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 α,ω-dihydrofluoropolyethers, which
represent a specific class of the hydrofluoropolyethers family with
the formula HF2C­(OCF2CF2)p(OCF2)qOCF2H. 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.