Rate coefficients for the gas-phase reactions of chlorine atoms with cyclic ethers at 298 K

Rate coefficients of reactions of Cl atoms with cyclic ethers, tetrahydropyran (THP), tetrahydrofuran (THF), and dihydrofurans (2,5-DHF and 2,3-DHF) have been measured at 298 K using a relative rate method. The relative rate ratios for THP and THF are 0.80 ± 0.05 and 0.80 ± 0.08, respectively, with n-hexane as the reference molecule. The relative rate ratios for THF and 2,5-DHF with n-pentane as the reference molecule are 0.95 ± 0.07 and 1.73 ± 0.06, respectively, and for 2,5-DHF with 1-butene as reference is 1.38 ± 0.05. The average values of the rate coefficients are (2.52 ± 0.36), (2.50 ± 0.39), and (4.48 ± 0.59) × 10^-10 cm³ molecule^-1 s^-1 for THP, THF, and 2,5-DHF, respectively. The errors quoted here for relative rate ratios are 2σ of the statistical variation in different sets of experiments. These errors, combined with the reported errors of the reference rate coefficients using the statistical error propagation equation, are the quoted errors for the rate coefficients. In the case of 2,3-DHF, after correcting for the dark reaction with CH₃COCl and assuming no interference from other radical reactions, a relative rate ratio of 0.85 ± 0.16 is obtained with respect to cycloheptene, corresponding to a rate coefficient of (4.52 ± 0.99) × 10^-10 cm³ molecule^-1 s^-1. Unlike cyclic hydrocarbons, there is no increase with increasing number of CH₂ groups in these cyclic ethers whereas there is an increase in the rate coefficient with unsaturation in the ring. An attempt is also made to correlate the rate coefficients of cyclic hydrocarbons and ethers with the molecular size as well as HOMO energy.