] This photoinduced dissociation has served as an excellent model system to study reaction dynamics due to their simple molecular structures [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48]. Photoreactions of 1,2-diiodoethane (C2 H4 I2 ) and its fluorinated analog, 1,2-diiodotetrafluoroethane (C2 F4 I2 ), were extensively studied as prototypes to explore the effect of fluorination on reaction dynamics and the molecular structures of reaction intermediates [9,10,11,12]
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