Journal of Molecular Graphics and Modelling 53 (2014) 23–30 Contents lists available at ScienceDirect Journal of Molecular Graphics and Modelling journa l h om epage: www.elsevier.com/locate/JMGM Theoretical studies on kinetics, mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom Ramesh Chandra Deka, Bhupesh Kumar Mishra ∗ Department of Chemical Sciences, Tezpur University, Tezpur 784 028, Assam, India a r t i c l e i n f o Article history: Accepted 7 July 2014 Available online 15 July 2014 Keywords: Hydrofluoroether M06-2X Isodesmic reaction Rate constant Atmospheric lifetime a b s t r a c t A theoretical study on the mechanism and kinetics of the gas phase reactions of CF 3 CHFCF 2 OCH 2 CF 3 (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid mod- ern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF 3 CHFCF 2 OCH 2 CF 3 and the most stable one is considered for detailed study. Reaction profiles for OH- initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH 2 group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for C H bonds are in good agreement with experimental results. The rate constants of the two reactions are deter- mined for the first time in a wide temperature range of 250–450 K. The calculated rate constant values are found to be 9.10 × 10 -15 and 4.77 × 10 -17 cm 3 molecule -1 s -1 for reactions with OH radicals and Cl atom, respectively. At 298 K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years. © 2014 Elsevier Inc. All rights reserved. 1. Introduction In order to reduce the adverse effect of chlorofluorocarbons (CFCs) toward Earth’s stratospheric ozone layer their commer- cial production is banned as per the Montreal protocol and an international effort has gone into finding environmentally more acceptable alternatives to replace chlorofluorocarbons [1,2]. In this context, a number of CFCs replaceable compound such as hydroflu- orocarbon (HFC) and hydrochlorofluorocarbon (HCFC) have been developed for short-term use because of their non-reliability toward protection of ozone layer. Volatile organic compounds like hydrofluoroethers (HFEs) are designed and widely recom- mended as a third generation replacement for CFCs, HFCs and HCFCs in applications such as cleaning of electronic equipments, heat transfer fluid in refrigerators, lubricant deposition and foam blowing agents [3,4]. Hydrofluoroethers do not contain chlorine and bromine atoms that cause the ozone depletion [5]. In addi- tion the rate constant for the reaction of HFEs with OH radical suggest that their atmospheric lifetime should be relatively short ∗ Corresponding author. Tel.: +91 3712267008; fax: +91 3712267005. E-mail address: bhupesh@tezu.ernet.in (B.K. Mishra). and thus HFEs appear to have less impact for the global warming [6]. Like most volatile organic compounds, HFEs containing C H bonds are removed from the troposphere by reactions with atmo- spheric oxidants, OH radicals being the most dominant oxidant. Although the reaction with OH radicals constitutes the main tro- pospheric sink for degradation of halogenated ethers, the chlorine atom also plays an important role in the atmospheric chemistry [7]. In fact, chlorine atoms have been monitored in concentra- tions in the order of 10 4 molecule cm -3 over the marine boundary layer [8]. The tropospheric oxidation of HFEs is known to produce corresponding hydrofluorinated esters (FESs) [9]. The degradation of FESs produce environmentally burdened product like trifluo- roacetic acid (TFA) and COF 2 . It has been reported that TFA as detected in surface waters has no known sink apart from rain- water and this species may impact on agricultural and aquatic systems [10]. Hence it is important to study the kinetics and mech- anistic degradation pathways of HFEs in troposphere for complete assessment of its atmospheric chemistry as well as its impact on global warming and climate change. Therefore, much attention has been paid recently on studying the reactivity of HFEs with OH radicals and Cl atom [11–22]. HFE-449mec-f (CF 3 CHFCF 2 OCH 2 CF 3 ), a C-5 HFE, which is alternative cleaning solvent having dissolv- ing capability of fluoro oils. It is synthesized by Natalia et al. http://dx.doi.org/10.1016/j.jmgm.2014.07.003 1093-3263/© 2014 Elsevier Inc. All rights reserved.