Estimation of gas-phase rate coefficients for the reactions of a series of α,β-unsaturated esters with OH, NO3, O3 and Cl

Abstract

Rate coefficients for reactions of a series of α,β-unsaturated esters with OH and NO3 radicals, O3 and Cl atoms have been estimated using different methods: i.e., physico-chemical correlations and Structure Activity Relationships (SARs). In this study new correlations to estimate rate coefficients have been proposed (only for α,β-unsaturated esters): logkNO3 = (13.9 ± 2.8) + (2.75 ± 0.26) × log (kOH); log (kOH) = (4.93 ± 1.14) + (1.60 ± 0.12) × log (kCl); ln(kOH/cm3 molecule−1 s−1) = (1.71 ± 0.21) × EHOMO/eV − (6.25 ± 2.24); ln(kNO3/cm3 molecule−1 s−1) =(5.94 ± 0.35) × EHOMO/eV + (27.87 ± 3.65); ln(kO3/cm3 molecule−1 s−1) = (2.20 ± 0.63) × EHOMO/eV − (16.75 ± 6.65) and ln(kCl/cm3 molecule−1 s−1) = (0.21 ± 0.23) × (EHOMO)/eV − (19.8 ± 2.4). The group reactivity factors necessary to estimate the rate coefficients by SAR methods have also been calculated for a series of α,β-unsaturated esters for the first time: f(–C(O)O(CH2)3CH3), f(–C(O)O(CH2)5CH3), f(–C(O)OCH2CH(CH2CH3)CH2CH2CH2CH3) for reactions with the NO3 radical, OH radical and O3. Furthermore, f(–C(O)OCH3), f(–C(O)OCH2CH3), f(–C(O)O(CH2)3CH3), f(–C(O)OCH2CH2CH2CH2CH2CH3), f(–C(O)OCH2CH(CH2CH3)CH2CH2CH2CH3) for reactions with chlorine atoms have been estimated.The results show that for NO3 and OH radicals these methods are generally satisfactory. In the case of Cl atoms, all methods used in this study reproduce the rate coefficient within a factor of 1.5. In general the best method for estimating the rate coefficient of α,β-unsaturated esters with the main atmospheric oxidants is the correlation of ln k versus EHOMO.