Reactivity of α,ω-Dihydrofluoropolyethers toward OH Predicted by Multiconformer Transition State Theory and the Interacting Quantum Atoms Approach

We report rate constants for the tropospheric reaction between the OH radical and alpha,omega-dihydrofluoropolyethers, which represent a specific class of the hydrofluoropolyethers family with the formula HF2C(OCF2CF2)p (OCF2)(q)OCF2H. Four cases were considered: p0q2, p0q3, p1q0, and p1q1 (pxqy denoting p = x and q = y) with the calculations performed by a cost-effective protocol developed for bimolecular hydrogen-abstraction reactions. This protocol is based on multiconformer transition state theory and relies on computationally accessible M08-HX/apcseg-2//M08-HX/pcseg-1 calculations. Within the protocol's approximations, the results show that (1) the calculated rate constants are within a factor of five of the experimental results (p1q0 and p1q1) and (2) the chain length and composition have a negligible effect on the rate constants, which is consistent with the experimental work. The interacting quantum atoms energy decomposition scheme is used to analyze the observed trends and extract chemical information related to the imaginary frequencies and barrier heights that are key parameters controlling the reactivity of the reaction. The intramolecular exchange-correlation contributions in the reactants and transition states were found to be the dominating factor.