ABSTRACT
The density functional theory with the BH&HLYP functional has been used in this work to clarify discrepancies found in the literature about the effect of the increasing carbon chain on the reactivity of trans-2-alkenals from acrolein (C3) to trans-2-octenal (C8) with nitrate radical. In this work, it was found that (i) the alkyl chain length of the unsaturated aldehydes has little or no influence on the NO3 reaction rate coefficients (ii) the abstraction of the aldehydic hydrogen from the alkenal is always dominant (83% for trans-2-butanal to trans-2-octenal). The addition channel, which mainly concerns the ß addition, has a small influence (17% of the total reaction for the whole series). These results are in good agreement with the experimental studies performed by Zhao et al. in 2011 and by Kerdouci et al. in 2012. All these findings will be useful to complete or improve structure-activity relationships developed to predict the reactivity of NO3 radicals with organic compounds.
ABSTRACT
Rate constants for the gas-phase reactions of the NO(3) radical with a series of unsaturated aldehydes, trans-2-hexenal, trans-2-heptenal, and trans-2-octenal, have been measured using absolute rate method at 294 ± 3 K and atmospheric pressure. This work was performed to clarify discrepancies found in the literature and thus led to a clearer view of the effect of the increasing carbon chain length on the reactivity of trans-2-alkenals. The rate constants were determined to be (4.7 ± 1.5) × 10(-15), (5.3 ± 1.6) × 10(-15), and (5.6 ± 2.3) × 10(-15) cm(3) molecule(-1) s(-1) for trans-2-hexenal, trans-2-heptenal, and trans-2-octenal, respectively. These results clearly indicate that the carbon chain lengthening of the trans-2-alkenals does not significantly affect the rate constant. In addition, the mechanism for the reaction of NO(3) with these unsaturated aldehydes was also investigated. Unsaturated peroxynitrate-type compounds that are exclusively formed through the abstraction channel were observed as the main products.
Subject(s)
Aldehydes/chemistry , Nitrates/chemistry , Free Radicals/chemistry , Gases/chemistry , Kinetics , Molecular StructureABSTRACT
A new structure-activity relationship (SAR), based on parametrization of the molecular structure according to the group-additivity method, is presented. On the basis of existing experimental data for the degradability of approximately 150 organic compounds by the NO(3) radical, this new SAR is developed to estimate the rate constants for reactions with NO(3) radical. At night, nitrate radicals are the most important oxidant of volatile organic compounds. The rate constants for their reactions are therefore essential to the understanding of VOC degradation and atmospheric modelling. The database used for the SAR development includes most classes of compounds such as alkanes, alkenes (acyclic and cyclic), dienes, terpenes and saturated and unsaturated oxygenated compounds (including alcohols, ketones, ethers and esters). The proposed SAR shows good efficiency, as 91% of the rate constants are reproduced within a factor of two. The overall agreement between measured and predicted rate constants is very good for most of the unsaturated and saturated compounds, although for saturated alcohols it is less reliable.
