Theoretical determination of the OH-initiated oxidation rate constants of $${\alpha ,\omega }$$-dialkoxyfluoropolyethers

Abstract

In this work, we have calculated rate constants for the tropospheric reaction between the OH radical and two $${\alpha ,\omega }$$ -dialkoxyfluoropolyethers, namely $${\mathrm{R}}{-}({\mathrm{OCF}}_2)_2{-}{\mathrm{OR}}$$ , with $${\mathrm{R}}{=}{\mathrm{C}}_2{\mathrm{H}}_5$$ and $${\mathrm{CH}}({\mathrm{CH}}_3)_2$$ . In terms of low atmospheric impact, dialkoxyfluoropolyethers are considered to be a promising class of the hydrofluoropolyethers family, although very little is still known about their reactivity. Calculation of the rate constants for these challenging molecular systems was performed by utilizing a cost-effective protocol for bimolecular hydrogen abstraction reactions based on multiconformer transition state theory and employing computationally feasible M08-HX electronic structure calculations. Within the protocol’s uncertainties and approximations, the results maintain the tendencies of our own previous work: (1) OH-initiated oxidation rate constants of dialkoxyfluoropolyethers involving the ethyl and isopropyl groups have the same order of magnitude, which in turn is approximately 10 times larger than the rate constants involving dimethoxyfluoropolyethers; (2) the branching ratios concerning the $$\alpha$$ -hydrogens are much larger than the ones concerning the $$\beta$$ -hydrogens; and (3) the chain length is seen to have a small effect on the rate constant, which is consistent with experimental work.